Capt. Crackup

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Does anyone know of a good site for delta wing design? Specifically power vs drag, and wing loading.

dusteater

http://beadec1.ea.bs.dlr.de/Airfoils/foil_fw.htm

dusteater

im out to build something faster than the diamond dust and whiplash. not made to roll fast, just to go very fast.

more of a swept back wing than the dd, and have the trailing edge sweep in to the center, fully cowled egine, on long and fast looking rear fin with the pipe of the rexaust going through it or someting, ill see what i come up with

WS

It's not the delta that will make a plane go fast, unless you are near the speed of sound, which most models are not even close. The low aspect ratio of a delta will make for more induced drag, if anything. Most airfoils have the best L/D with a lift coefficient of ~ 0.3. What a delta does do, is lower the structural weight requirement for a given strength. Less weight also means lower induced drag, so you'll have to figure out if the tradeoff from a higher aspect ratio wing is worth it.

Ollie

For a given power, speed is increased by reducing the total drag. At high speed, you want an airfoil with the lowest coefficient of drag at lift coefficients between zero and about 0.2. Low wing loading helps keep the lift coefficient low and therefore the induced drag low. This is vital in a low aspect ratio configuration like a delta.

The dominant item of drag in the drag budget of models like this is the parasitic drag so streamlining and cleaning up the airframe is the number one priority. Cowling engines, enclosing pipes, fairing spinners into the fuselage and, putting switches, jacks and fuel filler fittings behind hatches are some things to do.

dusteater

ok, so if i increase the sweep back of the diamond dust and thin the airfoil a bit, and put some sweep into the trailing edge will this work to lower the drag.
i need a website to read up on

thanks
chris

Ollie

Increasing the sweep angle won't make it faster and may slow it a bit by making the wing less efficient.

The S6063 had the lowest coefficient of drag measured in the low reynolds number tests by Dr. Selig at the University of Illinois. The wind tunnel test airfoil was not the true S6063 but had a slight reflex in the trailing edge. This modification is what you want.

Making the model lighter than the Diamond Dust and a little smaller to keep the same wing loading is the way to go. The more weight you can save, the smaller you can make the model. The smaller the model the less the drag and the lower the drag the faster it will go.

Making it more streamlined than the Diamond Dust will pay off big time. Another detail is to eliminate the drag of external control linkages by using RADs. There are high torque digital servos that are thin enough to be mounted entirely within the wing. Route the antenna inside too. Eliminate the weight and drag of landing gear by using a drop away dolly for take off. Belly land on soft grass or astro turf.

A single vertical tail of the same total area as the twin tails and mounted at right angles to the top of the wing will have less drag than twin tails not perpendicular to the top of the wing.

dusteater

ok, i am not familiar with what you mean by RAD
also, what is a reflex in the trailing edge.
where can i find the airfoil plotting software,
i know this is alot to help out but if i can make em go say 220+ or so with a jett 50 vs about 180 out of a diamond dust with the same motor that would be good.
i was also thinkin of running a quickke 500 or something from jett but with rear exhast to spin 30,000, a throttle would be good though.

but, anymore info anyone could give would be great.

Ollie

For RADS see:
http://www.irfmachineworks.com/rds/

A 22% increase in speed will require nearly a 49% decrease in drag for a given thrust. This is because drag increases as the square of the airspeed. to get such a large decrease in drag it will be necessary to leave no stone unturned in cleaning up the parasitic drag. Putting a streamlined cowl around the engine and pipe while decreasing the overall weight will require great structural sophistication.

See:
http://amber.aae.uiuc.edu/~m-selig/
for the S6063 airfoil coordinates and for the coordinates of the associated windtunnel test model. Comparing the two will show you what reflex is.

