Quick question for a Harrier driver, or JF

[GeeRam]

Unless this is classified.....:confused:

Not fussed about which version, and assume clean config, just curious as to what's the approx max ceiling in the hover......??

No reason other than to settle a 'bloke in a pub said' type arguement :p

[Airborne Aircrew]

I'm not a Harrier Pilot... But I played one once on the radio... :}

It's all about density altitude really... What's the temp and pressure at the location of your attempt? :8

[LowObservable]

Interesting question - since there would be no reason to do it (unless you wanted to vanish from your adversary's Doppler mode), has anyone ever hovered a puffer-jet higher than the starting point for the vertical landing descent?

[GeeRam]

Laddo was watching the thing with James May the other day obviously and so he chimes in with this absolute gem…..

A Harrier can only hover when close to the ground as because of levitation……

After composing myself and ceasing laughing I tried to explain that they only hover close to the ground as that’s really the only time they need to hover……

So, me thinking that messers Bedford, Merryweather and Farley etc must have tried a max altitude hover at some point during trials it would be easy to look up and point laddo in the right direction……but apparently not, hence I thought I’d offer said subject to those that might know or hazard an educated guess.

I vaguely seem to remember Harrier demos of years gone by when a rotating hover climb used to be done up to a few thou’ ish….??

[SammySu]

Two separate issues here. A 107 engined jet will confortably hover at 3500-4000ft AMSL. However it's only easy to do this when you are close to the ground so you have some visual references to look at. (though physical interaction with the ground is of no relevance). So if you are at a high altitude airfield then no problem. Try decelling to the hover at 3500ft AGL and things are more tricky - no visual reference for position or drift and substantially stronger winds to consider - bearing in mind the IMD issues between 90-30kts - normally a recipe for a departure.
I have seen a jet VTO'd straight to circuit height before - but that was a calm day!
JF will be able to give you all the detail.

[Tourist]

Stronger winds not an issue if no visual reference

[SammySu]

Not interested in wind speed effects on holding a steady hover position over the ground, but on windspeed / relative airflow effects and the avoidance of intake momentum drag during the decel, ie being able to keep the vane straight vs available control power. When close to the ground its easier to "see" the wind direction and fly an into wind decel, or to visually correct during a cross wind decel, which I would aim to avoid much above 35kts, - at height it's harder to know if you are crosswind and the wind is stronger.....

[Modern Elmo]

Interesting question - since there would be no reason to do it (unless you wanted to vanish from your adversary's Doppler mode), has anyone ever hovered a puffer-jet ...

That wouldn't work with an up to date radar, L. O.

[Tourist]

If not visual ground, then wind unless gusty is effectively zero in your hover transition.

ie you are hovering relative to the air not the ground.

[Smoketoomuch]

And what's the RoC in vertical level flight?

I seem to remember there was a competiton; brakes off to 5000 feet, and the Harrier beat all-comers. Correct?

[sycamore]

Given the same weight I think a Chinook would leave a Harrier for dead,even a Seaking.even with the brakes on

[ShyTorque]

And what's the RoC in vertical level flight?


It's exactly zero.

This hovering away from the ground is obviously so difficult; how on earth do those helicopter pilots do it?

[Flap62]

Shy Torque,

It probably doesn't matter to a helo if they are close to the dead stop hover so 30kts sideways at 3000ft is no big deal. Intake Momentum Drag in the Harrier means that either building up a ood deal of sideslip (or even too much reverse speed) can cause all sorts of problems.

Tourist.

So how can you tell when you're in the dead stop hover relative to the airmass around you? IAS stops indicating at 30kts and the vane ain't a lot of use.

[NigelOnDraft]

From a technical / performance pov, the value and caveat given by SammySu above are consistent ;)

NoD

[BOAC]

We really need JF here, but as NoD says, SS is spot on. Having tried to reduce to a semi-hover at height (to confuse my opponent:)) I merely succeeded in exceeding the yaw parameters and significantly confused myself as I dramatically fell, out of control, to the sound of much guffawing...............:)

[Tourist]

Flap.

