Harrier transition to and from hover [Archive]

LateArmLive

2nd May 2010, 21:50

When transitioning to the hover, are nozzles rotated to vertical and then airspeed left to wash off, while engine rpm is gradually increased to counter the effect of the unloading of the wings?

Yes, that's right. Nozzles are usually rotated in 2 chunks - 40 degrees selected downwind, then hover-stop (approx 80 deg as the jet sits 8 or 9 deg nose up in the landing attitude) at the deceleration point which is about half a mile from the desired landing spot. The pilot will be flying 10 alpha until the hover-stop is selected; he will then keep the jet level with increasing power as the wing lift gradually reduces. Below about 45kts the aircraft will be pretty much wholly jet-borne.

Fore and aft speed can be controlled in the deceleration and hover by pitch, although nozzle movements are generally used if more than 5 deg NU/ND is required.

Similarly, when transitioning out of hover, increase power and rotate nozzles slowly back as wings develop lift?

Exactly that. From the hover, add some power, pitch up a couple of degrees then nozzle out. The rate of nozzle movement depends on how much excess power is available.

Getting in and out of the hover is the trickiest part of VSTOL ops. In a steady hover the jet is pretty well balanced and flies like a sluggish helicopter. The transition can be tricky as all the variables are constantly changing. Keeping the aircraft in balance is of paramount importance, as Intake Momentum Drag can flip a jet over in fairly short order. I'll let a QFI explain that one........;)

Hope this helps

tartare

2nd May 2010, 22:36

Tks for that!
R/e water injection - I had heard about this - I assume water is sprayed into the compressor to increase the effective volume of air moving through the engine and also cool the engine ( I understand the Pegasus can only be run at full hover thrust for around a minute at any one time?)
Also, I note there's a yaw vane in front of the cockpit.
I assume this is to ensure that hover transitions take place into the wind to prevent the jet weathercocking - rolling over - seem to remember some film of a spectacular GR3 ejection at low level when the jet yawed unexpectedly..

Trim Stab

3rd May 2010, 08:22

How is the vertical landing carried out? It looks rather crude from the outside, as if the pilot just chops the power at about 30ft. But presumably you try to make the drop as smooth as possible? Or is the seemingly brutal drop deliberate in order to lessen the chance of instability in ground effect, or FOD ingestion?

NigelOnDraft

3rd May 2010, 08:37

I assume water is sprayed into the compressor to increase the effective volume of air moving through the engine and also cool the engine Direct into the turnine area IIRC... Basically reduces JPT, allowing more fuel / thrust / RPM keeping within the (now higher) JPT limits.

I understand the Pegasus can only be run at full hover thrust for around a minute at any one time?)There's a big table of limits... but the top rating is for 15s only :eek: (and flashing lights to warn you!)

Also, I note there's a yaw vane in front of the cockpit.
I assume this is to ensure that hover transitions take place into the wind to prevent the jet weathercocking - rolling overYes - not necessarily "into wind", you just keep it straight with rudder so the relative wind is fore/aft. If you don't the rudder pedals start shaking, the QFI in the back/on the radio shouts "Vane", and if you ignore all that :{ Critical period is 30K-120K - again IIRC. Below 30K no probs :ok:

How is the vertical landing carried out? It looks rather crude from the outside, as if the pilot just chops the power at about 30ft.Not really "chop" the power, but you do not "cushion" the landing - just keep the RoD on until impact :ooh: then idle straight away, and nozzles aft. It has been known at this point for people to do this in the wrong order (no names ;) ) which is great fun for any observers...:D

Or is the seemingly brutal drop deliberate in order to lessen the chance of instability in ground effect, or FOD ingestion? Spot on :D

NoD

BOAC

3rd May 2010, 10:50

To amplify NoD's coverage:

My QFI used to shout 'Vane ****'

This thread is bound to send a call to John F who will no doubt remind you all that the Intake Momentum Drag mentioned by LAL is effectively a function of a mathematical product of engine power x yaw angle x angle of attack, and that by keeping ANY one of those at zero, it is avoided (engine power - yes, that was a problem....:))

The ejection Tartare mentions is most probably the unfortunate US Marine who fatally forgot 'the rule'.

VinRouge

3rd May 2010, 13:51

To answer all these questions and more, I strongly reccommend JF's book "A view from the hover". Simple laymans explainations of lots of phenomena.

"intake momentum drag" sounds hideous but is relatively simple to understand. A jet engines thrust is actually a NET value, a summation of all the forces in the engine. The front fan creates significant drag, as the airflow entering the fan has to slow down considerably. This creates a force ahead of the centre of gravity, which, if the aircraft is allowed to yaw, will create an unstable situation whereby the force creates more yaw, which generates more force.

