simple radio controlled aircraft design at a level that is accessible to expansion, but this teaching series alone is not sufficient to build a radio controlled plane. Basics of RC Model Aircraft Design - Free download as PDF File .pdf), Text File ( .txt) or read online for free. Basics of RC Model Aircraft Design. PDF | On May 10, , Seth Kitchen and others published Design of an RC The plane was able to take oﬀ in ft, considerably faster than.
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AS AERODYNAMIC DESIGN DESIGN OF RC AIRCRAFT Submitted by, GROUP - M4 1. Debolina 51 Figure Front View of the RC Model Airplane. Download Page: Title ID= Basics of R/C Model Aircraft Design. Available PDF Download File [Title=raudone.info "Andy Lennon has written an outstanding book that covers all required aspects of the preliminary design process for model aircraft. Further.
Drag oz. And for the full-span, slotte d-flap ve rsio n at a sta lling speed of 14mph, percent-cho rd flaps at 40 degrees: Scale effect is measur ed by Rn.
In E, lift and pitching moments are little affected by th e reduction in Rn from , to ,, but profile drag increases substa ntially. The formula for Rn is simple: K at sea level is ; at 5, feet, it's ; and at 10, feet, it's Our samp le mo del's win g cho rd is 10 inches, and at a land ing speed of In Denver, the Rn wo uld be A quicker solution at sea level is given in Figure Layin g a straightedge from "speed" left to "chord" right, Rn is read from th e cente r colum n. Note that a tapered wing's roo t chord always flies at a hig he r Rn th an its tip chord at any speed, owi ng to the narrower tips whic h can be pron e to tip-stalls as a result.
Full-scale airfoil research da ta may be used for model airplane wing design-with careful regard for the major effect of scale on particularly lift, dra g and stall angles. The se ha ve noth ing to do with baseball! All cam bered airfoils have no se-down , or nega tive, pitch ing mom ent s.
Symmetrical airfoils have no pitching moments, excep t at th e stall. Reflexed airfoils may have low nose-down or low nose-up pitch ing moments. Nose- down pitc hi ng momen ts must be offset by a horizon tal tail do wnl oad tha t is ac hieved by havin g that tail's AoA set at a negative ang le to the down was h fro m the wing. Our sample Wing's nose-down PM is:.
Figure Increments of profile drag coefficient at CL max or increasing flapdeflections. As Figure 5 shows , the E airfoil has a negative CM of 0. Note that CM, like c. The pitching moment formula is: A moment is a force times a distance. In our sample, if a tailmoment arm dis tance were 30 inches, the tail download to offset the nose-down moment would be Chapter 8 goes int o thi s in detail. This is explained in Chapter 8.
It would obviously be poor judg ment to use a h igh -pitch, lowdiameter propeller on a large, slow flying, draggy model with low wing loading. Simila rly, a low -pitch , large-diameter prop on a low-drag , fast airplane with a high wing loading would be a poor choice. I hope that this chapter will over come any problems some reade rs may have wit h formulas in th is book.
To succee d, one mu st try! No effort , no success! It's expressed as "ounces per square foot of wing area. As a glider, is it a thermal seeker or a fast, sleek, aerobatic sailplane? Sport models are usuall y in the I S to 20 ounces per square foot range. Pattern mo dels have wing loadings from 23 to 26 ounces per square foot. Scale models are min iatures of existing aircraft. None of my scale modeling friends knows or cares what his model's wing loading is.
They relate gross weight, in pounds, to engine disp lacement to ensure adequate power. Scale models don't often involve the same design latitude as other types of model, but some are fantastic examples of excellent workmanship. I personally favor higher wing loadings because they result in the airfoil; and smaller, stronger, faster and-if you 're careful in the design and the estimated weight.
Your mode l's wing loading is one of Higher wing loadings, however, these major decisions-and sho uld result in higher stall and landing speeds. Level flight requires a higher angle of attack or greater speed.
The Gap seal 60 most serious impact of a higher wing loading is on centrifugal loads when engaging in maneuvers that involve heavy elevator action. Such maneuvers include tight turns, sharp pull-ups or dive-recoveries. An advantage of a higher wing loading is that, at an y given speed , the wing must Figure 1. Entry in to maneuvers that in volv e wing stalling, such as spin s, snap rolls and avalanches, is more readily achieved.
Once you 've est imated your design 's gros s weight with fuel and decided your wing loading, the wing area in square inches is simply: Wing loadings and landing speeds are closely related. Refer to Figure 2, and read up from th e 16 ounces per square foot point at the bottom of the chart to the C L of 1.
On the left side of the chart, you 'll see that the stall speed is 20m ph. Do th e same thing on the 36 ounces per square foot line, and you' ll see that the stall is 30mph.
Adding a "safety margin" of 20 percent to each stall-speed estimate results in landing speeds of 24 and 36mph. The latter is too fast for comfort. Centrifugal force is expressed in multiples of "G", where 1G is normal gravity. Its formul a, including the model's 1G weight, is:. Ju st think what thi s mean s bo th aero dy na mica lly and structurally.
This is why I favor stiff, stro ng, fully shee te d and stress-skin ne d structures. The lift coefficient in this turn wou ld increase The re's a hea lthy marg in before th e stall.
If th e Swift's airfoil were E with a CL max of 0. See append ix fo r Eppler airfoil data. It's impossi ble to gauge accurate ly th e mo del's turning radii from several hundred feet away, hence th is safety facto r is needed to avo id "high-speed sta lls" whic h would probably result in un commanded sna p rolls.
The Swift-slotted flap s up-Will land at 30mph. With flaps down 40 degrees, at a CL m ax of 1. Flaps thus eliminate th e adverse effect th at higher Wi ng load ings ha ve o n landing speeds. In high -speed, short-radius turning man eu vers, 20 degrees of flap deflecti on would in crease th e Swift's CL ma x to 1.