See:
http://www.compufoil.com/
for the best airfiol plotting software.
You can also get a free download of Profili but I have lost the URL.

dusteater

ok, heres my next thought.

since top fuel dragsters go the fastest and quickest and they are long and skinny, to make less turbulence right,

what about a delta wing that is shaped like a paper airplane. you know, the kind you can make out of a piece of paper.

anyways, would this have less drag than a model wider and not so long.

i think it would because for one, there is less frontal area... and it seems it would be like the top fuel dragster which is longer and disturbs the air less as it travels through it.
anyways, i dont know if what i say is correct, but the paper airplane style wing seems good. i think about a 18-20 inch wide at the widest part, maybe about 1 and 3 quaters or 2 times as long as a diamond dust.

thanks,
maybe i will create the fastest prop plane or atlest fast on a budget.
i should do tests with a tt46 on a dd as a test then put it on my plane. if its faster maybe ill sell plans. it could be called the dusteater.
but, of course it would not be nearly as manuverable as the dust.
also, probably a drop dolly to get up to speed as it couldnt hand lanunch.
but anymore info from you guys is great.

chris

WS

The diamond dust appears to have a good wing shape, taper ratio of 0.6 with 45 degree swept leading edge. It's just a matter of sizing the wing for the weight. If you wanna be able to land it at a reasonable speed, pick a wing loading to suit. For my field 500' in length, I'd say 30 is about the max without flaps, or 45 with flaps. For a 2.5 lbs model, that works out to 200 sq in of wing. Even at 300 sq in (20 oz wing loading), you're gonna under-cut the diamond dust's wing area (and drag) significantly and that will mean higher speeds, for sure! With the right prop, of course! You could probably get a good 25% more speed anyway....just don't expect a tight 'combat' turn radius! I dunno, is there a wing area rule for combat/pylon planes?

dusteater

ya wells thats what im hoping, i dont care if it cant turn tight or whatnot, im just out for speed. would a longer wing with more sweep back and less wingspan be better as it has less cross section area. also, more things to think about are wingtip design, if rounded swept back tips is better than straight tips.

even if i had to make a bungee cord out of glider-hi start tubing to slow it down, have a little wire skid on the plane to catch along the tubing which is strung out and held up about 3 feet of the ground with poles, maybe it would catch and slow it down better or something if the wingloading was too high.

i dunno, much planning must be done before the actual design begins. if you care to post anymore thoughts that would be great

Ollie

Increasing sweep back will be a detriment to speed because it makes the wing less efficient and increases induced drag and middle effect drag. You should only use enough sweep to give the minimum lateral stability you can tolerate. As it is, the Diamond Dust wings are operating almost entirely within the tip vortex. The increase in induced drag and middle effect drag will be far greater than the drag reduction due to reduced frontal area!!!

dusteater

so, ollie what i should do is just modify the airfoil of the dust to the s6063 and make it smaller is what you are saying, plus clean up the plane by cowling the engine and such. if you say sweeping the wings back more will not help, then i wount do it.

so should the tips and the TE be thin and rounded for less drag or what should i do. also, how thin should the airfoil be.
do i just limit it untill none of my components fit in the wing. also, i would have to use a bunch of 2 oz tanks all linked together to get the fuel tank completely in the wing, or will i have fuel draw problems even if i have a 1oz header tank right behind the carb, and about 3 2 oz tanks connected in series in the wing, with muffler pressure feeding them

WS

I think the latest theory is that 45 degree swept tips are better than rounded or elliptical ones. Look at Rutan's designs...

Anyway, a higher aspect ratio will help with reducing induced drag, so you'll keep more speed in tight turns.

dusteater

i dont care about speed in turns, as long as it can turn around without stalling im happpy, i just want max speed. we will see what evolves.
also, so if i just make it so there is the 45 degree backsweep on the diamond dust and it continues along untill it meets the trailing edge, that would be 45 degree tips, correct....
hmmm, i wonder how much smaller i could make this thing, but to make it lighter and stong would be another issue. i can get carbon fibre shafts thinner and smaller than the stock fibreglass ones. thatll save some weight. also, using maybe lite ply instead of plywood for the ribs, maybe 1eighth light ply.
also, have the ailerons thinned so its a carbon fibre sheet sandwhiched by 1 piece on each side of 1 16 or 3 32 balsa wood. also, make the vert fin the same way. also, use capstrips that arent so wide, and thats about all i could do to save weight, unless you have other ideas. maybe about a 20 inch span or so..

