Hello

I have a sience fair idea that i would like your opinion on.

I would like to build one basic spad with a simple .46 glow engine on it nothing too complicated and build three different wings (all same size but with different airfoils) now i would make sure each wing wights the same and that the incedence when mounted to the plane is the same for every wing this should basically mean that different wing types would make different amount of lift that would be reflicted in trim change

i could then record the trim differenece and go from there

of course there are a few areas that could change the results like the air getting warming through the test day that would casue a lower air density and therefore less lift.

I would like to hear your opinions on this and maybe evan help me pick 3 different wing types.

(this is for a grade 10 sience class)

Thank you

Steven

Sounds like a cool idea, but how would you measure lift? Had a friend do something like this but scaled down alot. He had a wind tunnel he made and had the wing mounted on a scale. He would zero the scale out with the wing on it, and when runnig the wind tunnel the scale would get negetive weight which was his lift. You could do the same thing in an empty room or garage, you'd have a better time controlling variables. Just try to route you exhaust out the house somehow.

well my theory is that lift would affect ele trim, this will give me my #'s making sure that all wings are at zero degress incedeince then i fly around at full power and trim the plane out[8D]

I would think that unless your building is absolutely perfect from one wing to the next you would even have trim changes with two identical wings. I think the idea of using a scale and even a makeshift wind tunnel would be more conclusive.

The changes in trim might be too subtle to measure, unless you have significant differences in the wings.
With the same chord, a short span, medium span and long span would appear to permit the changes in trim to be observed, but it won't be much from one to the next as the c.g. will be the same.
You would need to measure the speed as well as record the trims for each plane. That will be the most significant change between wings.
This photo plane with any of these wings flies pretty much the same.

In reguards to a basic semisymetrical wing as on the H-9 p-40 warhawk. Does anyone know if it's safe to balance at the 33% rule (spar). I have one of these and with a chord of 14.25" at the fuse 33% will get you about 4.7" from the le at the root. The MFG recomends 3" wich makes for a very nose heavy plane that will not even taxi w/o nosing over. can any one advise.

Scott

With the forward tapered wing you will need to calculate the MAC and then balance at 25~30% of the MAC. It will likely mean even further forward than the manufacturer recommends. The wheel position will then have to be placed slightly forward of this. All tailwheel a/c are taxied with full up elevator, even the full size, come to think of it even the full size trike a/c are taxied with a bit of up held in. On takeoff full up is held with both types until the rudder starts to respond and only then eased forward as unstick speed approaches.

You can answer this easily yourself if you do a few simple measurements. There is an online application that takes some simple measurements and plugs them into the stability formulas that have been used in aeronautics design for years and years. And proven over and over. All it takes is a yardstick and about 10 minutes.

Go to http://www.geistware.com/rcmodeling/cg_super_calc.htm and look at the 9 measurements needed to fill in that first lightpurple block. Fill in those 9 and then choose a static margin number. Click the "refresh" button and Taa Daa!!! You'll have a better answer than any WAG "conventional wisdom" sound byte that "everyone knows". Do a static margin of 10% and then one of 15% and you'll have a sensible CG range spelled out for you. Want to know how far back you can move the CG and still have control? Input 5% for the SM.

It's an excellent way to find the CG answer for yourself. It considers wing planform, aspect ratio, tail size and moment etc etc Everything that has an affect. And it works for almost every model you're going to build. Exactly. From the measurements of THAT model.

I used it for my KYOSHO 40-size Warhawk. Sucker taxiis in grass. Not perfectly happy with the grass, but does it. And flies like gangbusters.

You'll discover a tendency with the model mfg's we got that they don't always suggest as wide a CG range as they could. Guess they figure mushy is safer. It isn't. They usually have a way too small range, and it usually deadens the airplane. Can't blame them, I guess.

BTW, scott, next time it would be better to ask your question in a thread with it's own title. You can give it a title that applies to your topic. And you don't knock this thread offtopic.

A title like, "CG of my Warhawk" gets a lot of attention. Nobody coming into this topic is going to do so expecting to talk about a warhawk's CG.

BTW, you can cut the text out of your post and start it's own thread quite easily. And I can clean up this thread to stay on topic. It's just good manners.

