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Oct 18, 2021, 10:00 AM
Registered User
Thread OP
Help!

New Delta Flies POORLY


Hi guys! Need some help w/ this new delta wing. I think it looks pretty good, but it really flies POORLY. Flies straight and level right out of your hand on launch. But when you try to bank and turn, the inside wing drops too much and the nose heads towards the ground. It's a struggle to keep it in the air.

The CG was originally set where the on-line calculator said to put it. I've tried moving it fore and aft as much as 2 inches w/ no improvement.

I've already shortened the nose by 2 inches, and was thinking of chopping off more.

Other than that, I'm out of ideas!

Can you give me some suggestions to save this plane? Does anything look amiss to you?

THANKS!

Steve
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Oct 18, 2021, 11:53 AM
IMO ( In My Opinion ) →
balsa or carbon's Avatar
If your transmitter is capable , try lowering the rates and increasing the expo of the elevons . And if you are trying to fly the plane slowly , you may have to fly it faster .
Oct 18, 2021, 12:05 PM
Registered User
Thread OP
Already at 50% expo, but could go higher...

Can't understand why is drops a wing and then the nose in a turn.
Oct 18, 2021, 12:16 PM
IMO ( In My Opinion ) →
balsa or carbon's Avatar
You could try building a delta that is proven to fly well , then add a fuselage & winglets to it . The SSD would be a good choice : https://www.rcgroups.com/forums/show...h-simple-plans
Oct 18, 2021, 12:56 PM
gpw
gpw
“There’s no place like Foam”
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Just a WAG, I’d increase the size of the vertical fin area, and lower the tips a bit . it looks cool ! Should fly Great !!!
Does it tend to fall off in only one direction … could be thrust issues ???
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Oct 18, 2021, 01:01 PM
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Firstly your elevons are wrong, the outers should be smaller in width than the inner area.

The way you have it is causing the instability.

Also when inputting right stick, the right elevon should go up about 5-7mm more than the left elevon goes down. Obviously same deal with left stick applied.

Another problem is where your tips meet the main delta frame, you have angled the tip in somewhat. Note i am NOT talking about the angle sticking up of the wing tips, i am talking about the main delta to wing tip is not parallel with the whole centre line, but angled in.

Hence when you bank the tips are even more angled in and causing 'tucking'.

Best to rectify the elevons and try that first, the wingtip may not be an issue? Make a video.

Lastly a Delta should have reflexed elevons for stability. I.E. they both should be slightly up. On a model your size i guess around 3mm measured .

Note there are Delta experts here commenting but in truth can't say much other than make a plane from a proven plan!!!! Kinda great help indeed!
Oct 18, 2021, 01:47 PM
gpw
gpw
“There’s no place like Foam”
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What Ritchie said !!! Good eyes on spotting those angled tips RH ! …
Latest blog entry: Lost plans
Oct 18, 2021, 03:40 PM
Registered User
Thread OP
OK, the elevon thing I understand. Easy fix.

Not sure I agree about the wing tips -- I THINK the "root" of the winglet is parallel to the centerline, but I'll double check. It may just photo perspective.

THANKS to all for the ideas. Appreciate it!
Oct 18, 2021, 04:09 PM
Suspended Account
Another thing i forgot to tell you,,, and why it maybe the cause of wing dropping.... Have you got carbon spars underneath to stop twisting???

If not then that's a major problem,,, as you deflect your elevons,,,, your plane will be twisting thus causing wing 'fall out'.
Oct 18, 2021, 09:46 PM
treefinder
springer's Avatar
I agree with op, the tip root appears parallel in first pic, but tapered in in second; if the second pic is correct, then it will definitely add drag at the wrong time. Although I would expect it to behave more like adverse yaw and not roll into turn. On the taper of elevons, that is a whole discussion in itself. Conventional wisdom says taper in plan view center to tip. But my onesheetwing shown obviously looks a lot like yours and flies good and stable. But, I have pretty low throw on them.

On your controls setting, i suggest you do a high and low rate with low rate throw about half of full throw. Expo at 30% for both settings. High throw and high expo gets you into the response mode of nothing, nothing, everything! And it seems always a surprise when the plane responds dramatically. Expo is generally only to desensitize the center of travel when you are actually trying to fly straight (assuming the plane is stable and generally wants to fly straight).

Also, on the tip angle, while they don't look too much in the pic (roughly similar to mine), if you reset the PV angle, maybe reduce the FV angle too.
Oct 19, 2021, 12:13 AM
Registered User
Not clear from the pic how much up angle you've got for the winglets, but the projected side area also contributes to yaw stability. So those with the central vertical fin might be adding up to overly yawing into the turn, causing the inside wing to drop even more ("spiral instability" - look it up).
The slightly wider outboard elevon chord is unlikely the primary issue. I've done that on many a plane to simulate lower AOA for tip when elevon is deflected upward - never made a severe contribution to spiral instability.
Also, not sure if you know this: A fairly highly swept delta that's a bit on the heavy side will require quite a lot of pull on the stick in a turn to prevent the nose from dipping drastically (as is the case for my delta shown in the attached pic).
Last edited by nuteman; Oct 19, 2021 at 12:55 AM.
Oct 19, 2021, 08:34 AM
Registered User
Thread OP
Some interesting comments!

I do NOT have carbon spars, but don't THINK the wing is twisting. Seems pretty rigid but could always add a spar.

Tried changing the elevons today. Just reversed them - wide end inboard and narrow end outboard. No real improvement.

Going to try changing the Tx next per the post above: Lower rates and less expo.

Not sure what PV angle and FV angle means.

I will check out spiral instability.

Nuteman, you have an interesting plane in the picture! Like the canard on the nose. Is there a thread or any more info on this one?
Oct 19, 2021, 09:16 AM
treefinder
springer's Avatar
PV = Plan (top) view, FV = Front view.

Also, Nuteman makes a good point in that some bank and yank planes just require lots of "yank " to pull nose up and compensate for the natural tendency to roll and dive into the turn.
Oct 19, 2021, 10:05 AM
Registered User
Quote:
Originally Posted by Flyboy Steve
Tried changing the elevons today. Just reversed them - wide end inboard and narrow end outboard. No real improvement.
Yes, as I noted above that was unlikely the primary issue.

Quote:
Originally Posted by Flyboy Steve
Nuteman, you have an interesting plane in the picture! Like the canard on the nose. Is there a thread or any more info on this one?
No build thread, but here's some discussion in a video:

Mods for RC Mirage-style delta for improved high-alpha handling (4 min 31 sec)
Oct 19, 2021, 12:15 PM
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That's why i love designing, there is never an 'absolute' way to do anything.

Only limitation is our minds


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