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Harrier transition to and from hover

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Harrier transition to and from hover

Old 5th Mar 2014, 11:27
  #41 (permalink)  
 
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The film 'starred' the actor Richard O'Sullivan as a pilot and one of the scenes included a chap called Chris Humphrey, who was unfortunately killed before the film's release, demonstrating a Harrier to iirc the Swiss.
Anyone recall the title of this film, it had a very young air traffic controller (Mrs dctyke) in it.
This was one of the Flight Safety short films was it not? IIRC, this one was called "Flight Safety? Nothing to do with me!". Ended with Richard O'Sullivan lining up without clearance with someone on short finals.

The other one "Distractions" is probably better known. About a Jag Flt Cdr who forgot the MASS and lost an engine on take-off - couldn't jettison the tanks, and ejected too late.
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Old 5th Mar 2014, 11:37
  #42 (permalink)  
 
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Thank you, Gentlemen, very kind and illuminating. I did wonder about the "air cushion" concept such as helicopters have going for them but figured it probably didn't apply.


One more, for now, if I may?


During lift off in a conventional (or short) forward take off, does the aircraft rotate around the rear axle and gear? Just looking at it, the main gear leg appears to be aft of where as a layman I'd picture the CofG to be.
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Old 5th Mar 2014, 19:36
  #43 (permalink)  
 
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Embarrassingly enough having flown a fair few of each I can't answer the question. However it might help inform the debate to explain that a conventional and short take off are fundamentally different.

In a conventional you slam with zero nozzle and then apply progressive back stick at about 120 kts. Eventually some aviation happens. In a short take off you slam with zero nozzle (or ten if you want to keep the efflux off the tail) and then at a pre determined speed (or when the wheels skip) you snatch in a pre determined amount of nozzle - weight dependent but about 50 - and maintain the attitude with a little forward stick if anything.
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Old 6th Mar 2014, 04:39
  #44 (permalink)  
 
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I hate to be the pedant Orca, and as you know I'm not of the CFS persuasion, but I think we slammed with 10 nozzle on a CTO as well for the reasons you state...not that it matters, just nice to be talking about VSTOL again!!!
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Old 6th Mar 2014, 07:29
  #45 (permalink)  
 
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Not sure about other opinions on the matter but, with an armoury of quite a few different short take off options available, a CTO always felt 'wrong!' (or maybe I wasn't doing it right?! Conventional landings even more so; downright perverted, especially with a crosswind!
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Old 6th Mar 2014, 10:02
  #46 (permalink)  
 
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Helmut,

In truth all aircraft with tricycle undercarriage rotate around the main wheels during conventional take off. It is the pivot point, if you think about it. Also, the main wheels need to be behind the CofG otherwise there is a risk that the aircraft will fall on its arse when it's on the ground. Some, like F-35, have their mainwheels even firther back to make space for weapons spaces, etc.
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Old 6th Mar 2014, 11:25
  #47 (permalink)  
 
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Gents,

JF may well correct me, but I believe that the key aspect of a Harrier CTO is that it had a bicycle undercarriage layout, with the aircraft weight spread nearly 50/50 between the main and nose legs. In truth, the 'nose' leg was really a 'front main'. What that meant was that the Harrier couldn't really rotate about the aft main leg. Bicycle gear was very popular on jets in the 40s and 50s, see also B-47, B-52, Vautour. It was useful on the Harrier as it kept the main wheels away from the hot nozzle wash. (Again, so I've been told)

I have also been told that the undercarriage was modified during development to give the wing a higher incidence to make CTOs (and conventional landings) slightly easier and to shorten the TO run.

Main wheel location (on normal tricycle layouts) is driven by lots of things, including ground stability as well as takeoff and landing loads and dynamics. For naval aircraft, there also have to be margins for aircraft moving backwards on a rolling deck, as well as the peculiarities of cat and trap ops.