Ollie

It's important not to increase the wing loading. Therefore you can only make it smaller if you also make it lighter. It will be difficult to make it lighter if you are adding a streamline cowl for the engine and pipe. If you want to go much faster you must do every thing at once. NOTHING can hang out in the breeze. EVERYTHING must be inside. Space for fuel tanks can be solved by using bladder tanks. To save weight, don't carry any more fuel than necessary to take off, do a two way speed run and land immediately. If you are to succeed you must become fanatical about every possible drag and weight reducing measure. Nothing can be compromized that interferes with these goals. To beat the Diamond Dust by 22% you will end up with a plane that has just that one limited capability and nothing else.

WS

Ok, but what I'm saying is that you're gonna spend alot of time turning something that is really fast, no? You need to give yourself enough room to accelerate to top speed in straight and level. Having more speed coming out of a turn will help.

That's right, so if you drew a line from the end of the trailing edge, on a 45 up to the leading edge, you'd be cutting off some of the diamond dust's wing area (you keep the same span), giving you about 300 squares (and doubling the aspect ratio to boot!), which I think would be a good thing for flat out speed. The engine and pipe would end up back between the fins. You could also consider adding a wing fence about 1/2 semi-span, without too great of a drag penalty. In any case, please let us know how it turns out!

Flypaper 2

Take a look at the control line speed planes for ideas on engine fairings. They have experience with this for a long time.

dusteater

could someone tell me what a wing fence is

thanks

Ollie

Here are some weight saving ideas:
Use a small AAAA Ni metal hydride battery (0.19 oz. per cell) total weight 0.76 ounces.
Use JR 368 digital servos @0.9 ounces each. total wt. 2.7 oz.
Use Hitech 555 receiver @ 0.3 oz. total.
Use spyder foam because it has less than half the weight of even the lightest contest balsa.
Use unidirectional carbon fiber because it has at least 7 times the strength to weight ratio of aircraft spruce.
Vacuum bag the wing and use the wing skin as the elevon hinge.
Use kevlar in laminating epoxy wing skins.
Mold the engine and pipe cowling of Kevlar cloth in laminating epoxy for the toughest, lightest and most vibration resistant structure.

dusteater

ollie, i thought of making it a 3 rib design like the dd, cause wouldnt fully sheeted be heavier than just covering it with ultrakote?

also, ill have to look where to get spydar foam( you mean to use it instead of balsa)???, and i have to see what vaccum bagging is,
hmmm. this is harder than i thought, but will be worth it in the end.

WS

Wing fences,

Take a look at a Mig-15 or a Mig-21. About half way along the wing, there's a fence there that keeps the airflow going chordwise and not so much spanwise. I'm not really sure if it would necessary with a true delta, you'd have to fly it and see what it's stalling characteristics are like. Also, you'll wanna sheet the wing somehow. You don't want that covering to distort at high speeds. That'll ruin your airfoil shape.

dusteater

ok, heres another thing to consider, i think that tips that thin down to a very thin tip would give less drag than squared off tips, also, will tapering the trailing edge in so that the center of the trailing edge is inward an inch or so give any improvement or no.

so basically the design will be a delta wing, with one vert. fin, fully cowled engine and pipe, with a 45 degree sweepback all the way to the te, also smaller than the dd.

if i have the option of taking wing area off the chord or width, i think it should be the chord right? cause that would give a higher aspect ratio which would help in turns correct?
if so, look out whiplash, cause the dusteater is coming to get you.

Troy-RCU

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Ollie,
Your knowledge is very impressive (as usual) but your patience is what floors me .