Airfoil selection - Lifting sailplane

[JettPilot]

I would like to build a high lift, efficient, high aspect ration Sailplane like wing with good flight charactaristics. I will also be putting full span flaperons on it. Any suggestions as to which airfiols I should consider ???

JettPilot

[Sparky Paul]

The task would be?
There's many airfoils that can do high lift, but not too efficiently, and without good flight characteristics.
Full-span flaperons need some thought also.

[Langenase]

I would like to build a high lift, efficient, high aspect ration Sailplane like wing with good flight charactaristics. I will also be putting full span flaperons on it. Any suggestions as to which airfiols I should consider ???

JettPilot

Take a look here: http://www.mh-aerotools.de/airfoils/index.htm

I like those Martin Hepperle airfoils, specially the MH42 all-rounder :)

[Ollie]

The airfoil depends on the numbers:
Span?
Weight?
Aspect ratio?
Taper?
Low airspeed?
High airspeed?
Launch type?
You might consider airfoil high thickness for wooden spar or lower thickness for carbon spar.

Any old airfoil will have enough lift if you increase airspeed enough. So be specific.

[JettPilot]

Hi Ollie,

Thanks for looking at my question, here is the information you need.

Span will be 72 inches
Weight will be around 7 pounds ?? give or take a bit... You know how that goes....
Aspect ratio can be whatever I need it to be. Aroud an 10 inch cord ?
No Taper, constant Airfoil for the entire wing.
Full span flapperons
I will be hand launching it, and landing it in tight areas with no gear, so it needs to fly slow, but I would like it to be as fast as possible while not killing the slow speed flight.
Power will be a Saito 56 with a 12x6 prop
The wing will be EPP foam with large carbon spars, so streingth is not a problem. ( it can be thin).

Thats about it, if you need anything else let me know.

JettPilot

[Tom Harper]

Jett,

That's a 5 sq ft model with a wing loading of 22 oz per sq ft. A bit on the heavy side. A good old reliable Clark Y will do as well as any.

Why flaperons? I've set up my Sr. Telemaster for flaperons. The configuration reduces aileron control and doesn't make any real difference on landing.

[eflightray]

Wouldn't you be better off to split the flaps and ailerons. That way you could use 'crow' braking, ailerons up flaps down, as used by the competition glider flyers for landing.

It would also be handy to know what sort of flight characteristics are expected.

Your fast with a slow landing sound rather like a 'hot liner'.

[Ollie]

"Span will be 72 inches
Weight will be around 7 pounds ??"

It is very, very important to make your design on a weight diet!! See:
http://www.sigmfg.com/cgi-bin/dpsmart.exe/MainMenuFV4.html?E+Sig

"Aspect ratio can be whatever I need it to be. Aroud an 10 inch cord ?"

High aspect ratio is to lower wing drag. High aspect lift doesn't help wing lift at all!
You need lots of wing area to lower wing loading. So, make the wing chord 15" and make the wing loading about 12 oz./ square foot.

"No Taper, constant Airfoil for the entire wing."

OK.

"Full span flapperons"

Forget flapperons. Keep it simple.

"I will be hand launching it, and landing it in tight areas with no gear, so it needs to fly slow, but I would like it to be as fast as possible while not killing the slow speed flight.
Power will be a Saito 56 with a 12x6 prop"

The airfoil is important with a range from low lift coefficient (high speed) and high lift coefficient (low speed) with low drag. The Clark Y is good, like Tom said. A Saito 56 with a 12x6 prop wiil climb nicely with a 12 oz/square foot wing loading.

"The wing will be EPP foam with large carbon spars, so streingth is not a problem. (it can be thin)."

EPP is not good. EPP foam is bad because of low strength, high weight and high wing thickness. All Airfoils that have a wide range speed have lots of thickness! For this wing, the weight for EPP is around one pound! It is not worth it at all.

[Sparky Paul]

The SIG Seniorita is your airplane. Add a couple of bays to the wings to get the AR.
You would find it seriously overpowered with the Saito.
And hard to make it weigh as much as 80 oz.

[JettPilot]

[QUOTE=Ollie All Airfoils that have a wide range speed have lots of thickness! .[/QUOTE]

Ok, I can do a clark Y and about a 14 inch chord with a 72 inch span. How thick should the wing be ?