No argueing about the difficulty level of the hover, just pointing out that if you are not using visual references on the ground, wind is irrelevant.
In the same way that in a hot air balloon it does not matter once clear of the ground how much wind there is. 1 kt or 200 kts it is always calm in the basket.

[BOAC]

Tourist - make yourself a coffee and have a quiet think about how much control you have over your airspeed in a balloon:)

[Pontius]

BOAC,

I thought when you were on the Bona Jet the Montgolfier brothers were hanging out in Stamford. Is this why you know about balloons :O

General readers,

I too tried to exercise my amateur test pilot skills (all in the interest of learning my aircraft's capabilities you understand) and see when the donk ran out of puff. In the scenario suggested by SammySU (i.e. nil wind) I VTO'd and kept going up until I didn't any more (if that makes any sense). The mighty 104 engined FRS1 got to about 2500' before it decided to stop climbing. A similar experiment in a II+ got me to a decent shade over about 4000'. I think the latter would have been more impressive but I seem to recall the temperature being pretty high.

I'm not the owner of an ETPS strain guage, so don't know if these experiments (sorry envelope explorations) would be considered valid, but it might be enough for the original poster's question for the man down the pub.

[Tourist]

BOAC

You miss the point.

Once in flight, the only things effecting the airframe are gravity and airflow over the airframe. Groundspeed and drift are aerodynamically of zero importance.
For example, if you have a 100kt wind and you fly into it at 100kts your groundspeed is zero but if you fly with the wind your grounspeed is 200kts. In both cases however, the aircraft will react in exactly the same way, with exactly the same accelerations if you pull back the stick.
This is basic relativity. We, and this goes for everything from a R22 to the Space shuttle(in the atmosphere!), fly relative to the air, not the ground
The only time ground has any relevance, is when we give it relevance by trying to land or hover by visual references for example. In these circumstances we are deliberately flying out of balance to match a visual picture.

In the example above when there are no visual references, I stand by my assertion that windspeed is irrelevant.

[BOAC]

drift are aerodynamically of zero importance. - actually, of all the things to talk about, that has the potential to kill you - sorry, T, but you need to do a bit of reading about the Harrier. Research JF's excellent article and re-read SammySu's posts, particularly #7? The beast is a bit different to R22s and Space Shuttles.

Pontius - I was a relative latecomer to the GR3, and by the time I got there, they had advanced to balloons with oars for propulsion and more 'interesting' things used to happen in Stamford:). Reckon your exploit was quite brave too! No sign of limiters tripped, perchance.....:ok:

[CirrusF]

actually, of all the things to talk about, that has the potential to kill you - sorry, T, but you need to do a bit of reading about the Harrier

Tourist was talking about drift relative to ground, and he is correct. Drift relative to ground won't effect Harrier hover, as long as (from what I have read) there is no or little transverse airflow over the aircraft. It is perfectly possible to have a very significant sideways drift relative to the ground, yet have zero transverse airflow over the aircraft.

A similar experiment in a II+ got me to a decent shade over about 4000'. I think the latter would have been more impressive but I seem to recall the temperature being pretty high.

How do they recover at Kandahar then? IIRC the airfield is 4500' AMSL, and density altitude presumably a lot higher on a typical day in summer. I wouldn't expect ground-effect to give a signifcant assist in a Harrier.

[Wader2]

Interesting question - since there would be no reason to do it (unless you wanted to vanish from your adversary's Doppler mode), has anyone ever hovered a puffer-jet ...

That wouldn't work with an up to date radar, L. O.

Or with a very old pulse one either.

But dropping chaff would be something else.

[BOAC]

CirrusF - you are quite correct. It is a pity that the word 'drift' came into play, really, although one assumes that the original question was about a hover relative to the ground? There are, of course, 2 sorts of 'high hover', both extremely difficult to achieve in a Harrier, the 'relative to the airmass' (ie zero airspeed) one being impossible to identify due to lack of an airspeed reading below 30kts and both 'dodgy' due to intake momentum drag. Best left to the experts like JF etc. I expect GeeRam has by now got bored and sideslipped his way back to the pub...........:)

[CirrusF]

Could you not hypothetically use the GPS readout as a reference? I have succeeded in "hovering" a light aircraft at F120 in mountain waves in south of France using the GPS as a reference. After a few minutes of practise I managed to register zero ground-speed at my assigned flight level. I was flying IFR at the time so the Marseille controller was a little bit perturbed when the dot on her screen stopped moving!

