High accident rates in light twins an alternative?
Join Date: Mar 2008
Location: USA
Age: 48
Posts: 71
Likes: 0
Received 0 Likes
on
0 Posts
Pace:
Sorry but the Wiz is right on this one (but never mind the man behind the curtain! - sorry, couldn't resist). When you do flight test to determine Vy, you do climb testing at various airspeeds and construct the total drag curve shown in the reference he cited. The bottom of that curve is Vy and it gets published in the books. Vyse is determined in a similar manner with one engine out which automatically takes into account the added drag of using rudder to counteract the yaw moment. So there's no way to reduce drag by deviating from the blueline speed. Hence, if you're not able to climb at Vyse, reducing your AOA is going to result in a loss in altitude that you will not be able to regain. Not a good situation.
However, what I think your fighter jock friend was getting at is that for many airplanes, the bottom of that curve is rather flat. That means that if you have a little excess power available (i.e. a positive rate of climb at Vyse), you might be able to gain a significant amount of airspeed if you level off. But this effect can - and probably does - vary quite a bit between aircraft. On some it might work great. On others, it might not be worth it. Therefore it's not something you could teach folks to do unless you were willing to submit to requiring a type rating each aircraft.
Sorry but the Wiz is right on this one (but never mind the man behind the curtain! - sorry, couldn't resist). When you do flight test to determine Vy, you do climb testing at various airspeeds and construct the total drag curve shown in the reference he cited. The bottom of that curve is Vy and it gets published in the books. Vyse is determined in a similar manner with one engine out which automatically takes into account the added drag of using rudder to counteract the yaw moment. So there's no way to reduce drag by deviating from the blueline speed. Hence, if you're not able to climb at Vyse, reducing your AOA is going to result in a loss in altitude that you will not be able to regain. Not a good situation.
However, what I think your fighter jock friend was getting at is that for many airplanes, the bottom of that curve is rather flat. That means that if you have a little excess power available (i.e. a positive rate of climb at Vyse), you might be able to gain a significant amount of airspeed if you level off. But this effect can - and probably does - vary quite a bit between aircraft. On some it might work great. On others, it might not be worth it. Therefore it's not something you could teach folks to do unless you were willing to submit to requiring a type rating each aircraft.
Thanks Gr8, There"s no place like home!!
Pace,
One big difference between Skydivers (1200 jumps and an AFF rating, just by the way!!) and aeroplanes is that skydivers don't have engines!! Aeroplanes don't have "Terminal velocities". They accelerate until the total drag (which, we've established, INCREASES as speed increases at any speed above Dmin) is equal to the thrust.
I think you may be acknowledging that the best performance is indeed achieved at Vyse. What you then suggest, i.e that the problem is that at any speed below that, drag increases, is totally valid. If you have excess performance, indeed it may be wise to use it to climb at a higher speed, thus increasing your margins over the bottom of the drag curve. This will, however, lead to a reduced climb rate. If the terrain makes this acceptable, then it may be fine as a technique.
You did, however, indicate that you believe the aircrafts total drag reduced and performance increased at speeds in excess of Vyse and, I think I've shown, this is simply false.
Pace,
One big difference between Skydivers (1200 jumps and an AFF rating, just by the way!!) and aeroplanes is that skydivers don't have engines!! Aeroplanes don't have "Terminal velocities". They accelerate until the total drag (which, we've established, INCREASES as speed increases at any speed above Dmin) is equal to the thrust.
I think you may be acknowledging that the best performance is indeed achieved at Vyse. What you then suggest, i.e that the problem is that at any speed below that, drag increases, is totally valid. If you have excess performance, indeed it may be wise to use it to climb at a higher speed, thus increasing your margins over the bottom of the drag curve. This will, however, lead to a reduced climb rate. If the terrain makes this acceptable, then it may be fine as a technique.
You did, however, indicate that you believe the aircrafts total drag reduced and performance increased at speeds in excess of Vyse and, I think I've shown, this is simply false.