Of course, this yaw at slow speeds is combatted in the harrier using jets of bleed air, if the yaw force exceeds the reaction jet force, you are outside of restoring control to the Aircraft.

Thats how I understand it anyways!

BOAC

3rd May 2010, 15:27

'IMD' occurs on ALL jet engined aircraft with any angle of sideslip. It is the lack of directional stability from the fin at low IAS that causes VSTOL a/c to have this problem, and of course the Harrier experiences this 'force' much further forward on the fuselage than other a/c.

BrakingStop

3rd May 2010, 15:48

Intake Momentum Drag happens to all jet aircraft. If an ac is experiencing sideslip then the air being drawn into the intakes changes direction from the original relative airflow in order for it to pass directly into the intakes. This change of direction is a change of momentum and exerts a yawing moment on the side of the fuselage forward of the intakes. This yawing moment is IMD. At normal speeds (>120 kts) the tail has enough aerodynamic stability to overcome this yawing moment and so most normal ac don't observe any IMD. At slower speeds (30 - 120 kts) IMD can be a huge factor because the tail has little aerodynamic stability at these speeds. Once the yawing starts the pilot, if they catch it, is unlikely to have enough rudder authority (either aerodynamic or reaction control power) to stop the yaw from building and the ac will depart. IMD is avoided in the Harrier by keeping the vane straight (using rudder) and hence sideslip at zero. Alternatively, keep the AOA at zero, as has already been mentioned.

Standing-by to be corrected by JF.

BS

Trim Stab

3rd May 2010, 16:11

Critical period is 30K-120K

How does that effect carrier landings? Does the carrier have to sail at a speed and heading to keep the over-deck wind within certain limits?

Madbob

4th May 2010, 08:01

Tatare

NOD should also have mentioned FUEL, or more importantly the lack of it when down to hover weight.

On cool/cold day it is less of a problem but a hot one a VL might not even be possible but whatever the situation the trick is to keep the decel period to a minimum, establish over the pad, get into a stable descent and land without running out of fuel first!

Flashing lights certainly concentrate the mind.....

MB

lifts a gift

4th May 2010, 08:07

IMD, well explained by BS is not in itself a problem. It just makes the jet go sideways. The problem is that swept wings producing lift do not like to go sideways. The into wind wing loses sweep and Cl increases. The downwind wing has its effective sweep increased (and is shielded somewhat by the fuselage) and therefore loses lift. Result mega, rapid, uncontrollabe rolling moment. Not good during VSTOL.

The rolling moment depends on a) IAS b)alpha c) sideslip. Any one of these zero - no probs (no lift). Either b or c large and the other two small big probs.

Given that one must accel/decel through the 30-90 kt band where the jet is directionally unstable, and that to lift a war load wing lift is needed at these speeds b and or c must be minimised.

In my day in the GR1-3 8 to 10 units of alpha was reasonable 12 a bit gamey.

Sideslip is minimised by 1) Yaw autostabs 2)Rudder pedal shakers 3) HUD sideforce symbology and 4) THE VANE

Early signs of things going wrong are a lateral stick displacement to keep wings level. This is quite attention grabbing and the recovery actions are simultaneously 1. Rudder to get the vane straight. 2.Full pwr through the limiters to increase pwr of the 'puffers' and inc vertical lift thereby reducing AoA. 3. Stick fwd to reduce AoA. 4.Change trousers.

Hope this is of use. For all a/c but particularly the Bona-Jet

Lifts a Gift. But thrusts a MUST

Spon Clayton

4th May 2010, 10:02

Assymetric lift is the problem, as described above. Below about 30 KIAS there is no lift and assymetric zero is zero, thus no uncontrollable rolling moment. Zero alpha achieves the same effect-hence it is in the recovery drill.

Pontius

4th May 2010, 13:29

How does that effect carrier landings? Does the carrier have to sail at a speed and heading to keep the over-deck wind within certain limits?

Not a snag mate 'cos you're pointing into relative wind, so you don't get any of the nastiness described above. For instance, if the boat is sailing at 20kts into a 20kt wind then you'd have 40kts over the pad (I think the fisheads called it a deck). Now, this would take you into that dreaded band of IAS but it didn't matter because the wind would be aligned with the runway, your vane would be straight and your feet would be shaker-free.