Aerodynamically clean mod el aircraft tha t have powerful engi nes an d are correctly "propped" can ach ieve very h igh speeds. The no rm for patte rn shi ps is mph.
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My "Swift" h as a top speed of m ph ; its gros s weight is 92 ounces , and its wing loading is 22 ounces per square foot. At 90mph , it flies at a CL of 0. In a stee p tu rn of a SO-foo t radi us, th e load factor would be.
From wingloading at thebonom, read vertically to the appliicable liff coefficient andthen move leff horizontally to findthe speed in milesperhour. The stallspeed is based onanairfoil'smaximim liff coefficient. Tighter tu rns are possible witho ut danger of a h igh- speed stall. The Swift's sturdy flaps are strong enoug h to accept this treatment. The Swift was n' t design ed to be a stu n t m od el; it 's a "spo rt-fo rfun " model wit h a wide spee d range and low landin g an d takeoff speeds, i.
Its slott ed flap s aren' t suita ble fo r the wide range of aerobatics that pattern shi ps per form, both upright an d in verted. Plain flaps Figure 1 , h owever, in win gs with sym me t rica l ai rfoil sections , suc h as E sta n da rd o n pattern mod els wou ld function equally well angled down for uprigh t fligh t o r up for inverted flight. They ach ieve their C L max at 60 degrees of deflect ion an d would add an additional C L of 0.
At 20 degrees of deflecti on, the additional CL wo uld be 0. If we assum e: The pilot could extend th ese flaps up or down at any angle to suit th e m an euver in progress. Land ings, with a degree flap deployment, with a high wing loading of 28 ounces per square foot , would be at 28mph- a comfortable speed.
In addi tion, for sharp-turn ing m an euvers, lowering these flap s partially to 20 degrees would preven t high -speed stalls. At mph in level flight , a CL of 0. For a turn radius of SO feet at mph, th e load factor would be This calls for a CL of 0.
Th e degre e flap deflec ti on woul d provide a CL of 1. With flaps up , th e high er load ing wo uld move th e level-flight CL high er up th e lift slope, closer to CL max. In tu rn, th is provides easier entry into any man euver requiring th at th e win g be stalled. Patt ern sh ips have evolve d over tim e into beauti ful configuratio ns of startling similarity to one another. It's tim e to consider some fresh approaches to th eir design. Perh aps flaps and higher wing loadings are such approaches.
It weighs 92 ounces fueled , has square in ches of wing area 4. Max 0. Its top speed is mph , and flaps fully exte nded, it will stall at 18mph. Its wing loading is 22 ounces per squa re foo t, and its power loading is ounces per cubic inch of engi ne displacemen t. A detailed ana lysis of th e Swift's weight of 92 ounces reveals that Landing gear-tricycle with 2inch-diameter wh eels.
The rem aining weigh t of Th is portion is under the control of th e design er. The wing loading he selects will dictate th e wing's area, and gen erally, th e size of fuselage and tail sur faces.
It will also influen ce th e structure; lower wing load in gs an d lower speeds redu ce flight loads, particularly tho se du e to centrifugal force, pe rmitting lig h te r, less rugged structural design. It's poss ib le to design a model of square inc hes of wing area 5. Th is m od el wo uld ha ve a lower wing loading of Thus, flaps for landing wo uldn 't be n eed ed.
The weigh t of the fifth flap servo; the additiona l weig h t of the mAh battery versus mAh ; an d th e add it io na l weig h t of the flaps, th eir h in gin g an d thei r actua tio n would all be "saved.
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The point of all thi s is th at th e typ e of performa nce desired by th e des igner dictates th e win g loading and, to a large extent, th e structure. For the Swift, hi gh spee d and ma ne uve rabili ty were the obje ctives, calling for a rugged, stressskin ned and low-drag design. Thus, withi n reason able limits, win g loading governs performan ce and structura l design. Havin g selected th e power and control units and typ e of landin g gear, it isn' t difficult to closely estimate.
Sim ila rly, h av in g decided o n th e wi ng loading, the variab le weig h t of wings, tail surfaces and fuselage m ay be estimated with reasonabl e acc uracy. My own esti m at es h ave o nly ra re ly been "righ t on"; th e t enden cy was to underestimat e.
In compensatio n, the Swift 's gross was overestimated at ounces, whe reas the actua l is 92 o u nces- 8 o u nces difference. Whil e n ot p er fect , thi s rationa l but p racti cal approach shou ld n't result in a differen ce between th e est imate and act ual of m or e th an 10 pe rcent.
With weigh t estimates of both fixed an d var ia ble compo nen ts achieved and the wing load in g selecte d, th e wing area is easily calculated: It's useful at the ini tial stages of a new design to h ave a prelim ina ry estima te of th e new model's tot al weight and wing area. In Chapter 13, "Stressed Skin Desig n ," the weight versus wing area of 14 models is an alyzed, disclosing a surprising consistency in th e weight versus area relati onshi p of 0.
For those ado pti ng str essed -skin co ns truct ion, th ese figur es provide an easy weightestima te basis. For others who prefer lighter, mor e open structures, a study of constru ction arti cles an d product reviews will help. A word on tank size. SOci engine. Most sport flights seldom last more than 25 minutes so, on landing, the ounce tank is still half-full. Your model is penalized to about 1;2 pound carrying thi s useless weight. A guide to tank size relative to engi ne displacement is 20 ounces per cubic in ch of engine displacem ent.
Th us, for a AOci engi ne, an 8-ou nce tank is right on. Now, let 's cons ide r the many othe r design decisions to be made. It's fun! Figure 2 of Chapter 1. For wings of smaller models, this taper ratio results in narrow tip chords and undesirably low Rns at low speeds. Increasing the taper ratio produces larger tip chords. The resulting loss in efficiency isn 't great and is the "lesser of the two evils. A tapered wing can be lighter yet stronger than a rectangular wing of the same area.