Thread Starter
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes
on
0 Posts
Wizofox
>One big difference between Skydivers (1200 jumps and an AFF rating, just by the way!!) and aeroplanes is that skydivers don't have engines!! Aeroplanes don't have "Terminal velocities <
Firstly aeroplanes most certainly DO have terminal velocities!!! and sky divers most certainly DO have engines :-) Ok not in the conventional sense but in the Kinetic energy they are using returning earthbound and which was created hoisting them skybound. In the same sense a glider has an engine in its Kinetic energy which was created pulling it skybound and which is on tap to the glider pilot through the joystick earthbound. the joystick is his throttle if you like.
No again :-) Put in simple terms as I am a practical sort of pilot and not a mathematician what do you do if you are holding blue line, you are at 400 to 500 feet and rather than getting a climb your VSI and altitude are going down?
You either panic as do many low time twin pilots and pull back trying to get a climb and go into coffin corner or you put it down hoping you dont take out trees or buildings in the process.
Take my word for it there are many situations as above where the aircraft ends up as a hole in the ground. Hence the bad engine out record of twins.
You also know that while many twins really struggle especially on hot days at grosse weight and blue line does not work in giving you the desired climb or even maintaining altitude.
So you have two choices you either continue trying to get a climb and end up in coffin corner with the usual stall /spin hole in the ground or you close both engines use the kenetic energy( which incidentely was created by the aircraft engines dragging the plane mass to altitude) and become a glider to a forced landing. (using the inherant kinetic energy to control your speed on the way down ie your spare engine as with the Skydiver) :-)
Your other option is to try out what I have said on your next flight. Mathematics or armchair pilot discussions aside it does work. I have seen and experienced the reality of this with my own eyes.
Then when you have tried it come back and explain why.
As they say the proof of the pudding is in the eating
You are missing something in the science or the mathematics here but the clue has to be in the fact that light twins will happily cruise all day on one engine at 127 kts but will not happily climb at blue line in all conditions and that is a practical answer.
Pace
>One big difference between Skydivers (1200 jumps and an AFF rating, just by the way!!) and aeroplanes is that skydivers don't have engines!! Aeroplanes don't have "Terminal velocities <
Firstly aeroplanes most certainly DO have terminal velocities!!! and sky divers most certainly DO have engines :-) Ok not in the conventional sense but in the Kinetic energy they are using returning earthbound and which was created hoisting them skybound. In the same sense a glider has an engine in its Kinetic energy which was created pulling it skybound and which is on tap to the glider pilot through the joystick earthbound. the joystick is his throttle if you like.
No again :-) Put in simple terms as I am a practical sort of pilot and not a mathematician what do you do if you are holding blue line, you are at 400 to 500 feet and rather than getting a climb your VSI and altitude are going down?
You either panic as do many low time twin pilots and pull back trying to get a climb and go into coffin corner or you put it down hoping you dont take out trees or buildings in the process.
Take my word for it there are many situations as above where the aircraft ends up as a hole in the ground. Hence the bad engine out record of twins.
You also know that while many twins really struggle especially on hot days at grosse weight and blue line does not work in giving you the desired climb or even maintaining altitude.
So you have two choices you either continue trying to get a climb and end up in coffin corner with the usual stall /spin hole in the ground or you close both engines use the kenetic energy( which incidentely was created by the aircraft engines dragging the plane mass to altitude) and become a glider to a forced landing. (using the inherant kinetic energy to control your speed on the way down ie your spare engine as with the Skydiver) :-)
Your other option is to try out what I have said on your next flight. Mathematics or armchair pilot discussions aside it does work. I have seen and experienced the reality of this with my own eyes.
Then when you have tried it come back and explain why.
As they say the proof of the pudding is in the eating
You are missing something in the science or the mathematics here but the clue has to be in the fact that light twins will happily cruise all day on one engine at 127 kts but will not happily climb at blue line in all conditions and that is a practical answer.