Sometimes the cod faces enjoyed doing things which didn't involve the airfield being driven into wind and it could make things more interesting than your every day arrival. For instance, if you've got a tailwind on the boat from 45 degrees off the right side, then you'd come into the hover on relative bearing of 135, off the boat's front and vertically land facing that direction (and then have fun with the yellow shirts trying to park you).

Finally, IF it was all going for a can of worms and the boat HAD to face a particular direction AND you had to land from straight up the back of it, then the fisheads had a little spin-wheel where they could adjust their speed so the relative wind was within limits.

The real fun was when you were accelling and decelling during a display, with a 'challenging' on or off crowd wind. You obviously wanted to keep everything looking bona, so had to keep pointing down the crowd line but with the vane at 90 degrees and, if you hadn't already turned it off, the shakers going ten to the dozen. Quickest accells and decells I ever did (to get through the 'nasty' 30-120 regime).

Doesn't happen on a Boeing :)

Double Zero

4th May 2010, 13:46

On an unpleasant note for a minute, isn't 30 - 120kts pretty much the same regime as the AV-8A Stencel seat is regarded as extremely dodgy ?

You know, the Stencel which Art Nalls was forced to fit to Sea Harrier XZ439 after Martin Baker, in an inspired move, refused support ?! :ugh:

John Farley

5th May 2010, 09:43

A quote from page 80

The other problem stemmed from the intakes and meant that, if left to its own devices, a P1127 (or early Harriers) flying slower than about 100 kt wanted to go tail first. The pilot literally had to use his feet to keep the aircraft pointing into the airflow. This was directly analogous with the need for the pilot of a tail-dragger aeroplane to use his feet to stop it swinging and ground looping when landing, especially in a crosswind.

The reason for this was that the aerodynamic stabilising effects of the P1127 fin were no different from any other aircraft so faded away as one got slower. Unfortunately there was a destabilising force that increased as flying speed reduced and so defeated the residual efforts of the fin. This force was called intake momentum drag. It exists on all jet engine intakes and gets greater as rpm are increased. Thus whenever you were flying slowly and necessarily using jet lift not wing lift, up went your rpm and up went the intake momentum drag.

To understand why this destabilised the aircraft directionally we need to look at the airflow round the aircraft when viewed from above. In Fig 3 I have tried to indicate that everything is fine when the aircraft is pointing directly into the airflow.

Fig 3

http://img.photobucket.com/albums/v145/johnfarley/CH4F3.jpg

However, what happens if the aircraft starts travelling slightly sideways through the air because of a cross wind or a deliberate move by the pilot is shown in Fig 4.

Fig 4

http://img.photobucket.com/albums/v145/johnfarley/CH4F4.jpg

With the total airflow - represented by the blue arrow - now coming at an angle to the nose, we must think about its two components as shown. The green being that part which is straight on the nose and the red that part which is blowing directly across the nose.

The red arrow is of course the troublemaker because its effect is felt at the intake which is well ahead of the centre of gravity and so opposes the fin. Should the pilot allow the aircraft to swap ends and fly tail first you might think it would just be embarrassing for him because in his debrief he will be told to try harder on the rudder. Sadly he is unlikely to make the debrief because, at speeds greater than about 70 kt as the aircraft goes seriously sideways, the leading wing will generate much more lift than the other and the aircraft will roll out of control, thanks to what is termed ‘rolling moment due to sideslip’. Such asymmetric lift can easily swamp the aerodynamic and reaction controls.

Clearly some exotic technology was called for to help the pilot keep the aircraft pointing into the airflow. In fact all that was needed was a simple wind vane as seen on any church steeple. It is mounted in front of the pilot and always shows him where the airflow is coming from.

Later on Harriers were fitted with an artificial directional stability autostab (mid 70s) that helped keep the vane in the middle at mid transition speeds.

Re the Stencil seat this had an outstanding performance at low speeds because it used an explosive canopy spreading device which inflated the canopy quicker than the airflow could. The changeover speed between slow and highspeed modes was about 210 to 230 kts. The bad news was that if you got the low speed mode (with explosive spreading) at the top of the changeover band it might (might) break your neck. So either punch out above 250 kts or below 180 kts for a gentler ride. Not hard to organise as even gliding at 210 kts you could pull the nose up before ejecting.

Double Zero

5th May 2010, 13:23

Mr. Farley,

Please excuse me asking stupid questions; after all I usually do !

I take the hint that Art Nalls' seat may not be so dodgy after all, but can't help thinking Martin Baker scored a huge own goal for UK Ltd PR...

What's this 'canopy spreading' lark then, some sort of coaming level MDC ?

Thanks for the diagrams, most instructive for a pleb' like me ( who's only going to get near flying a Harrier via a simulator ).

