Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Predator Misalignment

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Old 08-01-2005, 08:54 PM
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hooaa
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Default Predator Misalignment

My new Predator 500 has a serious problem. Something is misaligned that places it in a constant left bank. I dialed in around 1/8"of right aileron and this didn't hardly affect the atitude. Next flight I dialed in some right rudder with same result. If I hold a lot of right aileron I can hold it horizontal.
The wing incidence is within 1/2 degree of the elevons. The CG is at 2-1/2" dry. Looking at the tail feathers from the rear the V looks symetrical with the wing. The one deviation I note is that the distance from the rear of a wingtip to the tip of the elevons differ by 1/2".
What am I overlooking?
As an aside the Jett 6oz. Slim Bubble-Jet Tank fits perfectly and puts more fuel near the CG.
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Old 08-01-2005, 10:39 PM
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Default RE: Predator Misalignment

That 1/2" difference....is the wing miss-aligned ? (not on straight)

Dave.
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Old 08-01-2005, 11:12 PM
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Default RE: Predator Misalignment

With the wing off the plane, it should lay flat on a table. Sounds like a twisted wing to me. It also sounds about par for the course, everything that can be said negative about this plane [ I thought} had already been said. I suppose if the VEETAIL was severely misalligned, that could cause a similar problem, but I bet the wing is twisted.
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Old 08-02-2005, 12:37 AM
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Default RE: Predator Misalignment

The wing appears to be straight, no warps. It is square with the fuselage. The difference of 1/2" indicates to me that the V-tail may be rotated slightly in the prefab cradle. I pinned it down while the 30-min epoxy set up so I don't know it may have rotated. I can say that eyeballing it appears as though it is straight and true. Does anyone have a systematic checklist for setting this model up?
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Old 08-02-2005, 10:05 AM
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Default RE: Predator Misalignment

It helps to have a ROBART incidence tool, but you can check for flyability with a ruler, a triangle and string. The firewall should be perpendicular to the bottom of the fuselage, set the fuselage flat on a table and check this. Bolting a flat plate where the prop goes makes a handy reference to check squareness at. With a high wing plane, any up thrust at all is a bad thing, and with any plane, any left thrust is bad too, always err on the side of having down and right, but try for zero-zero on this plane.. With the wing mounted, measure the distance to the table from the wings' leading edge and trailing edge, these measurements should be the same all the way around. This check will reveal your wings' incidence and if the wing is twisted or not. Should be sitting at zero-zero now. The veetail can be checked with the triangle and ruler using the table top as a reference. It is easier for you to just dive in and do it, than it is for me to explain. The non stretchable string is handy to check how squarely the wing sits in the top view. I use a pin that is pushed in as far back on the fuselage, top dead center, then tie the string to it. The other end of the string is stretched out to both wing tips, the measurement should be within a 1/16". Finally, inflight trim adjustments will reveal slight problems with the veetail. Check your planes' lateral CG, a finger on the prop nut, and the other on the tip of the aft end of the fuselage will reveal a gross imbalance, [ can't figure why a foam winged plane could be too far out here]. Good luck!
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Old 08-02-2005, 11:22 AM
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Default RE: Predator Misalignment

Is it rolling left constantly, or does it tend to fly somewhat straight but just banked/sideways or in a yaw ?

A roll is caused by a twist in the wing, or is often do to not properly aligning the two wing halves when joining them. At speed, a very tiny bit of twist in the wings will create a large amount of roll. Faster you go, the worse the roll gets.

The Predator rudder function is pretty much a pure yaw - very slight roll couple. A slightly misaligned V-tail (rudder) trim would not tend to induce a heavy roll. But if it is anything close to 'looking correct' it would not cause a condition that was beyond the range of basic trims... you would notice more of a problem in the turns. If the entire V-stab is indeed rotated a full 1/2" from the cradle, yeah..... that might cause some serious yaw.

You noted you had to hold aileron in it to keep it level. Do you notice it needs more trim when going faster, rather than at landing speed ?

Mount the wing on the fuselage. Lay it flat on the bench. Measure the distance to the LE and TE of both wings at the tip.

Re-measure other items as combatpigg noted.

Also, just on a hunch, measure the wing itself. Make sure it is centered (ie, both panels are the same size)

Im not sure where any of the more recent bad press came from on the Predator. The first batch were a mess, but that was a few years ago. Darrol Cady and a host of others worked with Lanier to improve the plane quite a bit. The planes sold for the past 2 years have been very good quality, and the 4 I built were all straight right from the box.

