High accident rates in light twins an alternative?
in a WAT limited FAR 23 twin your NOT trying to climb your trying to do a -shall we say a ''controlled arrival''---nothing is worse than a mishandled twin---except, you can stretch your 'glide' in this case--at Vyse...that's it... no guarantees otherwise---that's far 23
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Pugilistic animus
The proof of the pudding is in the eating IT WORKS! and is another option before you take to the trees. You can always still take to the trees if it doesnt :-)
pace
The proof of the pudding is in the eating IT WORKS! and is another option before you take to the trees. You can always still take to the trees if it doesnt :-)
pace
To clear up a few points yes it is obvious that the faster you go the more drag there will be, not in question.
VYSE is the speed set in the climb where on one engine you have minumum drag and the best speed to make the maximum climb possible.
Absoluttely. Being trying to get that across to you. Now, if the BEST rate of climb is zero, what rate of climb will you get if you fly faster (I'll give you a hint, it starts with a minus sign.)
I am shown graphs designed at a single engine climb and power from an engine and these are used to rubbish cruise. Fair enough but then that in itself is a blinkered misconception.
Wizofox fails to respond with the scientific/ aerodynamic reasononing for the above and gets out of it by demanding I answer irrelevent questions to the arguement of his first.
My guess not being a scientist is that in any climb situation there is only one energy source available and that is the remaining engine. That remaining engine has NO assistance from Kinetic energy as the aircraft and engine are in a negative situation. The remaining engine trying to drag the aircraft skywards and in the process making the most of the process by selecting a minimum drag profile and speed.
So Wizofox with all your knowledge please enlighten me to the relevant scientific facts of why a twin will fly happily for hours on one But will not climb?
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Pace - scimming through your posts I think you may have a misunderstanding as to what kinetic energy is. Kinetic energy is a form of energy that an object has by reason of its motion. The kind of motion may be translation (motion along a path from one place to another), rotation about an axis, vibration, or any combination of motions. The total kinetic energy of a body or system is equal to the sum of the kinetic energies resulting from each type of motion. The kinetic energy of an object depends on its mass and velocity. For instance, the amount of kinetic energy KE of an object in translational motion is equal to one-half the product of its mass m and the square of its velocity v, or KE = 1/2mv^2.
Both these statements are incorrect. Hoover maintains the kinetic energy state of his aircraft (speed is the only thing he has control over since its mass is fixed) by using his potential energy, which is the altitude available to him. When Wiz sticks the nose of his 777 down it accelerates because he is using up some of the potential energy available to him by virtue of his altitude. He is trading altitude to increase the kinetic energy of his aircraft (ie speed), but in doing so he is losing potential energy (height).
Bob Hoover looping his twin using nothing but Kinetic energy
leaves cruise thrust set and descends his aircraft will accelerate due to Kinetic energy plus his thrust
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The second engine may also go out while dealing with the first if, for example it is a fuel problem. If this were the case then a pilot will need all the potential energy he can translate.
Yes I agree that adopting the cruise attitude and airspeed would make it things easier but I would prefer to perform a blue line climb just incase the second goes.
Yes I agree that adopting the cruise attitude and airspeed would make it things easier but I would prefer to perform a blue line climb just incase the second goes.
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Im a little confused by all this discussion.
The blue line will give you the most efficient single engine Climb provided you havent modified your aircraft heavily - its been tested to exhaustion by the manufacturer.
If you cant reach the blue line on one engine at your present angle of attack, flatten your climb until you can reach it, and then increase climb to maintain. Do not turn or even breathe before youve reached it. If you have to flatten your climb until you're level to just make the blue line - that is bad.
If you cant reach the blue line even in level flight - that is worse: youre going down; find a good place so as not to bend her too much.
Thats about all there is to it.
regards, OORW
The blue line will give you the most efficient single engine Climb provided you havent modified your aircraft heavily - its been tested to exhaustion by the manufacturer.
