Take-off technique in light singles and twins
iAnother aircraft that can get quite exciting if the failure occurs at Vr is the MU2. No way can you safely fly that thing away from just off the ground with an engine failure. Yet to my mind - treated with due respect - the MU2 is the best light turboprop ever built.
I am a little confused about your references to V1 and Vr in regard to the MU2.
It has been many moons since I flew the MU2 and I never had the benefit of simulator on that type, so I will defer to those with greater experience on type.
My point is that some manufacturers of light turbines recommend rotation speeds that are sometimes implied to be equal to a V1, when in fact they are such thing. In fact using the term Vr is something of a misnomer too, as by definition Vr can only be equal to, or greater than V1.
The MU2 was touted as being semi STOL, rough field capable and was indeed a good bush aeroplane in the right hands, but the big split between recommended ‘unstick’ or Vlof (more appropriate terms?) and blue line meant there was a short period when you could be airborne but seriously compromised if an engine failed.
My point is that some manufacturers of light turbines recommend rotation speeds that are sometimes implied to be equal to a V1, when in fact they are such thing. In fact using the term Vr is something of a misnomer too, as by definition Vr can only be equal to, or greater than V1.
The MU2 was touted as being semi STOL, rough field capable and was indeed a good bush aeroplane in the right hands, but the big split between recommended ‘unstick’ or Vlof (more appropriate terms?) and blue line meant there was a short period when you could be airborne but seriously compromised if an engine failed.
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but the big split between recommended ‘unstick’ or Vlof (more appropriate terms?) and blue line meant there was a short period when you could be airborne but seriously compromised if an engine failed.
The RAAF had that problem with the introduction of twin jet aircraft like the Canberra bomber and Meteor fighter. Depending on weight typically the Canberra had a recommended lift off speed of 110 knots and a safe asymmetric speed of 160 knots at full load. The Meteor was similar. These numbers are off the top of my head and from memory so could be inaccurate.
Either way there could be a 40-50 knot spread between recommended lift-off speed and where, if an engine failed, the pilot had to make a decision to either reduce power on the live engine to help maintain rudder effectiveness (directional yaw) and hope the aircraft could still climb out albeit reduced rate of climb - or running out of rudder and risk rolling on its back. That spread of speeds was known as the dead man's gap.
The only other solution if an engine failed below single engine ‘safety’ speed was to force land straight ahead under control and pray there were no obstacles.
In the case of GA light twins, the spread (or dead man's gap) between POH lift-off speed and Blue Line is usually around 10-15 knots. You either accepted the miniscule risk of losing an engine inside those few seconds between airborne and single safety speed or you pulled up stumps and went home. .
So much depends on the flying skill of individual pilots and their technical knowledge of the single engine performance of each particular aircraft they flew.
Some pilots had their own personal ideas such as holding the aircraft on the runway until lifting off at single engine safety speed or ‘Blue Line’ speed. That could bring in other factors such as a high speed abort if an engine packs up just as you reach blue line while still on the runway. Examples are does the aircraft have anti-skid brakes? Is the runway wet therefore less braking efficiency?
Faced with so many variables some pilots may prefer to stick with POH recommended VR or lift off speed and accept that, unlike airliners certified to have a V1 and Vr capability, there will always be a window of indecision of a few seconds until reaching airborne blue line speed.
Last edited by Centaurus; 7th May 2020 at 04:43.
It has been many moons since I flew the MU2 and I never had the benefit of simulator on that type, so I will defer to those with greater experience on type.
My point is that some manufacturers of light turbines recommend rotation speeds that are sometimes implied to be equal to a V1, when in fact they are such thing. In fact using the term Vr is something of a misnomer too, as by definition Vr can only be equal to, or greater than V1.
The MU2 was touted as being semi STOL, rough field capable and was indeed a good bush aeroplane in the right hands, but the big split between recommended ‘unstick’ or Vlof (more appropriate terms?) and blue line meant there was a short period when you could be airborne but seriously compromised if an engine failed.
My point is that some manufacturers of light turbines recommend rotation speeds that are sometimes implied to be equal to a V1, when in fact they are such thing. In fact using the term Vr is something of a misnomer too, as by definition Vr can only be equal to, or greater than V1.
The MU2 was touted as being semi STOL, rough field capable and was indeed a good bush aeroplane in the right hands, but the big split between recommended ‘unstick’ or Vlof (more appropriate terms?) and blue line meant there was a short period when you could be airborne but seriously compromised if an engine failed.
