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NSEU
29th Mar 2009, 04:59
Do any cargo 747-400's have an HST (including the Boeing Converted Freighters)?

If not, is this because of a CG issue?

Thanks.
Cheers.
NSEU

B-HKD
29th Mar 2009, 05:10
Good question!

I know as a fact that no 74F has a HST and there is no option to have one.

What happens with the BCFs that have the HST?

Leo

SMOC
29th Mar 2009, 05:42
All 400s and some late model classics for that matter have the same horizontal stabilizer, it's just those with the tank have the required plumbing to make it a fuel tank, those that don't simply have blank plates fitted where required.

A BCF has the plumbing removed, the blank plates fitted where required and also the cockpit mods required such as the replacement of the overhead fuel panel and software changes to the EICAS and so forth.

NSEU
29th Mar 2009, 08:12
Excellent feedback as always :)

Thanks, guys.

Cheers.
NSEU

Dan Winterland
29th Mar 2009, 14:24
As for the reason why, it's because a freighter doesn't need to carry that much fuel and removing the pumps and plumbing saves weight. The HST doesn't get filled until the fuel load reaches about 150 tonnes. I can't remember the exact figure as it's 7 years since I've flown it. If you're getting anywhere near that figure, youré reducing the ZFT. On a freighter, it makes better economic sence to fly at max ZFW and tech stop rather than leave payload behind to increase range.

The HST is not a trim tank like it is on the A330/340. It's just another place to stuff fuel.

NSEU
29th Mar 2009, 21:21
The HST is not a trim tank like it is on the A330/340. It's just another place to stuff fuel.

That is not to say it won't seriously affect trim. I understand that it's not standard practice to fine tune the balance of a 744 by transferring fuel (manually), but if fuel is to be loaded in the HST, a certain ratio must be maintained between the CWT and the HST prior to takeoff - 6:1? And, if you can't burn fuel from the HST due to a malfunction, then you may end up dangerously out-of-trim.

Cheers.
NSEU

john_tullamarine
29th Mar 2009, 21:27
The HST is not a trim tank like it is on the A330/340

Some years ago, QF (after much harassment by a pilot) ran some studies on the 400 tail tank and found that significant payload dollars were available to be made on extreme range operations by using the tank for CG trim control ...

NSEU
29th Mar 2009, 21:33
P.S.

As for the reason why, it's because a freighter doesn't need to carry that much fuel

However, saying this, Boeing does offer the option of an AUX tank in the forward cargo on the ERF (and as far as we know, no HST). This leads me to believe it is a balance issue.

Larger items can be loaded in the rear of a freighter than in the front area (the ceiling is higher), so it makes sense to me that no HST is offered.

Dual ground
30th Mar 2009, 07:36
Just because an item is bigger it does not automatically follow that it is heavier. QF pax 400ER's were delivered with the AUX tank and the HST. I was under the impression that the fwd AUX tank is what actually made an ER an ER. Was there not an option of an additional AUX tank in aft cargo also?


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