Quick question for a Harrier driver, or JF
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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
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.
Last edited by CirrusF; 6th Oct 2008 at 11:37.
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But dropping chaff would be something else.
Per Ardua ad Astraeus
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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...........
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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!
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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.
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
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!
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!
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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?"
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?"
Avoid imitations
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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.
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.
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.
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ShyTorque
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
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
Easier than hovering the Gazelle at 50 feet, as we used to do when teaching baby Harrier pilots how to do it.
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
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
Avoid imitations
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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
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
Do a Hover - it avoids G
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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.
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.
Do a Hover - it avoids G
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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
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
