Harrier questions

[forthbridge]

HI all

Just a couple of quickies... for first gen harriers, and original sea harriers, does anyone know the thrust/weight ratio (which will obviously change depending on fuel) - I'm after the 'vertical takeoff' number if anyone has it ;-)

Also, as a rule of thumb, does anyone know the limit time-wise that a harrier can fly slowly/hover for without boiling the coolant?

[DaveB]

Hi Jim,

No idea what the answer is to your first question but for the second, everytime I've seen one at an airshow.. I seem to remember it having enough water for around 5mins (not that it would hover for 5mins so I guess that's a total of 5mins) Could be well off the mark though ;-)

ATB

DaveB :tab:

[forthbridge]

HI Dave,

Cheers. I am the same having seen them at Airshows - I remember the commentator at Leuchars stating the amount of water it went through for cooling just for the display - but I can't remember :doho: - IIRC, after that amount of hovering they need to land to cool things down a bit - but just not sure!

[DaveB]

That's it mate. Thing is.. they don't carry a great deal of water do they.. it's a matter of pints rather than gallons. Maybe one of the RAF guys has a bit of in-depth and will be able to fill the gaps for ya ;-)

ATB

DaveB :tab:

[Motormouse]

De-mineralised water (not water-meth) tank IIRC (since I last worked on 'em back in 1990) was @ 25-30 gallons,
and if working to the maximum weight would only last for @ 90 seconds, or @ 5 mins if a/c was 'light'.

ttfn

Pete

[DaveB]

That much Pete!! :o TaVM ;-)

ATB

DaveB :tab:

[forthbridge]

:o
Blimey! So in reality I would be owing the MOD for a few burnt out Harriers........... :flying:

[forthbridge]

Just noted on Wikipedia :roll:

A quoted TWR for the Harrier of 1.10 - compared to around 1.2 for the F 15, 1.18 for Eurofighter and 0.55 for the Tornado.

[SkippyBing]

Well to take off vertically you'd have to have a TWR of greater than 1, otherwise you'd just sit there burning fuel until it got to 1 anyway. 1.1 sounds about right to take off and climb away, you could work backwards from the rated max thrust of the Pegasus and the empty weight of the Harrier to figure out how much fuel/stores you could carry.

The figures for the F-15 and Typhoon sound plausible, but again it's unlikely they'd ever be operated like that as you'd be better off hanging some more fuel and stores on the thing so it'd do something useful once it got airborne. The Tornado one does sound more like an aircraft with a warload however, bearing in mind it hasn't got the punchiest engines going.

Edited to add at max tax off weight the F-15 gets a TWR of around 0.8.

[forthbridge]

Yeah, all perfectly sensible ;-)

What I am having trouble grasping is that (as with all things) the TWR is dynamic (unless basing it on the TWR of the engine on it's own) - so as you say a given load of anything will make some difference.

It's a little tricky trying to find what is *needed* as TWR for certain phases of the flight - for example, if we assume that a Harrier could take off with 50% fuel load, as this is used up, less engine thrust *should??* be required as fuel is burned off - but the output of the engine means the TWR for that specific weight/thrust output is the *same* TWR as using maximum thrust... :roll:

There must be some tables out there showing what TWR would be needed for a specific load - and more interestingly what the percentages of TWR are for 'vectored' flying in the harrier - for example - doing 25 knots IAS - what does this knock off the TWR needed to maintain the same descent rate as landing vertically?

(I must be bored today) ;-)