[Ollie]

See Clark Y airfoil:
http://www.nasg.com/afdb/show-airfoil-e.phtml?id=59
Or my pet S4233:
http://www.nasg.com/afdb/show-airfoil-e.phtml?id=1047
Or:
http://www.nasg.com/afdb/show-airfoil-e.phtml?id=814
Or:
http://www.nasg.com/afdb/show-airfoil-e.phtml?id=1152

You want around 3% to 4% mean camber and around 11% to 13% thickness.

[Phil R]

Take a look at Selig 3021...

If I'm not using a symmetrical airfoil, this is my standard choice for most other planes. I've used it succesfully on 6oz/sqft gliders to 1/4 scale planes with wing loadings in the mid 30s. I'm currently flying a 1/4 scale Piper Cub with an 80" span and a wing loading of about 25oz/sqft. It lands sooooo slowly and the stall is just a sort of mush. Nothing dramatic. Flies well inverted too... 3021 has a wide speed range (unlike Clark Y mentioned earlier) as my 100" camera plane demonstrates. It'll cover the sky almost like an F3B glider when I put it's nose down and let it off the reins....

[JettPilot]

We are also talking about this in another thread at:

http://www.rcgroups.com/forums/showthread.php?t=527016&pp=15

The two best choices so far appear to be the Clark Y or the Selig 3021...

That is a very impressive hanger of airplanes you have Phil ! I liked your homepage, and you have almost sold me on the Selig 3021 :)

My question is how the low speed handling compares to the Clark Y ? Will I be able to slow down and land in a small area, and handlaunch as I can with the Clark Y ?

[BMatthews]

...My question is how the low speed handling compares to the Clark Y ? Will I be able to slow down and land in a small area, and handlaunch as I can with the Clark Y ?

The airfoils are close enough that that any difference in low speed will be due more to the wing loading than the airfoil choice.

Bear in mind also that many of the differences between airfoils will be totally lost if the construction method does not replicate the airfoil accurately. If you're looking at open bay structure then the covering sag between the ribs will totally hide any differences between a whole range of airfoil nuances. Certainly any advantage or disadvantage of the Selig vs Clark would be totally hidden. For that matter with open bay structure any advantages of these two fine choices over even a curve drawn around your shoe sole would be lost as well. But if you make it light enough then even the shoe sole option will provide a slow speed landing.

Just trying to point out that we need to keep all the choices in mind when designing a model and not develop tunnel vision.

[Aio_1]

.....if you make it light enough then even the shoe sole option will provide a slow speed landing...
I used to find that a french curve doesn't get as much mud on the plan.;)
But seriously I've designed several planes using aerofoils plucked from my head that looked about right and could be built easily. They flew flawlessly. You can do much better if you put in the effort and carefully optimise all of the design parameters but the aerofoil is not the most important detail in most designs. I'm not in any way saying that aerofoils are unimportant but it's essential to understand that everything in aircraft design is about compromise and integrating all your desired design features. You can't just pick an aerofoil and expect that to make everything great.

In this thread the airframe seems to be open for negotiation but the aerofoil is getting all the attention. It seems a very unbalanced design approach from where I'm standing.

Aidan

[Langenase]

I .........In this thread the airframe seems to be open for negotiation but the aerofoil is getting all the attention. It seems a very unbalanced design approach from where I'm standing.

Aidan

I agree totally with Aio_1. Aeroplanes (airplanes?) are not airfoils with strange things hanging from it, first of all you must define the main parameters of your design, then the expected performances, airfoil comes later as it depends of A.R., WS, max. and min. desired flying speeds, type of control surfaces, etc.....
BTW
High aspect ratio is usually considered to be a value of 10 or more. Your proposed aspect ratios of 7.2 and 5.14 could not be considered as typical of sailplanes.

[JettPilot]

In this thread the airframe seems to be open for negotiation but the aerofoil is getting all the attention. It seems a very unbalanced design approach from where I'm standing.

Aidan

The airframe is already decided, thats why im really not asking or talking about it here. The rest of the design requirements for this airplane were given early on in this thread. So airfoil and possibly chord are the only things left to decide.

This wing has to be 72 inches for transport, and has to be one peice. The aspect ratio can be changed by the chord, but from earlier replys everyone seem to think a wider chord would be better for my requirements.

I

[Langenase]

Jettpilot

We were just trying to help you. If you already have a fuse, you must consider wing load as a priority. Once established, calculation of the chord represents a simple division. I'm a sailplane flyer/builder and when I rode that you wanted "sailplane like wings", tried to recommend you modern airfoils with good lift/drag ratios, and good characteristics in changes of camber, not classics as the ClarkY or the S3021, otherwise very good airfoils but considered as surpassed in the actual sailplane world.

