How do you decide the length of wing and fuse?

[skippyflyboy]

Hi,

I would really like to take on the task of scratch building my own designs. I know that there is some correlation between wing/fuse length. Is there an equation that I need to know? There has to be some mathematical calculation that allows for optimum lengths, right?

Also, tail surfaces. How do you determine elevator/rudder sizes. Obviously, more surface area and control surface movement = greater response. But I am equally sure that there is an area where the size can be too much (aside fom the pilots ability to handle response of the aircraft).

Any input would be greatly appreciated!

As a side note, my youngest son is autistic and does not usually have much interest in anything. That is, until Dad gets out the airplanes. He loves to look and touch and just generally seems interested. So this is where my desire to learn how to do this is generated. I think he would actually sit with me and enjoy "watching". Anyways, I hope to be able to apply what ever you guys (and gals) can teach me.

Thanks

Chuck

[CloudyIFR]

If you have MS Excel try Sailplane Calc here:

http://h1.ripway.com/cloudyifr/files.htm

Curtis
Montana

[BMatthews]

I make it look a lot like all the ones that already flew before my design and that I like the looks of.

In scientific terms it's called "plagarize"...

Yes it's funny and yes I'm serious.

Get into building and make a couple of simpler models with him. If he can have him add in a hand here and there. Make up something simple like a rubber band free flight catapult glider and with a little assistance like you holding and aiming the rubber stick peg for the rubber he should be able to let the model go and see it fly away. It's not always the big flashy looking radio control models that can make us grin like kids again.

[skippyflyboy]

BMatthews,

Great advice. He will not stand still long enough to watch them fly though (not sure how to fix that, or even sure if I can). But, amazingly enough, he will sit and watch me build (an endless string of Estarters, although I can actually keep it in the air nowadays, so time for something new :D ). I'm not sure why and to be honest I do not care. That something interests him enough to get him to stop walking endless circles around our table is a god send in my opinion.

Thanks for taking the time to respond, I appreciate it!

Chuck

[Ollie]

From Dr. Drela:
"Ch = (A_hori/A_wing) * (tail_arm/avg_wing_chord)
Cv = (A_vert/A_wing) * (tail_arm/avg_wing_span )

"A well-sized tail will be in the range...
Ch = 0.35 - 0.50
Cv = 0.02...

[Sail 'n Soar]

This is the process I use:

My target weight and wing loading determines the wing area.

The aircraft intended purpose defines the wing aspect ratio range and the aspect ratio then difines the wing span.

I determin the fuselage length, L, from the square root of the wing area ( for my standard sport designs, L = sqrt(a*A) , where a ~3 plus or minus. I generally choose a=3.1)

Place the wing quarter cord ~ 25%*L behind the nose and determine the tail surface areas from Ollie's Ch and Cv equations.

"a" is larger for Jets and piston fighter aircraft due to their longer noses and further aft wing positions. If you would like to check my equation out, take several models you are familiar with and calculate L^2/A, which equals the " a" in my equation. You should get a range of "a's" for yourself. In any case, I have been using process to define my model proportions and all have flown great first time out.

[vintage1]

I frankly don't think it matters a damn unless you are trying to build a Dr Drela performance sailplane.

You can fly almost anything.

What is important is getting stability in teh yaw and pitch planes. Even that will just be a matter of adjusting the CG..the only proviso there being if you want stability in BOTH planes the ratio of te fin to te fuselage side ears wants to be similar to the ratio of the taillplane to the wing.

If integrating areas and moments bores you get a sheet of balsa or depron and build a profile model. Top view and side view should be what you want to build. Chuck it and balance tlll it flies OK,. then copy the dimesnions for your model, You will be close enough.

If it goes into uncontrollable sideslips, it needs more fin.

[BMatthews]

I wonder if the sudden lack of intrest is becuase it leaves his focal location. While building he's seeing you work with your hands on something that he can be part of. But when it flys out and away then it's gone and not part of his sphere? I'm guessing here but the effect seems to be there. Perhaps try making a solid scale model that he can keep in his room. Nothing flashy and it should be tough as I'm sure it'll get dropped a lot. But something that he can be there while you're making it and perhaps share in the building of it? Or perhaps it's not the airplanes but the use of the tools? The idea of cutting and shaping the materials that he is fascinated with.