If you cant reach the blue line on one engine at your present angle of attack, flatten your climb until you can reach it, and then increase climb to maintain. Do not turn or even breathe before youve reached it. If you have to flatten your climb until you're level to just make the blue line - that is bad.
If you cant reach the blue line even in level flight - that is worse: youre going down; find a good place so as not to bend her too much.
Thats about all there is to it.
regards, OORW
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Mr Runway
Rather than reducing AoA a little at a time, isn't it safer to establish level flight first, then nibble at a climb? Seems like the proper sequence to me. Allowing for terrain clearance certainly. Level flight isn't necessarily "bad". It is what it is if that's what it is. You're sequentially trying to stay ahead of Stall, rather than chasing it from the safety of green flight.
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---and loving it---because I have more fun watching the students hang on to their youtube debating in my class room than my occasional jet jobs--- because -I love myself and I'm special- and everybody likes me---but most important like Lester I don't care!!!PA--Maytag Man
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>Easy, it won't. If it won't climb at Vyse, it won't cruise at any other speed. Simple<
Wizofox
I think I know what you are getting at! If you have max power on the remaining engine, Are holding blue line speed and have no climb then you will not be able to accelerate without loosing altitude. That I accept.
But lets take this further by using a different scenario. You decide to give up and make a forced landing. You shut down the good engine and become a glider to the nearest field.
You now control your speed with pitch. Ie you pitch for speed. You take whatever descent rate that gives to maintain your VREF and whatever profile.
(The 777 forced landing at Heathrow where they landed short both engines out) You now have only Kinetic or (potential energy) to power the aircraft.
Had you kept the other engine going you would have whatever power/energy that produced plus the Kinetic/or potential energy or Mickey Mouse energy or whatver you want to call it in pitching down.
Lets take an aircraft where the manufacturers claim no single engine climb at all ie no VYSE . ie the De havilland dragon rapide. Yet the aircraft will cruise level at single engine cruise if you loose it in the cruise. You say impossible as if it will not climb at VYSE it will not cruise level at any speed above that? So how come?
So we know that engine out like the 777 crash at Heathrow we have enough energy to maintain a VREF but we do not have enough energy to maintain level flight with one engine going if we can accelerate to single angine cruise by trading altitude for speed?
So in your books in that situation ie blue line and no climb at max power on the remaining engine. When you pitch for single engine cruise the speed will bleed back off to blue line?
But if at VYSE it even shows 50fpm you will be fine at a single engine cruise?
I can easely test this on my next twin flight. All I have to do is simulate an engine failure at say 2000 feet for safety (the plane does not know if its at 2000 feet or 500 feet) I then pitch for blue line and reduce the power until I get no climb or descent but maintain blue line.
No matter what I do with pitch looosing altitude in the process to get single engine cruise the aircraft will descend to the ground with that power setting selected?
Ok give me a couple of weeks and I will make a new thread here with the results include pitch angles, speeds, altitude lost etc as this is not what I see real world.
It is easy to google scientific calculations but there is something missing in those calculations as it is fact that light twins will cruise easely on one but will not climb easely on one.
I have shut down and feathered one engine for real on a few occasions at cruise but would not like to do that in the climb.
I for one am not happy with the explanations given here to what I have experienced for real and know to be true. This thread seems to be full of ego massaging and point scoring rather than a desire to get at the truth. I am happy to back down if I am wrong but as yet???
Pace
Wizofox
I think I know what you are getting at! If you have max power on the remaining engine, Are holding blue line speed and have no climb then you will not be able to accelerate without loosing altitude. That I accept.
But lets take this further by using a different scenario. You decide to give up and make a forced landing. You shut down the good engine and become a glider to the nearest field.
You now control your speed with pitch. Ie you pitch for speed. You take whatever descent rate that gives to maintain your VREF and whatever profile.
(The 777 forced landing at Heathrow where they landed short both engines out) You now have only Kinetic or (potential energy) to power the aircraft.
