HQ with fuel slosh
I’m constructing a flight test plan to look at the effect on HQ of a large low baffled fuel tank mounted within the fuselage of an aircraft. The tank has a fineness ratio of around 5:1 so fuel movement is significant. Static analysis of the fuel movement within the tank at pitch attitudes of +/-10 degrees indicates a CG movement of +/-2.7 degrees or a range of 5.4 degrees. Dynamic does not appear to be that bad.
Tests I’m considering are:
1. Pitch capture tasks (looking for changes in Fs/g) over range –10 to +10 deg
2. Thrust transients when pitch attitude = 0
3. Combined 1 and 2 from above in manoeuvres such as a go-around
4. SPPO about 0 pitch attitude at high and low IAS
5. Emergency descent man. (60 deg AoB to –15 pitch)
6. Takeoff and landing HQ
7. Large aileron throughs at low speed (ie. with alpha on-roll coupling potential)
Testing at the upper end of the airspeed range seems not so important as the low, and am considering down to 1.2Vs for config. The host aircraft is generally well damped longitudinally with strong LSS and LMS. Am planning around a fuel tank level of 50-66% as being most critical for fuel slosh.
A complex thread I know, but many minds produce better solutions than one. Thoughts appreciated on test techniques, what to expect HQ’wise of large CG shift within manoeuvre, and any other. Also on safety considerations. Please don’t all suggest heaps of tank baffling as this is a last option.
Thanks.