Ta,

DZ

BOAC

5th May 2010, 15:58

How re-assuring and unusual to find so many people agreeing on something on PPRune:)

00 - John refers to parachute canopy, not a/c. The MDC was, I think unchanged from the (one that didn't quite work for me) GR3

A 1(spit) Sqn friend told me how rapidly they learnt when coming alongside Ark to use only bank to manoeuvre over the deck, and not to be tempted to turn the bona-jet 90 degrees across the 40kt wind to hover-taxy onto the spot...............................

Old-Duffer

5th May 2010, 16:19

....... to which BOAC and tartare refer was a development aircraft being flown by a Major Rosberg and it happened at a Brit Aerospace airfield (Dunsfold - I think).

All the test flights were filmed at the time, hence the loss of the pilot was clear for all to see. A few years later, the RAF sought permission to use the film as part of a flight safety film they were putting together and BAe refused. However, they relented subsequently.

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.

BOAC

5th May 2010, 16:47

O-D - I don't think I saw the film with 'Huggy Bear' in it, but the 'raw' footage was certainly shown on the OCU in the late 70's as a firm reminder.

NoHoverstop

5th May 2010, 18:03

Well of course with our HS 1174 we 'ad it tough...

Firstly, 'the book' says helpful things like "minimise sideslip when the ASI registers" (i.e. at all speeds above 'hover'). So as a boffin trying to turn that into something a computer can understand it helped to know the science behind an appropriate, formal, interpretation of 'minimise' and what sorts of min IAS the ASI would actually stir into life at (bearing in mind that the air data computer used real gears and cams to do its sums). Some helpful chaps had left a nice folder (marked "John Farley's Rolling Moments") of plots in an acquired filing cabinet and and summarised the worst cases into 1/2 roll-stick boundaries as functions of sideslip and incidence for different speeds from 30 kts upwards. We also put in a 'don't be silly' limit on the rudder, to limit the amount of 'you're only making it worse' rudder (and hence yaw puffer) that could be demanded by our whizzy flexible experimental flight control system in the worst bit of the transition region. Of course, it was allowed to do some of that in the name of flexibility; no point in paying good money for a high-authority FCS only to cut out massive chunks of that capability with over-cautious lines on graphs coded into software.

Testing it all was of course great fun. Having learned the lesson from the initial phase over Bedfordshire (debrief: "no, we don't know what sideslip you got to, the sensors were off-scale, why didn't you stop sooner?") we switched to the skies of Wiltshire; obviously one doesn't want to do this sort of testing near one's own house. Once sorted with a 'complete' clearance, it was then a case of sticking to one's guns when the control law designers complained that the software limits prevented their wonderful stuff from freely expressing itself. Well, mostly anyway. Again, going back to earlier experiences in Bedfordshire skies, it was apparent that having got safe limits to let us begin to see what we could really get computers to do for the next generation, we would then learn where it was useful to relax those limits. Sometimes this required the safety pilot to take the boffin for a hover and say "look, your limits are here...., but actually you can get away with THIS...". Discussions were kept short, mindful that over-prolonged debate would be terminated, permanently, by lack of fuel (so discussions in the hover over how much nozzling-out to allow were very brief indeed). All straightforward really. Then we had to extend the FCS clearance for take-offs and rolling landings. And ski-jumps (the aircraft isn't even properly flying when it leaves the ramp), and real shipboard ops etc etc. So really we were very fortunate that JF and his colleagues had done such a good job in understanding (and explaining) the nature of V/STOL and designing such a good jet in the first place :ok:

noprobs

5th May 2010, 20:01

To get back to the original question, it is important not to try to descend too slowly when near the ground. One major problem is hot air reingestion, which can lead to an engine surge. There is also some handling instability as all that thrust (which is a must) comes back up and hits the airframe. As the mainwheel touches down and starts to upset the weight/thrust balance, you then need to get rid of the thrust quickly, which jet engine fuel control systems generally don't cope with too well. The Pegasus therefore, even with the current twin, dual-channel digital system, needs a rapid-acting mechanical fuel flow relief system to make it happen.

IMD is a whole other area that has been discussed at length on this forum, but JF's diagram does help to simplify the root cause. The resultant roll is the real killer. If by skill or luck you avoid it, the outcome may be acceptable. I have seen Harriers doing inadvertent 360 degree (or in one case 450 degree) yawing turns during a decell and then land safely. Incidentally, IMD can also occur in pitch, as other jet pilots have found out to their cost, specifically with over-enthusiastic take-offs. As to JF's backwards formation lead, as a Harrier pilot, I found it a little less amazing than his continuous yawing flight along the line of the runway. One thing to beware of in rearward flight is the reversed action of the tailplane (elevator). While the reaction controls continue to work in the natural sense, a high reversing speed can lead to the canard-like tailplane acting such that rearward control column movement (relative to the pilot) produces a nose-down pitching moment.

