Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Scratch build speed plane.

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Old 10-28-2005, 08:18 PM
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Edge 540
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Default Scratch build speed plane.

I am designing a home built speed plane. It will be pretty much a standard Q500 52" span 42" length with a .46 engine. I was considering using carbon fiber to reinforce the fuselage in some places but figured why not go all out? Can you make a light weight fuselage out of CF tubes? I was thinking about building a box fuselage out of trusses of CF epoxied together. Can a lattice work of CF be a practical way to save weight? I would like to have a removable wing, and it would be difficult to construct a wing saddle out of CF, so maybe the front of the fuselage could be standard light ply balsa and the tail from the wings TE back could be CF.
Also, I'm building a foam core wing that will be fully sheeted in balsa. Can you use 1/32 balsa instead of 1/16 to save weight? Keep in mind this will be powered by a standard sport engine. No high power stuff here, so it doesn't have to be competition level strength. My goal is to have the absolute, no questions asked, no doubt in ANYONES mind,.....the fastest plane in our club. [sm=bananahead.gif] >100mph will easily take the prize. Hopefully someone will challenge me, so we can start a rivalry! I can't wait.

Also, about how many G's will a wing and fuselage need to stand up to. I plan on, at the very least, static loading the frame before it gets in the air to make sure it will hold up to far more that flight loads should create.

My flight pack is 3 hitec 225's, a hs 81 on throttle, 270mah battery and hitec 555 receiver. All of that is less than 6 oz!
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Old 10-29-2005, 05:32 PM
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Default RE: Scratch build speed plane.

Has anyone used CF tubes or rods to make a light fuselage? What about 1/32 balsa to sheet foam core wings?
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Old 10-29-2005, 05:56 PM
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Default RE: Scratch build speed plane.

A average quickie with a normal 25 will crack 90 with little effort. A clean well designed one will hit 100 with a sport .25 engine. With a .46 you should be able to do around 120-125 with no special effort.

It is not necessary to try to save a lot of weigh if you are only interested in straight line speed. Are you planning on covering your carbon tube truss or what? I don't think that it will buy you anything over a normal balsa/ply structure.

1/32 balsa will not be enough by itself to hold a wing together. The top skin will fail in compression. Normal skin thickness for something slow is 1/16", and I use 3/32" or even 1/8" on the top skin for 160+ mph quickies and 1/16" with 1/2 wide carbon on the bottom skin.

G loading is determined by the speed of the model and the radius of the turn. Racing airplanes have to be able to withstand loads in the 30-40 g range. It's always fun to see who did their homework and who didn't. Racing with wind gusts really stress the center section. I went to a race in Texas once where 20% of the wings failed due to the conditions.

If your only interest is going fast on a straight line, I would also consider cutting down the wing span by 6-10" if using a standard quickie wing airfoil. Or better yet, copy something like a Q40 for a bit more speed. You can buy some Q40's with foam cores for low money and go a lot faster.
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Old 10-29-2005, 06:06 PM
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Default RE: Scratch build speed plane.

You need more strength in the wing then in the fuselage. If you want to put carbon fiber anywhere put it in the wing center section.
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Old 10-29-2005, 06:32 PM
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Default RE: Scratch build speed plane.

I was thinking about building a CF frame and sheeting it in balsa. This will then be covered. I guess I might as well build it all out of wood then, huh?
Good thing to know about the balsa on the wing. I will use 3/32. Thanks!
Lets see....40/G's on an ~3lb plane WOW! I plan to glass the center wing joint.

As far as the entire plane goes, I want this to be more like a Q500 pylon racer. I don't want only speed. I want this plane to go fast, but still have excellent turning abilities, and good slow speed characteristics as well. I don't really want to buy anything if at all possible. This is going to be an original design in every way.
Also I will be using a Q500 airfoil from here:
http://www.mh-aerotools.de/airfoils/index.htm
It will probably be the MH 16 or MH17 Although it recommends "advanced" construction methods, it may be possible to recreate these in foam. I know someone who can make ribs of these in metal on a CNC machine. If I can get two aluminum endplates in the correct chord, I can make a jig to hot wire cut this out of foam. I have lots of nichrome wire that works very nicely when powered by model train transformers DC. (fully proportional heat!) This method may be inaccurate because the wire will sag in the middle, but if each wing half is cut separately it might work better.
I really like the fact that the MH 17 has no pitching moment, and would make the tail design much easier. It would definitely be more difficult to cut though. Look at the TE! That last little bit is reflexed up like a flying wing. Cutting ailerons out of this TE would also be troublesome!
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Old 10-29-2005, 06:38 PM
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Default RE: Scratch build speed plane.