Bob
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Old 08-02-2005, 02:45 PM
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Default RE: Predator Misalignment

Hi!
Must be a twisted wing! Check it with a Robart meter!

Regards!
Jan K
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Old 08-02-2005, 02:46 PM
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Default RE: Predator Misalignment

There are still, to this day, PREDATORS disintegrating in mid air, maybe as we speak. Not everyone is aware of the critical points that need extra attention. Every now and then, I intercept a thread about one falling apart. At the speed this plane flys at, you don't need much of a wing twist for there to be a problem. Mine came as a completely assembled wing, and outside of the fact that the covering seams face INTO THE WIND, it is a very nice wing. I guess HOAAA could try a trim tab at one of the wing tips. I have never tried to unwarp an ARF wing like this, so maybe a trim tab is a good compromise?
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Old 08-02-2005, 04:06 PM
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Default RE: Predator Misalignment

Configured for sport speed or 424 racing, I have not personally seen one come apart, but I will take your experienced word on it

With a 428 engine, and no mods.......yeah, the wing is going to become a multi-piece assembly within about 20 laps.

As for fixing the roll, if you do find that you have a twist/warp, try this......

Outboard of the aileron is about 8" of fixed trailing edge. If it is rolling left, cut into the TE surface about 1" in on the bottom surface of the right wing. Do not cut through. Sorta make a trim tab of the fixed TE section. Bend it up a bit (depending on how bad things are) and CA or epoxy it in place while it is held in positon. Should only require a deflection of 1/8" at the very most. You can then align the aileron to the outboard TE. That will provide you with a great deal of right roll trim.

Bob
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Old 08-02-2005, 06:12 PM
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Default RE: Predator Misalignment

That's a good sounding fix, minimally invasive. Are these planes still being hot glued together? If so, what other Q500 ARFS are hot glued also? No racing plane builder with any conscience would hot glue the firewall and wing hold down blocks in a plane that comes towards my head 10 times a heat.
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Old 08-02-2005, 06:58 PM
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Default RE: Predator Misalignment

Bob,
Now I see the problem, the right trailing edge is 1/4" lower than the rest of the wing (wash-in?). I missed that completely, too focused on the tail.
As for how it handled, with the Nelson venturi half closed it was still a handful. The faster it went the more right aileron I had to hold. Even on power off glide I held a lot. I will cut the right trailing edge as you described. Perhaps I should put it up 1/4" to match the rest of the wing?
Then as Combatpigg warned I will toothpick the wing tie downs to the fuselage sides. The weak landing gear mount is already history as we fly in a pasture and 'normal' landings are near impossible.
jaka analyzed the wing warp correctly also. Maybe I'll do the 1/8" step first. At 150mph it should make a whale of difference.
Thanks to all, I'll update next weekend how it went.
The Jett 6 oz SLIM bubble-jett drops perfectly inside. No lead needed to set the CG at 2-1/2", just the battery located approx. under the aileron servo. To lateral balance it took 3/4 oz of lead in the left wingtip.

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Old 08-02-2005, 07:02 PM
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Default RE: Predator Misalignment


ORIGINAL: bob27s

Configured for sport speed or 424 racing, I have not personally seen one come apart, but I will take your experienced word on it
With a 428 engine, and no mods.......yeah, the wing is going to become a multi-piece assembly within about 20 laps.
Bob, why should it come apart? The center section is amply fiberglassed and the leading edge doesn't have any covering exposed. I already put three 2-3 minute flights on it, but seldom throttle wide open.
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Old 08-02-2005, 07:12 PM
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Default RE: Predator Misalignment

I "pasturized" my ARF PREDATOR by removing the gear and running the engine up right. Toothpicks will help somewhat, but the real fix is to wrap the outside of the firewall and forward fuselage with resin and cloth, and to add pine blocks under the wing hold down blocks. I had to scrape away the excess hot glue to work in the extra wing hold down wood. It is a nice plane once you get it sorted out, flys so smooth, it's almost boring.
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Old 08-02-2005, 07:31 PM
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Default RE: Predator Misalignment

I forgot to mention that I already did the firewall treatment at the suggestion of Bob27. I'll look into the hold down area.
Thanks
Now to cut the trailing edge. Can't waifor the weekend!
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Old 08-02-2005, 08:15 PM
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Default RE: Predator Misalignment

Just a quick comment: Always look for wing warps from the trailing edge, looking forward from the rear. This is where a warp will show up.