Pace
Last edited by Pace; 28th May 2008 at 21:09.
The rationale seems to be that even if your rate of climb at Vyse is pitiful, with no terrain to worry about it may be better to accept even half of pitiful in return for the better control that a speed above Vyse offers, since fatalities are typically associated with loss of control rather than CFIT. Since the curve is relatively flat, you may manage quite a speed increment without losing all your climb capability.
I can't see the point in step climbing. Surely a sustained, trimmed, shallow climb is preferable, and will return the same or better average RoC without having to flirt with Vyse from time to time?
I can't see the point in step climbing. Surely a sustained, trimmed, shallow climb is preferable, and will return the same or better average RoC without having to flirt with Vyse from time to time?
Thread Starter
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes
on
0 Posts
>I can't see the point in step climbing. Surely a sustained, trimmed, shallow climb is preferable, and will return the same or better average RoC without having to flirt with Vyse from time to time?<
We use that technique all the time in underpowered citation jets at high altitudes. It is again using your jet engine power which is insufficient to maintain an adequate climb and subsidising that power by adding the kinetic energy created in level flight.
While in a citation 2 you may struggle from FL350 and pan out trying to achieve FL370 at a given weight and conditions. You can get up there by allowing the aircraft to accelerate and then use the jet power plus the kinetic energy to give you the climb to FL370
Pace
We use that technique all the time in underpowered citation jets at high altitudes. It is again using your jet engine power which is insufficient to maintain an adequate climb and subsidising that power by adding the kinetic energy created in level flight.
While in a citation 2 you may struggle from FL350 and pan out trying to achieve FL370 at a given weight and conditions. You can get up there by allowing the aircraft to accelerate and then use the jet power plus the kinetic energy to give you the climb to FL370
Pace
Join Date: Nov 2001
Location: Somewhere in the Tropics UTC+7 to 9
Posts: 450
Likes: 0
Received 0 Likes
on
0 Posts
Twins are not unsafe nor is the accident record terrible... I can attest that if the pilot does what he is supposed to do... if you know what your doing, you will be fine.
Really?
Nice one SSG v4.0... I can't wait for V5.0
---
Another beer Pace?
PK-KAR
Join Date: Nov 2001
Location: Somewhere in the Tropics UTC+7 to 9
Posts: 450
Likes: 0
Received 0 Likes
on
0 Posts
Sorry mate, I miscounted...
It's v7.0 now... just waiting for v8.0...
At the rate this is going, I'd have liver failure pretty soon!
Oh whaddaheck... Here's another round of beer...
It's v7.0 now... just waiting for v8.0...
At the rate this is going, I'd have liver failure pretty soon!
Oh whaddaheck... Here's another round of beer...
Moderator
A few ill-conceived ideas floating around in this thread ..
(a) AEO/OEI, the climb performance graph is something of an upturned teacup profile .. with the AEO picture sitting a long way above the OEI
(b) the actual numbers will depend on the aircraft, configuration, atmospherics, etc
(c) regardless of the numbers, best climb performance is somewheres in the middle .. not at the ends of the graph
(d) typically, in a light twin other than at low weight and Hp/OAT, this OEI best climb performance will be modest .. or negative (ie a descent)
(e) if the aircraft flies slower/faster (presuming same thrust) it will be at a reduced climb/increased descent as appropriate .. you can't make something from nothing
(f) blue line is for one set of conditions and may not be appropriate for the actual conditions (including aircraft in-service deterioration) but it's probably a good place to start unless you have the flight test info to start with a different speed
(g) the problem of letting speed decay trying to chase mythical climb performance ... is one of flight management discipline and airmanship and has a predictable outcome in most cases ...
So far as ssg is concerned .. we will continue to remove posters who show an uncanny resemblance to him ... however, each new incarnation takes a little while to suss out. If it provides a modicum of amusement for the remainder of the folk, so be it.
