Is it good to plan the aircraft load slightly tail heavy?

[i_june]

As I have been told that it helps on fuel saving. Is it true and how could it be?

Thanks in advance for help me out of this doubt...

[Geoff44]

Tail heavy trim.

Yes a tail heavy trim is the best for fuel efficiency. Don't think it would make much difference on short flights but worthwhile on long haul flights.
I am not sure why but I am sure someone on here will know.

[kme]

Tail heavy

Consider a plane that is very nose heavy - think of hanging a big container off the nose of a flying aircraft.

To continue flying straight the plane has to compensate for this nose down moment. The way it works is that the plane is retrimmed to keep the balance and push the tail down (with the stabiliser) - This causes drag and increases fuel consumtion.

Now move the container just to the front side of the wing - here it causes a lot less moment that the tail has to compensate for - less drag = less fuel

There is other aspects to this but I hope this explains the question in an easy way without sounding too stupid..

[jerboy]

Generally yes. However it pays to beware of aircraft that have a tendency to tip on their arse on the ground when there's a heavy load in the back and no pax or load up front to balance it out.

I've seen an ATR72 do this when the crew were sat in the back during the turnaround and a heavy load was put in the rear hold. Quite funny to see and no damage was caused, but its hardly safe!!

[dc9-32]

In the days of Sabena, we used to load their 737-200QC's with a real aft C of G. Virtually no stab trim adjustment. The a/c used to do a double BRU-STN-BRU rotation each night and the crews always told us "the more tail heavy, the better".......

[TURIN]

Its basicaly assisting the elevator stab trim to produce a small ammount of lift as aposed to induced drag.

Eh?

Lift? From the Stab?

[SMT Member]

Don't know of any horizontal stablisers that can be trimmed to produce lift rather than down-force. That would imply the Centre of Gravity had moved behind the Centre of Lift, or at least very close to it, which might cause all kind of stability issues. Regardless, whether you're producing lift or downforce you're still generating induced drag. The trick is, obviously, to reduce downforce as much as possible, thereby reducing the induced drag from the stabiliser as much as possible, for the benefit of burning less motion lotion.

The real price to pay for a tail (or nose for that matter) heavy trim is a reduction in elevator trim available, and to a certain degree pitch authority.

As for tail-tipping, that's mainly a question of using the correct procedures during loading and un-loading. We'd regularly trim the MD-11F very close to the aft limit, target actually being right at the limit, and that aircraft is more prone to tail-tipping than anything else I've ever encountered (DOI around 96, it tips at index 100!). However, by following the established procedures it's possible to both load it for a very aft CoG and maintain ground stability.

The long of the short is that tail-heavy is beautiful. Doesn't matter if you're flying long, medium or short-haul; it all adds up and the potential cumulative savings are enormous. To give you an idea, the difference in fuelburn between an aircraft trimmed to forward most and aft most limits can be up to 5%.