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Feb 20, 2016, 10:47 PM
Slope-a-Dope
Steve 0's Avatar
Thread OP
Help!

I have a Stall Fiend!Crash Videos & Fixed problems videos added. Yay!


This is my tip stalling fiend. Bf-109, winter scheme of Hans Philip.

Yea, I know the scale on the wings is WAY off and therein may lie my problem.

It is my second scratchbuilt PSS warbird after my first, a stretched out Maachi Veltro which has no bad habits whatsoever and flies great fast or slow. It's on rails every flight.

My 109 is a bit of a floater due to the long wings and does okay, but when my rookie flying skills get lax WHAM! Nek Minit, tip stall. Not sure if it is called a 'flick' also, but that is what it does.

Got in two good flights yesterday for a few minutes each, first ended in a belly flop with no damage, second flop blew off the wing and loosened the stab.

So now that repairs are due I thought I'd ask two things.

1) shorten the wings and square them off by a few inches each side?

2) add more dihedral?

Will these two mods reduce the tip stall tendencies?

Both PSS planes have the same foil and weigh the same within an ounce or so.. The two big differences are less dihedral and longer WS on the 109 that makes them slightly higher aspect.

I have videos of both flights, not uploaded yet.

Flew my JART, jr. also which tip stalls predictably at low enough speed and too light of wind, but flew like a champ in the bigger wind.

Appreciate the advice.
Last edited by Steve 0; Feb 29, 2016 at 11:21 AM.
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Feb 20, 2016, 11:21 PM
Slope-a-Dope
Steve 0's Avatar
Thread OP

Specs on each plane


For reference,

Maachi Veltro:

31" fuse, 44 WS, 3.5 " dihedral with other wingtip flat , AUW 30oz

Bf-109:

33" fuse, 49.5" WS, 3" dihedral at wingtip or 2.375" at same point as Maachi WS

AUW 32 oz

I'm no Rubio, nor Brian, nor Maarten, nor any other great PSS slope plane builders......not even close!

But I would love to get this bird sorted and think the wing chop is the best solution all things considered.
Feb 20, 2016, 11:38 PM
It's not going to build itself
TRISME's Avatar
Steve, I agree to chop the wing tips. I usually run my ailerons out to the tip of the wing. You would probably need to use less deflection of your ailerons this way. Also check to see if the wing tips are twisted with any "wash-in". A couple of degrees would make a difference on a PSS plane. Make sure you're not tail heavy, use the ISR cg calculator or something similar to figure it out. Just my .02.
Tom
Last edited by TRISME; Feb 20, 2016 at 11:43 PM.
Feb 20, 2016, 11:42 PM
Slope-a-Dope
Steve 0's Avatar
Thread OP
Thanks, Tom. So if you or anyone clicks the pic twice to get it fully upsized, would you suggest chopping at the first panel line or even over to the aileron edge? When I cover the wingtip in the pic with my thumb, it looks better to the aileron. I realize this will mean more speed, wind and getting it on step before flying around.

I will reinstall a balsa block wing tip correctly shaped and repaint.

And BTW pretty is not my goal, flyability is. At 20 yards out and moving they all look good.
Feb 20, 2016, 11:48 PM
It's not going to build itself
TRISME's Avatar
I'd cut it at the first panel line and round things off a little. Try it there before adding a block and such.
Feb 21, 2016, 12:00 AM
Firecracker!
BillO's Avatar
I wouldn't cut the wing just yet. 32 oz is very light for this kind of plane, and that makes it hard to keep your speed up. Just keeping your speed up, no floating around, is going to keep the tip stalls away. My suggestion would be add about 10 or 12 oz of ballast and fly it on the bigger days, say 15 to 20, and don't slow down!
Feb 21, 2016, 12:01 AM
IT'S NOSE HEAVY!!!!
cityevader's Avatar
It's nose heavy!!!!
Feb 21, 2016, 01:18 AM
characters welcome!
Mark Wood's Avatar
Nose heavy won't cause a tip stall but an aft CG sure will if you let the speed drop.

mw
Feb 21, 2016, 01:27 AM
F3Foamie Pilot
Steve,

I would try some washout if you can. The horizontal stab looks pretty small (scale) too, so as others mentioned your gonna have to keep the speed up.

Many years ago I had a friend that built a powered ME-109 (Royal Kit). It was very close to scale with the small horizontal stab. He got one flight because it wouldn't slow down with out snapping.

Ken
Feb 21, 2016, 01:48 AM
Slow builder
_AL_'s Avatar
Before you go cutting it up, check the simple stuff first.