(a) AEO/OEI, the climb performance graph is something of an upturned teacup profile .. with the AEO picture sitting a long way above the OEI
(b) the actual numbers will depend on the aircraft, configuration, atmospherics, etc
(c) regardless of the numbers, best climb performance is somewheres in the middle .. not at the ends of the graph
(d) typically, in a light twin other than at low weight and Hp/OAT, this OEI best climb performance will be modest .. or negative (ie a descent)
(e) if the aircraft flies slower/faster (presuming same thrust) it will be at a reduced climb/increased descent as appropriate .. you can't make something from nothing
(f) blue line is for one set of conditions and may not be appropriate for the actual conditions (including aircraft in-service deterioration) but it's probably a good place to start unless you have the flight test info to start with a different speed
(g) the problem of letting speed decay trying to chase mythical climb performance ... is one of flight management discipline and airmanship and has a predictable outcome in most cases ...
So far as ssg is concerned .. we will continue to remove posters who show an uncanny resemblance to him ... however, each new incarnation takes a little while to suss out. If it provides a modicum of amusement for the remainder of the folk, so be it.
400 to 500 feet and rather than getting a climb your VSI and altitude are going down?
Last post for me as you've proven you're not good at listening.
If, in the above situation you now lower the nose to accelerate (assuming you were at the correct Vyse at the time), your descent will increase and will stay that way. Thus your hole in the grond will be nearer and deeper.
As to "Step climbing" a Citation, if you didn't have the excess thrust to get to 370 in the first place, you won't have the thrust to stay there.
Find me one authioratative text that refers to an aircrafts level airspeed as a "Terminal velocity."
As to being an "armchair pilot", MY armchair is located at the front left of a Boeing 777!
Thread Starter
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes
on
0 Posts
>If, in the above situation you now lower the nose to accelerate (assuming >you were at the correct Vyse at the time), your descent will increase and will stay that way. Thus your hole in the grond will be nearer and deeper.<
So what you are saying is that even at 2000 feet and a blue line climb with no climb. If you reduce the AOA and increase speed you will descend all the way to the ground from 2000 feet?
>As to "Step climbing" a Citation, if you didn't have the excess thrust to get to 370 in the first place, you won't have the thrust to stay there.<
Again step climbing is used by many citation pilots where the climb rate is so low that the only way you can stop it going on the back of the drag curve is to allow the speed to increase, lower the angle of attack and use the kinetic energy to assist that last bit of climb. As you level and the aircraft accelerates and angle of attack reduces so does the drag making the available thrust sufficient.
At high level the gap between the Ias and stall is small and yes there will be a level where to maintain that gap you would start sinking.
It is not just about available thrust its also about AOA and drag.
>Find me one authioratative text that refers to an aircrafts level airspeed as a "Terminal velocity."<
Every object will have a terminal velocity
So what you are saying is that even at 2000 feet and a blue line climb with no climb. If you reduce the AOA and increase speed you will descend all the way to the ground from 2000 feet?
>As to "Step climbing" a Citation, if you didn't have the excess thrust to get to 370 in the first place, you won't have the thrust to stay there.<
Again step climbing is used by many citation pilots where the climb rate is so low that the only way you can stop it going on the back of the drag curve is to allow the speed to increase, lower the angle of attack and use the kinetic energy to assist that last bit of climb. As you level and the aircraft accelerates and angle of attack reduces so does the drag making the available thrust sufficient.
At high level the gap between the Ias and stall is small and yes there will be a level where to maintain that gap you would start sinking.
It is not just about available thrust its also about AOA and drag.
>Find me one authioratative text that refers to an aircrafts level airspeed as a "Terminal velocity."<
Every object will have a terminal velocity
Last edited by Pace; 29th May 2008 at 05:31.
Thread Starter
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes
on
0 Posts
Wizofox
Rather than point scoring over each other I would rather leave it with you and beg to differ. You will not change my opinions and I will not change yours.
All I will say is that the accident rate is very poor for engine failures on Light twins and that is an unacceptable state. So something has to be wrong somewhere?
