BlueMax3

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Hello,

Does anyone know what the wing and stab incidence should be on a GSP Spitfire?

Right now I am at +2 degrees on the wing relative to the stablizer and the plane needs a lot of down elevator trim to maintain level flight. I added some down thrust, but that just made things worse. When inverted, the plane will fly level with just a touch of down elevator, but when in an inverted climb, she wants to go more inverted with no elevator input. At the top of loops, I have to really add up elevator to get it to complete the loop. CG is dead center in the range at 125mm. When trimmed for level flight at full throttle, if I cut the throttle to idle, she climbs. According to the NSRCA trimming chart, I should reduce the amount of downthrust, but that will require even more down trim for levle flight. Suggestions?

Thanks,

Travis

sbd-5

My Feedback: (4)

before anything else i would decrease the down thrust.in fact try 1 degree up thrust and see what happens.you may find that things get better not worse.by adding the upthrust if you were to draw a new centerline so that the engine was now set at a new zero you will now have reduced the wing incidence and added a bit of neg stab incidence.

BlueMax3

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sbd-5,

Thanks for the suggestion. I can see how this would improve things in certain respects, but not others. For example, I can see how this would help during inverted flight and reduce the tendency of the plane to climb when I reduce throttle when the plane is right side up. But I imagine it would increase the amount of down elevator trim required to maintain level flight when right side up, since I would not be changing the relative incidence between the stab and wing.

Do you know the typical relative incidence between wing and stab is for warbirds?

Thanks,

Travis

Richard L.

My Feedback: (24)

I don't remember mine needing a lot of down elevator trim to fly level. When I drilled the two holes up front for the two wing dowels, I drilled them slightly lower on purpose to lower the LE of the wing, which gave me almost 0 degree wing incidence relative to the rear stab.

butlern

My Feedback: (15)

Travis,

Glad to hearthat there's someone else out there that believes this plane's wing/stab incidence is messed up. I had mine flying great for a very long time and then I decided to start playing with the balance and the engine thrust. I have have been chasing my tail with this set-up for so long now, I can't remember where I started, and each flight (landing) is VERY different than the last. It's extremely frustrating, and now I have to repair the gear rails on the left side as a consequence of my decision to begin experimenting.

I just picked up an incidence meter from a friend, so it's clear we're both thinking along the same lines. When I get the rails repaired and the wing back on the plane, I'll let you know what I find.

If you learn anything in the meantime, please forward it along to me.

Thanks and good luck.

Noah

BlueMax3

My Feedback: (1)

Richard L. -- In general, is it best to try to get no incidence difference between the stab and wing on a warbird? It sounds like that was what you were considering when you located the holes the the wing dowels. This would seem to be the goal, but I am not sure. Can you confirm that a positive wing incidence with respect to the stab generally causes an airplane to want to climb (everthing else being equal)?


Noah -- Sorry to hear about your troubles. It's tough landing a warbird with a non-optimal setup, especially when changes are made! The trimming charts that I have found all recommend first setting the correct cg, then moving to wing/stab incidence and thrust angle. I know my cg is dead center in the middle of the range and the flight characteristics confirm that it is fine, although I might move it slightly forward for added stability. But, I have a solid +2 degrees of wing incidence relative to my stab, which I believe is the cause of my plane needing a lot of down trim. I removed the down thrust that I added and I plan to shim the wing to get it more parallel to the stab and I will do some testing this weekend. I just got my incidence meter a few weeks ago and this has been a great learning experience. I'll let you know what I find out.

Travis

Richard L.

My Feedback: (24)

It depends on the plane but in general, you want the wing to be at 0 degree on a warbird. Yes, in most cases, a positive wing incidence with respect to the stab will cause an airplane to climb at high throttle setting.

sbd-5

My Feedback: (4)

what richard l said is correct but there are also aetups where the wing is at a positive incidence and the stab is the same incidence as the wing to offset the climbing tendencies but is nit seen very often,this set up was used in the 60's and early 70's.maybe you can epoxy some hardwood dowel stubs in the locating holes cut them flush and re drill new locating holes a bit lower

PineBaron

My Feedback: (38)

I have the same problem with my second Sportsman Aviation Spitfire. The first one had a YS FZ91, that one required some weight in the tail to balance the cg and flew perfect. The second one has an OS91fx and this one needs lots of down trim to fly level. Down thrust did not help, zeroing 2 degrees of wing incidence did not help; I moved the cg forward by 10mm (using an aluminium spinner),now making perfect takeoffs and landings a breeze, still need down trim for flying. I resigned and set my down trim with my TX subtrim; the good thing is, I am now having fun flying it.
PineBaron

BlueMax3

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Problem solved! Thanks to all the suggestions provided here. I removed 1.5 degrees of the wing incidence, leaving about 0.5 degrees of wing incidence relative to stab incidence. This reduced the tendency of the plane to climb and of me having to add down elevator trim. I was then able to remove the extra down thrust, leaving the original down thrust provided by the manufacturer. I also moved the cg forward about 2mm. The plane now flys level with no trim elevator trim or maybe one click of down. She's now a real smooth and straight flyer and doesn't baloon on landings when I reduce the throttle, since the down thrust was taken out after the wing incidence was changed. I sure learned a lot through this experience, which I will use on future planes!

Travis

LDM

My Feedback: (15)

Hey Travis , I have always had trouble with measuring wing Incidence , can you please suggest or recommend the tools you used and how you kept your plane level when measuring ? I am about to build a bi plane the incidence is critical to good flight
Thanks

BlueMax3

My Feedback: (1)

I use the Great Planes laser incidence meter and it includes instructions on how to perform various measurements. The plane does not have to be perfectly level to make the measurements. The meter is setup on the stab and then zeroed. It is then moved to the wing to provide a relative measurement. So, the plane does not have to be perfectly level. It was actually pretty simple.

Travis

LDM

My Feedback: (15)

Thanks Travis

Tsutomu Mabuchi

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Not Spitfire, but I reduced wing incidence by 2 degrees on my
Hangar9 AT-6 Texan.
Now it is almost zero degree relative to the stabilizer.
Before that it flew with much climb tendency at high power.
It flys very stable and easy like a trainer now.
Just a refference.

Tsutomu Mabuchi

Wing-Ding

LDM,

Here is the most precise meter available for measuring incidence (and your plane doesn't have to be leveled first ).

[link=http://www.aeroperfect.com/incidence.html]AeroPerfect[/link]

Richard L.

My Feedback: (24)

H9 also has a digital one that can measure exact control surface throws to 1/10th of a degree and works as a precision level:

[link=http://www.horizonhobby.com/Shop/ByCategory/Product/Default.aspx?ProdID=HAN192]AnglePro 4-in-1 Digital Throw/Incidence Meter[/link]

LDM

My Feedback: (15)

Thanks WD/Rich , I asked this question about 4 months ago on a Global Blue max , plane wanted to go up and up , CG was in check , engine incidence was in check , it was the wing incidence . This seems to be an area that many modelers advoid or simply dont understand and I am learning just how important it is .