Rudder pedal shakers and yaw stabs do help to keep you out of trouble, but few mechanical devices are trouble-free. When yaw stabs were still a novelty, I well remember taking off from a narrow strip that had very tall jungle close to each side of it. Shortly after lift-off, the system decided that it needed to demand maximum yaw, giving me a very impressive view of the trees before I booted the rudder back the other way!

But at least life in that cramped cockpit was never boring.

jimgriff

6th May 2010, 08:02

Double Zero- Ballistic canopy spreaders are a pyrotechnic device where the base of the canopy is "shot" out in all directions (360*) by small "bullets" attatched to the shroud lines /canopy base by a "gun" which is timed to fire when the chute has reached full stretch but not yet full of air.
Normal parachutes use airflow to "inflate" the chute but sometimes this can prove too slow when there is insufficient airflow going into the chute to inflate it as happens with very slow speed ejections.
The balistic spreader "forces" the mouth of the chute open to catch any availible air in the chute at low speed.
Can be a complicated proceedure and yet another "widget" to worry about when you need a system to work flawlessly 100% of the time.

Helmut Mann

4th Mar 2014, 13:02

Hi All,

My apologies for digging up an old thread.

I am beginning a scratch build scale AV8B and I have a question which research on the web hasn't answered for me. If anyone can assist I'd be grateful:

I understand there are puffer jets on the wingtips of the Harrier for roll control during the hover. My guess is there are also jets on the nose and/or tail for pitch. Is this correct?

Is there also a puffer jet or pair of jets for yaw?

LowObservable

4th Mar 2014, 13:26

I recall reading a Raymond Baxter account of a sortie in G-VTOL that started with JF's famous/infamous takeoff, and JF's safety brief, which included a warning that Baxter would not hear EJECT more than once...

cornish-stormrider

4th Mar 2014, 13:44

Kudos to digging up this thread
I never realised how much of a handful the harrier was, and why the jockeys regarded themselves as the creme de menthe,

A heartfelt RIP to all those it bit, and congrats to all who made it safely to the end of their time on the jet

Moreover I do declare this thread to be fascinating and such deserves the accolade of
"Science, bitch "

KG86

4th Mar 2014, 14:52

Mention of the various fatals above reminds me of a rumour that was rife in RAFG in the 80s.

The German F104 had so many fatal accidents that it was nicknamed the 'widow maker'. But I was led to believe that the accident 'rate' for the Harrier GR1/3 was, percentage-wise, worse than the F104.

BOAC

4th Mar 2014, 15:46

Helmut - you have been ignored!!

Yes, nose and tail for pitch and 2xtail for yaw.

thing

4th Mar 2014, 15:53

But I was led to believe that the accident 'rate' for the Harrier GR1/3 was, percentage-wise, worse than the F104. Percentage losses for all RAF Harriers was much higher than the F104, I seem to remember a figure of over a half were lost although I'm willing to be corrected on that.

Interestingly the Luftwaffe F104 percentage loss rate was around 30%, around the same as the Lightning and only slightly more than the RAF Phantom which panned out at around 28%.

Having said that the Luftwaffe had I think nearly 900 F104's so 30% of that is a lot of tin.

John Farley

4th Mar 2014, 16:04

Helmut

Yep, there are puffers for all three axes.

http://img.photobucket.com/albums/v145/johnfarley/Puffers_zps6a9e7390.jpg

The shutters are mechanically connected to the relevant aerodynamic surface so the effect is that the aircraft responds to stick and rudder in the hover as if it was flying conventioally. Magic. The front puffer is connected to the stick and opens if you pull back.

The air to the puffer system is turned off mecanically with nozzle angles less than 20 deg. So the pilot does not have to do anything - like remember to turn it on when slowing down.

kg86.

One can be led to believe all sorts of things in this life......