Does it stall as in flying slowly & drops a wing, or is it stalling when applying elevator at speed & flicking onto its back? If it's the latter, it's more than likely a forward CG & too much elevator throw. As suggested by Cityevader, nose heavy means more elevator throw & higher risk of high speed stall.
If it needs more than a little down stick when inverted it's probably nose heavy.

  • Is wing / tail incidence 0?
  • Is the wing & horizontal stab aligned correctly?
  • Is one wing heavier than the other?
  • Is there a warp in a wing?
  • Are the ailerons binding & giving you a double center?
  • Is something moving & changing the trim &/ or CG in flight
I can't see increased dihedral making any difference to stalling. Shorter wings will increase the wing loading & may make it worse.


Check the easy stuff before you do anything. Murphy's law says you'll cut it all down & still have the same issues.


Al
Feb 21, 2016, 02:27 AM
Closed Account
The horizontal stabilizer is too small. But it should fly okay with the right CG anyway. You're gonna want a horizontal stab that's about 25-30% of the wing area.

Al is right though, check everything else as well. Keep playing with the balance, look for mechanically induced differential in the linkages. Look for loose areas in your linkages. The wrong incidence is a likely cause for too stally behavior. If your incidence isn't 0/0 then you might check for warps in the wings. Look for problems in the programming of your radio especially if you set custom curves on any channels. Apply slight pressure to your control surfaces while wiggling the sticks. Watch where the ailerons and elevator return to center when you let go of the stick at maximum range.

If you can't find any issues then chop the wings or make a bigger tail, and if that doesn't work then just remember you won't stall at all if you just keep the nose down.

Justin (left my EPP at the dairy... Nek minit)
Feb 21, 2016, 02:32 AM
Slope-a-Dope
Steve 0's Avatar
Thread OP
Thanks for all the tips! Went and watched Red Tails while waiting on responses.

Lots to sleep on. No wing chopping right away.

I have cg'd before every flight and also double checked that with the calculator more than once during the build and before the maiden.

I will look closely at each wing for twist. During level flight and launching it goes straight because I launch right handed. It will fly hands off when trimmed.

After the maiden, I upsized the vert because of yaw and tail wagging. My Maachi has a nice sized fin and it tracks perfectly.

No one else has flown it, yet. There are some great builders and pilots around just not always flying as frequently as I do. Spencer or Loren could tell me in a second and I have handed off a tx and plane to Loren for help a few times.

It certainly isn't tail heavy as I know what a handful that can be. It is a one way flight down struggling with the stix all the way down. The cg might be off some.
Nothing is loose inside, though.
Both tip stalls this weekend were during tight turns at speed coming back towards the slope.

I will start checking things over closely and pause the saw and Dremel.

Probably will increase the horizontal stab up 20-25 percent.

Ailerons need redoing as one is detached.

I will upload a video asap showing the stalls.

If things look straight, I will try what BillO says and put it back together then ballast 10 oz up on a big air day and no loitering. With the throws lowered and expo upped.
Feb 21, 2016, 02:34 AM
Closed Account
If you're going by what the CG calculator tells you, that may be the problem. Keep moving some sticky weights around the fuse until your thumbs find the most comfortable spot. "Use the force, Luke"
Feb 21, 2016, 03:05 AM
Slow builder
_AL_'s Avatar
I'm going to suggest the CG is a bit too far forward & you're having to use too much elevator throw to get it to come around.

Once you get it fixed try a dive test & then an inverted pass.
If it climbs out of the dive test hands off &/ or needs lots of down elevator while inverted, start creeping the CG back (and reducing the elevator throws) & see if it improves.

I'll put a lazy $5 on it getting better as you move the CG back. Just don't try to move it back too fast. Small adjustments & test.

Al

Quote:
Originally Posted by Steve 0
Both tip stalls this weekend were during tight turns at speed coming back towards the slope.
Feb 21, 2016, 03:17 AM
Aerotow and sloping Holland
MaartenX's Avatar

I have a Tip Stall Fiend! Grrrrr!


There might be a simple cure: add tubulators.
Just cut a strip of masking tape, about 1/4 inch wide and 8 inches long. Stick it on the top if the wing running from the tip towards the root. About an inch from the LE.

I have had great succes with this. It helps to prevent the airflow from separating from the tip.

I agree with Al's CG theory. A forward CG seems safe but leads to more drag and unwanted behaviour. Optimise the CG and take it from there.

Good luck,

Maarten


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