Suggest an airfoil for 1200 sq in powered

[gkamysz]

I want to build a new model or maybe just replace the wing on my Ultra Stick Lite.

I want to fly a 11-12Lb model at ~60MPH. I'll likely use flaps on the inboard 50% of span to aid in landings. I was going to use RG14 or RG15 because I'm familiar with them. Would this be a good choice? Construction will be foam core, balsa, and film or 1/2 oz. glass.

I'll be using it to test engine modifications, no aerobatics, engine will be fully cowled, so low drag is the goal.

Thanks,

Greg

[vintage1]

For speed use a semi symmetrical thin wing. About 10%.Probably semi elliptiacal planform. I don't think the actual section is that critcal at our speed/chords.

[BMatthews]

Well, 60 mph is pretty much a regular sport model speed.

Unless you're willing to use a construction method that ensures a high degree of accuracy to the shape I'd say just stick with a generic choice. The big fan up front makes any sort of gains you get for choosing the better but more critical airfoil rather pointless for most flying anyway.

[lincoln]

I think you'll find yourself flying faster than 60 if you clean everything up. I think we once had a radar on the field and clocked an Ugly Stick at 50mph. I'm thinking RG15 is probably not bad. You might go to something even faster, depending on power.

Partly it depends on how precise you want to be as a builder. There are some specialized airfoils out there which would be quite low drag, but you'd have to be very careful in building.

One that comes to mind is the SD 7003. But you can probably find even lower drag.

[MCarlton]

I think you would struggle with RG14 or 15 on a model like this to be honest, those sections being designed primarily for sailplane models. To me they have altogether too much lift and you would end up with either a handful of down trim or a lot of downthrust to keep things level at speed.

I'd follow V1'a advice on this one and make a decent semi symmetrical section wing (if you must use a "specific" section then have a look at something like MH24 at 9% which would give you a decent enough top speed and also keep things moving in turns.

If you want this to test engine modifications though, it probably doesn't matter, simply because whatever section you choose, if your modifications yield a performance increase, it will still be visible.

To my mind, 60mph for a 12lb model is not actually that fast, certainly not venturing into the realms of speed models, bearing in mind that even a tiny SP400 pylon racer will be galloping along at around 85mph or more.

If you modify your ultra stick, be aware that changing the wing and trying to make the model move faster is going to impose higher forces on the remaining structure that it may not have been designed to take.

[gkamysz]

Thanks Guys. The model has probably flown at 70-80MPH already. The goal is to go around 60MPH with as little power as possible. I'm going to build another airframe because I need another. So in this case, there is more to be gain by paying attention to the details, fairings, incidences, etc., than there is in the actual wing profile.

[Brandano]

Lowering wing loading will give you a lower AOA to maintain the same speed, hence a slower stall. The wing profile will affect the stall angle, but only within a limited range. Increasing the wing surface and lowering the weight will allow you to slow down, though the increased wing surface will add drag and require more power. Simply lowering the weight will mean a smaller AOA, smaller induced drag and better overall low speed handling, though it will increase sensitivity to wind gusts.

[MCarlton]

The goal is to go around 60MPH with as little power as possible

I would attack this objective from another angle. What you need is to design a nice slippery model that looks a little like a sailplane, I'm thinking something along the lines of a light F3f machine. Doesn't need to be moulded, but that general shape.

Like my rubbish "paint" sketch, but you get the idea

Then make the fuselage so that you can squeeze something like a .25 IC engine in there, couple that up with a prop which will give you a pitch speed of around 80mph which by my reckoning is around 14,000rpm.

Bingo, you'll have a model maintaining height and zipping along at about 60mph without needing a load of motor power to do it.

The theory goes that if the model can glide fairly efficiently at around 60mph without an engine, then you don't need much oomph to counteract the sink rate.

Just my thoughts

Cheers

Matt

[gkamysz]

The engine is going to be a 50-90 four stroke. Obviously a glider type design would be wonderful, but won't hold some of the equipment I have in mind nor the 2-4 liters of fuel. Essentially a UAV type, without any mission other than flying, for long time.

The model is not intended to be fast. The weight stated is probably very accurate with my original idea of making a new wing for the Ultra Stick Lite. Dropping undercarriage would certainly drop a pound and reduce drag, but I don't think I'm giving them up.

[vintage1]

Take a tip from the days of racing monoplanes: DH comet with a single engine is about what you want.

Thinnish elliptical wing, spatted undercart if you wont use retracts, and keep it light.

Section tapering in chord ratio as well as planform. semi symmetrical.