All the best
Pace
Rather than point scoring over each other I would rather leave it with you and beg to differ. You will not change my opinions and I will not change yours.
All I will say is that the accident rate is very poor for engine failures on Light twins and that is an unacceptable state. So something has to be wrong somewhere?
All the best
Pace
Join Date: Dec 2007
Location: France
Posts: 481
Likes: 0
Received 0 Likes
on
0 Posts
We all know that the accident rate for light twins is attrocious with an engine failure.
Infact I believe you are more likely to survive a single engine failure and the subsequent forced landing than an engine failure in a twin.
Infact I believe you are more likely to survive a single engine failure and the subsequent forced landing than an engine failure in a twin.
The fact is that following engine failure in a twin, providing the subsequent landing is safe, there will be no formal 'publicity'; the event is non-reportable and will not be investigated. Thus the numbers are slewed - all the published reports you see relating to twins with one engine out are accident reports, because something has gone wrong.
The assertions above are simply rubbish. Even if you wanted to prove them, you couldn't, because there are no statistics to help you. Many engine failures occur in light twins, and end in safe landings on proper runways.
Thread Starter
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes
on
0 Posts
>The fact is that following engine failure in a twin, providing the subsequent landing is safe, there will be no formal 'publicity'; the event is non-reportable and will not be investigated. Thus the numbers are slewed - all the published reports you see relating to twins with one engine out are accident reports, because something has gone wrong.
The assertions above are simply rubbish. Even if you wanted to prove them, you couldn't, because there are no statistics to help you. Many engine failures occur in light twins, and end in safe landings on proper runways.<
FrontLefthamster
You may have a valid point and it would be nice to see those statistics and how they arrive at them?
But fair dues a pilot of a light twin always has the option of closing both down and treating it as a forced landing.
That is the difference the second engine gives you more options than in a single my suggestion was another further option to have up your sleeve.
If that still doesnt work close them both and take your chances with what lies ahead. Your not loosing anything and it does work science or no science.
Pace
The assertions above are simply rubbish. Even if you wanted to prove them, you couldn't, because there are no statistics to help you. Many engine failures occur in light twins, and end in safe landings on proper runways.<
FrontLefthamster
You may have a valid point and it would be nice to see those statistics and how they arrive at them?
But fair dues a pilot of a light twin always has the option of closing both down and treating it as a forced landing.
That is the difference the second engine gives you more options than in a single my suggestion was another further option to have up your sleeve.
If that still doesnt work close them both and take your chances with what lies ahead. Your not loosing anything and it does work science or no science.
Pace
Pace, the difference is that I am stating facts, not opinion.
Best rate of climb, single engine is just that. Minimum drag is just that. Maximum altitude is just that. You claim to somehow magically be able to make an aircraft climb at BETTER than BEST rate of climb by achieving LESS than MINIMUM drag, and climb to HIGHER than MAXIMUM altitude.If that's the case, Boeing needs to talk to you now!!
Best rate of climb, single engine is just that. Minimum drag is just that. Maximum altitude is just that. You claim to somehow magically be able to make an aircraft climb at BETTER than BEST rate of climb by achieving LESS than MINIMUM drag, and climb to HIGHER than MAXIMUM altitude.If that's the case, Boeing needs to talk to you now!!
The problem is not so much the marginal rate of climb following an engine failure shortly after take off, but the failure of the pilot to take instantaneous corrective action including the feathering procedure. The flying schools teach an often inappropriate lengthy period of identification via various methods, and often critical seconds have gone by the time the pilot gets around to actually feathering the propeller.
A generic drill mouthed by the pilot may include identification of the failed engine by the direction of initial yaw (dead side - dead leg etc). Then a careful check of the engine instruments to confirm the cause of the initial yaw. Then a further confirmation takes place by slowly retarding the throttle of the suspect engine. All this time the colossal drag of the windmilling propeller is taking steady toll of airspeed and within literally seconds the airspeed has dropped 10-15 knots from the initial engine failure figure.
