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Parkzone spitfire flight problem! Help!

Old 02-01-2011, 07:27 PM
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CPomeroy
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Question Parkzone spitfire flight problem! Help!

Okay, so I've been learning to fly on the PZ spit (bad Idea, I know! don't tell me!). I can fly it fairly well, and landing it is no real problem. However, recently it crashed (as a result of signal loss, I hasten to add!) and I've bodged a repair to replace the shattered nose. It looks more like a focke-wulf nose than anything now, but I'm not bothered by that. The problem is this: I took it for a short flight recently, performing all the preflight checks, everything was running fine, all control surfaces were centred and there was no servo jitter. I hand launched it, having just been trialling an (unsecessful) launching dolly, and almost immediately, It pointed it's nose skyward and started stalling. Only some hasty down elevator saved it from crashing tail first into grass. But from then on, the flight charachteristics were wild, to say the least. It required almost full down elevator to keep it in a straight line. After a few involuntary loops, bouts of inverted flight , grass-skimming, nail biting low passes and times that I thought it would simply fly away, I cut the engine (which made it slightly easier to control) and belly landed it in a handy thicket. I took it home and checked the thrust vector, which was fine, and I checked all the control surfaces, which seem fine. I double checked the CG, which was as it was before. The only think that I could see is that the horizontal stabiliser was not paralell with the main wings (not taking into account dihedral), but I did know that all the first flights had had the stabiliser not perfectly horizontal then, as well. So I don't think that was the problem. If anyone has any ideas about what might have caused the erratic flight behaviour, I'd much appreciate them, so I can get it back in the air and behaving normally again!
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Old 02-01-2011, 07:44 PM
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Ok, these are terrible quality, but I hope you get the idea of what the nose looks like.
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Old 02-02-2011, 01:23 AM
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The gears could be stripped in the elevator servo. Apply a small amount of resistance to te elevator with your finger while moving it up and down with the transmitter. If it jerks or has a free spot, it is a stripped gear.
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Old 02-02-2011, 03:11 AM
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I'd put money on the thrust angle being off. It could be moving as you wind up the throttle. If it's angle is looking correct, see if it changes when you apply throttle.

Might just be the foam is weak where the motor mount is attached. This would allow the prop to pull the motor up and make it very hard to control.

Or what you think is right isn't and it need more down thrust.
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Old 02-02-2011, 03:13 AM
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It sounds a lot like the center of gravity being too far back, as well.
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Old 02-02-2011, 09:58 AM
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Well the motor isn't attatched directly onto foam, It's attatched to some plywood which is in turn screwed diectly onto the plastic skeleton that goes inside the body (and holds the wings on)
I'll check the thrust angle when throttled up, see if that changes anything...
I'll also go and check the sevo, but I don't think it's likely to be that because the crash did't go anywhere near it, it just took the nose off.

Would it wok if I were to adjust the elevator p/ rod so that there is a bit of constant down elevator, so it flies straight?

(and the CG was foward of what was reccomended by parkzone)
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Old 02-02-2011, 01:50 PM
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Originally Posted by CPomeroy View Post
Well the motor isn't attatched directly onto foam, It's attatched to some plywood which is in turn screwed diectly onto the plastic skeleton that goes inside the body (and holds the wings on)
I'll check the thrust angle when throttled up, see if that changes anything...
I'll also go and check the sevo, but I don't think it's likely to be that because the crash did't go anywhere near it, it just took the nose off.

Would it wok if I were to adjust the elevator p/ rod so that there is a bit of constant down elevator, so it flies straight?

(and the CG was foward of what was reccomended by parkzone)
Adjusting the push rod to add in some down elevator might help, but also adds in some degree of drag, so if you can find and fix the real cause that would be a better fix. Having said that, you mentioned in your first post that the horizontal stab was not in the same plane as the wings, are you talking side to side or front to back? Could your crash have made the front to back alignment bad so that the plane of the horizontal stab is digging into the airflow, causing a pitch up? Check the length of the fuse to see if there are any compressed areas you might be able to straighten. If this is the cause and the compression is too much to fix, than you might need to add whatever push rod correction makes it able to fly reasonably and just accept the increased drag on the airframe.
Good luck
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Old 02-02-2011, 05:02 PM
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When you are happy with your setup try a few throttle off glides and see how it responds then introduce the throttle gradually. This should tell you if its an incidence/CofG/Control surface problem or indeed is thrust vector related.

Good Luck.
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Old 02-02-2011, 05:38 PM
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Originally Posted by squidger View Post
When you are happy with your setup try a few throttle off glides and see how it responds then introduce the throttle gradually. This should tell you if its an incidence/CofG/Control surface problem or indeed is thrust vector related.