Th is is the "ideal" win g planform. These factors in crease for tap ered or rectan gular wings. See Figures 2 and 4 of Cha pter 1. Structurally, th e elliptical wing is difficult to produ ce.
Each rib is different an d wing skins all have a double curva ture, chordwise and spanwise. The Spitfire 's elliptical win g is a classic exam ple. Sweptback wings. This causes similar behavior to decreased taper ratio smaller tip chord and leads to early tip-stalls with a nose-up pitch, since the tips, being behind the CG, lose lift.
The resulting drag imbalance works to oppose the yaw. Large sweptback angles increase induced drag and lower the wing's maximum lift. Wings of moderate taper ratios 0. Rectangular wings. Th is is the easiest typ e to design and build. All ribs are th e sam e, and wing skins ha ve a sing le chordwise curvature. Structurally, the wing roots need reinforcing , owing both to narrower root chords and higher bending moments.
The cen te r of lift of each win g hal f is farthe r from the cen te rline than an elliptical or tap ered wing. Tapered wings. A taper ed wing with a tip cho rd of 40 percent of th e root chord comes closest to the ideal elliptical planform in both induced AoA and induced drag see: These wings tip-stall readily for easy entry into wing-stalling maneuvers such as snap rolls, spins, etc.
Structurally, a sweptback wing's lift tends to reduce the Wingtip'S AoA, particularly at high speeds and high centrifugal force loads. A stiff wing structure will prevent potentially damaging wing flutter. Swept-forward wings. These tend to stall at the wing root first. The unstalled tips promote good aileron control at high angles of attack. The root stall reduces lift aft of the CG, causing a nose-up pitch. Forward sweep is destabilizing in yaw. The centers of drag and lift of the advancing wing panel move inboard; on the opposite, retreating panel , these centers move outboard.
The unequal drag moments increase the yaw, while the unequal lift moments cause a roll, but in a direction opposed to the yaw. Control of this instability calls for increased vertical tail surface area and effectiveness, along with generous dihedral.
Structurally, a wing very stiff in torsion is required to overcome the wingtips' tendency to increase their AoA. Any flexibility could be disastrous at high speeds. In full-scale airplanes, modest sweep forward moves the wings' main spar aft, out of the way, and. Delta wings. The triangular shape of a delta wing is so called because of its resemblance to the capital letter delta d in the Greek alphabet. These have very low ARs.
Low-AR wings stall at high angles of attackbut with high induced drag. Vortex flow is high , since a delta wing is virtuallyall "wingtip.
Power-off, they have the glide charac teristics of a brick! A tailless delta-wing model, with the whole trailing edge composed of elevons , is highly maneuverabl e and will not spin , but requires symmetrical or reflexed airfoil sectio ns for longitudinal stability.
Structurally, deltas are ve ry strong. The deep, wide center chord promotes strength, and the low AR reduces the bendin g moments at the wing's center. The AR of a wing has a major impact on its "induced drag"defin ed as th at drag caused by th e development of lift-and is separate from th e drag caused by th e wing airfoil's for m an d frictio n, called "profile drag.
The classica l formula for the induced drag coefficien t is: Lift coefficient2 st. Co m b ined rectan gular and tapered wings. This planfor m is rectangular for roughly 50 percent of the semispan in board and tapered for the remaining 50 percent to the wingtip. Piper Warriors and Cessna s typify this planform. It comes close to the elliptical in shape and efficiency, yet is more ea sily produced than a tapered or elliptical wing. Th e com men ts earlier regarding th e hazards of low Rns of narrow wingtips apply.
The rectangul ar inner portion is wider in chord, which provides a stro ng win g root, and bending moments are lower than for a rectangular wing. The Swift 's wingspan is Its AR is: Obviously, th e high er the AR, th e lower will be the induced drag coefficient-an d the lower th e induced drag. Th is is wh y soaring gliders h ave suc h lon g, narrow high- AR wing s. An airplane's tot al drag is composed of two types: Figure 2 illustrates thi s relati on sh ip.
Induced drag has a very significant difference from both lift and parasite drag. The latter two are pro portio nal to th e square of th e speeds; induced drag, however, is inve rsely prop orti on al to the squa re of th e speed. It's lowest at h igh speeds and h ighest at low speeds. Lift and parasite drag are low at low speed and h igh at high speed. At m ph , th e tot al of profile and induced drags for th e Swift is At 30mph, tot al wing drag is 4. It's th is relat ion ship that explains th e power-off, brick-like glide of a delt a wing.
The low AR and h igh lift coefficients result in very high induced drag for low-speed delta flight. Figure 2 depicts typical airplane drag curves. Where the induced drag equals the parasite drag is th e speed of the maximum lift-to-drag ratio and of the maximum range. Range, for model airp lanes, is n ot a factor of any consequence, except in rare instances, since most powered RIC flights seldo m exceed half an ho ur in dura tio n.
The narrower chord tip s result in smaller wingtip vortices; th e lift per degree of AoA increases so that th e model flies at a lower AoA. These all favor high ARs. Scale effect causes an increase in wing profile drag, a redu ction in maximum lift an d lower stalling angles.
The centers of lift of each wing half are farther from the fuselage for high-AR wings, resulting in substantial increases in root bending loads. In addi tio n, long, na rrow wings must be stiff in torsion to preven t twisti ng un der loads from two sources-pitch ing-mo ment changes as th e mo del man euvers and the opposed action of ailerons. Typical airplane drag curves. Parasite drag varies directly as the speed squared; induced drag varies inversely asthespeed squared.
The up-going twists th e lead ing edge up. The model banks in a direction opposite to that intended by its bewildered pilot. High ARs result in weight increases, particularly for models designed for high speeds where high centrifugal loads are encountered. Increased weight results in higher wing loadings and higher parasite drag. Obvio usly, there must be some compromises.
With his neck "stuck way out," thi s author suggests th e following classifications for radio-controlled mod el aircraft see Table 1: From this designer's poin t of view, to obtain th e maximum efficiency,.
