flight dynamics problems
Posted: Wed 8. Jun 2011, 14:27
As mentioned at SOH this is a really GREAT plane!!
Despite the use of the ‘coupled MOI’ there are a few rather serious problems with the flight dynamics
Rudder
Power on:
E.g. if you try to do a ‘flat’ turn with the rudder only at around 120kts she yaws extremely fast (about 90deg/sec) and if not checked with the elevator she will be in a 90deg nose down attitude after a 90deg turn.
If you just try to keep the nose down from dropping with a bit of pull during the flat turn, she will immediately perform a rapid flatspin like maneuver .
Full rudder produces a very high roll rate but the yaw rate is much less, a behaviour that’s normally only associated with fast jets and swept wing planes.
When performing a hammerhead you can start the rudder input at as low as 2-5kts and she will come around within 1-2sec.
If you apply full rudder on ground at e.g. 2-3kts she does a very fast (2sec) 360deg turn almost on the spot .
Power off:
The roll rate with the rudder is almost as high as with the ailerons.
It’s not possible to do a slip at approach speed e.g. 80kts with full rudder because the aileron authority is too low to counteract the yaw.
On the ground at only 2-3kts with the throttle almost at idle the yaw moment from the rudder is excessive. Turns feel like there is a tailwheel steering.
If you look at the various videos with the 108 taxiing there’s quite a lot of rudder movement with only very little yaw at low speed as there’s almost no airflow over the rudder.
Stall
In an accelerated stall she does a violent snap roll, almost like the Fw190.
Something that shouldn’t happen with the slatted wing and that didn’t happen with the 109 either.
She’s rather unstable along the longitudinal axis even in a ‘normal’ straight and level stall, again that shouldn’t be the case with the slatted wing.
Once stalled there’s no stall break (trimmed for a 70kts glide) and the nose doesn’t drop with full up elevator.
Interestingly even when you release the stick she remains in the stalled nose high descent attitude
Last but not least the wing contact points seem to be way too far inboard.
That may sound like a lot of complaints but this is just a precise as possible problem description and I do enjoy this plane a lot!!!!
Best regards
Bernt
Despite the use of the ‘coupled MOI’ there are a few rather serious problems with the flight dynamics
Rudder
Power on:
E.g. if you try to do a ‘flat’ turn with the rudder only at around 120kts she yaws extremely fast (about 90deg/sec) and if not checked with the elevator she will be in a 90deg nose down attitude after a 90deg turn.
If you just try to keep the nose down from dropping with a bit of pull during the flat turn, she will immediately perform a rapid flatspin like maneuver .
Full rudder produces a very high roll rate but the yaw rate is much less, a behaviour that’s normally only associated with fast jets and swept wing planes.
When performing a hammerhead you can start the rudder input at as low as 2-5kts and she will come around within 1-2sec.
If you apply full rudder on ground at e.g. 2-3kts she does a very fast (2sec) 360deg turn almost on the spot .
Power off:
The roll rate with the rudder is almost as high as with the ailerons.
It’s not possible to do a slip at approach speed e.g. 80kts with full rudder because the aileron authority is too low to counteract the yaw.
On the ground at only 2-3kts with the throttle almost at idle the yaw moment from the rudder is excessive. Turns feel like there is a tailwheel steering.
If you look at the various videos with the 108 taxiing there’s quite a lot of rudder movement with only very little yaw at low speed as there’s almost no airflow over the rudder.
Stall
In an accelerated stall she does a violent snap roll, almost like the Fw190.
Something that shouldn’t happen with the slatted wing and that didn’t happen with the 109 either.
She’s rather unstable along the longitudinal axis even in a ‘normal’ straight and level stall, again that shouldn’t be the case with the slatted wing.
Once stalled there’s no stall break (trimmed for a 70kts glide) and the nose doesn’t drop with full up elevator.
Interestingly even when you release the stick she remains in the stalled nose high descent attitude
Last but not least the wing contact points seem to be way too far inboard.
That may sound like a lot of complaints but this is just a precise as possible problem description and I do enjoy this plane a lot!!!!
Best regards
Bernt
Infact I did sneeze on one take-off and prompty ground-looped it. Even the natural analogue imperfections of my joystick rudder in the neutral position are sufficient to cause yaw instability and oscillations in this aircraft and surely this cannot possibly be right (having to use a larger deadzone than any other aircraft).