IRRenewal
20th Mar 2009, 08:01
I was doing a check flight in a light single (TB20) which performed to the book on everything apart from the stall speeds, which were a bit on the high side (both for stall warning and actual stall).
With 2 pilots and 250 litres of fuel on board, the CofG was inside the envelope but close to its forward limit at 39.1". The forward limit at the weight we were at is about 37.7", the aft limit is 47.3".
A/C manufacturers like showing their product in the best possible light, so I was wondering if the stall speeds in the book could be for an aircraft with a CofG nearer the aft limit.
Is there a way of estimating the change in stall speeds with a CofG change?
The maintenance organisation is checking the airspeed calibration for me, but given that all other tests were spot on the book numbers I don't think it's too far out.
An added complication is that the Socata manual aren't particularly clear in stating wether data is IAS or TAS. The 'stalling speeds' graphs just say 'stall speed (kt)', were other graphs in the POH state either IAS or TAS. Also, there is no usable IAS-TAS correction graph in the POH. There is a bizarre statement on page 5.3 (for those of you with access to the POH) which says:
AIRSPEED CORRECTION
Vp: Speed relative to ground with no wind
Vc: (conventional speed) = Vi (indicated airspeed) + airspeed correction
Vc=Vi
I have a feeling something got lost there in the translation from French to English.
Any thoughts greatly appreciated (before I go and fly the A/C again with my observer in the back seat, shifting the CofG backwards by about 4").
With 2 pilots and 250 litres of fuel on board, the CofG was inside the envelope but close to its forward limit at 39.1". The forward limit at the weight we were at is about 37.7", the aft limit is 47.3".
A/C manufacturers like showing their product in the best possible light, so I was wondering if the stall speeds in the book could be for an aircraft with a CofG nearer the aft limit.
Is there a way of estimating the change in stall speeds with a CofG change?
The maintenance organisation is checking the airspeed calibration for me, but given that all other tests were spot on the book numbers I don't think it's too far out.
An added complication is that the Socata manual aren't particularly clear in stating wether data is IAS or TAS. The 'stalling speeds' graphs just say 'stall speed (kt)', were other graphs in the POH state either IAS or TAS. Also, there is no usable IAS-TAS correction graph in the POH. There is a bizarre statement on page 5.3 (for those of you with access to the POH) which says:
AIRSPEED CORRECTION
Vp: Speed relative to ground with no wind
Vc: (conventional speed) = Vi (indicated airspeed) + airspeed correction
Vc=Vi
I have a feeling something got lost there in the translation from French to English.
Any thoughts greatly appreciated (before I go and fly the A/C again with my observer in the back seat, shifting the CofG backwards by about 4").