While here may I say that the Harrier has many unsung advantages. To name but three you can aim weapons very accurately in the hover (although best limited to targets such as hospitals or women and children queuing for soup) if the taget does fire back you can of course retreat while still facing the enemy (useful for some nations) but propbably best of all leading a display team by flying backwards means you can see just how well they are doing.

http://img.photobucket.com/albums/v145/johnfarley/heloteam_zpsdc3d5e92.jpg

Wander00

4th Mar 2014, 16:12

ISTR Gnat attrition was pretty high, and may have been at least part of the reason for re-introducing the Hunter at Valley, unfortunately about 3 or 4 courses after I had left.

dctyke

4th Mar 2014, 17:01

bonajet

5th Mar 2014, 03:35

You are correct "thing" - of the first 110 ordered up to XZ445 in 1979, I think 60 were lost, or 54%. By XZ999 at the end of 82 it was 67 out of 134 or 50%. The F104 has always got a bad press due to the large number in service.

Wholigan

5th Mar 2014, 06:39

You may perhaps be interested in this discussion of the F104 accidents back in 2005.

http://www.pprune.org/military-aircrew/203620-f-104-accidents.html

bonajet

5th Mar 2014, 07:53

Thanks RW, I hadn't read that thread. Lots of good stuff. The Aug 79 F104 crash at Yeovilton was, rumour has it, because the Display Control asked the pilot to complete his display quickly. He did.

Helmut Mann

5th Mar 2014, 09:44

Thank you BOAC and John, that is what I hoped to see. Good work! It shouldn't be too hard from here..... ;)

Does anyone know what the two ventral strakes are for as shown in this image? Sorry I can't link to the image itself. Some sort of tech issue.

http://upload.wikimedia.org/wikipedia/commons/f/f6/Harrier_AV-8B_banking_left,_revealing_under-fuselage_section.jpg

John Farley

5th Mar 2014, 09:56

Helmut

As easy one. They are called LIDS (lift improvement devices) and are fitted to all Harrier II aircraft if the guns are not being carried. They give about 1400 lb more VTO lift capability by trapping the so called 'fountain' of exhaust air that bounces back off the ground and goes up towards the fuselage. If in your pic the gear had been down you would have also seen the cross dam that comes down in front of the stakes making a three sided box to contain the fountain. The LIDS work well to about 8ft wheel height by which time you have upwards momentum and can corry on with the lift and into the transition. The other postive effect once you have started to go up from the ground is that the temp of the air finding its way into the intakes reduces with corresponding increase in thrust (some 100lb per deg C).

Dan Gerous

5th Mar 2014, 09:57

I'm sure someone will be along to answer it correctly Helmut, but as I had it explained to me once, it is an air dam. When the wheels are down, they, along with the strakes, make an enclosed area, which provides an air cushion, which helps with vertical landing. They either had to have these, or the gun packs fitted permanently.

Thanks to all who provided techy explanations in this thread, it was very interesting and easily understood.

(John beat me to it, and explains it better.)

Trim Stab

5th Mar 2014, 09:59

Thanks RW, I hadn't read that thread. Lots of good stuff. The Aug 79 F104 crash at Yeovilton was, rumour has it, because the Display Control asked the pilot to complete his display quickly. He did.

Wasn't the Harrier crash at Kandahar also allegedly partly because the controller asked him to "expedite" on finals?

Fox3WheresMyBanana

5th Mar 2014, 10:22

The shutters are mechanically connected to the relevant aerodynamic surface

But if one of those mechanical connections becomes disconnected, life in the transition gets quite interesting.....:ooh:

Tigger_Too

5th Mar 2014, 10:27

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.

Helmut Mann

5th Mar 2014, 10:37

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.

orca

5th Mar 2014, 18:36

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.

AutoBit

6th Mar 2014, 03:39

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!!!

MSOCS

6th Mar 2014, 06:29

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!

Courtney Mil

6th Mar 2014, 09:02

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.

Engines

6th Mar 2014, 10:25

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

Rocket2

6th Mar 2014, 14:28

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?

Flap62

6th Mar 2014, 14:31

The HP and LP spools rotated in opposite directions to minimise gyroscopic effects.

John Farley

6th Mar 2014, 15:12

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.

Engines

6th Mar 2014, 15:52

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

John Farley

6th Mar 2014, 17:40

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.

ex-fast-jets

6th Mar 2014, 18:45

:{

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!!:)

orca

6th Mar 2014, 19:32

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!;)

John Farley

7th Mar 2014, 10:04

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.

Wander00

7th Mar 2014, 10:24

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.

noprobs

7th Mar 2014, 10:25

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.

John Farley

7th Mar 2014, 11:07

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.

Pontius

7th Mar 2014, 11:18

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 :ok:

LowObservable

7th Mar 2014, 13:55

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.

