Question on aerofoils

[Gandrews]

Hello! As is probably evident, I'm new here. My father and I hope to build a replica Sopwith 1 1/2 Strutter soon. We bought replicraft plans, but we wondered about the aerofoil shape. To our (untrained) eyes, it looked fairly frail and inefficient. Yet, looking around here, it seems a fairly standard shape. We are considering altering the shape a little bit (mainly in terms of thickness) to try and get some extra lift out of it. Is this necessary? Is there any great advantage or reason to do this?

Hopefully one of you gurus out there would lend a few words of advice
Many thanks,
Geoffrey Andrews

[jumpinjan]

The problem with those RAF airfoils are the abrupt stall characteristics (I think). I assume that with some conservative pilotage, it shouldn't be an issue. "If it work good then, it should work good now..."
(Off-the-record, that's what I was told when I also brought up this issue to the replica builders. However, if you are considering changing to a better airfoil, the NACA 4412 is a good, dirty airfoil that is forgiving in light aircraft)
Hey, look at this:
http://www.baylor.edu/content/servic....php/41147.pdf

[Gandrews]

Alright, thanks. Were the stall characteristics a result of the aerofoil though? I was under the impression that they were due in large part to the rotary engines.

[jumpinjan]

No the engine; Yes the airfoil. Its due to the sharp leading edge and its thinness. Because these replicas fly under 100 mph, the shape doesn't mean a whole lot, but the thickness doesn't need to exceed 12%, which is about the thickness of the ClarkY or the 4412.
(the engine used has nothing to do with the stall characteristics)
Jan

[Gandrews]

alright, well thanks for your help.

Originally Posted by Gandrews

Hello! As is probably evident, I'm new here. My father and I hope to build a replica Sopwith 1 1/2 Strutter soon. We bought replicraft plans, but we wondered about the aerofoil shape. To our (untrained) eyes, it looked fairly frail and inefficient. Yet, looking around here, it seems a fairly standard shape. We are considering altering the shape a little bit (mainly in terms of thickness) to try and get some extra lift out of it. Is this necessary? Is there any great advantage or reason to do this?

Hopefully one of you gurus out there would lend a few words of advice
Many thanks,
Geoffrey Andrews

Geoffrey,

What you and your father have discovered, is the first hurdle to overcome regarding a flying WWI replica,.......Authenticity -vs- Practicality.

Yes, more modern airfoil shapes are more efficient.

Yes, it worked then it will work now.

Yes, it requires more attention from the pilot.

No, it wont fall apart if built and flown as designed.

"...We are considering altering the shape a little bit (mainly in terms of thickness) to try and get some extra lift out of it..."

I myself am discovering during the course of my own research, that this "ain't" so easy. Subtle changes have effects that were not expected elsewhere. Not impossible by any means but, requires tremendous self discipline.

Best of luck.

[greatwarpilot]

Geoffrey,

The museum I work with operates a Sopwith 1 1/2 Strutter, and its wings are built to replicraft plans.

There is NO need to modify the airfoil. We refer to the machine as the Emperor's Barge, largely because it is a little heavy on the controls (in roll mainly). I've heard no adverse reports of the stall characteristics, and can see no reason to deviate form the original.

I also fly a full scale SE5a replica, with the correct airfoil, and the stall characteristics are nothing to be afraid of - even accelerated stalls and stalls in turns.

Some food for thought anyways. Please keep us informed of your progress and how you decide to proceed in terms of the airfoil.

Cheers,

[Gandrews]

Alright, thank you all very much. We are, understandably, a bit green in the whole area of building and flying replica aircraft. Thanks for your time, we'll take this all into consideration.

Originally Posted by Gandrews

Alright, thank you all very much. We are, understandably, a bit green in the whole area of building and flying replica aircraft. Thanks for your time, we'll take this all into consideration.

Geoffrey,

I must admit to the same initial temptation but, as I see this coming together in 3d, it's plain to see the beauty in the form. It would be a true shame to alter this from the original.

The airfoil on the Baby is similar if not identical to the 1 1/2 Strutter.

Edward is correct, there is no need to modify the airfoil.

That aircraft in particular, with it's massive area and light weight, would likely want to float forever in ground effect.

It is truly beautiful in the air.

[sheppo]

If you begin to change the wings about you may immediately be opening up a pandoras box of potential issues.
If you suddenly add "bags of lift" with airfoil 'X' then where do the additional forces go to?
The fitting, flying wires and attachment points?
From there the forces have to be managed by the fuselage frame.
Do you need to bulk that up to cope with the loads?
Do all the fittings suddenly change in size (and weight) to accomodate larger longerons ?
Now you may need to redesign the whole fuselage!
and so on....

Could the larger section wing cause unusual drag or airflow charactaristics?

EG: The sopwith Pup my father used to fly was horrid on landing flares as the lower wing apparently masked a lot of the rudder effect and affected the elevator somewhat. Not so much of an issue on a huge open field if you land at an angle to what was intended but it is possibly treacherous on a landing strip.

Could a thicker wing cause this to be worse still? Stranger things have happened!

In the end you may end up with something approaching unmanageable in the air , overweight, out of balance etc. Tailheavy isnt good ( and many ww1 planes were already so, consider also they were usually younger and smaller pilots than the average homebuilder these days sitting in the back. Im already 10kg's over the supposed pilot allowance for the Dva).... & carrying extra ballast up front to maintain trim may well negate the whole exercise of increasing the lift on the wing anyway.

A quick example of a simple problem I faced:
Im not too sure what the sopwith used for metal fittings etc but in the Albatros its only .5mm-.8mm, 1mm for many of the tubes in the elevator. If I was to source this from Aircraft spruce I would be adding a LOT of extra weight where I dont want it-right up the back. The US tube walls are too thick for the diameters I need.
I need to be very careful what I use in my construction materials for this reason, & Im not even starting to contemplate altering the design.

I would very strongly suggest NOT tinkering with the design, unless you are an aeronautical engineer. Indeed, Id rather be flying earlier than redesigning, test flying, perhaps altering a number of times- what could be an entirely "new" plane that has already been built and flown by the multitude in an existing format.

Sopwith built a good plane when its said and done, Id go with the existing design.

There are notional "sopwith pups" out there with steel tube fuselages, thick chord wings and Russian Mp14 radial engines. I figure that you might as well have bought a Pitts and done with the WW1 pretence on that account.

Thats my 2cents anyway.

hope it helps.

cheers
chris