We know that V1, Vr and V2 give guarantees, at least on paper, of achieving certain abilities to stop, go and climb out at required gradients and are calculated for each and every take off and for a current set of conditions. Aircraft below 12,500lbs (5700kgs) however had only one guarantee and that was at sometime it had been demonstrated that it could achieve a 1% climb gradient at 5000' at ISA with one engine inoperative to achieve certification. P charts were provided to calculate take off and landing distances with all engines operating.
In the case of the MU2 many speeds were published like Vs, Vmca, TOSS and Blueline. TOSS (110kts) only meant acceptable margins above VS and Vmca for T/O configuration, it didn't mean much else. Blue line speed (152kts) was best climb speed, clean, at Max TOW, it didn't mention best rate or best angle of climb
It was unfortunate that sim training was not easily available for all MU2 pilots, at least once. An new MU2-B-60 was over a $1m USD in 1980, insurance around $40K per year yet $ 3000 was considered too much to send a pilot off for a week to Flight Safety, it would have been the best investment operators could make. Thats GA though, I was in it for long enough.
Centaurus, I am not sure of certification requirements for military aircraft. But I imagine an ejector seat negates any serious considerations.
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That short period after airborne and attaining blue line speed (usually about 10 seconds) applies to many light piston and turbo prop twins.
The RAAF had that problem with the introduction of twin jet aircraft like the Canberra bomber and Meteor fighter. Depending on weight typically the Canberra had a recommended lift off speed of 110 knots and a safe asymmetric speed of 160 knots at full load. The Meteor was similar. These numbers are off the top of my head and from memory so could be inaccurate.
Either way there could be a 40-50 knot spread between recommended lift-off speed and where, if an engine failed, the pilot had to make a decision to either reduce power on the live engine to help maintain rudder effectiveness (directional yaw) and hope the aircraft could still climb out albeit reduced rate of climb - or running out of rudder and risk rolling on its back. That spread of speeds was known as the dead man's gap.
The only other solution if an engine failed below single engine ‘safety’ speed was to force land straight ahead under control and pray there were no obstacles.
In the case of GA light twins, the spread (or dead man's gap) between POH lift-off speed and Blue Line is usually around 10-15 knots. You either accepted the miniscule risk of losing an engine inside those few seconds between airborne and single safety speed or you pulled up stumps and went home. .
So much depends on the flying skill of individual pilots and their technical knowledge of the single engine performance of each particular aircraft they flew.
Some pilots had their own personal ideas such as holding the aircraft on the runway until lifting off at single engine safety speed or ‘Blue Line’ speed. That could bring in other factors such as a high speed abort if an engine packs up just as you reach blue line while still on the runway. Examples are does the aircraft have anti-skid brakes? Is the runway wet therefore less braking efficiency?
Faced with so many variables some pilots may prefer to stick with POH recommended VR or lift off speed and accept that, unlike airliners certified to have a V1 and Vr capability, there will always be a window of indecision of a few seconds until reaching airborne blue line speed.
The RAAF had that problem with the introduction of twin jet aircraft like the Canberra bomber and Meteor fighter. Depending on weight typically the Canberra had a recommended lift off speed of 110 knots and a safe asymmetric speed of 160 knots at full load. The Meteor was similar. These numbers are off the top of my head and from memory so could be inaccurate.
Either way there could be a 40-50 knot spread between recommended lift-off speed and where, if an engine failed, the pilot had to make a decision to either reduce power on the live engine to help maintain rudder effectiveness (directional yaw) and hope the aircraft could still climb out albeit reduced rate of climb - or running out of rudder and risk rolling on its back. That spread of speeds was known as the dead man's gap.
The only other solution if an engine failed below single engine ‘safety’ speed was to force land straight ahead under control and pray there were no obstacles.
In the case of GA light twins, the spread (or dead man's gap) between POH lift-off speed and Blue Line is usually around 10-15 knots. You either accepted the miniscule risk of losing an engine inside those few seconds between airborne and single safety speed or you pulled up stumps and went home. .
So much depends on the flying skill of individual pilots and their technical knowledge of the single engine performance of each particular aircraft they flew.
Some pilots had their own personal ideas such as holding the aircraft on the runway until lifting off at single engine safety speed or ‘Blue Line’ speed. That could bring in other factors such as a high speed abort if an engine packs up just as you reach blue line while still on the runway. Examples are does the aircraft have anti-skid brakes? Is the runway wet therefore less braking efficiency?
Faced with so many variables some pilots may prefer to stick with POH recommended VR or lift off speed and accept that, unlike airliners certified to have a V1 and Vr capability, there will always be a window of indecision of a few seconds until reaching airborne blue line speed.
