Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
HS Incidence
- Thread starter N53LW
- Start date
Richard L Bentley
Member
Yes, on both my RV4 and recent RV3B the Stab. was raised a total on about 3/8 inch. Just right now..CU RB
db1yg
Well Known Member
I see that you have no response from RV 8 builders on your question. I have an RV9a and I did adjust the angle of incidence on the HS. Actually, my plans explain how to do this if necessary--if I remember correctly it is in the flight testing section of my manual.
After the aircraft was rigged properly, I set it up in my typical cross country configuration. This included my wife and I along with 60 lbs in the baggage compartment (she really has to work to stay within her baggage wt limit but I digress), mid fuel levels, 65% power, and a cruise altitude of around 10k density. I then checked where the elevator counter wts were relative to the HS "caps". Mine were up (elevator trailing edge down) by around 3/8 to 1/2 of an inch. This indicates that there was too much "down force" built into the HS given my eng/prop/cg and therefore the elevator has to be down (counter wt up) to balance this condition. I discussed this with Ken K. at Vans and we estimated the thickness of an additional shim for the front attach of the HS to correct this condition -- BTW, Ken also did this to his RV6. I am sorry but I don't remember the exact dimension needed to correct but we hit it the first time. The elevator is now in trail in my typical cruise condition.
If you decide to do this be careful and follow the instructions in the manual---all aircraft need some HS downforce to provide stability. If you change the downforce too much you could negatively affect the stability of your aircraft!!! Some of our aero engineers can explain the implications of this far better than I .
BTW, I was expecting a speed increase as a result of this. I thought that the elimnation of drag created by the elevator being down in cruise would result in increased cruise speed--if it did it was a very small amount.
Hope this helps!
Cheers,
db
After the aircraft was rigged properly, I set it up in my typical cross country configuration. This included my wife and I along with 60 lbs in the baggage compartment (she really has to work to stay within her baggage wt limit but I digress), mid fuel levels, 65% power, and a cruise altitude of around 10k density. I then checked where the elevator counter wts were relative to the HS "caps". Mine were up (elevator trailing edge down) by around 3/8 to 1/2 of an inch. This indicates that there was too much "down force" built into the HS given my eng/prop/cg and therefore the elevator has to be down (counter wt up) to balance this condition. I discussed this with Ken K. at Vans and we estimated the thickness of an additional shim for the front attach of the HS to correct this condition -- BTW, Ken also did this to his RV6. I am sorry but I don't remember the exact dimension needed to correct but we hit it the first time. The elevator is now in trail in my typical cruise condition.
If you decide to do this be careful and follow the instructions in the manual---all aircraft need some HS downforce to provide stability. If you change the downforce too much you could negatively affect the stability of your aircraft!!! Some of our aero engineers can explain the implications of this far better than I .
BTW, I was expecting a speed increase as a result of this. I thought that the elimnation of drag created by the elevator being down in cruise would result in increased cruise speed--if it did it was a very small amount.
Hope this helps!
Cheers,
db
vic syracuse
Well Known Member
You probably won't see much, if any, of a speed difference, as the total aerodynamic drag remains about the same within the range of changes you are making. Note that if you change this after you have fitted the empennage fairing, you will most likely have to do some fiberglass work around to make it fit again.
If you adjust this too much for the aft CG in cruise, there is the potential that you might not have enough up elevator in the landing flare to avoid a hard arrival. So becareful before making large changes. There's a lot of these flying and if assembled per the plans, shouldn't require large tweaking of flight controls. Miniscule changes end up being for aesthetics only, and really won't by you much.
Vic
If you adjust this too much for the aft CG in cruise, there is the potential that you might not have enough up elevator in the landing flare to avoid a hard arrival. So becareful before making large changes. There's a lot of these flying and if assembled per the plans, shouldn't require large tweaking of flight controls. Miniscule changes end up being for aesthetics only, and really won't by you much.
Vic
OK, I'll give you at least ONE RV-8 response....nope, I didn't change it a bit from the plans. I have good control throughout the entire CG range, and the elevators are aligned very closely in cruise, with or without a passenger (the difference is pretty small).
Paul
Paul
Andy Hill
Well Known Member
db
To affect the stability, you would need to alter the total downforce from HS + Elevators, which is only achieved by altering the CG... Aft CG reduces Long stability which to a point is "good" and "fun" and then gets "exciting" and then
Andy & Ellie Hill
RV-8 G-HILZ
Whilst the theory is correct, by altering the HS angle all you do is swap HS downforce for elevator downforce and v-v. Stability does not care which
To affect the stability, you would need to alter the total downforce from HS + Elevators, which is only achieved by altering the CG... Aft CG reduces Long stability which to a point is "good" and "fun" and then gets "exciting" and then
Andy & Ellie Hill
RV-8 G-HILZ