Had you kept the other engine going you would have whatever power/energy that produced plus the Kinetic/or potential energy or Mickey Mouse energy or whatver you want to call it in pitching down.
Lets take an aircraft where the manufacturers claim no single engine climb at all ie no VYSE . ie the De havilland dragon rapide. Yet the aircraft will cruise level at single engine cruise if you loose it in the cruise. You say impossible as if it will not climb at VYSE it will not cruise level at any speed above that? So how come?
So we know that engine out like the 777 crash at Heathrow we have enough energy to maintain a VREF but we do not have enough energy to maintain level flight with one engine going if we can accelerate to single angine cruise by trading altitude for speed?
So in your books in that situation ie blue line and no climb at max power on the remaining engine. When you pitch for single engine cruise the speed will bleed back off to blue line?
But if at VYSE it even shows 50fpm you will be fine at a single engine cruise?
I can easely test this on my next twin flight. All I have to do is simulate an engine failure at say 2000 feet for safety (the plane does not know if its at 2000 feet or 500 feet) I then pitch for blue line and reduce the power until I get no climb or descent but maintain blue line.
No matter what I do with pitch looosing altitude in the process to get single engine cruise the aircraft will descend to the ground with that power setting selected?
Ok give me a couple of weeks and I will make a new thread here with the results include pitch angles, speeds, altitude lost etc as this is not what I see real world.
It is easy to google scientific calculations but there is something missing in those calculations as it is fact that light twins will cruise easely on one but will not climb easely on one.
I have shut down and feathered one engine for real on a few occasions at cruise but would not like to do that in the climb.
I for one am not happy with the explanations given here to what I have experienced for real and know to be true. This thread seems to be full of ego massaging and point scoring rather than a desire to get at the truth. I am happy to back down if I am wrong but as yet???
Pace
Last edited by Pace; 3rd Jun 2008 at 00:39.
AND if you attach a rocket you could climb SE at VN
E, if you please, but You'll need a huge twin tail
Lester
E, if you please, but You'll need a huge twin tailLester
Last edited by Pugilistic Animus; 3rd Jun 2008 at 00:56.
Please do Pace.
Set yourself up on one, then reduce power so you are only holding altitude at Vyse. If you are light this will be a few knots below blue line (which is Vyse at MTOW), so experiment to find the speed which allows you to maintain height with minimum power.
Now, with that power set, do your bunt manoeuvre. You will have a height loss, a temporary increase in speed, but then, to maintain height, you will indeed bleed back to your min power speed again.
Next, set that same speed up and put in enough power for, say, a 200' per min climb. Now level off (no need to lose height) and accelerate to SE cruise. It will be a substantial increase in speed.
The error you are making is in your concept that the aircraft is somehow "Helped" by having more kinetic energy. The ONLY source of energy in a powered aircraft in level flight is it's engines.If it only produces enough power to hold level flight at minimum speed, that's the only energy you have. You can tap the potential energy of your height, but once it's gone, it's gone. Your increased kinetic energy is then robbed by the increase in drag because of the higher speed.
By the way, the Dragon Rapide would not maintain height in single engine cruise OR climb.
Set yourself up on one, then reduce power so you are only holding altitude at Vyse. If you are light this will be a few knots below blue line (which is Vyse at MTOW), so experiment to find the speed which allows you to maintain height with minimum power.
Now, with that power set, do your bunt manoeuvre. You will have a height loss, a temporary increase in speed, but then, to maintain height, you will indeed bleed back to your min power speed again.
Next, set that same speed up and put in enough power for, say, a 200' per min climb. Now level off (no need to lose height) and accelerate to SE cruise. It will be a substantial increase in speed.
