Fully symmetric flying wing

[emoone]

I'm building a electric powered flying wing from fan fold foam (pusher prop). I would like to use a symmetric airfoil in it as this will really simplify the building process.

Will a symmetric airfoil work OK on a flying wing? Do I need to add any up or down thrust with the motor?

Thanks!

Eddie

[Tony Oliver]

Yes you can get away with it, but you'll need some 'up' set on your elevons (possibly a little wider elevon chord than usual will help)and a very accurate CG position. It's probably safer to slope it first to get that bit right. You will also need to have some upthrust on the motor (shaft pointing down to the rear).
Make it adjustable within a range of around -4 to -10 degrees , (starting at -4)you're unlikely to need more than that.
Good luck.
Don't forget the age-old-advice. Change only one thing at a time.
That would be my approach. Others will have different ones I'm sure.
Tony

[emoone]

Tony,

Thanks! I knew I'd need a little "reflex" in the elevons especially since there will not be any washout in the TE. Sounds like I can get away with this.

I may even build a little 24" version just for flight test.

Eddie

[Tony Oliver]

Don't forget that iif you feel happier with it, and you make the elevons from balsa, you can carve in the reflex towards the tip. Just taper the wood to a normal t/e section at the inboard end and reverse it at the tip.

Tony

[Tony Oliver]

Sorry, forgot the sketch!

[emoone]

I hadn't thought about building some washout into the elevons. That's a real nice suggestion! I usually use coroplast for my control surfaces , but balsa sounds just right for this application.

I did build a little 24" mockup of my wing last night for some glide tests, but I haven't had a chance to chuck it yet.

Thanks!

Eddie

[YEAP CHIN POH]

This is really remarkable becasue I am also building a fully semetrical swept flying wing too. Mine is made of balsa and is 34" w/s. I was thinking about the same questions and now I have the answers. :D

[LuckyArmpit]

I just made a wing out of fan fold. I had coroplast in as elevons.
But, there isn't enough throw when I push the stick for descent.
There is 1/2 inch at the trailing edge and I used 2 mm coro.
I cut them off and put on balsa aileron stock. The wing is partly
symmetrical. First few test flights resulted in wobbly behavior.
Partly due to tail heaviness. I took off the coro winglets (ala fma razor) and made much bigger ones out of foam. Haven't tried it yet.

Dave...

[member73]

Dave, how can a flying wing be tailheavy? :D

[YEAP CHIN POH]

I am having a case of uncertainty here. I am not sure what I am doing is "right".

I have build with balsa a 34" flying wing. It does look like a Zagi. I used a fully symatrical NACA 16% airfoil and intend to power it with a S400 7.2 v. I will be using a 7 cell 1000 MaH Nimh pack. Projected weight should be about 14 oz and wing loading about 7 oz psf.

I reckon the plane will be tail heavy so the battery goes all the way front. An advantage of balsa is that the battery will be inside the plane.

From what I gather a reflex is needed. Would 1/4 inch be enough. Motor downthrust of 4 degrees is also needed. Doesn't this cancel each other out?

I plan to use the Graupner CAM folding prop mounted with the blades in reversed?

The plane is at advance stage. I hate to plough the field with it. Can anybody confirm that this will be fine?


Regards


:D

[Sparky Paul]

1/4" reflex should be OK.possibly too much, depending on the chord of the surface.. YOu might be prepared to feed in a little down elevator on the first flight right after launch..

[Tony Oliver]

Can I take it your model has a pusher motor with the motor shaft pointing down a few degrees?
How have you decided the ideal CG position? That will have more effect on the trim than the motor thrustline.
At 16% thickness, it's likely to be a fairly docile model as far as reaction to control input is concerned but is relatively heavily loaded for its span. It will probably need a fairly fast heave into the air, so a handlaunch over long grass, or off a slope would probably save some heartache if it's not quite right at first.

The reversal of the prop blades is right. The convex side of the blade always points to the direction of flight.(except when you want to reduce the power on a freeflight model until trimmed out safely). Is the motor set for reverse running?

Sparky Paul's right on with his recommendation of 1/4 in of reflex. Whether you need to be ready with up or down depends on your CG position, which is why I asked.

Tony

[YEAP CHIN POH]

Thank you Sparky Paul and Tonyo for your replies.

The plane is at an advance stage and will probably be ready for flight (family permitting) next week.

The plane is a pusher.

The inspiration came from the Klingberg Wing as well as the Zagi.

This project is a first for many things for me.

I place the CG at 32% of the wing area. This is calculated as 32% front and 68% behind it. Again I am not certain this is right but may build a small 6 inch model to test or alternatively test glide over long grass.


Regards

[Sparky Paul]

You'd be safer using a more conventional method of locating the c.g.
For a symmetrical flying wing, it's possible to place it at 25% of the -mean aerodynamic chord-..
But it's safer to start with it forward of that point, maybe 15 to 18%..
Here's a link that shows how to figure the m.a.c.
http://home.earthlink.net/~pjburke1/cg.htm
"32%" is WAY too far aft for a flying wing.

[YEAP CHIN POH]

Whoa!


I will work on that. Battery location may have to change.

[YEAP CHIN POH]

I assume all our calculations exclude the outboard elevons. This is so because the elevons are just flat and therefore should not figure in the calculation of wing area.

Can I assume that.

[Sture Smidt]

You mus INCLUDE the elevons in the calculations!!!!!!!!!!

They are contributing to the wing area (even though they are flat).

Give me your planform on a sketch and I will look into the CG calcs. Remember to put on all relevant dimensions.

[YEAP CHIN POH]

Dear Sture


I solarfilmed the plane last night. It looks good and it would be a shame to smack it on the first flight.