The fact is the feathering of the propeller must take place immediately after the engine failure is detected in order to stop the danger of speed decay. The risk of closing down the wrong engine must be balanced against the certain potentially fatal loss of airspeed that will occur unless the dead engine is feathered without delay. The act of closing the throttle of the suspect engine as a means of confirmation, raises the question of how fast do you close that throttle lever. It is generally accepted as a slow movement just in case the wrong throttle has been closed and you don't want to momentarily lose all power (wrong throttle pulled back and dead engine already dead equals a problem!).
A slow pull back of the suspect engine loses more precious seconds of windmilling drag and thus decaying airspeed. To competently handle an engine failure after take off at low altitude requires instantaneous correct feathering action without the luxury of "dicking around". This way, the danger envelope of windmilling drag is minimised to perhaps around 5-8 seconds. But to arbitarily state the pilot should deliberately close both throttles and crash straight ahead simply because the altitude is less than 500 feet when an engine fails, is shutting off all options that may have been available.
A generic drill mouthed by the pilot may include identification of the failed engine by the direction of initial yaw (dead side - dead leg etc). Then a careful check of the engine instruments to confirm the cause of the initial yaw. Then a further confirmation takes place by slowly retarding the throttle of the suspect engine. All this time the colossal drag of the windmilling propeller is taking steady toll of airspeed and within literally seconds the airspeed has dropped 10-15 knots from the initial engine failure figure.
The fact is the feathering of the propeller must take place immediately after the engine failure is detected in order to stop the danger of speed decay. The risk of closing down the wrong engine must be balanced against the certain potentially fatal loss of airspeed that will occur unless the dead engine is feathered without delay. The act of closing the throttle of the suspect engine as a means of confirmation, raises the question of how fast do you close that throttle lever. It is generally accepted as a slow movement just in case the wrong throttle has been closed and you don't want to momentarily lose all power (wrong throttle pulled back and dead engine already dead equals a problem!).
A slow pull back of the suspect engine loses more precious seconds of windmilling drag and thus decaying airspeed. To competently handle an engine failure after take off at low altitude requires instantaneous correct feathering action without the luxury of "dicking around". This way, the danger envelope of windmilling drag is minimised to perhaps around 5-8 seconds. But to arbitarily state the pilot should deliberately close both throttles and crash straight ahead simply because the altitude is less than 500 feet when an engine fails, is shutting off all options that may have been available.
Thread Starter
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes
on
0 Posts
>Best rate of climb, single engine is just that. Minimum drag is just that. Maximum altitude is just that. You claim to somehow magically be able to make an aircraft climb at BETTER than BEST rate of climb by achieving LESS than MINIMUM drag, and climb to HIGHER than MAXIMUM altitude.If that's the case, Boeing needs to talk to you now!!<
Wizofox
Yes I appreciate best rate of climb single engine. I appreciate Minimum drag at best rate of climb BUT I am not talking about climbing at all or minimum drag in the climb.
The reason I am NOT is the very fact that even with new aircraft where the miserly 200fpm are achieved on standard days, Many light twins may be 20 years old, be covered in hangar rash, have tired engines and the temperatures may be above standard.
Most light twins quote 200 fpm as new test aircraft, some not even that. So the point is not to climb at all but even low level to go for a single engine cruise.
With any climb you are looking at an increase in angle of attack and with an increase in angle of attack you are looking at DRAG.
Remove that drag and as I stated as fact a seneca will accelerate to near 130kts on one engine in a level cruise. Push the nose over and that 130 would increase as the aircraft traded altitude for its inherant kinetic energy.
Drop below blue line and you are into coffin corner as the drag increases dramatically and that is where the margins are very small.
The guy who does everything right establishes blue line, has the aircraft clean and still has no climb or even a descent has two choices one is to close both throttles and glide to a landing ie using kinetic energy alone to control his speed to a landing or he can reduce the drag of a climb and set up a level cruise.
Its not Magic but pure fact that a light twin will cruise for hours happily with one shut down but will not climb happily with one shut down.