As for flying successfully I've seen designs with 0 tail length (plank style flying wings) to models that are longer in the fuselage than their wingspan along with everything in between and they all fly fine with some obvious advantages in some areas and disadvantages in others. Then there's delta wings, flying saucers, biplane flying saucers.... You just gotta understand how the areas work with the balance point and how to build in some form of pitch stability.

[vintage1]

Autism means living in a different world ..it seems to me that walking around would create a constantly changing 3 dimensional view. By making things you are showing him another way to change the three dimensional nature of what is going on.

Why he needs to do that who knows? But maybe building blocks would be something.. Maybe he is simply overwhelmed by spatial reiationships to the exclusion of all else.

[Sail 'n Soar]

As for flying successfully I've seen designs with 0 tail length (plank style flying wings) to models that are longer in the fuselage than their wingspan along with everything in between and they all fly fine with some obvious advantages in some areas and disadvantages in others. Then there's delta wings, flying saucers, biplane flying saucers.... You just gotta understand how the areas work with the balance point and how to build in some form of pitch stability.

With so basic a question as how to determine wing span and fuselage length I interpreted the initial question to be that of someone with relatively limited experience. In that case, choosing something that is almost guaranteed to fly well (vs. successfully - I should have chosen my adjectives more carefully) should weigh in someplace. You can make almost anything fly "successfully" if you put your mind, or trial and error, to it - you didn't mention all of the flying Snoopy dog houses, Harry Potters on broom sticks, etc., etc.. The first scale flying planks I saw flew successfully in the sense that they were controlable, but their performance stunk - quoting the builder/flyer. (Before you waste any words definding the virtues of lying planks I'll acknowledge some have been built that satisfy there intended purpose well.) Delta's are great for high speed models and have really benign stall characteristics, but they have very low L/D and, as a conseqrequire lots of power for their size.

[Dereck]

Okay, this is kinda vague - but a long while back, one of Radio Control Modeler's columnists ran a couple of months concerning this sort of thing. Somewhere in the basement, I have part of one part of his efforts, though where I have no idea - having designed quite a few models, they sort of happen (if you plagiarise yourself, there's no-one to sue ;) )

I recall that the writer was a very long time columnist, but passed away sometime mid to late 1990s. If you can find a RCM fan, mag collector or just long-time reader of US mags, they may be able to help. The columns were written prior to my moving to the US in 1994, and possibly as early as the early 1980s.

Real paper books are a really good source of this info - anything by the late Andy Lennon is solid info, though perhaps a little more than most of us need. Try Flying Models magazine, they sell a bunch of good paperbacks on all sorts of model aircraft info.

Sail'n'soar - I've done a half dozen or so 'plank' wing models, from TD 010 powered to OS32. One brave soul in England did a really large scale version of one at 80" span for twin 60s - even I thought that was awesome. 4:1 AR, symmetrical section of 12 - 14%, CG at 16% MAC maximumn aft, 14% if you're nervous ;) Rudder kind of artistically inclined, its hingeline about about 3/4 MAC behind the rest and 'larger than usual' always got me by, engine around one MAC ahead of the LE, UC 1/3 MAC ahead of the CG (about the same distance ahead of the CG as a regular taildragger). Light blue touch paper, hold tight.

Evans' 'Simitar' variants are legion, but wouldn't stall or spin - all my tailless designs would :D

Right now, there's a version of my old 049 "Little Bit" tearing it up in England aft of an AXI baby outrunner, and I'm poised to do another one of my own pretty soon... They are not for the nervous though ;)

If stuck, Chuck - start with your favourite sports model plan. Do not change any moments or areas by much, and keep things logically shaped - rudders should look like rudders, for example. Build your work-over of old faithful and off you go with the only one like it at your flying site. A true OD comes next...

