Wing Incidences?

Decided to look into wing incidence to reduce the amount of elevator down trim required on Pepsi. The plans show no figure in degrees so assume it was not needed as the wing saddle is preset by design. My wing did not sit in well so I had to fiddle a little at the rear end to get the trailing edge to drop in. I am wondering if I have created some negative incidence which will tilt the tail down making the plane tending to climb?

Hi Phil

Only just catching up with forum posts. Hopefully you haven't changed the thrust line as you suggested on your other thread, as I noticed no trim change with changes in power settings on the test flight.

If you want to remove the down trim you will need to reduce the wing incidence. You have too much positive incidence not negative as you say above. If you lower the leading edge by a few mm you will get rid of it. However it probably won't effect the flying characteristics so you could just live with it.

Glad you jumped in now Jon. I decided on not playing with thrust line as you never brought the subject up whilst flying it. So, I thought I would put the plane on level ground and spirit level the cockpit floor which is parallel to centre line (according to plans). I then placed a straight edge along the chord line and laid the same level on it. The bubble showed that the wing chord is pointing down at the front. I then backed off the wing bolts gradually and managed to get the wing sitting nearly level.

But from your comment I seem to be going the wrong way.

If you think about it Phil, the model needs down elevator trim to fly level, the down trim will raise the tail which effectively reduces the wing incidence, therefore you have too much incidence, reducing it will then reduce the down trim .

Sorry Jon, I am losing it just lately, so much going on. Yes, of course your right. You have put in 13 clicks of up elevator on the TX.

I think I may have confused the issue because up elevator is down on the TX screen - what a dumb ass! :lol: Time to go to the S of S category!

Edit: Just had another look at it. Isn't that bad really, elevator is not up much in reality.

Lessons in Aeronautical Engineering is all gained knowledge.

However, ailerons are the next subject......

Up elevator trim makes more sense!

Next time you take the model out, bring some 16th balsa sheet then add a piece at a time between the trailing edge and wing seat and test fly, after a bit of trial and error, you will then be able to remove the trim. Once you know how much packing is required then fix it permanently and reform the wing seat to suit.

Aileron trim is either a heavy wing or a warp, check first that the ailerons or flaps aren't twisted, then check the incidence at each wing tip to make sure they are the same. This will confirm if this is your problem.

JonTappin wrote: Up elevator trim makes more sense!

:lol: :lol: To everyone else!

Packing will do next time.

I suppose even having the flaps slightly out would have an effect on ailerons. I will recheck these with the stick method you suggested some time ago when aligning independent control surfaces. What would be the best method of checking the wing incidences at the tips?

I have spare channels so could give each aileron it's own trim, that might help?

Hi Phil, one of these might help. Combined with a cheap digital "spirit" level (mobile 'phone app) should show what's happening from root to tip.
www.modelflying.co.uk/forums/postings.asp?th=106477
Nothing to do with your current problem, but have you noticed how much down elevator trim a Spitfire has in level flight?
Good luck with the aerodynamics biz. I don't believe in the formula approach, its all magic! Wouldn't work otherwise.

Thanks Brian for the link. I have got a bit of Depron so may make my own "cheapskate" version using a similar principle.

Funny how the longer you are into this flying malarky, the more picky and technophobe you become. No longer satisfied that it just flies and to hell with it. :lol: Or is it just me?

Phil - Good looking model, all that hard has work paid off.
Picking up on a couple of points :
Up elevator trim - could this be a symptom of the model being slightly nose heavy. ?
When checking out the C of G I roll the model inverted, I like just a tiny touch of down
elevator to maintain level flight. This is a my preference other flyers will have theirs.

Ailerons & Flaps - If you have enough channels it is well worth having a separate channel
for each ail & flap.

Slightly off message - lovely header pic on the web home page - we are in the U.K and have Petrol engines
not Gas engines, you need to live in Trumpland for that.

Colin.A