Higher flight speeds result with lower lift and profile drag coefficients and lower induced drag until the to tal drag equals the th rust. To provide the optimum strength-toweigh t ratio to overcome h igh centrifugal force loads, stressed-skin structu ral design is suggested.
To reduce landing and takeoff speeds, slotted flaps are recommended. Figure 4. Asair tlows pasta wing from leading edge to trailingedge, positive pressure is created below theWing, while negative pressure exists above.
At the wingtip, the positive-pressure bottom wing air flows around thetip andis drawn Into thenegativepressure region above the wing. This action gives rise to the wingtip vortex, as well asto lesser vortices along thetrailing edge. Figure 3 illustrates how the various wing planforms stall at high angles of attack.
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Note th at th e rectan gu lar wing stalls root first, perm itt ing effective aileron control well into the stall. There are a variety of ways in whic h tip -stalling may be delayed to higher angles of attack. The best and simplest form is the NASAdeveloped and tested partial-span wing -leading-edge droop. This feature has been used very successfully on six of my model designs.
Figure 6. The downwash and wake for a conventional, rear-tailed, aircraft.
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Note thesuggested droop fuselage thatwould decrease drag. Time frames above the wing are spaced farther apart to Illustrate highervelocity air.
Figure 9. The major difference in efficiency between the elliptical planform, considered the best, and other planforms is largely due to wingtip losses. The elliptical has no pro nounced tip-one could say it is "all tip "- whereas the rectangular planform has the widest tip. Tapered wingtip widths vary with taper ratio. Figures 4 and 5 portray the airflow over and under a wing and particularly the tip vortex flow. Figure 6 shows the wake and downwash resulting from the wing 's production of lift.
Obviously, the narrower the tip, the lower the tip losses with due regard to stall patterns and scale effect, particularly at low speeds. A tip-stall close to the ground may be. Over the years, aerodynamicists have explored many wingtip configurations in their search for improved wing performance. Two forms, somewhat resembling each other, have emerged.
First is the Schuemann planform Figure 7. The second is the "sh eared" wingtip, largely developed by c. Van Dam of the University of California. Figures 8 and 9 provide an outline of a sheared tip along with its spanwise load distribution.
Note how close "modified" is to "elliptical" in Figure 9. This form of tip has been, or is being, applied to full-scale aircraft designed by such no ted aerodynamicists as Burt Rutan and Peter Garrison. This author us es a modified sheared wingtip that is both sim ple and rugged.
Figure 13, a top view of the Snowy Owl's wing , illustrates this tip form. Earlier model designs, such as th e Snowy Owl, had slotted flaps wh ose chord was 26 percent of th e win g's chord and were close to 60 percent of the wing 's semi-span in len gth see Figure After being throttled back and having their flaps fully extended, these model s porpoised upward suddenl y. Elevator down -trim applied simultaneously with flap extension would prevent this behavior, which was annoying.
Comparison of increments of section maximum tift coefficientfor three flaps ona NACA airfoil. The wing 's AoA and lift increased, an d the model zoo med upward until the excess speed bled off. The mo del the n nosed ove r in to th e flap-d own , slow glide.
Experi ence with three of my models Sea Gull Ill, Sea Hawk and Swift has proven that widen ing th e flap chord to 30 percent of th e wing chord produces a ba lance between these "nose-up" an d "n ose-do wn" forces, flap s full y extended. All three models exh ibit no change in pitch on lowerin g flaps-but fly mu ch more slowly. On landing approach , groun d effect redu ces th e downwash angle and in creases the nose-down pitch.
The glide close to th e ground steepen s, but appro priate up -elevator action raises the nose so th at a gentle, slow landing result s. For sport models, it's customary to locat e the CG at the wing's aerodynamic center 25 percent of MAC.
There is, howe ver, a range of CGs both ah ead of and behind the wing's aerod ynamic center. These positions result in varying degrees of long itudinal stability. The steel ball in a saucer is a very graphic manner of describing pitch stability at various CGs see Figure 1.
Note that at position 4, the neutral point, the ball is on a flat surface and may be moved in any direction without returning to its original location in contrast to positions 1, 2 and 3, where the ball does return. At point 5, the ball will roll off the inver ted saucer, indicating serious instability.
The following will outline the various CG advantages and limitations. Th e most forward CG possible depends on the downward lifting capability of the horizontal tail. When I designed the Swift, the tail download needed to offset its wing. A CG at 5 percent of the MAC, almos t 2 inch es ahead of the aerodynamic center, wou ld further increase the required tail download.
This results in three things:. It reduces the ho rizontal tail's pitch maneuverability. This is because a major part of th e tail's lift capaci ty is taken up with overcoming the nose -down combination of pitching moment and CG. This limited capacity makes achieving a full stall attitude difficult, if not impossible, in ground effect th is pressure of the ground reduces downwash. Moreover, with slotted flaps fully extended, the wing's nose-down pitching moment is further increased even with full up-elevator.
However, at this forward CG, the model's longitudinal stability would be h igh, and it would recover by itself from any pitch disturbance, returning to level flight. It would be easy to fly, but not highly. Mov ing the CG rearward improves man euverability but redu ces pitch stability.
Modern aerod yn amic ana lysis for assessing the stability of an airplane is based on the fact tha t a win g an d tailplane represent a pair of airfoils in tandem. Each has its own aerodyn am ic center, but th e combination will also have a correspo nding MAC equiva lent to th e point whe re the total lift and drag forces of th e two airfoils effectively act. It follows th at th e NP will lie betwe en th e aerodyna mic cen ters of th e two airfoils and closest to the larger or mor e effective lift producer, i.