[Ollie]

Jett,
You can't make a fine Lady's silk purse out of a sow ear. Fuselage, engine, radio and tail are too heavy then the airfoil won't do the job. If the tail area is small and the fuselage is short compared to wing chord, then the handling is poor. You have to give the whole weight and other measurements.

[JettPilot]

Jett,
You can't make a fine Lady's silk purse out of a sow ear. Fuselage, engine, radio and tail are too heavy then the airfoil won't do the job. If the tail area is small and the fuselage is short compared to wing chord, then the handling is poor. You have to give the whole weight and other measurements.

I wanted a sailplane like wing, but it appears that the chord will have to be wider for the weight of the plane. From the information you guys have given me, I will not get my highly efficient sailplane like wing as I had hoped in just 72 inches of span, but 72 is the limit for transport. The plane is not short coupled and the tail area is sufficient for the wing area involved, even with a wide chord. Nothing I can do about the weight, that is what the equipment I am carrying is ...

So my question is very simple now, given the limitations I have and the 8 pound weight, what airfoil can I best use that I might be able to hand launch and fly and turn slowly in some tight areas.

I do appreciate some of the peoples help here, it has given me some good information and ideas to this point. Others have just made this way more difficult than it needs to be by getting sidetracked and talking about everything except specific airfiols and designs.

So if anyone has the best and most simple answer for this wing, it would be appreciated.

JettPilot

[BMatthews]

Why limit the wing to a one piece affair?

But actuallly that's just for discussion as well.

Bottom line is that it's going to be incredably hard to hand launch an 8 lb airplane of this size. Even with a wide chord the wing area will not support the model at the speeds that it will leave your hands.

The airfoil can be chosen for the best possible low speed operation but the difference between a super high lift airfoil like the Selig 1233 and a basic Clark Y is still not enough to allow super slow speed flight. For that you need low wing loading.

The only way you'll be able to get your 6 footer to the point that it can be decently handlaunched is to get the weight down to around 5 lbs. MAYBE 6 at the most. Any heavier and the stall speed of the model will be higher than you can throw it at even with a moderate headwind. I'm not even sure that you can throw a 5 lb model to enough speed for that matter.

I base this on an 84 inch old timer model I fly with a 35 engine. It's got a wide chord of about 16 inches and weighs 5.5 lbs. I think I could launch it but it would need to be a full throttle affair. And it's got a nice high lift undercambered airfoil on it. It's also a polyhedral design as so many of the old timer free flights were. If you were to copy the same layout it would at least offer enough stability that you could use two hands for the launch. One to support the model under the wing and the other back by the tailplane for a nice powerful javelin followthrough.

But at your size and weight specs it would definetly be a no go situation. The most suitable airfoil going won't change that. And neither will adding flaps. You need to get lighter to make it work.

[vintage1]

I wanted a sailplane like wing, but it appears that the chord will have to be wider for the weight of the plane. From the information you guys have given me, I will not get my highly efficient sailplane like wing as I had hoped in just 72 inches of span, but 72 is the limit for transport. The plane is not short coupled and the tail area is sufficient for the wing area involved, even with a wide chord. Nothing I can do about the weight, that is what the equipment I am carrying is ...



Ah.



So my question is very simple now, given the limitations I have and the 8 pound weight, what airfoil can I best use that I might be able to hand launch and fly and turn slowly in some tight areas.



I think what you want is the old clark Y...and at least a sheeted leading edge, huge INBOARD flaps and a lot of washout to make slow speed handling predictable..

I find the weight very high for the span...deep chord, or even a biplane, may be indicated. If you want the thing to fly sub 20mph or so...

I do appreciate some of the peoples help here, it has given me some good information and ideas to this point. Others have just made this way more difficult than it needs to be by getting sidetracked and talking about everything except specific airfiols and designs.

So if anyone has the best and most simple answer for this wing, it would be appreciated.

JettPilot

I think in the following way...

- to get landing speed down requires a lot of wing area and big flaps..that means big chord or biplane.

- stability at low speeds and high angles of attack, with massive flaps deployed means inboard flaps or lots of washout, and big ailerons outboard, probably with serious differential ...flaperons NOT ideal.

- wing section is almost irrelevant for low speeds, since flaps will be changing it radically....probably would use the type of flap that slides backwards to increase total wing area as well.

