Re: Drop tanks!

Date:         17 Jan 99 02:37:15 
From: (arch)
Organization: McK&A
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In article <airliners.1999.12@ohare.Chicago.COM>, wrote:
> I keep reading about aircraft manufacturers struggling to extend
> the range of their aircraft, and i was just wondering why not use
> drop tanks?  After all, if the plane can ferry an engine under
> the wing (making the plane appear to have five!), then why not
> drop tanks?

First, fix your reply to reply once, you've posted five times.

[Moderator's note: He only posted once.  Perhaps your news server is
having a problem.  -- Karl]

Drop tanks are a design, operations and maintenance nightmare.

Drag on a station pylon is very big (undesirable, minimizes payback).
Conformal tanks reduce some drag but increase effective cross-section.
All tanks require stressed attachment points and plumbing for:
   effective filling (residual fuel and partial fill hazards)
   effective draining (residual fuel and cg)
   effective transfer (drops-wings-(tail)-main bags, what order?)
   emergency dump (time, control and cg)
Fire (detect, suppress, jettison?)
Fire (extra fuel, skin thickness, vulnerability (also to ground vehicles))
Non-tank aircraft have over-designed landing gear and other "extra" weight.

Now which aircraft have that configuration?
How to shuttle aircraft through dispatches to the one or two routes that
really need this gas.
How to get tanks up/down loaded effeciently when not needed.
Pilot training (normal and emergency)

relays, wires, pressurization
storage, shipping, prepositioning and relocation of tanks
people quals to up/download (currency)
corrosion control