From: zwork@starfighter.den.mmc.com (Michael Corvin)
Subject: Re: U-2/TR-1 air restarts
Organization: Martin Marietta Astronautics Group
Date: Sat, 12 Sep 1992 00:31:06 GMT

In article <18qvk6INNhq5@darkstar.UCSC.EDU>, zap@ucscb.UCSC.EDU (ZaP!) writes:
|> 
|> 
|> 	Here's a question that has held my cuirosity off and on:
|> 
|> 	The U-2/TR-1 utilise their good glide ratios to extend range and
|> endurance by shutting down thier engines in flight.  What equipment is
|> necessary on board to ensure reliable airstarts?  Many aircraft of that
|> era used cartridge starters, which seem to me to be a rather risky proposition
|> in the air.
|> 
|> 
|> -Ford					Internet: zap@ucscb.ucsc.edu
|> 					UUCP    : zap@gorn.santa_cruz.ca.us
|> 
|> [Insert tautology here.]
|> 
|> 

I would be very surprised if they shut down the engine on purpose at
any time in flight.  I am not sure if the U-2/TR-1 (Dragon Lady...)
has powered or unpowered flight controls, but in any case the engine
probably has to keep running to provide accessory power for all the
systems during regular operation.  Air for cabin pressurization
is also engine-supplied compressor bleed air (I don't know if the
full pressure suits they wear are O2 or bleed air pressurized).

Also, the mission profile of these birds is to get high and stay high.
Maintaining altitude requires keeping the engine running.

The tremendous glide ratio really means that the aircraft is
aerodynamically efficient - this it self gives good powered range.
It is also the secret to the aircraft's tremendous altitude
capability.  An aircraft's climb ability depends on having excess power
beyond that required to maintain level flight.  Put a huge jet engine
into a an efficient glider and you've got that excess power available
in spades up to rather lofty heights...

As I understand it, the U-2/TR-1's altitude limit is actually defined
by the 'coffin corner', the point at which the aircraft's critical 
Mach number and the stall speed come together, a function of the
density altitude.  The U-2/TR-1 is decidedly a subsonic aircraft and
flying in the coffin corner is like walking on egg shells.  If you
overspeed you can break the bird but if you stall you will probably
overspeed while trying to recover - and only a few knots separate
these two unpleasant scenarios.

There have been various .legends about U-2s making mind-boggling
glides home after engine failures.  If one assumes a 30:1 glide
ratio, from a typical 80,000ft altitude one would manage about
400nm in a straight glide (gold badge material ;-) ).  A 40:1
ratio would increase this to about 526nm.  (Anyone know what
a U-2/TR-1 glide ratio is?  Probably better than an F-104,
which is something around 2.4:1 with the engine windmilling
and the ram air turbine extended...)

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Michael Corvin 	      PP-ASEL, PP-G		zwork@starfighter.den.mmc.com
just another spaced rocket scientist at    Martin Marietta Astronautics Group
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===============    My views, not Martin Marietta's   ========================
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