[richard hanson]

streamlining is a complete waste of time
wingloading is the answer
build it as light as you can with as much wing area as you can
the airfoil means nothing --- a 6-1 aspect ratio will be about the easiest to do to get where you want to be a rectangle is fine - no tips no flaps etc..
1100 squares - I do this at 9 lbs
10 lbs easily --and this was on fully foam unlightened balsa covered wings
on competition pattern planes which only allowed 11 lbs
draw a 12% thick wing- any airfoil easy to do and if you fully I beam spar it -- it should be strong enough a box fuselage -at the speedyou want this smal trying to streamline only adds weight
all the aero textbook stuf - really has little application in this size speed.

[MCarlton]

streamlining is a complete waste of time
wingloading is the answer

Not sure I agree there, I get your point, but I'd contest it based on a couple of observations.

I had two models, one a vintage style high wing monoplane, one a sleek low wing sport model.

Same size, roughly the same wing loading, same engine, but different designs and wing sections. Very different performance and top end speed, plus very different abilities to slow down on landing and low throttle settings

build it as light as you can with as much wing area as you can

surely more wing area = more induced drag. Otherwise, why are pylon racers not equipped with great big wings with 12% sections of "any airfoil" ?

trying to streamline only adds weight

That depends how you streamline, if you make that streamlining part of the structure then there's no reason it should add much extra weight.

[richard hanson]

Not sure I agree there, I get your point, but I'd contest it based on a couple of observations.

I had two models, one a vintage style high wing monoplane, one a sleek low wing sport model.

Same size, roughly the same wing loading, same engine, but different designs and wing sections. Very different performance and top end speed, plus very different abilities to slow down on landing and low throttle settings



surely more wing area = more induced drag. Otherwise, why are pylon racers not equipped with great big wings with 12% sections of "any airfoil" ?



That depends how you streamline, if you make that streamlining part of the structure then there's no reason it should add much extra weight. I understand your comment - -IF you make streamling part of the structure -you really win
here is whre many get lost - the shape of many wings is predicated on required strength.
For the model mentioned the thinner the better and at low wingloadings the shape -simply is of little consideration --that is - it can have thick/thin le te makes no real difference
just make a"thin clamshell" if youwill and the highpoint wherever it will furnish the best strength. The subject model is a aerobat - the setup for a racer - does not apply. BIG DIFFERENCE
"theory " on wings as you approach extremely low wing loadings and slower speeds becomes relatively unimportant - the speed range -the low loadings call for a simple flat board as power used to control attitude and speed becomes the real factor
Not theory --actual practice
for the last few years I have done many designs with wing loadings running down to 3 ozs per squar ft (all aerobatic stuff) here is a 4 oz per sq ft model

[lincoln]

Ok, the real way to do this is to make it look like an airliner. (ALthough it's more complicated than just a resemblance.) Figure out what is the highest takeoff and landing speed you can live with. Pick a wing that is just large enough that you can take off and land at that speed, and no larger. The RG15 may be a good choice for this, depending on the ratio between the takeoff speed and the desired flight speed. For instance, if you take off and land at 30mph (that's kinda fast), and you can reach Cl of 1 with 10 degrees of flaps, (I assume you can droop the ailerons that much for takeoff and landing), then cruise will be at Lc of 0.25, which is in an efficient range for the RG15. Make the wing as high aspect ratio as you can. For this example, you'd want around 5 square feet. You might want to add a turbulator at around 55% as Profili shows a performance improvement at high speeds and a smoother curve for drag at low speeds. (which might improve handling) Reflex doesn't seem to help on the high speed end.

You might try the 7032. You could use 5 degrees positive flap and maybe 2 degrees reflex. And make the wing 20% smaller, which would reduce the profile drag. The section is a bit thicker so you wouldn't have to lower the aspect ratio very much. However, the RG15 is not a bad choice either. Especially if you need a slower landing speed than 30mph, and, therefore, a wider speed range. (I know that seems a bit counterintuitive, but if you need to land slow, then at high speed you'll be at a lower lift coefficient, and the RG15 has a small advantage there.)

The fuselage would probably be a major source of drag, so you'd want to do some serious streamlining and make tail surfaces with a real airfoil, etc.

I don't know if you wanted to optimize to this extent, but the problem seemed interesting. I'm slightly suspicious of of the results, as I'd expect the RG15 to do better than Profili shows at the low lift.

I don't guarantee this is exactly correct, but I bet it's close. I also think it's possible that there will be other airfoils that might be a little better, but the fuselage etc. may be more productive areas to concentrate on.

If you can live with a really high takeoff and landing speed, use something like a 7037, or maybe a Drela airfoil, and make a wing that operates at the airfoil's best L/D lift coefficient when you're going 60mph. The wing will probably look pretty small. You'll probably take off and land at 45 mph! And the wing would be really small, maybe 2 square feet. (look at a cruise missile sometime)

[gkamysz]

Thank you all for the input. Lincoln provided some insight and I will take that itno consideration.