Funnily enough, I am in the early stages of a very long term project to build a scale model with these sorts of characteristics..and 72" span is about where it comes in at..

Here's a photo of the full size...wing section is NACA 4413 derived.

I wouldn't go for twin fins though..with the rudders out of the prop wash and a castoring tailwheel, the only way to steer the full size on the runway was with the brakes...not good. I've seen this machine take off. It is all over the place till the speed comes up..;)

I just revisited the Motocalc predictions fo this model..with no flaps deployed, Motocalc estimates that at 7lb weight this model will stall at 24mph..that's HOT..very hard to fly much less than 30mph...bending the camber and angle of attack in Motocalc gets stall speed down to 21mph..still pretty hot. I prefer to keep stall speeds below 15mph if I can for easy landing in small places..

[HELModels]

Build your fuselage light and your wing strong. Wings tend to be the lightest part of a plane, which means you can increase wing area and lower wing loading to carry a heavy load. A pod with a boom will minimize the structure of the fuselage. You want the mojo in the wing, so minimize the weight and drag of a fuselage. Sailplanes look this way for a reason. You could pick a sailplane layout and make the pod a bit bulikier for carrying all your stuff. It wouldnt look like a great sailplane, but it would be slicker than a full length fusleage.

Camber and thickness combinations generally are enough to pick a foil, with the variations in how the camber and thickness is distributed determining the exact L/D. A bigger chord means a higher reynolds number and that will boost performance. Follow advice about 10:1 aspect ratio as a minimum. Balance all your criteria, weighing priorities and accepting compromise where you must. As for specific airfoils, an Eppler E387 is about as good as a Clark Y or Clark Z or Selig 3021. A NACA 4412 looks identical to the Clark Y.

[Ollie]

I think many and I have advised you. Your project is not very practical for many reasons. You can't fix the project with just airfoil and wing chord. You can't use an over weight fuselage. You can't throw an over weight plane. However, you can land an over weight plane with a large parachute. See:
http://www.wonderhobby.com/rarecorcpapa.html
The catch is low speed but not high speed. You can get the cake but not eat it too.

[HELModels]

Just do it. Increase your wing area and reduce your loading. The first electric planes had the same problem - too heavy, so people boosted the wing area and they flew.

[Aio_1]

The airframe is already decided, thats why im really not asking or talking about it here. The rest of the design requirements for this airplane were given early on in this thread. So airfoil and possibly chord are the only things left to decide...
Forgive me for not letting this drop but there still seems to be something odd about how you're looking at this. How can you say that the airframe was already decided when something as fundamental as the wing chord hadn't been decided. If you were trying to choose between 13" chord and 14" chord that would be fair enough but you've gone from a vague idea of 10" chord to 14" chord and you appear to consider this a fairly minor design decision. I agree you had decided on your design criteria (ie. AUW, max span, hand-launchable... etc) before you started the thread but you certainly hadn't designed "the airframe".

I think you may have to accept that hand launching the plane at 7 or 8lbs may not be practical. Also while increasing the chord to reduce the wing loading will help with low speed flight it also results in a very low and pretty inefficient aspect ratio. Although the low aspect ratio and flaps will reduce the flying speed you may find it will also make the plane even harder to throw fast. I would think the additional drag will be noticable when throwing a plane this size. Is it possible to use a catapult or bungee for launching or is hand launching essential?

Incidentally I agree with Vintage's comments about using inboard flaps rather than flapperons. Low speed roll response would suffer and tip stalling may be a problem if you try using full length flapperons. You could perhaps use some flap outboard by mixing a smaller amount of flap with the ailerons while having dedicated flaps inboard.

Aidan

[biber]

http://www.do27.com/do27/pagebilder/Do_3d_3.gif

biber

[Sparky Paul]

A similar thread on getting a sailplane to 80,000 feet foundered on the same problem... insufficiently defined parameters, and a reluctance to admit that, when assistance and experience was offered.

[JettPilot]

Thanks guys for all the great info, especially to AIO_1 for the great technical anaylisis of my project and those that recommended airfoils and ways to make this plane do what I need it to do. I have taken your suggestions and will put them in my project and will post the video of the first hand launch :)

I used to pitch a 75 MPH fastball, so I hope I can manage to launch my plane at 20 MPH... And most importantly not getting mixed up and launching the transmitter instead of the plane :eek:

JettPilot

[sodman12]

So you ever build it?