My orginial idea was 2 have 3 wings of the same size same span cord and thikness with 2 completly different airfoils if the wings are rougly the same thikness they should apply the same about of drag (or close) So basically what i would need would be 3 DRASTICLY diffferent airfoils so that there is a change......

sorry for taking the forum off topic, thought there was a relationship due to the type of airfoil. Thanks for the info.

So in the end would this project work? what airfoils would i need to use ???

It's a science fair project so you need to do something that LOOKS different, something that is easy to see is different.

You might actually build a couple of different wing planforms with the same airfoil. A non-tapered one to start. Then one of the same area but with a LE taper. And one with a straight LE but tapered TE. It's easier to see when a wing is a different shape than it is to see different profiles.

As for doing different wings with different airfoils, you've only got three major families of airfoils. Cambered (flat bottom), symmetrical, and reflex. But you could do a rectangular, like the flat foamies have.

Odd ones that are distinctive? A diamond is really a symmetrical. But it's distinctive.

Any cambered is going to work as a representative. So do a Clark-Y. It's obviously flat bottom. Then do a 12%-18% symmetrical. It'll look symmetrical, but look about the thickness of the Clark-Y. A reflex will need to have an obvious undercamber (and just might be a pain to build). The blownup foamy..... Whatever looks right. It's going to bring some chuckles. And do the diamond one to the same thickness you do the symmetrical, with the max thickness located the same chord station.

I wouldn't bother with the reflex if I were you.

So a try the clark-y and 12-18% symetricle and the diamond one

one question what do you mean by "And do the diamond one to the same thickness you do the symmetrical, with the max thickness located the same chord station"

do you simply mean to make all 3 wings the same thikness at the same point (distance from the LE)?>?

thanx for all the help

Steven

Is this what you ment by using a dimond airfoil? the overlay of the black lines is over an naca0015 airfoil.


Steven

Just a general Q i ahve for anyone wanting to answere with a .46 sized glow what size wings would you make? im thinking about 56" plus the width of the fuse this would or am i better going with a larger wing lets say 60 inch then the play will fly slower? whats the stall speed considering wingloading wtih these airfoils??? i must stay above that speed..... and of course what wing cord would be ideal?

Andy Lennon's book, "BASICS OF R/C MODEL AIRCRAFT DESIGN" is something you really should find and buy. I've seen it in LHSs all over the place. It's usually $20 there.

It's really an excellent textbook, but doesn't read like a textbook. And it covers almost everything.

Yup, that's almost exactly what we did to make diamond airfoils.

One thing..........
Don't make the LE a sharp point like your drawing. It's too hard to maintain.

We used to make that LE with a piece of square stock and found out that rounding the LE lots easier to maintain. And the wing flew better.

We used them in about the best "laboratory" modelers ever had for comparison study. Control Line flying.

Using a diamond airfoil in your display will give the display some interest to the public. Diamond airfoils LOOK different. And will catch the public's attention.

You betcha........

To do a somewhat meaningful comparison between things, the things have to have something in common. In aerodynamics, you'd want the wings to have the same area and the airfoils to be the same thickness. THEN change stuff to compare.

Look at some of the 46size trainers and use those planform measurements. Whatever is going to work on you model airplane after the exhibit is over.

Jeez, now you're asking an almost impossible to answer question. Stall speed actually depends on lots of things that're just as important as loading. You need to read that Andy Lennon book at least once.

The ideal chord would depend on your airplane's needs. If you pick a span that works for you, then the chord will be easy to come up with simply. Designers usually have in mind the area they're going to need. The often figure the span based on how big the back seat of their car is or the back of their minivan or whatever. Then they work out the chord from the span and area.

But they also consider the planned use of the airplane model. A racer won't have much wing. An aerobatic won't have the smallest wing, but not a huge one either....... see the situation.


BTW, when you do any posters or charts for your project, work at spelling the terms correctly. Diamond Chord etc It's supposed to be a learning experience, right.

How does this look for wing design. i ahve rounded the le out a bit more the it was before

What would you think of going electric with this it would be more costly but would it offer much better resuluts the advatage would be that i would ahve no balance or wight shift during the flight if i regualt an 11.1 volt pack to 10v then the esc/motor would get the same power throught the entire flight

just an idea that i would like comments on

Steven

I was playing around with compufoiul (i think thats the one i downloaded) and it stated that the clark y is 11.7% so is naca 0012 close enough or should i look for numbers that are closer....? on this size project does 0.3% really matter?