Trailing edge question for wing

[Hucker]

I'm making good progress on the zephyr and am looking at the trailing edge behind the motor. It is almost an inch thick. It seems to me that that is not a good thing. I suspect it is draggy and that the turbulence it creates going through the prop can't be good.

I'd like to trim the motor area into a more airfoil like shape. I looked at a bunch of pictures of wing trailing edges and haven't seen anyone do this though there aren't many good pictures. Is there a reason not to?

[Derek_S]

I cant think of any reason not to. I did this on my scout bee even though the TE was only abouyt 1/4". That should reduce drag and make it more quiet as well.

[ZobZibZab]

many do trim that area afaik.

I'm not entirely sure of the impact of this aerodynamically speaking. If the TE is thin then the air collides in a different fashion before hitting the prop. The flux logic here is complicated and maybe only simulation can tell what is really better.

I would be very interested if someone could enlighten us on the technical aspect of this topic (aka not "it felt better with it trimmed" but the actual reason for it, or against it)

[roberto]

yes, many do taper that area and it makes the bird less noisy and certainly a bit more efficient. go for it, you can´t go wrong.

[M'ck'y]

On my next wing, i'll certainly taper more, behind the motor area and also leave the elevons uncut to reduce drag.

[volto]

Yep I did this and it's pretty quiet and efficient, no idea how much it helped because I didn't try it without the taper.

http://fpvlab.com/forums/attachment.php?attachmentid=1836&d=1310076698

[brosius85]

didn't taper it. my motor is a looooong wat from it though so the prop is quiet and efficient annyways :p

[Hucker]

On my next wing, i'll certainly taper more, behind the motor area and also leave the elevons uncut to reduce drag.

I was wondering if I should sand those guys down a bit... darn more projects...

[Hucker]

@brocius85: Can you see the gopro with your FPV cam?

[brosius85]

nah hucker its just out of view. also its just velcro so i can adjust it out further if i put it on a bit too close

[Pooch]

Cool paintjob brosius!

Never realised the Zeph was so thick, that's one big unit...

[volto]

...so thick, that's one big unit...

That's... what.... she said!

Couldn't help myself.

[Pooch]

ಠ_ಠ

[Dionysos]

Hi,
I would probably leave it the way it is... This vertical surface creates some drag, sure, but the prop actually sucks all the vortices away. "Design-wise" this cut chord is not a good solution from an aerodynamics point of view. Why? because a swept wing shifts the lift distribution towards the tip of the wing, so to say, you need lift in the middle. Now there is very little lift where you 'd need it the most. However, I believe that you couldn't get a healthy CG if you wouldn't cut it and place the motor at the very end.

There is an old design rule, this is translated so it may not sound elegant but here it goes:
If lift is missing locally there is 2 things you can do:

1. Increase the angle of attack
2. Increase the lift creating surface (i.e. chord length)

... long story short: There is so many zephys flying around, it'll work for sure. If you started sanding, continue, otherwise, let it be... but don't worry about that detail... It'll work :)

Thanks and regards,

Dio

[Hucker]

I know it will work since I've seen both versions flying I'm just at a decision point and wonder what is 'better'. Shaping to a pointier TE is easy. From your words of the vorticies being sucked away it seems like the best it will do is improve the power off glide o bit. Some free glide for a bit of work is something I'll do.

If the rule is German, could you write it out?

[Dionysos]

Hi,
there it goes:

Was lokal an Auftrieb fehlt, kann durch eine lokale Tiefenerhöhung und/oder Anstellwinkelerhöhung ausgeglichen werden!

Regards,
Dio

[Hucker]

Vielen Dank!

[ZobZibZab]

Another solution is that one :

--<--*

superb ascii art where -- is the wing's "fuse" and < is the wing, * is the motor

aka the motor is deported via a long "spar" or "tail bom" (im not sure how you call that).
it's done on a few commercial UAVs with pushers.

Not really a pure wing anymore tho.

[Hucker]

Foamaroo? After seeing that platform I sort of wish I had done that. I like the big fuselage and folding wing.

[ZobZibZab]

yeah that sort of stuff

[Trappy]

when you angle the trailing edge around the motor it appears to be more quiet. I don't see any reason not to do it, especially if you protect the corners where you cut with some glass fiber spars for strength.

[Vitamin J]

Is there a point where moving you can move the motor too far back and screw up the way it flies? I built a new wing and am having a hard time getting it to fly well and the motor is extended pretty far back, almost past the tips of the elevons. Could this be part of the problem? CG is at the right spot.

[ZobZibZab]

the right/left side of the prop makes a big diff too