The error you are making is in your concept that the aircraft is somehow "Helped" by having more kinetic energy. The ONLY source of energy in a powered aircraft in level flight is it's engines.If it only produces enough power to hold level flight at minimum speed, that's the only energy you have. You can tap the potential energy of your height, but once it's gone, it's gone. Your increased kinetic energy is then robbed by the increase in drag because of the higher speed.
By the way, the Dragon Rapide would not maintain height in single engine cruise OR climb.
Pace,
I'm going to just add one thought here to try and get the point across.
Do you agree (assuming our relationship is amicable enough to allow me to ask questions!!) that an aircraft which is not climbing or descending is flying level?
So, we are dealing with an aircraft that is in level flight with full SE power at Vyse (and, let's face it, that's BETTER than some light twins will do!!).
You are then suggesting that the same aircraft, with the same power, will ALSO fly level at some different, higher speed. You initially seemed to indicated you believed this was because the aircraft produced less drag at the higher speed, but now seem to concede this is not the case, so how do you believe this is possible?
Can you, in your Citation, fly at two different level speeds for the same power settings? Don't think so.Why should a twin on one be any different?
I'm going to just add one thought here to try and get the point across.
Do you agree (assuming our relationship is amicable enough to allow me to ask questions!!) that an aircraft which is not climbing or descending is flying level?
So, we are dealing with an aircraft that is in level flight with full SE power at Vyse (and, let's face it, that's BETTER than some light twins will do!!).
You are then suggesting that the same aircraft, with the same power, will ALSO fly level at some different, higher speed. You initially seemed to indicated you believed this was because the aircraft produced less drag at the higher speed, but now seem to concede this is not the case, so how do you believe this is possible?
Can you, in your Citation, fly at two different level speeds for the same power settings? Don't think so.Why should a twin on one be any different?
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Wizofox
Of course we are amicable :-) i will run these tests but yes I think I will get the results that you are indicating as I have always had a climb at VYSE when going level and it may have been my interpretation which has been wrong ;-)
Addendum
This nevertheless does not negate going for level flight as another option for these reasons.
Firstly in the climb at VYSE your margins are small ie get down draughts, turbulence, distractions, poor piloting skills and it is very easy to loose that target speed and start going into coffin corner. Less speed, more control inputs more AOA, more induced drag and no speed safety margins.
While I appreciate that you cannot create speed if you are only flying level with max power at VYSE, if you do get a climb even a small climb that can be exchanged for cruise speed by leveliing off. With that extra speed in level flight your controls are not all crossed over. You do not have as much aeleron or rudder in put. You do not have such a dead feeling unresponsive aircraft.
So with minimal climb converting that to level cruise is a much more comfortable situation with more margins for error. As your speed builds to say 125 kts in cruise use the trim wheel to climb.take a taget speed well above VYSE say 105 kts allow the speed to bleed off in that climb until it comes back to 105 kts then trim forward again for level flight. Allow the speed to build again to 125kts and again trim for a kinetic energy assisted climb again.
I wish someone would try this and report back as it is a lot more comfortable in a light twin and I believe has less room for error and hence the high engine out accident rates using conventional methods in low performance twins.
Take care
Pace
Of course we are amicable :-) i will run these tests but yes I think I will get the results that you are indicating as I have always had a climb at VYSE when going level and it may have been my interpretation which has been wrong ;-)
Addendum
This nevertheless does not negate going for level flight as another option for these reasons.
Firstly in the climb at VYSE your margins are small ie get down draughts, turbulence, distractions, poor piloting skills and it is very easy to loose that target speed and start going into coffin corner. Less speed, more control inputs more AOA, more induced drag and no speed safety margins.
While I appreciate that you cannot create speed if you are only flying level with max power at VYSE, if you do get a climb even a small climb that can be exchanged for cruise speed by leveliing off. With that extra speed in level flight your controls are not all crossed over. You do not have as much aeleron or rudder in put. You do not have such a dead feeling unresponsive aircraft.