Says he, who's first OD was a 20 powered 48" span scale model of a Hannover CLIIIA German WW1 recce bipe with a biplane tailplane...

Regards

Dereck

[skippyflyboy]

Thank you to everyone that volunteered information.

I believe the the logical step for me is a simple trip to the library.

I have some limited building experience with paper airpalnes (not the folded kind that we threw at the teacher in highschool), and I have built several GWS estarters (don't aks ne why I built several LOL). I am in the process of converting an estarter into a J3 Cub, and I have learned some interesting things along the way.

I will post my first attempt at a ground up design in the very near future and you guys can let me know what you think.

Thanks again

Chuck

[crashsiegel]

R/C Model Aircraft Design by Andy Lennon
Published by MAN (Model Airplane News publishers)
Good book.
Crash

[skippyflyboy]

Crash

Thanks for the suggestion

Chuck

[garrcass]

just look at some planes i have been bulding small balsa gliders sence i was a kid i used to just look at a plane and usualy the fusulage was 3/4 to 1 to 1 the lenght of the wing the horisontal stabalizer was 1/4 the length of the wing and 3/4 of the width and the vertical stabalizer was 1/2 of the horizontal i use to make some so small they where smaller than the palm of your hand made of the thinest balsa i could get then i would find the right screw or nut or whatever to balance them out with the celing fan off i could get some to glide from the front door all the way down the hall this was when i was like 12 years old so realy you could do anything like the guy before said i beleve is true if you have enough surface area then dehedral and corect cg is all you need

[garrcass]

oh on the net somewhere there is some really cool paper airplanes that you print out and glue together they are litle 3d paperairplanes theres a bunch for free somewhere

[skippyflyboy]

Hey gang,

Just thought I would post this so that you can see what I was talking about.

The thread is here:
http://www.rcgroups.com/forums/showpost.php?p=8800697&postcount=37

I still want to scratch build, but this need built anyways, soooooooo...

I decided to mod, learned a lot about how to sand foam while doing this project :D

Thanks again for all of the great advice form everyone.

Hope you all had a good xmas

Chuck

[Airwolf911]

Well, hi guys, I`ve always used this rule of thumb for my designs and it have worked verry well and it is as follow:

Fuselage lengh is equal to the 75% of the wing span.
For example If the wing have a span of 64 inches, then the fuselage should be
(64 x .75 = 48) 48 inches long.

Another rule of thumb I use is
From nose to LE of the wing is equal to wing`s root chord, and from wing`s TE to Rudder`s farest point is equal to wing`s root chord x2.
For example if wing`s root chord is 12 inches, then nose should be 12 inches from wing`s LE and tail should be 24 inches from wing`s TE. So the fuselage is
12+12+24=48 inches.

I hope it help you new designers.

[Brandano]

There's always the TLAR rule. Incidentally...
http://k53.pbase.com/u12/tomsview/large/38389120.FlyingLawnMower.jpg

[Sail 'n Soar]

Well, hi guys, I`ve always used this rule of thumb for my designs and it have worked verry well and it is as follow:

Fuselage lengh is equal to the 75% of the wing span.
For example If the wing have a span of 64 inches, then the fuselage should be
(64 x .75 = 48) 48 inches long.

Another rule of thumb I use is
From nose to LE of the wing is equal to wing`s root chord, and from wing`s TE to Rudder`s farest point is equal to wing`s root chord x2.
For example if wing`s root chord is 12 inches, then nose should be 12 inches from wing`s LE and tail should be 24 inches from wing`s TE. So the fuselage is
12+12+24=48 inches.

I hope it help you new designers.

I have seen similar rules of thumb to yours published previously, for example those listed as "Basic airplane proportions" in Andy Lennon's R/C Aircraft Design. Your two rules of thumb corresponds to a plane with a wing aspect ratio of 5 1/3. Those are great proportions for a general powered sport model, if that is what you like to build and fly. For other aspect ratio wings your two rules of thumb give mutually exclusive fuselage length values.

