Roll/Aileron trim

[Timothy]

For years and years I have never been able to get the roll trim right in my Aztec. Even if I do get it right for one configuration it seems to be quite considerably affected by load (ie which side pax sit.)

The aircraft does not have internally adjustable aileron trim, only bendable tabs.

I have just had a top overhaul on one engine which resulted in a lot of single-engine runs which in turn meant that I took off today with a considerable fuel imbalance, which I fixed with crossfeed. I noticed a considerable change in aileron input during the crossfeed (it was all on outboard tanks) which set me thinking.

The question for this august forum is, is it legitimate to compensate for poor aileron trim by use of crossfeed, or will this create an out of balance/skid/sideslip?

TIA

Timothy

[John Farley]

Timothy

Using fuel crossfeed to laterally balance any aeroplane will have no effect on directional or longitudinal trim that cannot be properly (and normally) dealt with in the usual way. So it has no aerodynamic disadvantages or complications..

Whether you are increasing your chance of a fuel management pigs is another matter and depends on you as well as how big the imbalance needs to be to trim wings level. I would have thought it need be only small if you have set your fixed aileron tab to give approximately wings level in the cruise config.

BTW I have never noticed any august people here, just those who have tended to specialise in aspects of aviation that (by and large) avoid boring hours in the cruise.

Regards

John

[Timothy]

John,

Thank you. That seems the way to go then.

I am aware of the dangers of fuel mis-management, and the only time I use a checklist is for crossfeed, as it depends on so many binary choices, several of which could result in a double engine failure if misremembered.

Unfortunately the checklist is phrased in terms of "Fuel Pump - Operative engine" and "Fuel Pump - Inoperative engine" which means that you have to start the whole thing by making the binary choice of whether the side you want to move fuel to is "operative" or "inoperative". I have been known to fall at that first hurdle. :uhoh:

Timothy

[LOMCEVAK]

Timothy,

I have no experience of the Aztec, but if it has positive and reasonably strong lateral static stability (rolls well with small rudder inputs) then you can correct an out of trim roll condition by applying rudder trim away from the "heavy" wing. This will create extra drag so you will cruise more slowly, but if lateral static stability is strong enough then it should not be too much of a penalty. Likewise, if you find that the applied rudder trim is yawing you noticeably off heading then this technique is probably not going to work in an Aztec. Worth a try, perhaps?

Rgds

L

[Timothy]

L

I have in the past done as you suggest...it just seems an ugly way to fly to me...sort of in a permanent forward slip.

Do you agree with John that the use of fuel as trim ballast is a nicer way to do it?

Timothy

[Tinstaafl]

Hi Timothy,

I've used x-feed frequently to correct a lateral imbalance. Works in singles (ie L & R selector) & twins. It doesn't take much of a fuel imbalance to make a difference *provided* the aileron ground adjustable tabs are adjusted properly.

I've also used rudder trim to achieve the same result. I'd usually rather fly slightly inefficiently than have to hold continuous control pressure.