Also, I want a standard tail with a pure rudder. Should I set the wing and tail both at 0 degrees incidence? If the airfoil has 0 pitching coefficient, it won't require any,....right?
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Old 10-29-2005, 07:06 PM
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Default RE: Scratch build speed plane.

"Keep in mind this will be powered by a standard sport engine. No high power stuff here..."

Just thinking out loud here... if U want speed, woudn't it be better to invest in a Jett engine instead of all that carbom fiber?
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Old 10-29-2005, 07:18 PM
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Default RE: Scratch build speed plane.

I have an os 46 FX for the project. I don't have the budget for new engines. The carbonfiber I was looking at was from midwest. You can buy 24" sections for less than $5 a pair. The fuse would only require 8 or 10, so that is only $25. I'm not so sure about the idea anymore anyway, so it is irrelevant.
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Old 10-29-2005, 08:56 PM
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Default RE: Scratch build speed plane.

What kind of AR should I be looking for in a pylon racer? More specifically, what chord for a ~50" wing?
Is the 0 incidence on wing and tail the way to go?
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Old 10-31-2005, 11:41 AM
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Default RE: Scratch build speed plane.


ORIGINAL: Ultra Stick

What kind of AR should I be looking for in a pylon racer? More specifically, what chord for a ~50" wing?
Is the 0 incidence on wing and tail the way to go?
Check this web link out for more Q-500 models option, http://www.pylonworld.com/rc_pylon/q...500_planes.htm

As for the chord of the wing, it doesn't matter as long as you have the total area of at least 500 square inches with minimum and maximum span between 50"-52" long per rules book. However, I prefer to keep my wing chord at 10" to make it simple and play with the tips with remaining 2" option.

Hope this helps.
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Old 10-31-2005, 12:46 PM
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Default RE: Scratch build speed plane.

I'm using the full 52" length allowed by the rules, and a 9 3/4" chord. This makes things a little more difficult with the tips, since most sheeting comes in 48" lengths. 2" tips are kinda big.

Personally, I would stick with a simpler, less radical airfoil (R140) would be a good choice if you plan on sticking with a sport .46 (120-130 mph range).

Your flight pack looks perfect, try and keep the weight around 3 1/2 lbs.

I would also suggest fiberglassing your fuse and painting. As long as you can do it lightly. The added strength transfers power better IMO.
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Old 11-01-2005, 04:49 PM
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Default RE: Scratch build speed plane.

DAVEN:

You can design, experiment and test for about 20 years and maby come close to one thats allready available. Go to www.matleymodels.com and look in their Q-500 kits. You will find a super screamer there that is not race legal, looks like a formula and a great overall performer. For $75.00 bucks, how could you go wrong. Have ordered mine for a Jett 50, next years super suprize for out clubs real fast guys now on my butt big time!
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Old 11-01-2005, 05:11 PM
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Default RE: Scratch build speed plane.

yeah Daven,

Go dump that seeker in the river and .... opps .. gettin' a little fired up here.

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Old 11-02-2005, 01:47 PM
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Default RE: Scratch build speed plane.

The point is not to beat what is already out there. I love aviation, and get just as much satisfaction from building/ designing my own planes as I do from flying. I have spent countless hours just testing balsa gliders that I designed. Beating the other planes is just icing on the cake. 70% of the satisfaction is in what leads up to that. For me anyways.
This is a project I'm doing for my physics II class in high school. I will be making lots of calculations, measurements etc along with the normal build/ fly process. I have a flight data recorder that will add to the physics/math part of the equation. This should be interesting.
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