The effect of positionning elevons on the inside of a 2 peice-wide wing..

[ScottM]

Kind of hard to explain, but what is the effect of putting elevons on the inside of a wing?

|Body|===========|===========|
| |(elevon is here)

\/
Tail.



... Hard to explain, but the wing folds out from underneath during flight, it's a boost glider... so the only surface I can put the elevons on is the inside 1-foot of the wing. The total wingspan is 4 feet. 2 feet fixed, and 1 on each tip that fold out.

(flat bottomed aerofoil, so no lift when it's folded, plenty when it's extended)

... anyways, I can explain more if people ask me questions and can help...

-Scott

[Flight Engineer]

"Elevons"?

As far as the Aileron side of things go, you will have reduced authority, simple force times distance thing.

You will also have increased induced drag as the lateral pressure gradients are much more severe.

For the elevator side of it. They would be pretty ineffective anyway. Are they coupled to the V tail? Are they used to increase elevator authority or as flaps or spoilers? If you don’t need them I would be tempted to remove them as they will only make the aileron throws even larger so the problems mentioned above would be more severe.

On the plus side the problem of adverse aileron yaw will be reduced.

It will work but is not optimum. Can you rotate the outer portion of your wing i.e. wing warp?
I would use the V tail as "Elevons" as this reduces the loads and structure on the main plane.

I think I read about a free flight guy employing folding wings with great success.

I would look into a swing wing design too. I think that would work well.
Good Luck.

[ScottM]

It's already designed and partially built.

The wings swing out from underneath, and that's it.

All this sucker has to do, is go up, deploy the wings via Channel 5 (switch), and then be able to be controlled on it's way down. I just need to know that the elevons will be at least partially effective.

As for the "V-tail", that's not how my glider works... I'd have to get some mighty long servo extension wires (1.5 feet) to make each servo reach all the way back to the tail... that, and I don't know how the servos will like being blasted by model rocket motors, roughly 1.5 feet away (engines at nose).

... I suppose the V-tail idea is better. It eliminates my aileron issues...

But how do I calculate how big the V-tail needs to be, and how do I mount the servos, etc?

-Scott

[MattLarson29]

How about pushrods? The servos don't have to be located at the actual control surface, and 18 inches is certainly managable for a pushrod system.

Matt

[ScottM]

Originally posted by MattLarson29
How about pushrods? The servos don't have to be located at the actual control surface, and 18 inches is certainly managable for a pushrod system.

Matt

Question is... heavier or lighter than servo extensions?... Probably about the same.

[ScottM]

For those who want to see roughly what it looks like...

Enjoy ;-)

*ducks as the questions come flying at him*

... no pun intended ;-)

[ScottM]

Oh by the way... the non-folding peice of wing actually continues out both sides, I just didn't want to draw both sides, so you get a better view.

The center peice is 2 feet wide, and the wingtips will be somewhere just short of half that (1 foot each)...

Unless someone can help me calculate how much lift I'll get from a 4 foot wing with a 0.446 Lift Coefficient (approx), and a 4.15 inch chord (roughly). Approx total weight is 275.9g , with the wing being 160 of it.

NOTE: The point of the folding wing is that it produces no lift on takeoff, then when I deploy them, it produces enough lift to glide... well, that's the theory, anyways...

Anyone?

I'd happily use less width of wing if I knew it would fly.

[DanSavage]

Originally posted by ScottM
I just need to know that the elevons will be at least partially effective.

Elevon controls on the inboard section of the wing will be partially effective, IMO.

It won't be an unlimited aerobatic ship, but you should be able to control it on the way down.

In "elevator" mode, the elevons will act like flaps and spoilers to increase or decrease the lift of the main wing, which should make the model go up and down.

In "aileron" mode, the elevons will act like, well, like ailerons.

I've got pretty small ailerons mounted inboard on my WB-57N and they work okay. I wouldn't try an Aresti pattern, but they should be effective enough to fly the model.

Good luck!

Dan

[ScottM]

Originally posted by DanSavage
Elevon controls on the inboard section of the wing will be partially effective, IMO.

...

I've got pretty small ailerons mounted inboard on my WB-57N and they work okay. I wouldn't try an Aresti pattern, but they should be effective enough to fly the model.

Good luck!

Dan

Thanks dan!

Do you know anyone who can calculate the lift that I need for me?

[DanSavage]

Originally posted by ScottM
Do you know anyone who can calculate the lift that I need for me?

Sorry to taking so long to respond.

Not too sure what you're asking. Can you clarify what information you're trying to obtain?

Dan

[ScottM]

Doesn't matter anymore.

Went with seperate ailerons/elevator.

The wings are super nice though. A local rcPilot helped me build them :-)

[Ollie]

You don't need elevons to control the glider after launch! If you make the outer panels swing through about 195 degrees so that in the glide mode the tip panels have about 15 degrees dihedral, the glide can be controlled by ruddervators on the V-tail. Sullivan 1/32 steel cable push rods running in nylon tubes will make good control linkages for the ruddervators. The nylon tubes can be CA'd to the outside of the tail boom. The ruddervator control horns can be mounted underneath the ruddervators to keep them out of the hot exhaust.