Any disturban ce in pitch that mom entarily upsets th e n ormal flight path of th e aircraft will cause a ch ange in AoA of both air-. In Ihis illustration, a ball bearing in a saucer simulates therelative pitchstability of various CG locations. Spinner, prop, engine, muffler, engine mount,fuel tank, fuel cowl 3 oz. Receiver 6-channel , mAh battery, five servos, switch, two extension cables, foamrubber protection for receiverand battery. Mass balanced. Length from the engine bulkhead to the rudder tail post is This comes to Experience with several models indicates an average fuselage weight of 0.
This will be tran slated as an increase or decrease in th e total lift at th e NP. The system is longitudinally stab le if th is change in lift pro duces a correc ting effect, which it will if the NP is beh ind th e CG.
A nose-up disturbance inc reasing lift would apply this lift inc rease at th e NP, behind the CG, causing th e nose to drop and vice versa. The degree of inhe rent stability is governed by ' th e distan ce between th e CG and the NP aft of it.
It's also the farthes t aft pos ition possib le for th e CG wh ile still avoiding instability. Calculation of the NP's precise location is very complex. The re are man y factors inv olved:. Further movement of the CG aftward to behi nd NP would result in serious longitudina l instability. The NP's position govern s the margin of stabil ity available static margin, or distance between CG.
For practical mod el design purposes, the "power-on " NP is located at 35 percent of MAC from its leading edge. The "power-off" NP moves a few percentage points fart her aft, so tha t a mo del is more stab le in an "engine-idling" glide.
As fuel is consumed, th e CG mo ves back an d could easily reach a po int behi nd th e NP, leading to pitch instab ility under power. Patt ern- sh ip design ers recognize th is risk an d position their fuel tanks on the mod el's CG. As fuel is consu med, the CG does not sh ift. Engi ne -dr iven pu m ps force the fuel to the carburetor.
These designers use symmetrical wing airfoils with lower CL max because of their little or no pitching mo ments and aft CGs close to the NP.
A sma ll tailplane upload balances th e aft CG. The result is a h ighl y man eu verabl e model-but. As the ph ot o of th e Swift's win g clearly illustrates, th e wing cen ter sectio n is open ahea d of the main spar and behind the aft spar. This he lps in providing access. This aut hor makes the following suggestions for the installation of the cont rol components: Positio n the receiver aft so that it and the an tenna are away from the wiring to th e servos-and keep th e antenna as far away from the contro l cables as possible.
Using the techniques describedin this chapter, the Swift's CG was righton themoney. No ballast was needed.
Since th e stability is close to neutral, any distur ban ce will divert th e mod el from its flight path, but th e aircraft will not seek to return to its origina l course volunta rily, as a positively stable model would. You have design ed and bu ilt your very own model airplane.
Wisely, before you go out to th e flying field, you decide to check th e ph ysicallocat ion of your model's CG. To your disma y, you fin d it's well away from its design location.
You are not alon e; it has happened to others, including thi s author. To correct th is situatio n, you' ll find th at you do n't have as much flexibility in rearrang ing thi ngs as you might think.
Your eng ine , fuel tank and servos are in fixed locations. The onl y items that are readily moveable are the receiver and batte ry. Questions of CG inevi tably lead to a consideratio n of the arrange me nt of in ternal components and linkages. Bitter experience in dicates that wiring from servos to receiver should be kept well away from both receiver an d an tenna to avoid radio in terference.
This author dislikes dowel push rods from servos to rud der and elevator, and wire push rods. Such installation s requir e that rudde r and elevator servos be located near the wing trailing edge and tha t th e fuselage be "open" interna lly back to th e tail surfaces.
In addition, th ey vibrate he avily when th e engine is running, doing both servos and control surfaces no good. Bellcran ks lead to "slop" at th e contro l surfaces. Stranded stee l cables run ni ng in plastic tubing permit the fuselage servos to be moved forward for easy access; th e cables are run down th e in side walls of th e fuse lage, or th rough th e wing ribs, out of th e way, and permit direct "no -slop" linka ge between servos and control surfaces.
No bellcran ks are needed; cables do not vibrate as do link ages. Position engine, rudder and elevator servos close behind the tank. Position servos for ailerons and flaps in the open wing center section, between the main and aft spar. The receiver's battery sho uld be located so that "ma jor surge ry" isn 't requ ired for its removal and replacem ent.
Finally, all in-fuselage and inwing equipment should be readily accessible. These objectives hav e been realized in the Swift. The front top of the fuse lage is rem oved by unscrewin g one bolt. Similarly, th e lower engine cowl is even easier to remove. All compo nents are readily accessible for adjustment, replacement or any othe r reason. The tan k is fueled with the fuse lage top "off. Getting back to your new design; if you are un able to relocate your actua l CG to where you want it, your on ly recourse is to add ballast, either up front for tail -heaviness-or aft Side view of theSwiftplan with power, control andlandingfor nose-heaviness.
The balance-line fulcrumis in position at the Lead shot, lightly coatlower center. I used a triangular draftsman's scale as a fuled with epoxy or crum, but a spare piece of 3A-inch balsa triangle stock would also work well. Tank sizes are nominal, in fluid ounces, wh ich is a measure of volume, not weight. Use your scale to weigh the tank, both empty and full.
The differen ce is fuel weight! A scale is essential for good design. The author uses an old beam scale, but th e type used for weighing ingredients in cookin g is available at low The balance beam is onthe fulcrum and the weight-at the shortend- is positioned so that beam andweight a drafts- cost.
It is recommended that you use one with man's "duck" balance onthe fulcrum. Added weight actual , physical CG durin g the doesn 't improve the model's design process lead to developmen t performance. It may be used on any confi guration, con ven tional, canard, flying boat, etc. Used for the Seagull 1Il flying boat during the design stage, th e balancing act resulted in moving the engine nacelle forward 2 inches; its weight of 31 ounces compensated for a substantial tail heaviness.
On completion, this model required no ballast. Time spent on th e balancing act avoid ed maj or and difficult modifications to the finished model-or addition of a substantial weight of ballast up front. Here are the steps needed:. Gat he r all the fixed-weight components that you possess. For those you don't have, make "dummies" of th e same weight.