On F-35, the main legs are actually located outboard of the weapons bays, their fore and aft location was mainly driven by structural aspects. However, during the weight saving effort, the main legs were raked forward to reduce the control loads required for CTOL (and STOVL) variant rotation during takeoff.

It should also be noted that the F-35B nose leg takes only about 10% of the static load, compared with the 50% of the Harrier. Many of us on the programme were surprised at the 'spindly' look of the nose gear, but that was just a result of our own ignorance. It's actually a tough little mother.

Hope this helps, interesting thread (until this post, that is)

Best Regards as ever

Engines

Last edited by Engines; 6th Mar 2014 at 13:38. Reason: Spelling
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Old 6th Mar 2014, 15:28
  #48 (permalink)  
 
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Forgive a silly question but did the engine / fan produce much of a gyroscopic effect on what is arguably a short aircraft when the throttle was slammed?
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Old 6th Mar 2014, 15:31
  #49 (permalink)  
 
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The HP and LP spools rotated in opposite directions to minimise gyroscopic effects.
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Old 6th Mar 2014, 16:12
  #50 (permalink)  

Do a Hover - it avoids G
 
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Helmut

The Harrier as Engines said has a bicycle gear so cannot rotate during any sort of ground roll (think B-52, B-47 etc) because with a bicycle CG is so far in front of the rear leg.

For this reason the wing is mounted leading edge up on the fuselage to that it has 8 AoA during any ground roll thuis generating significant lift with a few knots. (I was not aware that this changed from the P1127 prototype days Engines - but my awareness has always been a bit variable)

This inability to shed wing lift when doing a conventional landing is the reason for some of the fun seen after high speed landings on old conversion movies in the days before two seaters or simulators. It is also the reason the outriggers did not break off when going sideways on some of them.

Last edited by John Farley; 6th Mar 2014 at 18:13.
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Old 6th Mar 2014, 16:52
  #51 (permalink)  
 
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John,

Thanks for coming back.

I was told that the tweaks to ground attitude were very early on in the P.1127 programme, possibly even prior to first flight.

I was also told that the whole issue of landing gear was a problem area for the programme from day one right up to (and after) the GR.1 entered service. Shimmy on outriggers, bounce on landing, problems with nose steering - the team at Dunsfold just about had the lot. And they had to cope with rough field ops. The end result was tough, dependable and above all in a powered lift aircraft, light.

Undercarriage design and development is another bit of aircraft engineering that looks easy until you try to do it. Again, us Brits have a very strong track record in this area. So do the Russians - some of their designs are novel, and highly effective.

Best Regards as ever to all those trying to get the wheels to go up and down and stay on and go around,

Engines

Last edited by Engines; 6th Mar 2014 at 17:19. Reason: spelling
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Old 6th Mar 2014, 18:40
  #52 (permalink)  

Do a Hover - it avoids G
 
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Engines

Yes the u/c was a problem for 8 years from the first tethered hovers to a year or so before entry into the RAF in '69. It was completely solved by Ralph Hooper's idea of a self shortening main leg.

With a bicycle the gear has to be designed so that the main gear takes the intial landing impact loads. This means the nose and outriggers are still clear at touchdown (or should be!). When the main starts to shorten the nose and O/R get in the act and the aircraft stays flat. However after the vertical descent has been killed only the weight remains so the main leg starts to extend again and in the case of the Harrier this puts the O/R back in the air so the thing flopped one side or the other giving very bad ground handling and (because of the aforementioned lift due to wing AoA) a tendency to shoot off the side of the runway especially with crosswinds.

The self shortening leg was brilliant. On touchdown the oil that did the job of absorbing the impact was then fed into an accumulator rather than kept at the top of the leg under pressure as with a normal oleo. Thus there was no rebound from the main leg and so the jet settled wings level. When the main leg next left the ground on a takeoff, its weight made it fall down and fully extend sucking the oil back into the oleo for normal operation on the next landing.
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Old 6th Mar 2014, 19:45
  #53 (permalink)  
 
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So sorry to learn now that my immaculate VLs and VTOs were due to oil and some spurious accumulators, rather than my outstanding skill!!