So with minimal climb converting that to level cruise is a much more comfortable situation with more margins for error. As your speed builds to say 125 kts in cruise use the trim wheel to climb.take a taget speed well above VYSE say 105 kts allow the speed to bleed off in that climb until it comes back to 105 kts then trim forward again for level flight. Allow the speed to build again to 125kts and again trim for a kinetic energy assisted climb again.
I wish someone would try this and report back as it is a lot more comfortable in a light twin and I believe has less room for error and hence the high engine out accident rates using conventional methods in low performance twins.
Take care
Pace
Last edited by Pace; 3rd Jun 2008 at 11:01.
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Airfoilmod
I see what youre getting at. Yes of course, you are correct. If I was doing a practice single engine climb from, say, 1000 ft I would do exactly that: stable in level flight first, and them try climbing and see what happens.
In fact I remember doing just that in days past, and even using a speed slightly higher than blueline specially if it was slightly bumpy, because I knew that if you got too slow, much bad karma would result. (To be honest, engine out on a light twin prop is just not a nice feeling, even if you can get 500ft/m on a plane which isnt heavy)
In a real failure on takeoff, I would however not do that. Chances are that there are trees rushing at you, and you must get air between you and the ground ASAP. That means blue line (or because I'm chicken, slightly faster).
Wizofoz, you are right, in fact I think NO light twin can maintain level at a higher altitude, if it is not almost empty. If you want to cross mountains at say, 16000 ft, you must plan very carefully so you know which way to turn at what point, if one engine gives, and you need to drift down at 150-200 ft/min.
regards, OORW
In fact I remember doing just that in days past, and even using a speed slightly higher than blueline specially if it was slightly bumpy, because I knew that if you got too slow, much bad karma would result. (To be honest, engine out on a light twin prop is just not a nice feeling, even if you can get 500ft/m on a plane which isnt heavy)
In a real failure on takeoff, I would however not do that. Chances are that there are trees rushing at you, and you must get air between you and the ground ASAP. That means blue line (or because I'm chicken, slightly faster).
Wizofoz, you are right, in fact I think NO light twin can maintain level at a higher altitude, if it is not almost empty. If you want to cross mountains at say, 16000 ft, you must plan very carefully so you know which way to turn at what point, if one engine gives, and you need to drift down at 150-200 ft/min.
regards, OORW
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Wizofox
With your expertise we got there in the end :-) Now I am off thurs to Florida to ferry a Citation S2 back to the uk so will be out of the loop until Sunday after tomorrow. I can even play around with step climbs or energy climbs at high level but with a reasonable climb on both to get level cruise to step ;-)
Pace
With your expertise we got there in the end :-) Now I am off thurs to Florida to ferry a Citation S2 back to the uk so will be out of the loop until Sunday after tomorrow. I can even play around with step climbs or energy climbs at high level but with a reasonable climb on both to get level cruise to step ;-)
Pace
Last edited by Pace; 3rd Jun 2008 at 13:13.
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If you are flying at blue line on your ASI on anything other than an ISA day at MAUW you are flying too fast and will not get the best rate of climb.
You should really calculate the new blue line speed before you go as part of your perf calcs. It can be as much as 10% different.
eg
MAUW = 3000lb and Vyse = 88kts
Actual wt = 2000lb
new Vyse = Old Vyse x sqroot(Actual wt/MAUW)
new Vyse = 88 x sqrt (2000/3000)
new Vyse = 88 x 0.8
new Vyse = 71kts
so if you fly at 88kt you have speed in hand therefore climb rate in hand
You should really calculate the new blue line speed before you go as part of your perf calcs. It can be as much as 10% different.
eg
MAUW = 3000lb and Vyse = 88kts
Actual wt = 2000lb
new Vyse = Old Vyse x sqroot(Actual wt/MAUW)
new Vyse = 88 x sqrt (2000/3000)
new Vyse = 88 x 0.8
new Vyse = 71kts
so if you fly at 88kt you have speed in hand therefore climb rate in hand