Good Luck.
Have you tried that with your PZ Spitfire?
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Old 02-02-2011, 06:52 PM
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Thanks for all the comments. I'll be sure to check the stuff you've mentioned. Although, I'm not sure about the 'chuck it and glide it' idea, the spit seems reluctant to glide without power. As for drag, there is a gaping intake at the front to solve an overheating problem I had with the plane (which is what I think caused the first crash (the overheating, not the drag!)), so I don't think I'm too worried about drag. Here are some pics about what I meant with the horizontal stabiliser, and some more photographs so maybe you can see something I can't.
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Last edited by CPomeroy; 02-02-2011 at 06:53 PM. Reason: Didn't make sense!
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Old 02-02-2011, 07:01 PM
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Originally Posted by Gohmer View Post
Have you tried that with your PZ Spitfire?

You're right I should have chosen my words a little better.

By throttle off glides I don't mean launching it with no power. I mean getting to a safe height under power and cutting the throttle to see how it glides.Then applying the throttle gently to see how it responds. I don't have a spitfire but do have a Parkzone P51 Mustang and it glides beautifully with no throttle at all for quite a while till the airspeed drops off too much and climbs at about 20 degrees under full throttle.
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Old 02-02-2011, 07:21 PM
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"I mean getting to a safe height under power"

I think, what with its current flight characteristics, actually getting it to any height at all would be simply dangerous! I could always throw it off something high, though... My front garden has a 45 degree hill at one part of it, that might work.
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Old 02-02-2011, 10:11 PM
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At the risk of offending someone and please don't be offended by this but perhaps you can get an accomplished flier to carry out some tests. The problem here is that you have a low wing warbird which are notoriously not easy to fly that has a problem and with the best will in the world you are trying to learn to fly with it. I'm sure that once the models flying characteristics are sorted out you will be able to fly it quite well, but as it is you are only going to struggle with it. When a model is missbehaving the last thing you need to do is troubleshoot close to the ground for obvious reasons so height will be your friend and very possibly your saving grace.If you are unable to safely get it to some height then perhaps someone with a little more experience may have more luck with it and subsequently be able to rectify the issue leaving you with a model that you will be able to enjoy and gain valuable experience on.If all looks OK on the ground ie surfaces at neutral incidence angles correct and a CofG in the right place then your next step is to test fly and provided all the above checks out then theres no reason why an experienced flyer shouldn't be able to fly it and trim it out/adjust as necessary leaving you a better chance of success.

Once again please don't take offence. Experience comes only with time and the goal here is to make sure you get the most you can out of your hobby and enjoy many hours of fun rather than give up after trying to fly an unflyable model.
I wish you every success in your quest to fly.Let us know how you get on.
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Old 02-02-2011, 10:27 PM
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I think getting someone to look at it (I have a friend who will almost definetly be able to help) is a very good idea. I will certainly do that if i can't solve it myself!

I admit I've only flown an aeroplane about 7 or 8 times (!!!), and only built one, so I may just be missing out something simple.

Oh, and to prove that I CAN actually fly, here's a video (in case you are staring at the '7 or 8 times' and saying 'why a warbird!?')

(and yes, the video was on my first day of flying ever!)

[media]http://www.youtube.com/watch?v=aTPn_N9GG8Q[/media]
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Old 02-02-2011, 11:24 PM
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For someone with as little experience as you have that is some impressive flying taking into account the type of model you are flying. At the time the model (I take it it's the model that is now playing up) Appeared to be flying pretty well which means you can concentrate on having fun. On the other hand if it wasn't flying well as is the case at present then you would have to call on all your skill (Which you obviously have) to be able to keep it in the air and all your experience (which you currently have little of) to be able to diagnose why it is not flying correctly. It looks to me like you have an obvious flair for the hobby. Hopefully your friend will have enough experience to help you out and you will enjoy it whilst gaining your experience.

Why don't you try flying something a little easier like a high wing model so you can get a comparison between the two. Or even a mid wing model which will give you the best of both worlds.
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Old 02-02-2011, 11:33 PM
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Well, I have a Nieuport 11 sesquiplane ([media]http://www.youtube.com/watch?v=zJsRlXHuenw[/media]) to fly, but since it was a scratchbuild I'm extremely wary of taking it up! Also it was my first build of an aeroplane, and I don't want to break it! The friend I mentioned did let me have a shot of a high wing trainer, which (although not allowing taking off or landing) did help with my flying(although that was after the flight in the video). I'm making a clip-on set of wheels for the spit to practise landing and takeoff with when (if) it becomes airworthy again.

Last edited by CPomeroy; 02-02-2011 at 11:35 PM. Reason: remembered something to say!
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Old 02-03-2011, 01:47 AM
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I've gotta be honest here. I would wait till I have more experience if I were you before flying the biplane that obviously took you alot of time to build. I don't know what your finances are like but my advice would be to go for a Wot 4 Foamy which is a Chris Foss model and is pretty easy to fly and will also take a bit of abuse and be easy to repair. It flies really well and is capable of just about any manoevre in the right hands yet can be flown really slowly too and is really stable so easy to land.It will allow you to gain loads of experience whilst also having fun and from watching your vid I reckon you will be able to fly it pretty easily.