Your scale is used here. Expired AA, C and D batt eries, lead shot, fishin g sin kers, et c. Similarly, make dummies for each of the variable weight items and win g, fuselage and tail surfaces, both horizontal and vertical. On ce selected, these are items over which the designer has no weight control; the engine is an exam ple.
If you don't alread y have th ese components on hand, their indi vidual weight s are easily obtained. Don 't be fooled by the tank size. All the actual anddummy, fixed and variable weights in position-andagain thebalance beam is level. The actual and design CGs now coincide. Positi on th e CGs of the variabl eweight items as follows: Because of th e concave aft contours of the Swift's fuselage, this was adva n ced to 35 perc ent. Seagull III.
The original design hadthe engine nacelle farther back. The "balancing act" indicated that it was tail heavy. The nacelle was moved forward 2 inches; no ballast was needed when the model was completed. Draw a side view, full-scale, of yo ur design sh owing the positi on s of your fixed- weight it em s. Show your de sign 's CG clea rly-but don't det ail any internal structure.
Locate and identify th e CGs of your variab le-weight items-wing, fuselage and horizontal and vertical tails. Draw vertical lines from th eir CGs to th e board th at will be used as a balance beam.
Place a fulcrum, e. The fulc rum should be vertically in line with the model's CG. Place th e "balancing beam" on th e fulcru m and weight the short end so th at th e beam is balanced on th e fulcrum. If balance is achieved-good. If th e beam tilt s down at the tail end, your design is tail heavy. Slight forward movement of power components, nosewheel unit and possibly fuselage servos should achieve balance. Measure th e distance of this forward move, and elongate the design 's fuselage accordingly.
The best solu tion is to move the design's wing forward. Carefully move the beam and its weigh ts backward-then move wing, wing servo and landing gear or dummies forward to the original positions relative to your side view. Some trial -and-error movement will achieve balance. The distance the beam is moved backward will indicate the distance the wing must be moved forward to get the actual and design CGs to coincide.
Now tha t the posit ions of all the components have been established for the correct CG, mark your drawing acco rdingly. The fuselage. See "Stressed Skin Design. Having to add gobs of weight, fore or aft, to your model to pin down that elusive CG to its design location is no t good engineering. The balancing act will surely reduce the amount of weight needed, if it doesn't eliminate it entirely. The Swan canard, flaps extended onIts cradle.
Twelve ounces of ballastwere needed-and providedfor-as a resultof using the "bafancing act. What area should it have? How far behind the wing should it be locat ed? Where should the tail be located vertically, relative to th e wing? What ang le of incide nce shou ld it have? Wha t airfoil? What proportion of its area should the elevators have?
And what type of construction should be used? Th is cha pter will answ er th ese que stion s.
An airplane in steady level flight is a remarkable "balancing act. Wha t are these forces? CG placement. A CG ahead of the wing 's center of lift causes a nose-down reaction. Behind the wing's center of lift, a nose-up actio n takes place.
A CG vertically in line with the Wing's aerodynamic cen ter, i. Pitching moment. The pitching moment of semisy m me trical or flat-bottomed airfoils causes the aircraft to nose down. Symmetrica l or. Symmetrical sections are popu lar for aeroba tics; they fly equally well upr igh t or inve rted.
Reflexed sectio ns are used on tailless mod els. Upwash and down wash. Upwash origi na ting ahead of th e wing strikes both prop eller disk and fuselage at an angle , ah ead of th e wing , and th is causes a nose -up reac tio n. Down wash from the wing's trailing edge strikes both the aft fuselage and th e horizontal tail downward, and thi s also causes a nose-up reaction.
Thrust line. A thrust line above the CG causes a nose-down reaction. If it is below th e CG, a noseup reaction result s. Cen ter of drag. A high-wing model has its center of drag above the CG. A nose-up reaction occurs. A low-wing mod el reverses this reaction. A mid - or sho ulder-wing location perm its th e cen ters of lift, drag, thrust and gravity to be closer to each other.
This, in turn, min imizes th e im balance of forces th at frequently oppose one another. The horizontal tail sup plies th e balan cing force to offset the net result of all th ese forces, and its chord line mus t be at an angle to th e downwash th at provides either th e upward load or most often the down load requ ired.
Obviously, no self-respec ti ng horizontal tail should find itself located in this very disturbed wake. The angle of the downwash depends on th e lift coefficient at which the wing is flying. An airplane ha s man y level flight speeds, from just abo ve th e sta ll at low engine rpm to its maximum speed at full throttle. At low speed, th e wing's angle of attack mu st increase, as does its lift coefficient, and the downwash angle is high. At top speed, th e reverse is true, and the downwash angle is low.
At low speed, the hori zontal tail's downward lift must be increased to force th e wing's airfoil to a h igh er AoA. Part of this download is supplied by th e increase in the downwash angl e. At high speed, the tail 's down load must be reduced to lower th e wing's AoA- but again, since th e downwash angl e is reduced, th e tail download is reduc ed. The point of all thi s is th at as the model's level flight speed varies with the throttle setting from low 1. The tail surfaces of a con ventional, rear-tailed airplane operate in a very disturbed atmosphere.
The air sweeps down ward off the wing 's trailing edge as the result of th e lift generated. This airstream is called th e "wake. On mod el airpl an es, th is is acco m plishe d by changing the an gle of th e elevators.
This angl e is controlled by the elevator tr im lever on th e transmitter-literall y at o ne's fin gertips a little upelevator at low speed and some down for high speed. The an gle of incidence of th e fixed portion of th e horizontal tail , i. For semi symmetrical or flat-b ottomed wing airfoils , an angle of incidence of minus 1 deg ree as measured against the da tum lin e is appropriate.