[Pontius]

How do they recover at Kandahar then? IIRC the airfield is 4500' AMSL, and density altitude presumably a lot higher on a typical day in summer. I wouldn't expect ground-effect to give a signifcant assist in a Harrier.

I can't say definitely what they do because I've never been there and never done it. However, having operated in the deserts of Arizona and Nevada, where it was a just a tad warm, I would speculate that the Kandahar boys do not bother trying to hover. If the strip is long enough (I have absolutely no idea how long it is) I would suggest they might wobbly nozzle it. If they need to land slowish, then a rolling vertical landing would probably be the order of the day. As I said, I've never been there so am not trying to say that IS how it's done, just saying how it might based on 'in my day' operations :rolleyes:

Having said all that, I do recall a nice, tedious story for the insomniacs ;). We were mucking around dropping things in the Fallon ranges and were operating from Fallon which, I seem to remember was some way above sea level (but nothing like the numbers suggested for Kandahar). The OAT was 110-115F (well, they were American toys) and I recall looking down at my VSTOL performance page of the II+ and seeing hover weights of about 1700lbs dry and 2500lbs wet. My gob was well and truly smacked, especially as the day-attack beasts were falling from the sky. Someone with an idea about these things later explained 1161 engine (or whatever it was) really came into its own when the temps really got up, as opposed to more normal temps where it didn't make a HUGE amount of difference (quite a bit but not as noticeable as the desert experience). Perhaps this quirk of engineering helps the chaps in sunny Afghanistan.


BOAC,

Limiters!! How could you suggest such a thing, sir. No, I saved those for the 7th wave off the pointy(ish) end of the boat, when it all went for a ball of chalk worms :O

[SammySu]

Cirrus

My favourite trick in the mighty Tucano was to find some nice Yorkshire lee wave, put the flaps down, slow to min IAS and then watch the Tacan range increase whilst flying inbound towards the beacon - confused ATC no end! However despite the fact that I was going backwards relative to the ground I was of course still flying forwards at about 65kts relative to the air mass.

This is the crux of the above debate. In all other flying machines attaining a hover relative to the ground or zero airspeed still involves getting lift from an aerofoil - tourist you are of course hanging from the ones rotating above your head. Hence you are still aerodynamically in control in the hover, hanging from your rotating wings.

In the Harrier I am not getting any aerodynamic lift - instead I am opposing gravity with vertical jet thrust. I am not aerodynamically in control in the hover, control is purely by bleed air reaction controls. Consider yourself as a plate being spun on top of a stick as you balance on 4 columns of air. If there is zero wind then all is well. If there is any wind and it comes from anywhere other than directly on my nose then the action of that airflow as it is straightened to flow down my large and ugly intakes causes a yawing and then rolling moment - Intake Momentum Drag. Above 30 kts windspeed this yawing and rolling moment becomes a greater force than my flying controls (jet reaction controls) can counter = uncontrollable rolling departure. Above about 90 kts my converntional aerodynamic flying controls become powerful enough again to counter IMD effects.

Hence in the critical band of 90-30kts I really, really, want to minimise sideslip. Close to the ground I have visual cues, a nice wind vane and some even better pedal shakers to warn me. At altitude I still have all these things, but the visual cues are nigh impossible to see, the stronger winds mean that a small gust or change in direction can flip my vane to the 90 (30 kt wind backing by 20 deg close to the ground has a smaller side component and therefore controllable effect compared to a 70 kt wind doing the same at altitude) and the pedal shakers merely inform me what I should have done before the world started rotating.

Establishing a high hover is very difficult, zero knots can be achieved in a push over but I want to avoid even the tiniest amount of sideslip, for the reasons given above.

In Kandahar we land in exactly the same way as we land everywhere else.

Nice to have a thread thats actually about flying, rather than petty banter and whingeing!

[CirrusF]

Perhaps more of a question for JF, but is one of the reasons for the very pronounced anhedral of the Harrier wing to reduce roll divergence in the hover transition?

