Re: Drop tanks!

Date:         17 Jan 99 02:37:15 
From:         arch6@mail.inlink.com (arch)
Organization: McK&A
References:   1
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In article <airliners.1999.12@ohare.Chicago.COM>, tedperez@hotmail.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.

Design:
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.

Operations:
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)

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