Back to the potting shed and a bottle of red wine!! It all seems so much better there!!
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Old 6th Mar 2014, 20:32
  #54 (permalink)  
 
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I hear your accumulator banter engines old fruit - but you could still get the old girl to bounce if you weren't pretty quick with the throttle to idle when you landed/ hit / impacted!

I think the Harrier design was staggering given when it was done. Those were clever boys. I was most impressed by the fact that the hot and cold nozzles didn't produce an uncontrollable pitching moment. Probably quite straight forward to a grease chimp, but it impressed this stick monkey!

By the way MSOCS old friend, the conventional in the Harrier II was a doddle!
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Old 7th Mar 2014, 11:04
  #55 (permalink)  

Do a Hover - it avoids G
 
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Bomber and orca

Good to hear from you if rather disappointing that I clearly did not explain things properly. My comments were purely about ground handling and how that was improved by the self-shortening leg which allowed both outriggers to be in contact with the ground after any landing was over.

The proclivity to bounce (or otherwise) on a VL is a whole new topic and of course is totally down to the pilot not the aircraft design. Descending at a steady rate for a VL the 8 tons of jet clearly has some momentum based on that rate of descent. However because it is a steady rate of descent the weight of the aircraft is totally supported by the donk. Thus if the throttle is not chopped on touchdown the gear only has to deal with the momentum and not the weight as well, so the springs on the nose and outriggers will easily push you back up to x ft and you have the whole thing to do again.

God I hate people who have to explain their jokes.

As Engines pointed out there were other problems with the gear especially the outriggers but these were all sorted by the end of the development period.
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Old 7th Mar 2014, 11:24
  #56 (permalink)  
 
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Never flown the Harrier (though did once have a go in the sim) - however, I hope I am not the only non-Harrier reader to be enthralled and educated by John Farley's posts. We have never met, but many thanks John.
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Old 7th Mar 2014, 11:25
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There is always more interesting detail to follow (if you are so inclined) in most aspects of this sadly discarded aircraft.

I seem to remember that the tendency to bounce on VL required a fairly crude fuel bypass modification to the complicated fuel control system in order to achieve rapid wind-down on throttle closure.

The castoring outrigger wheels sometimes stuck at odd angles, leading to worse shimmy than that which they were supposed to stop. The wheels were fixed some time in the mid 70s.

The wide range of landing speed options required a wing that stalled gracefully, rather than suddenly losing lift. The Harrier 1 wing had a fascinating range of devices on it, including the oddly-labelled vortex generators added in 2 steps. Harrier 2 had a much different wing, which may have shared the odd quirk with the F18 wing due to a stray algorithm in the MD computers.
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Old 7th Mar 2014, 12:07
  #58 (permalink)  

Do a Hover - it avoids G
 
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this sadly discarded aircraft
Only by the UK for reasons best not gone into here.

The USMC have declared they will not start rundown until 2027.

The Indian, Thai, Spanish and Italian navies all seem happy with the jet with no end off service dates announced.
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Old 7th Mar 2014, 12:18
  #59 (permalink)  
 
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Well, as a student, I was such an expert in the art of the power bounce that I starred in the Harrier Horror Movie . Do I win US$8.38?

(Very pleased with the II & II+ solution to steal power when the wheels hit the ground so one couldn't bounce up again so easily).

Watching Bloggs perform conventional landings whilst peering nervously to one side of his head from the back of the T4.....oh, deep joy
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Old 7th Mar 2014, 14:55
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Does the need to absorb vertical impact momentum and mitigate bounce have anything to do with the tyre issues on the F-35B? It seems that there is a conflict between VL and CTO requirements but it is not clear what it is.
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