John Farley

7th Mar 2014, 14:47

LowObservable

Dunno why the type of landing should affect the tyres - unless of course you are trying to keep below a wheel/tyre RPM limit at very high conventional touchdown speeds.

sandiego89

7th Mar 2014, 15:31

I believe the F-35B has been experiencing high wear rates on the tyres/tires. The B has a different tire maker than the A and C models. Perhaps a design or manufacturing issue. I wonder if heat from V/STOL operations and the rough non-skid on deck contributes to the high wear rates.

Good article here: http://defensetech.org/2013/09/19/5th-generation-fighter-1st-generation-tires/

Engines

7th Mar 2014, 15:40

JF, Guys,

During the F-35 weight reduction effort all three variants were looking for pounds to lose and the landing gear came under scrutiny. (yes, should have been done during design first time around but LM didn't have a Chief Designer at that time and they took their eyes off the weight ball).

Anyhow, it was found that some conservative assumptions had been made for landing speeds, weights, temperatures, surfaces, runway lengths, repeated landings etc., which had led to fairly chunky wheel and brake units. On further examination, the LM team found some new tyres (I think they were French) that offered good performance with significant weight reductions. I think that they ended up with three tyre types for A B and C, choices driven by conventional landing weights/usage spectra. Brake units were also tailored across the three variants (remember that the F-35A and C had serious weight issues as well).

So, the main balance for F-35B was to provide the best possible conventional landing braking performance (and tyre life) while keeping weight down as much as possible, driven by the need to achieve the mandated Vertical Lift Bring Back (VLBB) figure.

Hope this helps a little

Engines

John Farley

7th Mar 2014, 17:14

Engines

Many thanks.

JF

orca

7th Mar 2014, 18:30

Noprobs,

I think the crude device was termed the Pressure Drop Regulator...pushes spectacles up nose with right trigger finger...it was certainly PDR on all the diagrams.

Helmut Mann

8th Mar 2014, 19:50

Some great info here, thanks guys.

I was looking at a pic of the Harrier (II, I think) with the gear extended and I note the nose gear doors are closed at the tyre end of the system but the leg end is obviously open around the pivot end of the leg with a very tight opening allowed around the leg. Why is this? Does the door-closed system prevent damage to internal systems (eg Hydraulics) during the vertical take off or landing, from FOD produced by the downward thrust or is there something more to it?

achillesat23

13th Mar 2014, 12:22

Dear john farley sir....

I am one of harrier frs mk 51 operators from india.... recently in one of the aircraft during AMTFi noticed a peculiar problem.... the details are as follows...

1. During trim checks... at 450 knots, with mid flaps.. the rudder and aileron trim is out by half gauge width... with nozzles aft and undearriage up... however... during 190 knots with flaps mid, nozzles aft, uc down the trim required is neutral...

we carried out rigging and took her up again.... now the defect reversed... ie at 450 neutral trim and at 190 knots trim reqd is high...

2. Another observation that, at any speed during straight and level flight, just by increasing engine speed and with no increase in speed the aircraft is rolling to left....and on decrease in engine rpm the aircraft is rolling to right....

we are trying to find a solution but unable to find any reasons.... could pls suggest some ideas as to why it should happen....we ecently changed the engine.... previously there was no defect.... regards

John Farley

13th Mar 2014, 18:49

achillesat23

Poor you! Over the years there have been many cases of odd trim changes.

When you think about it there are so many things that can affect the trim of a Harrier aircraft that it is amazing that there are two aircraft the same!

However you say you carried out rigging checks but not if you changed anything or things. So I would suggest the following:

Make sure the aerodymamic control surfaces are rigged within limits including the flaps when in the mid position.

Carry out the 450 knot check carefully and adjust the gauges as necessary to indicate zero on both.

From now on only adjust/change one thing per flight

If you are still unhappy with the 190kt gear down, flaps mid and nozzles aft situation look at your engine options.

Individual nozzle angles when aft selected. (having a rear one down even a little can change a lot of flow at the back end)

If these angles need changing re fly and do the 450 check and adjust again.

If still unhappy:

Swop the front nozzles (L/R)

Reset the 450 kts as required.

Finally - and this is the most likely cause of the confusion - swop the rear nozzles. These of course contain the engine trimmers which have been known to significantly affect overall aircraft trim with changing RPM at constant IAS. We have also found moving a trimmer's position in its own nozzle can also help.

Reset the 450 kts as required because in the end of course what really matters is the 450 kt trim setting as this affects gun aiming accuracy.

Good luck!

JF

Dan Gerous

14th Mar 2014, 12:07

Helmut, have you recently acquired a Harrier, without an owners manual?

Hawker Siddeley/Bae Harrier Manual: An insight into owning, flying and maintaining the legendary 'Jump Jet' Owners Workshop Manual: Amazon.co.uk: Denis Calvert, Brian Johnstone MBE, Technical Consultant: Books

achillesat23

19th Aug 2015, 16:05

Dear John sir..