To continue the subject of trying to confuse ATC, I once rather naughtily looped a Fuji while flying along an IFR airway in southern Germany. Most controllers would have had a "wtf" moment, but not the Germans - "and ze next time you try ze looping you ask me first, ok?"

[BOAC]

........there was me thinking it was so the outriggers would reach the ground.:E

[CirrusF]

Yep I'd overlooked that possibility! Serves me right for wasting so much time at university :)

[ShyTorque]

Shy Torque,
It probably doesn't matter to a helo if they are close to the dead stop hover so 30kts sideways at 3000ft is no big deal.

Flaps62, then again, it might do. Perhaps one day maybe I'll learn more about helicopters. :oh:

I did get a go in a two seater Harrier once - it was relatively easy to hover. Easier than hovering the Gazelle at 50 feet, as we used to do when teaching baby Harrier pilots how to do it.

[GeeRam]

I expect GeeRam has by now got bored and sideslipped his way back to the pub...........

:)

Not bored at all :ok:

[NigelOnDraft]

ShyTorque Easier than hovering the Gazelle at 50 feet, as we used to do when teaching baby Harrier pilots how to do it.Actually "hovering" the thing ain't too bad... It was getting to that "hover", and over a tiny pad, when you only had a window of a minute or two to do so (OK maybe extended by 60s of water!) and establish that hover over a 70'x 70' pad, and land.

I'm glad you showed baby Harrier pilots how to do it... My Gazelle mate muttered something about avoid curves, refused to hover at 70', and we chased sheep for 6 hours :D

As also stated above, the 90K-30K phase was what killed people, and ironically the Harrier II could be more difficult in the decel, because those big wings kept working until well into that phase before losing all lift abrubtly :{

NoD

[ShyTorque]

NoD, Yes, I understand the transition was the tricky bit. A failure of a wing puffer duct control killed a good friend of mine (NS) as I drove through the main gate at EDUO, to begin my rotary tour there.

P.s. 70ft x 70 ft to land on? Sheer luxury. We used to have big "Harrier" fore and aft and lateral markers set up, more difficult than real flying ;)

[John Farley]

This started as a simple performance question – how high can you hover?

Since the thrust available must equal your weight we need to consider both. How light could you make a modern jet? Dunno modern empty weights but probably about 17000lb with only a little fuel and certainly less than 18000 I would guess.

Thrust varies due to pressure and temp – the Pegasus family loose/gain thrust at about 100lb per deg C and 13lb per millibar so you can do your own exciting sums on the effect of altitude on the thrust available with the modern big donk being around 24000lb at sea level.

But don’t get too carried away because the engine must stay below about 108% corrected RPM (corrected RPM being cockpit gauge RPM divided by the square root of the absolute temperature outside and it is also limited to 104% to 107% on the cockpit gauge depending on the version of donk).

For mates who are used to the conventional corrected limit being a fair bit below 108 (as arranged by the PRL) that is so that you can yank the stick back to 15ADD and do a hot reslam at the same time. If you are hovering you are pulling bleed (very good for improving the surge margin) hence the 108 number. I have been to 110 corrected and 108% cockpit gauge on a VTO because the engine designer (John Dale) said I would never surge it with bleed on and the fan would not fly apart until probably 112% on the RPM gauge and we were looking at throttle chops in the hover to get a feel for attitude changes that might happen if the donk stopped. Not being other than a controlled coward that required the aircraft to be going up through 3-400 ft following a v good go from VTO.

If you want a wild guess based on the modern big donk and a clean light jet I would think over 5000ft up an alp. The last three words matter.

If you were not alongside an alp you would not be able to tell you were in the hover as the instrument information is not adequate to tell you that.
BOAC is dead right about watch the aerodynamics as you slow down (both AOA and sideslip) as with the wrong combination of these between say 40 and 120 kts you will roll uncontrollably and as everyone knows not much comes down faster than a Harrier with its jets pointing upwards.

[John Farley]

Oh dear Oh dear

I have just read my post again - big boob.

For absolute temperature read relative temperature (or theta) as it is normally writ.

I am clearly not up to this stuff any more and need ploughing in.

JF

[Tourist]

We had all noticed your mistake and were just being polite, honest......