Thanks for your offer of calculating the CG for me. I do not know how to draw a sketch on this reply for you, could you make do with the stats.

Wing dimensions (excluding elevons).
Wing chord at root (middle) 10.75"
Wing chord at end 5.375" (50% taper)
Overall wing span measured from tip to tip 34"
The sweep is obtained by pushing the middle forwards 3.5"

Elevons are 2" wide at tip and 1" wide at center. Gap is given for the prop (pusher) and the elevons start 3.5" off the center.

The planform is akin to the Tornado featured in this month's Ezone. My plane is made conventionally with balsa and the airfoil is a fully symetrical NACA. Power is a pusher S400.




Regards

[Sture Smidt]

Is this what you mean?

[Sparky Paul]

A 20% c.g. on this shape is close to 50% of the root chord...

[Sture Smidt]

Hi, Sparky

Have you used the FULL root and tip chord?
What is your static margin?

This is a rather simple and fairly accurate method for trapezoidal wing planforms with a moderate sweep.

[Sparky Paul]

"static margin".. on a plank type wing, with a symmetrical airfoil, the c.g. -can- be as far aft as 25%. Any more than that requires an extremely good pilot or some sort of added stability.
A 20% c.g. is reasonable for this airplane.
The root chord is based on extending the cut-off in the elevon to the root.. and the tip chord includes the elevon chord.

[Sture Smidt]

Sparky:

So, for the sake of good order, the static margin is approx 5% of the mean aerodynamic chord (MAC).

Builder:

Good luck with your first flight! It will most probably work out nice for you.

[YEAP CHIN POH]

Dear Sparky Paul and Sture



Both your replies are really most helpful. Its funny to see my planform in the computer and yes; that is how it looks like. With the CG in hand I can now fit out the plane & hopefully get it ready for flight this weekend.

I weighed it last night on my postal weighing machine; (not exactly 100% accurate) but it came up to 5 oz (empty). This was in spite of the holes I bore out of the elevons, fins and hatch. I know this is heavy and I have to watch it the next time (if I build a 2nd).

Do you think it wise to attach the fins with velcro? a'la Zagi and the rest. I desire the ability to pack it in a case & take a bus to (600 miles away) Singapore to slope soar next year! There is a very active aeromodelling community in Singapore.

Once again my thanks.



Regards

[YEAP CHIN POH]

Hi Sture Smidt, Sparky Paul & Tonyo



After delays due to an unsuitable prop and rain the fully symetrical flying wing has finally flown.

The 1st and so far only flight is a unqualified sucess. All your advice on the reflex, thrust angle and CG is right on the money. No trims were required.

After doing some test glides to confirm the CG etc, the wing was launched and the motor was applied. Much to my amazement it just took off and proceeded to climb with good speed & authority. The wing proved to be very stable and very manouverable. It looked funny in the air as I was more atuned with conventional airplanes.

As would be expected my hands shook as this is a first flight and footballers entering the pitch didn't calm things too. The throttle was halved; no trims again were required and after a few circuits the wing was ready for its first landing. It was controllable right up to the landing.

In flight the motor could be heard. No fault of the APC 5.5 X 4.5 which I got from AEROMICRO. An earlier Graupner proved likewise. The sound effect is generated by the drumming effect as the motor is mounted on top of the wing. IT IS A BUILD UP FLYING WING.

It was a short and beautiful flight. I still dream about it before I go to sleep!

I do not have a digital camera but many conventional pictures were taken. I will scan them when ready.

Once again my thanks guys. WIthout your input I doubt I would have reached this stage in one piece.


Regards

[Sture Smidt]

I'm glad it worked out for you. This demonstrates that a little theory before the first flight can save a lot of time and money. This time we found the proper CG location (thanks Sparky) and it flew. Most times a little thinking, math and aerodynamics can do wonders for new models.

[Tony Oliver]

Same from me!
There's something special about a first flight of your own designs when it all goes right.
Cheers

Tony

[Sparky Paul]

Taking the mystery out of this stuff is fun! :)

[Tony Oliver]

My sentiments entirely!

And if I can stop someone stepping on the same rake as I did, all the better.

Tony

[Sparky Paul]

Originally posted by YEAP CHIN POH
Hi Sture Smidt, Sparky Paul & Tonyo



After delays due to an unsuitable prop and rain the fully symetrical flying wing has finally flown.

The 1st and so far only flight is a unqualified sucess. All your advice on the reflex, thrust angle and CG is right on the money. No trims were required.

After doing some test glides to confirm the CG etc, the wing was launched and the motor was applied. Much to my amazement it just took off and proceeded to climb with good speed & authority. The wing proved to be very stable and very manouverable. It looked funny in the air as I was more atuned with conventional airplanes.

As would be expected my hands shook as this is a first flight and footballers entering the pitch didn't calm things too. The throttle was halved; no trims again were required and after a few circuits the wing was ready for its first landing. It was controllable right up to the landing.

In flight the motor could be heard. No fault of the APC 5.5 X 4.5 which I got from AEROMICRO. An earlier Graupner proved likewise. The sound effect is generated by the drumming effect as the motor is mounted on top of the wing. IT IS A BUILD UP FLYING WING.

It was a short and beautiful flight. I still dream about it before I go to sleep!

I do not have a digital camera but many conventional pictures were taken. I will scan them when ready.

Once again my thanks guys. WIthout your input I doubt I would have reached this stage in one piece.


Regards
.
Here's a composited photo he sent...

[Tony Oliver]

Great stuff!

A well thought out model, well built and it flies well - what more can you ask for.

Tony

[BMatthews]

Originally posted by member73
Dave, how can a flying wing be tailheavy? :D

Trailing edge heavy? Fin heavy?

:D