[ScottM]

Originally posted by Ollie
You don't need elevons to control the glider after launch! If you make the outer panels swing through about 195 degrees so that in the glide mode the tip panels have about 15 degrees dihedral, the glide can be controlled by ruddervators on the V-tail. Sullivan 1/32 steel cable push rods running in nylon tubes will make good control linkages for the ruddervators. The nylon tubes can be CA'd to the outside of the tail boom. The ruddervator control horns can be mounted underneath the ruddervators to keep them out of the hot exhaust.

Lol...

Good to keep in mind, but a bit too late.

I built the wing, it's 4.25inch by 4 feet. It has a lift coefficient of 0.445, and has ailerons.

Putting in the elevators in thursday, and launching on friday.

Once I get the video processed, I'll post it here on the boards.

It'll be a hell of a flight :-)

[Sparky Paul]

For the "B" change, Ollie's method will work well...
or since aerobatics isn't a priority, the elevons on the inboard panels would work.
But I would try Ollie's method first.

[Flight Engineer]

Standard gravity constant = 9.806

Lift = CL × ½rV² × S Newton’s

r=1kgm3
S =121.92*10.541
=.128515872m^2
Lift=weight=.275kg*9.806=2.69665newtons
CL=.446
2.69665=.446 x 1/2x1xV^2 x .128
47.236722253363228699551569506726=½rV²

V= 9.7meters/second or 21mph


So that’s your stall speed.

I don’t believe I’m so bored I did that for you……..

[ScottM]

Originally posted by Flight Engineer
Standard gravity constant = 9.806

Lift = CL × ½rV² × S Newton’s

r=1kgm3
S =121.92*10.541
=.128515872m2
Lift=weight=.275kg*9.806=2.69665newtons
CL=.446
2.69665=.446 x 1/2x1xV2 x .128
47.236722253363228699551569506726=½rV²

V= 9.7meters/second or 21mph


So that’s your stall speed.

I don’t believe I’m so bored I did that for you……..

... I need to maintain that speed...?

Oh sh*t...

Well, it may just plummet rather than glide :-P

It weighs 200g approx.

[Flight Engineer]

200g auw gives 18.5mph stall speed,

This is the stall at cl.446 the cl changes with aoa depending on the aerofoil used the clmax will be much higher.

so to put it a different way. your min level flight speed is 18.5mph at zero pitch angle.

[ScottM]

To ask a simpler question... Can I land it from somewhere around 100-500 feet?

[Ollie]

The stalling angle of attack will probably be greater than has been assumed. I would estimate that the coefficient of lift at stall will be closer to 0.7 than 0.446. The proper approach speed for landing will allow for some stall margin but will undoubtedly be less than 18.5 MPH. furthermore if a touch of up elevator is applied just before touch down the landing approach can be flared and the stall margin of speed can be bled off for an almost stalled touch down. That's the way the space shuttles' landings are performed. The glide of your model will be far superior to the space shuttle and far easier to land. Having said that, I highly recommend that you get flight instruction and flying experience before attempting to fly a new design. After all, test pilots should be the most highly skilled and experienced available.

[ScottM]

I used to fly

I feel comfortable landing this model

It's going to be flown once in a large field. If I land it, It'll be flown again...

I think i'm going to setup a giant pillow/net to aim for :-P

[Bill Glover]

Originally posted by Flight Engineer
200g auw gives 18.5mph stall speed,

This is the stall at cl.446 the cl changes with aoa depending on the aerofoil used the clmax will be much higher.

so to put it a different way. your min level flight speed is 18.5mph at zero pitch angle.


With no maths (just lots of r/c flying experience!) that sounds an awfully high stall speed for a 48" span model with an AUW of 7 oz and wing loading under 5 oz/ft sq !

I've got an S280 powered glider that's pretty similar (span is about 45", flat bottomed section, high a/r) but heavier at around 9 oz AUW. In the lightest breeze that lands with no forward speed at all. Pic below (minus prop & spinner).

[ScottM]

Originally posted by Bill Glover
With no maths (just lots of r/c flying experience!) that sounds an awfully high stall speed for a 48" span model with an AUW of 7 oz and wing loading under 5 oz/ft sq !

I've got an S280 powered glider that's pretty similar (span is about 45", flat bottomed section, high a/r) but heavier at around 9 oz AUW. In the lightest breeze that lands with no forward speed at all. Pic below (minus prop & spinner).

LOL, that looks a *lot* like my rocket.

I promise to post pictures when i'm done. You guys deserve that much for helping me.

[Flight Engineer]

As I said in my last post.

so to put it a different way. your min level flight speed is 18.5mph at zero pitch angle

If You assume clmax of .7 as ollie thinks then the stall speed will be 5 meters/second or about 10mph. As I don't know what profile the wing has it's all much of a much.