Lifting Nosewheel on T/O - Why So?
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Lifting Nosewheel on T/O - Why So?
It seems that lifting the nosewheel off the bitumen at a certain speed was de rigueur on early British jets, certainly the Comet and Vampire. In the Comet case the procedure was responsible for the first two crashes, and brought about the introduction of the Vr call concept. The question is, what was the thinking behind the lifting of the nosewheel? Particularly in the case of the Comet, if there are any drivers from that era reading. Was it the same on the Canberra and V-Bombers?
Thanks in advance to all.
Thanks in advance to all.
From the Meteor F 8 Pilot's Notes:"Ease the nosewheel off the ground at approximately 90 knots; the aircraft will unstick at 110 - 120 knots with 1/2 flap down" - i.e. present the wings to the airflow at the appropriate angle of attack and the aircraft will fly off when it is ready. Of note a couple of paragraphs later it states: "The safety speed is 150 knots (155 knots on aircraft with large intakes)". This speed is usually known as V2 therefore between 120 and 150 you would not be able to control the yaw following an engine failure and would have to throttle the live engine back and land ahead!!
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On the Vampire you lifted the nosewheel to prevent Nose Wheel Shimmy which was pretty fierce. On the T11 if you got shimmy the instruments became unreadable. On the Vulcan B2 with the 301 engines we called Rotate but it was going to go up whether you liked it or not (unless you pushed the control column forward).
ACW
ACW
Minimum take off roll.
Keeping the nose wheel on the ground reduces induced drag so the aircraft accelerates faster and reaches take off speed sooner with less runway, tyre wear, engine life, etc.
Rotating at about 15 knots before calculated take off speed enables the pilot to pull off the aircraft smoothly without snatching and risk scraping the tail.
At least that is what I was told at my Valiant conversion course in 1962.
Keeping the nose wheel on the ground reduces induced drag so the aircraft accelerates faster and reaches take off speed sooner with less runway, tyre wear, engine life, etc.
Rotating at about 15 knots before calculated take off speed enables the pilot to pull off the aircraft smoothly without snatching and risk scraping the tail.
At least that is what I was told at my Valiant conversion course in 1962.
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Hmmm, that technique is likely to causes a tail scrape on most modern passenger jets and even if it doesn't, the extra drag will significantly increase takeoff roll.
As demonstrated all those years ago, not a great idea on big jets because of drag rise.
I'd guess, less of a problem on props because the propwash directs the airflow along the chordline of the wing.
Re rate of rotation, never ceased to surprise me how many captains, who should have known better, rotated too fast. It wasn't due to lack of training or comment by trainers.
ORAC, I'm guessing yer man in the B727 was:
a) Trying too hard for a smooth touchdown. (Hate it when that happens)
b) Avoiding nosewheel banging along on a less than smooth surface. (I usually just put one wheel each side of the lights
)
Time he politely told the boss some facts about big jet handling. Although, TBH, at their TO mass they can probably get away with it.
I'd guess, less of a problem on props because the propwash directs the airflow along the chordline of the wing.
Re rate of rotation, never ceased to surprise me how many captains, who should have known better, rotated too fast. It wasn't due to lack of training or comment by trainers.
ORAC, I'm guessing yer man in the B727 was:
a) Trying too hard for a smooth touchdown. (Hate it when that happens)
b) Avoiding nosewheel banging along on a less than smooth surface. (I usually just put one wheel each side of the lights
)Time he politely told the boss some facts about big jet handling. Although, TBH, at their TO mass they can probably get away with it.
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Early mark Canberra PNs didn't call it Vr but originally said that the nose should be raised 5kt before the calculated unstick speed, and they did warn that allowing the nose to rise earlier would extend the T/O run. Eventually it dawned on someone that the gap between unstick and Vmca could be reduced a bit by keeping the nosewheel on the runway for longer. Unfortunately tyre limitations meant that the nosewheel had to be raised at not more than 140kt, which was still way below Vmca.
As an aside, why are the relevant speeds called out as V1 and V2 on some types, and as "decision" and "rotate" on others? The latter terms were always used on the Victor, whereas I recall V1 and V2 being used when I flew as "supernumerary crew" on various RAF transport types.
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I may have missed something
Thanks for the Vampire shimmy explanation.
Lifting Nosewheel on T/O - Why So?
Could the ONLY reason for lifting the nose wheel on T/O possibly be the avoidance of water/slush ingestion into engine intakes, particularly rear mounted engines ? This was a technique used by SAS DC9s in the past to prevent such an occurrence.
The strategy was limited to raising the nose wheel only about six inches from a contaminated runway until Vr was called from whence the T/O was SOP. And it worked very well on the shorter -10s and -20s.
You will of course be aware that the later DC9-30s and MD80s marks were fitted with a nosewheel deflector plate to reduce the directing of any runway contamination into the engines.
I also accept all your arguments regarding degraded performance, possible tail strikes and possible loss of directional control in the event of an engine failure !
The strategy was limited to raising the nose wheel only about six inches from a contaminated runway until Vr was called from whence the T/O was SOP. And it worked very well on the shorter -10s and -20s.
You will of course be aware that the later DC9-30s and MD80s marks were fitted with a nosewheel deflector plate to reduce the directing of any runway contamination into the engines.
I also accept all your arguments regarding degraded performance, possible tail strikes and possible loss of directional control in the event of an engine failure !
The film Cone of Silence gives a good insight into the hazards facing early jet airliner operation. The 'Phoenix' (Avro Olympus-Ashton) aircraft flown in the film suffer a number of accidents due to the nosewheel being raised too early - exactly as happened in some early Comet accidents.
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On the Dominie the nosewheel tyres were 'chined' so as to throw any standing water/spray sideways and away from the rear mounted intakes.
You might be interested in what D P Davies had to say about the Comet 1. Start at around 46mins - but the rest is rather good too!
You can listen to all his interviews here, they are ALL well worth listening to:-
D P Davies interviews on certificating aircraft
You can listen to all his interviews here, they are ALL well worth listening to:-
D P Davies interviews on certificating aircraft