Bad tracking in Loops and climbs

[FlyinBrian]

I am currently flying a Balsa Craft "Street Machine" built from the kit not the ARTF. this is a 50" span pattern type ship, I'm using an Irvine .36 and 10x6 prop and the plane weighs 4lb.

In a loop or in a prolonged climb it drops the left wing, after three loops it is almost at knife edge unless I correct it.

I have checked the lateral balance and it is now spot on with about 1oz of weight on the right wing tip.

The side thrust is built in and difficult to alter, I've tried inputting a little rudder during the loop but this is hard to judge.

I hate it when a plane won't track straight in loops, can anyone suggest a routine of checks which will find a fix for this?

Brian

[rcav8r2]

Have you checked for a warped wing, or mis-aligned rudder?
I've seen "strange" things on a few of the planes I've flown where they fly fine upright, but require lots of trim (rudder/aileron) to fly inverted. On a plane that I built, the vertical was on a bit off, and one a few that I've flown for others, the wing had a slight warp.

[avie]

I would check first that your horizontal stab is parallel to the wing. if it is, check that both portions are moving the same distance for a given stick movement. if the servo is connect to one side of the elevator, and the other is conneced through music wire, make sure it is rigid and doesn't twist much under load.
if non of this helps, and you have a digital Tx, program in some mixing to compensate.

good luck getting it right!

Avi

[FlyinBrian]

Rcav, avie - thanks for the input.

The wings are veneered foam and are straight so far as I can measure them though I don't have an incidence meter. If the lateral balance is correct and the same wing dips in positive or negative loops does that indicate a warp?

Stab is straight and parallel to the wing and the elevators are level and connected with 1/8 music wire, I doubt this would twist.

A little extra info, this seems to occur at all speeds, if I do a slow fly by and put in some elevator to climb out there is a noticible drop of the left wing.

In my previous post I should have said in a prolonged vertical climb it angles off to the left rather than drops a wing.

Other than this quirk its a nice plane, smooth, fast & goes where you put it.

I can certainly play with the mixers but that usually leads to complications (does for me anyway) and I had hoped someone might have had an easy fix.

Brian

[avie]

to check if te wing is twisted place one wing on a table so it stands stabe on the spur and one side of the TE (should be the root side if it's right side up). measure the distance of the other edge of the TE from the table. now do the same for the other wing.
before all this make sure the TE don't look banana like, meaning it should be straight. you can check with a ruler or a peice of string.

come to think of it, the problem isn't in the wing. if it only happens when you pull up (only when you move the stick) ten it's an elevator problem.
if it's a constant problem that doesn't happen only with stick movement, then it's something miss aligned..

one thing I didn't understand is the same wing dips down in pos and neg loops, or dips out of the loop ? I mean, when you give down, is it still the same wing that dips ? the later would be very strange:confused:

Avi

[FlyinBrian]

Avi,

Hmmmmm - I'm getting myself a bit confused now, I am pretty sure that when looking from behind the model the left wing dips, ie the model rolls left, whether looping upright or inverted. Definately when climbing vertical with the top of the plane towards me it pulls over to the left. On its own I'd correct the climb problem with more sidethrust but as mentioned its going to be a job to alter it as its the firewall thats angled.

I have trouble understanding your suggestion for checking for wing twist. The TE tip of each wing is equi distant from the top of the fin so I'm pretty sure its aligned OK, there may be a warp in the wing but its not visible to my eye.

If it might be an elevator problem I can put two smaller servos at the rear of the plane as its quite a deep fuz and then drive each half of the elevator seperately, that will be pretty easy to do. It will also move the CG rearward so I can get rid of the lead (2oz)I'm carrying on the tail wheel

Brian

[avie]

Hi Brian
to add side thrust to the left (?) simply put a washer on the right bolts that hold the engine mount to the fuse.
to check if the elevator can twist, hold firmly one side and try move the other without extreme force if you think you might break it, it TOO much force. if it doesn't twist much, more then a degree or two, it's ok.

I would start with the side thrust first, especially if it crabbed side ways whenever you changed speed.

good luck
Avi

[FlyinBrian]

Thanks for all the input, I have solved the problem - I broke the plane! Rolled inverted from knife edge then gave up;- at 2 ft too low!

Brian

[Phill K]

Greetings

A couple of links for you, first is a the trim chart its self explanatory.

http://www.wtp.net/DBEST/trimchrt.html

Second is a New Zealand bloke's web page and has very good links to all sorts of things.

http://homepages.ihug.co.nz/~atong/

I'm also at a stage where I want to progress my flying skills, aerobatics is one way, an other is to play follow the leader, two planes similar preformance, and one follows the other through verious routines. Its harder than it sounds but beats just blasting round the sky.

Cheers
Phill

So much reading - so little time!

[CurtD]

Static lateral balancing is only the beginning. You must also dynamically balance the aircraft for proper tracking. If you are seeing the same wing drop on both inside and outside loops you almost certainly have a heavy wing (assuming wings are straight, no twist in fuse, etc.). Another test is to trim the aircraft to fly dead level hands off upright, then roll it inverted. Leave the ailerons alone and watch which wing drops. Add weight to the other one until it flies wings level both upright and inverted with no trim changes needed.

As indicated in earlier posts, there are a number of sights that have info on trimming a pattern ship. You can't rush this either. To get one trimmed perfectly may take many flights, but it's worth it. When flying competition there's nothing worse than having to fight an out-of-trim aircraft while doing precision maneuvers.