ScottMcLeod

I think i'm in a little over my head on this one...

I've manged to get help from John Dreese (the maker of DesignFoil) to help me design an aerofoil for my rocketry project in physics here, but I have NO CLUE how to use this software...

Does anyone have good experience with it?

2nd question:
I need a material to make the wings out of. I'm using a microreceiver, 2 micro servos, and micro batteries + mixer to drive 2 elevons that will be on the end of the wings.

What material should I use? This rocket probably won't be much bigger than 1 foot wide by 1-2 feet tall, yet needs some way of gliding.

Thanks for the help!
-Scott McLeod

ScottMcLeod

I just designed an aerofoil/wing, that has:

Coeff. of Lift: 0.183
Coeff. of Drag: 0.0080
Coeff. of Momentum: -0.0213

It has a wingspan of 1 foot, a root chord of 1 foot, a tip chord of 0.25 foot. It has an Oswald E (efficiency?) number of 0.8.

It's total area is 0.63 square feet, aspect ratio of 1.59, taper ratio of 0.250.

Mean chord : 0.700 ft.
Span location : 0.200 ft.
25% MAC chord from Root LE : 0.18 ft.

... Does anyone either know that this is all good/bad, for my rocket glider, or know someone who will know this?

Thanks!
-Scott McLeod

Tall Paul

You left out something....
The leading edge sweep.
This makes a HUGE difference in where the c.g. will be.
Also the size of the elevons.
A lot of trailing edge sweep as shown in the black image moves the elevons forward, making them less effective as pitch controls.

ScottMcLeod

Did you do that with DesignFoil?

Anyways... I take it you know your stuff about wing design.

... wait a second!

jeezuhs. I realised I designed the wing backwards...

What will be effective as a wing on a rocket/glider?

Glider, in the forms of the term that I can land it once it's out of rocket boost, not so it can gain more altitude.

Thanks Tall Paul!

Tall Paul

Either of the shapes, or anything at all can work when the c.g. is located properly.
For a rocket glider, you'd probably OK with the magenta shape, as the thing would be a tailless delta.
Your boost speed vs glide speed can be a problem with any airfoil other than symmetrical.
Take the completed shape and throw it as a glider to see if your c.g. is correct.
To position that, using the m.a.c. you already have, put that on the diagram of whatever shape you decide on, and find where 20% of that distance is. Project that location to the root of the wing to find it on the fuselage.
Note how the m.a.c. is at the same location regardless of the sweep, but the c.g. position is quite different...
Drawn up in TurboCad, refined in Paint Shop Pro 8.

ScottMcLeod

Alright, I wasn't planning on using a fully symmetrical, but if that's the way it's gonna work, then that's the way i'm gonna do it! :-)

Can you explain what the MAC will affect, and what I'm supposed to do with it? (is that the highest point in the aerofoil?)

I understand the idea of balancing CG though, and that's gonna be part of my physics calculations for the boost vs. glide stability.

Thanks for all the help :-)
-Scott

Tall Paul

The m.a.c. is the mean aerodynamic chord. It's only a dimension.
The c.g. is located using the m.a.c.
Airfoils can have a pitching moment depending on their camber.
Normally shaped airfoils pitch nose down. The horizontal tail is added to the plane to provide a down-lift at the back of the plane to counteract this.
In addition, the position of the c.g. can be adjusted over a wider range.
Tailless planes therefore have no staibilizing thing at the back, and have to provide some other means.
The first is to use a symmetrical airfoil, which has no pitching moment. These can be used with a c.g. as far aft as 25%. Tailed planes almost always go further aft than this.
The next fix for lack of a tail is to change the airfoil if cambered to a reflexed trailing edge. (tilted up a bit). This can change the pitching moment to whatever value you desire.
When efficiency becomes important, then investigating these styles of airfoils becomes useful, but if all you want is a measure of stability and a less-than-an-anvil descent, then symmetrical with the c.g. forward of 25% will do the job.

ScottMcLeod

K... when it comes to a symmetric airfoil... that provides a neutral lift, right? (because of the identical speed of air travelling above and below the wing...

Could I get away with no aerofoil, and building my wing out of thick balsa like the Estes Nightflyer?

Tall Paul

.
"..neutral lift..."????
No.
A symmetric airfoil lifts at an angle of attack greater than 0.
You (the pilot) establish this angle by trimming the airplane to the flight speed/descent rate you require.
A flat plate works, but a streamlined flat plate works better. (less drag)

ScottMcLeod

o/'' I can see clearly now... o/''

I get it now.

So, a symmetric aerofoil would offer no lift during a rocket launch, and on the way down, I could glide it in slightly nose-up, and still maintain flight.

Never flown a symmetric before, and I guess I didn't quite understand the physics behind it.

Thanks tall paul!