Heres a vid of mine.

http://www.youtube.com/watch?v=SuDhuomNKZ8
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Old 02-03-2011, 03:48 AM
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Looking at your last set of pictures, the first one (view from the rear) looks like it is the wing that is out of line with the fuse. The horizontal and verticle stablizers appear to be alligned with each other and with the fuse.
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Old 02-03-2011, 06:27 AM
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Originally Posted by CPomeroy View Post
Thanks for all the comments. I'll be sure to check the stuff you've mentioned. Although, I'm not sure about the 'chuck it and glide it' idea, the spit seems reluctant to glide without power. As for drag, there is a gaping intake at the front to solve an overheating problem I had with the plane (which is what I think caused the first crash (the overheating, not the drag!)), so I don't think I'm too worried about drag. Here are some pics about what I meant with the horizontal stabiliser, and some more photographs so maybe you can see something I can't.
That Tail is definitely out of alignment ... but as long as it's horizontal aspect is in line with main wing ... then should be ok ...

Looking again .. is it the tail to the right or the the main wing that is tilted to left in comparison to the fuselage ? I wonder if it's the wing ?

Anyway ... your post describing the flight style indicates to me :

a) When you rebuilt the front end - you may have introduced an upthrust situation, I did similar on my Me109 and that now has a marked down elevator now. What happens is that you think the bits go back nicely together at the breaks and you glue up. But in fact compression of foam has occurred in the fuselage top as there is no wing to brace the structure against it as in the lower section. So all looks fine - but in fact if you were to place a straight edge long the fuselage - you'd then see the effect.
b) You say that the frint now more resembles a FW ... well that has a blunt nose and again indicates to me a) .....

The overall effect is to give you upthrust or at least reduced downthrust on your motor ... making the model climb or pitch up under power ... and nose will drop when power is taken of ... If you have a combination of forward CofG, lack of downthrust and have down elevator - you are going to have wild change of model attitude when power goes on and off ...

So if possible get an undamaged or straight PZ Spit to place that straight edge along to get an idea ... a base line to work to. Then go home ... check against your Spit ..... cut at suitable point and then reglue with parts held properly straight. You will likely have to fill in the small gaps in the foam using something like gorilla glue or similar AFTER the primary gluing has set.... any expanding gap filler will try to force the parts apart - so get them glued and set first !

That Tail - you can take a scalpel or model knife and cut it free ... trim fuselage and reglue ...

Here are photos of my repairs basically in same areas as you mention ... (sorry about 1 photo - the camera was just failing !!)





After repair ...





So don't be afraid to make that cut ... foams very forgiving - just make sure it's a very sharp blade ... and no saws ! They remove material which is not what you want to do ...
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Old 02-03-2011, 02:46 PM
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I'll check it with a ruler, and get back to you, but I think I kept the original thrust vector (of about 3 degrees downwards and 4 degrees right), but if it isn't that, I'll see what I can do to fix it.
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Old 02-03-2011, 05:58 PM
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well I'll certainly be able to do some changes to it now, I flew it again having altered the trim and everything, and it didn't seem to have changed at all. Needless to say, this time I wasn't so lucky and it came down harder than expected, cracking along the line of moulding between my balsa fix and the old body. The foam nose also cracked a little, but still, nothing that can't be fixed with PVA.
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Old 02-04-2011, 09:20 AM
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My choice of glue is quick epoxy ..... 5 min if I can get it. It's strong ... and sets quickly .............
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Old 02-04-2011, 09:37 AM
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I find gorilla glue works best as it expands to fill any gaps in the foam.You just glue one side of the joint and spray water over the other side and you get a really strong bond.
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Old 02-04-2011, 10:17 AM
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Originally Posted by squidger View Post
I find gorilla glue works best as it expands to fill any gaps in the foam.You just glue one side of the joint and spray water over the other side and you get a really strong bond.
I keep reading about this stuff ... but never seen it. Over here in Latvia - I don't know if its available.

Just an aside - I went to Lumley Road School as a child in Horley !!
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Old 02-04-2011, 04:56 PM
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Well from what I can see in your picture, it's amazing you are able to fly it.

Obvious misalignment of the wing to the fuse/tail feathers.
Left aileron is up compared to the right one.
Elevator is up.

Guessing the aileron is trimmed to try and compensate for the dihedral problem in the wing, the up elevator is giving you a climb condition. (And why you are having to dial in down elevator)


Going to take some serious reworking to get her "squared" away, just in this, let alone if the motor angle is off.

You need to jig up the fuse so the tail feathers are are level and square.
Then look at the wing mounting to see what's wonky in it. Get that worked out then start looking at the motor issue if there is one.

Like was mentioned measuring the angles of the motor to the firewall aren't going to work if the firewall angles are off due to the foam being compressed behind it.
To check it take 4 measurements from the tip of the rear fuselage to the top/bottom/and both sides of the firewall.

If anything it should measure slightly longer on the top and left side, which would give you the down and right thrust on the motor.

Then check the same measurements on your motor, they should be similar to what you found on the firewall measurements, slightly longer on top/left. If one or two are way off from the rest you're going to have to shim the mount to get it where it belongs.

Best of luck on it.
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