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Old Feb 07, 2013, 06:50 PM
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United States, CA, San Jose
Joined Mar 2012
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Help!
ParkZone UM P51D Pitchy?

Hi, I got a crashed ParkZone UM P51D from a friend. The tail was broken which i glued in with 5-min epoxy and reinforced with a bit of tape. The tail looks study now.

When I took it out to fly, it was going all over the place. I was able to trim it during the flight which enabled me to at least predict its behavior. However, the one thing that i could not get rid of was the pitchiness. Basically, the plane goes up then stalls, then come down for a bit, then back up and repeats this without much input from the radio. Kinda moving like a wave. Is this called pitchy behavior?

After some reading, I figured that CG might be off. I checked to make sure that CG with battery was at 35mm from leading edge of wing at the fuselage as mentioned in the manual. I did the index finger balance method and it seemed like the plane was a tad nose heavy which is expected i guess. For ultra-micros the index finger method might not be very accurate as the plane is small. Also, there is hardly any room to move the 1S battery to adjust the CG if at all

I have the DX6i in dual-rates with low rate at 70% and no expo. I am fairly comfortable flying even though i've been in this hobby for only a few months now. Can you guys please shed some light into what else I could check?

Thanks in advance...
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Last edited by iamtheone; Feb 07, 2013 at 10:03 PM.
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Old Feb 07, 2013, 07:25 PM
Shelter Kitty "Orange Death"
bartricky's Avatar
United States, FL, Monroe
Joined Jan 2008
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Expo is the very best feature of a computer Tx.
Try putting in about 40%.
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Old Feb 07, 2013, 11:57 PM
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United States, CA, Alpine
Joined Oct 2007
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Your tail section is now heavy. Even a simple piece of tape on the horizontal stab on these airplanes is enough to throw the CG off. You will need to carefully remove the tape or add a bit of weight in the front of the airplane to bring the CG back in order.

The airplane wanting to pitch nose up and stall is a dead giveaway. In order to achieve level light you are not having to trim the horizontal stab down, which can cause some of the sensitivity you are experiencing.
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Old Feb 08, 2013, 12:33 AM
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United States, CA, San Jose
Joined Mar 2012
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Quote:
Originally Posted by Xpress.. View Post
Your tail section is now heavy. Even a simple piece of tape on the horizontal stab on these airplanes is enough to throw the CG off. You will need to carefully remove the tape or add a bit of weight in the front of the airplane to bring the CG back in order.

The airplane wanting to pitch nose up and stall is a dead giveaway. In order to achieve level light you are not having to trim the horizontal stab down, which can cause some of the sensitivity you are experiencing.
@Xpress, when I tried the CG test with index fingers, it seemed to be nose heavy. Are you saying that it might not be accurate? I'll try adding some nose weight and fly this weekend.

@bartricky, I'll add expo too and check it out.
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Old Feb 08, 2013, 02:37 AM
Grumpy old git.. Who me?
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Aberdeen
Joined Mar 2006
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It sounds like you just need to add some down-trim.. Seems almost too obvious to mention, but have you tried it

Also (counter-intuitivly) being nose heavy can cause this type of behavior so I'd try to get the plane to balance as per manual. An 'extra bit' of nose heaviness is not necassarily a good thing.

If it just starts the pitching up and down when you give high power then it could be a thrust line problem. These small foamy models quite often get the prop and motor bent out of alignment if they are crashed. The prop shaft should point just slightly downward.

Expo as suggested above is also a good idea, though if it's pitching when you are not even touching the sticks then it's unlikely to be the main cause of the problem.
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Old Feb 08, 2013, 01:57 PM
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Quote:
Originally Posted by JetPlaneFlyer View Post
It sounds like you just need to add some down-trim.. Seems almost too obvious to mention, but have you tried it

Also (counter-intuitivly) being nose heavy can cause this type of behavior so I'd try to get the plane to balance as per manual. An 'extra bit' of nose heaviness is not necassarily a good thing.

If it just starts the pitching up and down when you give high power then it could be a thrust line problem. These small foamy models quite often get the prop and motor bent out of alignment if they are crashed. The prop shaft should point just slightly downward.

Expo as suggested above is also a good idea, though if it's pitching when you are not even touching the sticks then it's unlikely to be the main cause of the problem.
Yes, I have quite a bit of down trim. I did this when I first tried flying.

I have the Hobbyzone champ also and the shaft of the P51 seems about the same in terms of pointing downward. I hope there is no serious problem with the thrust line. If there is, do I have to replace the motor?
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Old Feb 08, 2013, 03:26 PM
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Livermore, CA
Joined Sep 2004
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I think the Down Trim he's talking about, is the the elevator pointing down, to push the tail up.
I had a slightly broken tail on one of my Champs, I reinforced it a lightly as I could, but I still had to add a dime under the nose to get it right.

To check your C/G, fly the plane at medium cruze speed, and trim for level flight.
Then land it and see if the elevator is level.
If the elevator is up a bit, its nose heavy, if a bit down, its tail heavy.
If its level and still pitchie, you may have a loose servo or mis-aligned tail.
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Old Feb 09, 2013, 09:31 AM
Grumpy old git.. Who me?
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Quote:
Originally Posted by iamtheone View Post
Yes, I have quite a bit of down trim. I did this when I first tried flying.
Add some more down trim. If the trims are maxed adjust the Z bend in the linkage to give more down.

If the model is already more nose heavy that the factory recommended position the last thing you need is more nose weight.
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