3dbob
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Old 08-03-2005, 12:19 AM
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Default RE: Predator Misalignment


ORIGINAL: combatpigg

I "pasturized" my ARF PREDATOR by removing the gear and running the engine up right. Toothpicks will help somewhat, but the real fix is to wrap the outside of the firewall and forward fuselage with resin and cloth, and to add pine blocks under the wing hold down blocks. I had to scrape away the excess hot glue to work in the extra wing hold down wood. It is a nice plane once you get it sorted out, flys so smooth, it's almost boring.
When the Nelson Q500 is upright the muffler would be in the way of the wing. The only way to get the muffler off the bottom would be to put it on top of the wing. Instead I will beef up the front half of the bottom with fiberglass.
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Old 08-03-2005, 05:46 AM
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Default RE: Predator Misalignment

To lateral balance it took 3/4 oz of lead in the left wingtip.
Did you add the weight before you flew it. Maybe that is why it is rolling to the left. Before you do anything else I would suggest you remove the wing tip weight and fly it again. there may be a difference. I do not know any racer that adds wing tip weight before the airplane is flown.

Ed S
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Old 08-03-2005, 05:58 AM
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Default RE: Predator Misalignment

I believe there is a method posted on Darrol Cady's websight that discribes how to straighten a warped foam/composite wing without cutting into it.

Scott
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Old 08-03-2005, 07:42 AM
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Default RE: Predator Misalignment


ORIGINAL: hooaa


ORIGINAL: bob27s

Configured for sport speed or 424 racing, I have not personally seen one come apart, but I will take your experienced word on it
With a 428 engine, and no mods.......yeah, the wing is going to become a multi-piece assembly within about 20 laps.
Bob, why should it come apart? The center section is amply fiberglassed and the leading edge doesn't have any covering exposed. I already put three 2-3 minute flights on it, but seldom throttle wide open.

The wing will most likely will not come apart. None of mine did. Even with the 428 engine on one. When I noted no mods, I was more refering to the early versions of the airplane. But from some reports, there were some wings that were apparently light on glue/resin/glass and ended up with wing and wing mount failures along the way.
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Old 08-03-2005, 08:40 AM
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Default RE: Predator Misalignment


ORIGINAL: Ed Smith

To lateral balance it took 3/4 oz of lead in the left wingtip.
Did you add the weight before you flew it. Maybe that is why it is rolling to the left. Before you do anything else I would suggest you remove the wing tip weight and fly it again. there may be a difference. I do not know any racer that adds wing tip weight before the airplane is flown.

Ed S
Yes, the plane was balanced laterally before it was flown.
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Old 08-09-2005, 12:25 PM
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Default RE: Predator Misalignment

Thanks for all the helpful suggestions. I added 1/8" of up trim to the outboard 8" of the right wing trailing edge. I was to report on the results this past weekend but my plans got interupted. I am now 'pasturizing' the front 1/3rd of the bottom with added plywood and fiberglass. If it ever crashes badly the landing gear area will remain fully intact I'll report the final results next weekend.
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Old 08-14-2005, 08:56 AM
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Default RE: Predator Misalignment

Final report on my Predator misalignment. Those who said it could be a warped wing were correct. I cut the last 8" of the right trailing edge and raised it 1/8". Upon launching it this weekend it did not require the slightest amount of aileron trim. I also 'pasturized' the landing gear area and that survived well.
Thanks for the tips on where to look for this problem.
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Old 08-14-2005, 09:22 AM
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Default RE: Predator Misalignment

Glad to hear the trim issue is taken care of

Enjoy the plane.
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Old 08-14-2005, 11:44 AM
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Default RE: Predator Misalignment

When I was first learning the little tricks to having success with AMA C/L combat, I noticed that the top dogs could sight down their planes' trailing edge, from the rear looking forward, and spot right away if they had an out of trim plane. If you try to fly one of these models too far out of trim, a 2 horse NELSON can destroy the 9 oz airframe within a couple of laps. I think it is interesting that an ARF foam wing could pass a QC check and get slammed into a box being so far out of whack. Over in one of those factories, a rejected part would probably cost someone a job.
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