Risking the wrath of the "I can make anything fly" contributors to this thread, for higher aspect ratio wings such as on the Alpavia RF-3, 4 or 5, a fuselage length of 3/4 the span is longer than necessary and a fuselage length of 4 cord lengths is too short. Similarly, for lower aspect ratio wings, your fuselage lengy should be longer than 3/4 span (~90% at AR = 4 for a sport model) and should be shorter than 4 cord lengths.

You might reconsider my earlier suggestion of making the fuselage length equal to ~sqrt(3.1*A) and make the nose and tail lengths proportional to those you defined. For your AR = 5 1/3 example my formula gives the fuselage length as 76% of the wing span, almost identical to your 75% rule of thumb, while providing good fuselage length guidance for alternate wing plan forms.

I go for lower aspect ratio designs for my gas models, but I personally stick to AR 6 - 8 or higher for my electrics just to improve the L/D, which relates directly to flight time for a given capacity battery.

[skippyflyboy]

Sail and Soar,

If I understand your post, is this why modern jet fighters have longer fuses than wings, because the wings are low aspect ratio?

As always, thanks to everyone who has contributed to this thread. I have learned much in a short time span thanks to you all.

Chuck

[Airwolf911]

There`s a lot of information found in the internet about aerodynamics. Some rc pages have very good information from where I obviously adopted my rules of thumbs. The most rewarding experience of aeromodelling is designing and building your own flying model. That`s what for my very own opinion is a true aeromodelist. Others just fly models. So I encourage everyone of you to get information and start designing your own model and feel proud of what you`ve created.

[Texas Buzzard]

For something to fly that is stable yet will respond to controls start with a normal monoplane either high wing or midwing. Avoid low wing for now.

Usually this works well for a Piper Cub type layout of the Old Sweet Stick layout.

Make the fuse length 70 to 75% of the wing span.

Make the back of the prop to front of wing equal to the chord of the wing.

Put the C of G 25 to 28%of the chord back of the L.E. of this straight wing

Place the axels of the wheels at a 30 degree forward of the C of G.

Make the STAB/ELEVATOR area 22 to 25% of wing area ( dont skimp here)

Make the FIN/RUDDER 6 to 7 % of the wing area.

All this assumes you are building a tractor .

[skippyflyboy]

Buzzard

thank you for the information.

Just out of curiosity, why not a low wing now? are there differences between the low wing as compared to the mid/high wing as far as the numbers?

I recently modified an Estarter into a J3 Cub, and in doing so I inadvertently "skimped" on the rudder/elevator surface area when I reshaped them. Wow, what a difference. Not a good difference either. I have to make new tail feathers with more surface area.

Anyways, thanks again for your input. I appreciate it.

Chuck

[Texas Buzzard]

Hi Skipy,

Yessir. Stick with those parameters and it will be stable AND IT WILL FLY.

Of course WEIGHT is your Enemy. Try to resist adding extra plywood and other heavy things except in the joint in the middle of the wing - the dihedral brace. Use some plywood here.

The parameters I gave you are at least 30 years old. I have designed maybe 25 RC planes and built them. Most were glowplug engines from between size 00.15 to 0.60 cubic inches displacement.

Just get some big cheap rolls of brown paper, a good yard stick or better a meter stick and have at it.
The very first thing to do is to draw a straight line thru' where your thrust line will be. Let that left end be the back of the prop. Then make marks where the wing will be (one chord length back) and where the elevator hinge will be. That total distance is the FUSALAGE LENGTH. Then get HAPPY, MAKE A HIGH WING FIRST. Dont try to get fancy on the first one - make it fly , you will be happy. With a high wing electric use some 1/16 th CF struts set into reinforcements like thin ply and use epoxy not the fancy foamsafe high priced stuff. I have gone to 5-min epoxy and GORILLA GLUE - the gorilla is S T R O N G!

THE REASON THE LOW WING IS AVOIDED AT FIRST IS THAT THEY ARE MORE "TWITCHY" IN FLIGHT AND ALSO THEY CAN TIP STALL MORE EASILY WHEN LANDING. GO TO IT. :) :rolleyes: :cool: :)