In first place I would like to convey my apology for not getting back on the harried unintended roll issues as I had got transferred out shortly there after...

A brief on the previous problem.. We had carried out all kinds of combinations as you suggested and with no result we were about to name "the rogue" as the rogue again... However the problem was solved by replacement of fin.. Which to our surprise the least suspected part... The aircraft is still up in the air and she is as beautiful... Just did a 90deg turn during hover and landed her...

Thank you sir...

Courtney Mil

19th Aug 2015, 16:23

Thank goodness. I've been worrying about that for a year and a half now.

achillesat23

19th Aug 2015, 16:25

Dear john sir...

We are presently at the final phase of Harrier operations and are faced with new problems.. Till date the Harrier never ceases to amaze me with respect to its capability and technical brilliance this aircraft posses...

Coming to the issue at hand...

Presently the engines that are being rolled out of the overhaul facility are sitting close to high margins due to use of various components including turbine... Notwithstanding they are within test bed acceptable limits...

However, when installed on aircraft... The hover performance values are sitting extremely high at Wh -7(minus 7) and Jpt of +40.... Which is completely out of the graph itself... We are faced with the dilemma...

The fact that I am again back as Sqn Harrier Eng Officer forces me to look to various factors and forces me to think out of the box ideas to sustain the jets for some more time...

My concerns and questions are as follows:

1. What does the hover performance indicate with regard to overall health of the engine... (The case in point is.. Though the perf hover values are high.. The ELR counts are less.. It eats abt 3 to 5 per normal sortie.. That's in Indian conditions )

2. Can the aircraft/ engine still be exploited with such hover values primarily for non VSTOL flight regimes keeping VLanding to completley minimal (beggers can't be choosers.. So is the question )

3. We had 3 engine surges during PRL checks in last one year... Is it anyway connected to poor hover performance leading to poor perfoance of the engine through out normal flight envelop...

These things have not been answered in publications and manuals.. It becomes imperative to draw conclusions... The primary aim being not to reject an engine without proper reason... The case in point being... VSTOl opeartions are not that imp as we are trying to sustain this beauty just for few more months...

Your valuable inputs will be greatly appreciated sir... Hope I haven't made a fool of myself asking this... On the lighter side sir...

Regards... Probably Last Engineer of Legacy Jumpjets... Achilles...

achillesat23

19th Aug 2015, 16:29

Ha-ha.. Thanx a lot for concern and extremely sorry for late reply.... Loved to see you remembering abt the problem....

peterperfect

24th Oct 2016, 19:41

Going through an old photo album recently I found this unusual shot of a Sea Harrier on RFA Olwen, I'm guessing its John F ? Love to hear any good tales of trials flying off a flight deck that small !

cornish-stormrider

25th Oct 2016, 11:56

Nice to see that the bona jet is still out there and you are still having the old fun n games trying to keep it in the air

TEEEJ

25th Oct 2016, 12:25

Nice to see that the bona jet is still out there and you are still having the old fun n games trying to keep it in the air

The Indian Navy retired the Sea Harrier during May 2016. Replaced by the MiG-29K.

The illustrious and unique Sea Harriers of Indian Naval Air Squadron (INAS 300) were given a befitting farewell in a function organised at INS Hansa, Goa on Wednesday.

The function was attended by Admiral RK Dhowan, Chief of the Naval Staff, Vice Admiral Sunil Lanba, Flag Officer Commanding in Chief Western Naval Command, serving and retired Officers and men of the Indian Navy and all personnel who have served in the INAS 300.

.....

In appreciation of the faithful service to the nation by INAS 300 'White Tigers', an impressive ceremony was held today which saw the Sea Harriers fly for one last time, and MiG-29K flanking their outgoing cousins and ceremoniously taking their place.

The air display included supersonic pass by MiG 29s and formation flying by two each Sea Harriers and MiG 29Ks.

The composite air display symbolized a smooth transition from the old to the new in continuance with the proud legacy of the INAS 300.

On completion of the Air display, 'washing down of the Sea Harriers' was carried out in a traditional manner. A first day cover was also released by Admiral RK Dhowan to mark the occasion.

Indian Navy bids farewell to iconic Sea Harrier, welcomes MIG-29K fighter jets | Latest News & Updates at Daily News & Analysis (http://www.dnaindia.com/india/report-indian-navy-bids-farewell-to-iconic-sea-harrier-welcomes-mig-29k-fighter-jets-2211408)