The step climb works on the fact that you are dipping into Kinetic energy to add to the available power from your engine and gain some altitude.
I will give an example from the seneca.
You have one engine running your speed in level flight is 127kts (fact) you are not going down but level. Now you pitch for a climb. You still have the power of that one engine which is constant but you trade some speed for extra climb. As you pitch up the drag increases and the aircraft is now climbing with the constant engine power plus the kinetic energy. What happens is the speed starts to decay but you get a greater climb rate than you would at blue line. Allow the speed to decay from 127 kts to say 105 kts and then pitch for level flight again maintaining altitude. Slowly the speed will increase. when you are back to 127 kts go through the process again.
All I am saying here is make the plane do what it can happily do ie fly level not climb. If you cannot see that I really do not know what to say Other than I will beg to differ with you these are facts not suppositions and I am happy to demonstrate to you any time. If I am right you pay for the flight if I am wrong I pick up the bill.
Pace
Wizofox
Yes I appreciate best rate of climb single engine. I appreciate Minimum drag at best rate of climb BUT I am not talking about climbing at all or minimum drag in the climb.
The reason I am NOT is the very fact that even with new aircraft where the miserly 200fpm are achieved on standard days, Many light twins may be 20 years old, be covered in hangar rash, have tired engines and the temperatures may be above standard.
Most light twins quote 200 fpm as new test aircraft, some not even that. So the point is not to climb at all but even low level to go for a single engine cruise.
With any climb you are looking at an increase in angle of attack and with an increase in angle of attack you are looking at DRAG.
Remove that drag and as I stated as fact a seneca will accelerate to near 130kts on one engine in a level cruise. Push the nose over and that 130 would increase as the aircraft traded altitude for its inherant kinetic energy.
Drop below blue line and you are into coffin corner as the drag increases dramatically and that is where the margins are very small.
The guy who does everything right establishes blue line, has the aircraft clean and still has no climb or even a descent has two choices one is to close both throttles and glide to a landing ie using kinetic energy alone to control his speed to a landing or he can reduce the drag of a climb and set up a level cruise.
Its not Magic but pure fact that a light twin will cruise for hours happily with one shut down but will not climb happily with one shut down.
The step climb works on the fact that you are dipping into Kinetic energy to add to the available power from your engine and gain some altitude.
I will give an example from the seneca.
You have one engine running your speed in level flight is 127kts (fact) you are not going down but level. Now you pitch for a climb. You still have the power of that one engine which is constant but you trade some speed for extra climb. As you pitch up the drag increases and the aircraft is now climbing with the constant engine power plus the kinetic energy. What happens is the speed starts to decay but you get a greater climb rate than you would at blue line. Allow the speed to decay from 127 kts to say 105 kts and then pitch for level flight again maintaining altitude. Slowly the speed will increase. when you are back to 127 kts go through the process again.
All I am saying here is make the plane do what it can happily do ie fly level not climb. If you cannot see that I really do not know what to say Other than I will beg to differ with you these are facts not suppositions and I am happy to demonstrate to you any time. If I am right you pay for the flight if I am wrong I pick up the bill.
Pace
Last edited by Pace; 30th May 2008 at 15:35.
Join Date: Nov 2001
Location: Somewhere in the Tropics UTC+7 to 9
Posts: 450
Likes: 0
Received 0 Likes
on
0 Posts
The reason I am NOT is the very fact that even with new aircraft where the miserly 200fpm are achieved on standard days, Many light twins may be 20 years old, be covered in hangar rash, have tired engines and the temperatures may be above standard.
Whenever we got one engine out on take off, I have to rush back to the hotel and pick up clean underwear... not too often, but you know what I mean.
At 33C, we're often reduced, because otherwise, we'd be forced to do what Ssg does on N-1 at anywhere during the take off, abort... I refused a "symbolic" V1 for the ops... reduce the load thank you! The first time I saw that light twin do a near MTOW run after maintenance, the engine conked out and 3000m runway suddenly looked very short!!!!! (thanks to a former CASA/MDCA guy who advised we avoid MTOW citing reasons Pace mentioned).