For symmetrical wing airfoils, an angl e of incidence of zero degre es is suggested. Th ere are some exceptions to these rules, as you will see. This is easier to visualize if one con siders th e airplan e fixed with the air passing at level flight speed, as in a wind tunnel. This reducti on adversely affects th e tail's effectiveness. The greater th e vertical distance betw een th e Wing's wake and th e hor izontal tail , th e smaller flatte r the downwash angle is and the less the reduction in velocity of the air is.
A T-tail location, atop th e vertical tail surface, raises it well abov e th e win g's wake and puts it in less disturbed air. Other T-tail advantages are:. Th e elevato r ma y be sit uated above th e prop slipstream. It is out of th e fuselage's bound-. For high -wing models, a low-set horizontal tail brings it well belo w th e wake. In addition to its vertical location, the effectiveness of th e. It is, in effect, th e lever on which the tail's area wor ks. Many m od el s in co rpo rat e flat balsa sheet or flat built-up tail surfaces.
These are less effect ive, aerodynamicall y, th an sym metrical airf oil s. Figure 1 shows polar curves CL versus Co for a flat plate airfoil at low Rns. Lift is greater, and drag is less for E As explain ed in Chapter 13, "Stressed Skin Design ," symme trical tail surfaces may be made lighter an d stronger than shee t balsa and much stronger th an built-up surfaces and only slightly heavier.
Based on experience, this author uses a simp le meth od for establishing the horizontal-tail area HTA. If you have a wing AR of 6 and a tailmo ment arm that is 2. Here is the formula: For short TMAs, this formula will increase th e tail area ; for long TMAs, area is reduced , but wha t aerodynamicists call "tail vo lume, " i.
For sma ller models, however, th e tail 's ch ord sho uld not be less than 5 inches to avo id unfavorable low Rn effect s. An AR of 4 to 5 with constant cho rd is reco mmen ded. Both lift and d rag increase substa ntially, and th e model's speed dec reases. The wing's nose-down pitc hi ng moment increases sha rply. Th e down was h angle also increases in proportio n to th e lift increase from th e lowered flap s.
Thi s increases th e horizon tal tail download. Experienc e with th e Seagull III, th e Seahawk and th e Swift indicates th at the flap chord in percen t of th e wing's chor d influ ences th e model's flaps-down beh avior.
Flaps with wider ch ord s-up to 30 percent of th e win g's cho rd- gene rate very little pitch cha nge when extended. When a plane is in grou nd effect: The wing beh aves as though it had a h igh er AR; lift increases and th e sta ll AoA decreases see Figures 2 and 3. The induced drag of the wing decreases see Figure 4. The most im portan t ch ange is a severe reduction in the downwash an gle to about hal f its value at high er altitude.
It is very satisfying to lower full flap, after th rott ling back and have th e model continue on its m erry way, with out nosi ng up or down , but flying noticeably slower. For narrower chord 2S percent flaps, th e flap-induced tail down load is greater th an th e nose-down wing pitching moment. When th e flaps are extended, this causes the model to nose up sha rply an d rather alarmingly.
Wh en an airplan e is on fina l approach and descen ds to half its wingspan abov e ground or water Lowering flaps causes an increase in th e down wash angle and in the nose-down pitch; but th e severe downwash angle reduction , du e to gro un d effect, red uces th e tail 's dow nlo ad, causing the mod el to nose-down in a sha llow dive.
This is part icularly noticeable for models with wide-chord up to 30 percent of th e Wing's cho rd slotte d flaps. This beh avior requi res consider able up-elevator force to sto p th e dive and to raise th e aircraft's nose to th e n ear- st all touch down posture. The larger th e elevato r area , in proportio n to the ho rizontal ta il's tot al are a, th e mor e effective th e elevato r, as shown in Figur e S.
For slotted flapped mode ls, an elev ator are a of 40 perc ent of th e h ori zontal tail's area is suggested. Th is prop ortion provides adeq ua te elevator auth or ity to achi eve n earfu ll-st all lan d in gs, with fla ps ex te n ded an d in gro u nd effect.
Wit h out flaps , a pro po rtion of 30 to 3S percent is adequate. Full eleva to r deflection of 2S degrees, both up and down , is appropriate. Th is m ay, at first, prove sensitive but , with practice, has proven to be no problem. At high speeds, elevator low dua l rate is suggested. Th ere are, h owever, ad vantages and di sadvantages in h eren t in positioning the CG ah ead of o r behind the Win g's aerodynamic cen te r.
See Figur e 6. A CG ahead of the wing 's aerodynam ic center ha s only one advantage: The model's maneuverability is reduced , particularly when centrifugal for ce comes into play. More on th is subject further on. The tail download to balance the for ward CG adds to the load the wing mu st support, in addition to the model 's weight. Profile and in duce d dr ags called "trim drag" of both wing and tail increase. In gro und effect, and particularly for a flapp ed model, more powerful tail downlift is needed to raise th e model' s nose for a flapsdown landing.
This is more pron ounced for wings using cambered , i. For sym m et rical-win g airfoils, the tail download need o n ly balance the nose-down moment of the forw ard CG and the nose-down pitch from the ex ten ded flaps. With respe ct to an y m aneuver involving centrifugal force an d there are few that don 't , that force acts at the CG and also substan tially increases the load the wing must support.
See Chapter 4, "Win g Loading Design. In a tight turn at h igh speed, centrifu gal forc e increases the wing lift and the weight at the CG ahea d of the wing's aerodynamic cen ter. A force couple results that resists the turn. Th is imposes a he avy addit io n al load on the horizontal tail th at , even with full up elevato r, it ma y be unable to su ppo rt- an d it stalls-limiting the model's maneuverability.
What do you need to make an RC plane? The frame Arguably, the most important part of the entire RC plane has to be the frame. When it comes to making an RC aircraft, choosing the right frame is the first hurdle you need to cross. Interesting fact: In the early days of RC devices, people used wood for the frame.
