ORIGINAL: BillS
I know this is likely to be a stupid question.
One of my airplanes (a Kougar) has 3/4 to 1 degree positive wing incidence. The incidence should be zero. I did not build the airplane but apparently the horizontal stabilizer was put on with the front of the stab down relative to the wing. To compensate the prop has 4 degrees of down incidence relative to the stab.
Does anyone have a trick to correct the stab incidence without a total makeover. Is there is a way to partially correct the incidence.
Bill
Bill,
Make the wing incidence the same as the stab. Then adjust the engine thrust .
The followingis not a trick, but a sequece of flight tests to perfect your planes trim, incidence, CG, engine thrust etc. if you really want to correct the planes defeats. Use if needed.
Regardless of what the stated engine thrust, wing incidence and stab incidence say on the plansflight trimming is the only way perfect the planes flight characteristics.
If you already understand flight trimming addthis chart to you collection. If not the chart below will blow your mind as far as how much better your palne will fly. There are several Flight Trimming Charts or Guides available inthe forums and on the web.The static measuring offered on plans is great to get you started but the only accurate way to perfect your planes trimis through actual flying or "Flight Trimming."All that's required is to learn how to check your plane against one of the charts while flying it.
As an example i had purchased a Kaos of craigslist that was badly trimmed when built. Thefirewallhad 4 degrees of downthrust. The wing had +1.5 degree incidence on one side, and -1.8 on the other. The stab was misaligned badly as well with one tipbeing closer to wing than the other. I was told that the Kaos was not designed for knide edge flight but after using the chart below. I have a very well trimmed plane that acutually flies in knife edge with ease.
Too get it there I firsthad to cut off the stab with a razor saw to align it correctly to the wing and set it to 0 degree incidence. The wing was fixed by using my heat gun to shrink the Monokote alternately on each side. Then I startedthe flight trimming tests. Checked the CG first and got it nailed based on the tests.Next, was the decalage (incidence.) I had to adjust thewing incidence several times and it was finallyset at0 degrees, once again based on the tests.Next , through thetests the engine thrust was also set at0 degrees. I was also able to determing that indeed the Kaos did not have enough rudder area and stab height for knife egde flight. That was fixed by adding a 1"h x 4"L small triangle stab on the bottom of the fuse and 1" as well to thebottom of the rudder.
Here's the first one I ever used. It's from the Futaba 8uafs 8uaps 8uhfs 8uhps radio manual. It says Pattern Aircraft Flight Trimming Chart buttest 2 really applies to the Old Classic Pattern planes. Other thanthatall the other tests are usefull for all planes. Someoneelse said to start with CG and I agree so for the chart below start a No. 1, ignore No. 2, and switch tests 3 and 4so you start with CG than goto Decalage (incidence).
If your plane is flyable spend a day learning to fly the these sequencesto check out your planes flight characteristics against the chart before youmake any other changes to your plane.