For ref: It was a C402B, a DAMN OLD one...
PK-KAR
Pace,
We are actually closer to agreement than you recognize, at least in terms of technique. Flying level at a higher speed rather than climbing slowly at Vyse may indeed have merit as a technique where terrain is not a factor.
What I am NOT willing to let you go on is some of your more outrageous errors when it comes to aerodynamics, as they have led you to make statements that work only in the magic kingdom.
Your statement:-
and then say
Shows that you neither appreciate or understand a fairly basic concept.
Minimum total drag occurs at a particular angle of attack, which, at a given weight, will correspond with a particular speed. Whether you climb, descend or stay level at that speed depends on how much power is applied. You continue to imply that accelerating , because it lowers the angle of attack reduces drag. It REDUCES induced drag whilst INCREASING form drag, thus INCREASING total drag. Minimum means minimun, anything else is an increase.
Vyse is not exactly Min drag, but it's close, as it takes into consideration things such as control drag. BUT it is the BEST RATE OF CLIMB SPEED and thus, by definition, any other speed has LESS rate of climb (Look BEST up in the dictionary!). If the BEST rate of climb is zero, flying any other speed produces a descent.
Go ahead and and fly level all day. As I said, it may be resnoble under some circumstances. Just don't imply you can somehow make an aircraft do BETTER than BEST!.
By the way, have another look at that chart that gave you 127kts cruise on one. TAS right? At what weight and what height? Work out what INDICATED speed that corresponds to, and get back to me!!
We are actually closer to agreement than you recognize, at least in terms of technique. Flying level at a higher speed rather than climbing slowly at Vyse may indeed have merit as a technique where terrain is not a factor.
What I am NOT willing to let you go on is some of your more outrageous errors when it comes to aerodynamics, as they have led you to make statements that work only in the magic kingdom.
Your statement:-
I appreciate Minimum drag at best rate of climb BUT I am not talking about climbing at all or minimum drag in the climb.
With any climb you are looking at an increase in angle of attack and with an increase in angle of attack you are looking at DRAG.
Minimum total drag occurs at a particular angle of attack, which, at a given weight, will correspond with a particular speed. Whether you climb, descend or stay level at that speed depends on how much power is applied. You continue to imply that accelerating , because it lowers the angle of attack reduces drag. It REDUCES induced drag whilst INCREASING form drag, thus INCREASING total drag. Minimum means minimun, anything else is an increase.
Vyse is not exactly Min drag, but it's close, as it takes into consideration things such as control drag. BUT it is the BEST RATE OF CLIMB SPEED and thus, by definition, any other speed has LESS rate of climb (Look BEST up in the dictionary!). If the BEST rate of climb is zero, flying any other speed produces a descent.
Go ahead and and fly level all day. As I said, it may be resnoble under some circumstances. Just don't imply you can somehow make an aircraft do BETTER than BEST!.
By the way, have another look at that chart that gave you 127kts cruise on one. TAS right? At what weight and what height? Work out what INDICATED speed that corresponds to, and get back to me!!
Join Date: Feb 2006
Location: UK
Posts: 170
Likes: 0
Received 0 Likes
on
0 Posts
When I flew twins off a reasonable runway, I would get the old girl airborne let her accelerate to about Blue line +20 before putting the gear up and climbing away. I would be through 1000' AGL in no time. That way, if one quit prior to blueline +20 I didnt have to worry, I would just put her back down on the runway if I needed to and once the gear was up, I was gauranteed a climb with a healthy margin above blue line until about 1000' AGL where I could level out and asses the situation. My reason for flying like this was for the exact reason PACE asked the initial question. To keep a healthy speed above blue line!
Bear in mind, this option isnt advisable on a short runway!
OSOP
Bear in mind, this option isnt advisable on a short runway!
OSOP