Of course, times changed and so did the primary ingredient of the product. Nowadays, one of the more favored materials for this purpose is carbon fiber. In many planes, you will see that carbon fiber has been used and it actually gives a better shape to the plane as a whole. The only issue that comes along with carbon fiber is its high cost.
There is no doubt that cost does have an important role in choosing materials and parts for the plane, but if you are willing to spend a little more, then carbon fiber is the best choice. These are easily available materials and, of course, they are affordable.
Moreover, Depron is another material that is in demand for making the airframe of the plane.
The reason most of the RC plane enthusiasts are opting for this material is its ability to mix flexibility along with rigidity which is not something that you get in common airframe materials. In addition, this particular feature of the product allows the RC plane to absorb a lot of stress that it might encounter whilst in air. If you are building an aircraft for a beginner, then using expanded polypropylene would be a wise idea.
We say this because this product is known to support any kind of abuse — and this will definitely happen if the plane goes to a beginner. The tail One of the things you absolutely need to build an RC plane is the tail.
For starters, the tail is used to give the flying machine proper direction while in flight. It is also responsible for making sure that the plane has the necessary stability. One of the reasons why people tend to choose the V-tails is the simple fact that they create lesser drag and they are lighter. However, you will also find another type of tail in the market. Given the importance of these parts, it would not be a bad idea to look carefully while deciding what kind of parts you are going to use.
Lastly, you must remember that these tails are controlled with the help of an external product such as remote controls and a transmitter which is why you must make sure that the tails are functioning and are in sync with the transmitter.
The receiver The transmitter and receiver are of the utmost importance for your plane. So, if you want to be able to fly it correctly, you must make sure the products you choose are of the highest quality.
Moreover, if you are using a radio transmitter for this purpose, then make sure to check the number of channels it offers. These channels control the movement of the RC plane. Usually, radio transmitters are known to provide at least 2 different channels. Still, if you are looking for a good transmitter, then try to find one with 4 channels as they are known to provide better control over the plane.
The usual job of the 4 channels is to control the throttle, rudder, elevator and ailerons. How you power your receiver depends on the power system of the aircraft you are building. The situation is a little different for electrically powered planes. In this case, since there is already a source of battery power in the device, you could just make use of the batteries that power the propellers.
This connection can be done via a battery eliminitor circuit. Some of the well-known brands for receivers we can recommend are: HiTech,Futaba, Airttronics and the likes. Tip: If you are going to fly multiple planes, you can just get one radio transmitter and programme your receiver to have n number of memories. In this way, you can switch from one aircraft to another, working on the same transmitter.
It saves a lot of money since with every new plane, you would just be downloading a new receiver! The servos No matter what kind of RC plane you are trying to build, you will need good servos for the purpose. This is perhaps the most important part of the airplanes as they are solely responsible for proper functioning of the device.
This is actually the motor which controls and helps the movement of rudders, throttle and flaps, all of which are necessary for the flight.
Also, more importantly, these elements come in all shapes and sizes which means that no matter what size your RC plane is, you will always find a servo for your device. One thing to be noted here is that the torque generated by the servo depends on the size of the servo you choose.
Again, you have a different type of servos for electric powered and gas powered RC planes, which is why choosing compatible elements is an absolute must.
The controller Let us now take a look at that element in any RC plane that makes its movement possible from point A to point B.
One of the most crucial features you need to look for in your controller is the number of functions it offers. More functions would give you better control. Also, it would be a good idea to give your aircraft and controller a trial run to identify whether they are compatible or not. Some of the controllers you have in the market include the likes of Futaba, Laser, etc.
Keep in mind: Make sure the stick on the controller is not very rigid as it might unnecessarily restrict the movement of the plane. The Power source Before even starting, you need to decide what kind power source is required by the device you are making.
For example, if you want to build an electric powered RC aircraft, then you will see that they work or fly very quietly. Usually, you will see that RC planes using electricity are smaller in size and faster by nature. Moreover, these types of planes are known to use batteries, especially rechargeable ones.
For this purpose, it would be prudent to use Li-Po batteries as they have a proven track record in this field. To get much more familiar with this topic, we suggest checking out our article about drone batteries. This is necessary to drive your RC plane, so keeping an eye out for the best powerplants is not a bad idea. Some of the most common powerplants used by these devices include electric motors, internal combustion engines, and the likes.
Designing the plane Now that we know some of the key components we should have before we start building our first ever RC plane, let us look into some of the basic steps to be followed. Having a design with the different dimensions will help you construct the plane perfectly.
But, in order to build the design, you first have to go through several steps. Step 1: What is the purpose of your RC plane?
This is the first question you should be asking yourself in order to build the perfect device. Why are you making the plane? It could be just as a hobby for having some fun flying. In other situations, you could also add a camera to the plane and use it for getting a view of the world from above or even for aerial photography.
The purpose will help you decide how you want your aircraft to be built. Step 2: The huge collection of electronics. What comes with the RC plane is an array of electronics that will be included in the structure. This would include the batteries, servos, receiver and the likes. The more electronics you include, the more it will increase the weight of your aircraft.
In general, it would be advisable to select the motor and battery in a way that your device gets the right thrust and yet gives you long enough flight times. Collect all the electronic components you need and keep them ready.
The total list of electronics would include electric motors, ESCs, battery eliminator circuit, channel receiver, and servos. Step 3: Make an idea of the total weight of your RC plane.
Making an RC plane is not a very simple task.For short TMAs, this formula will increase th e tail area ; for long TMAs, area is reduced , but wha t aerodynamicists call "tail vo lume, " i.
A perfect complement to RCadvisor's online model airplane calculator, this book stands completely on its own. In modern aircraft, the pitch change is done automatically, and the propellers are referred to as constant-speed propellers.
Part 01 this download is supplied bythe. The pitch is the theoretical distance travelled, by the prop, in one revolution.
Aerodynamics is the way air moves around things.
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