Engine Out and Enough Altitude to do a 180...
08-18-2010 | 09:23 PM
#12
Line Holder
Joined: Jan 2008
Posts: 88
Likes: 0
From: AT-301-600G
If you have an engine out and have plenty of altitude, say 6000' AGL, and you wanted to turn 180 degrees after calculating that you can make a field behind you, would you bank sharply (knowing you will lose altitude, but gain airspeed that you can then use to gain altitude again up until hitting best glide speed), or would you bank shallow and make a slow turn at glide speed?
I ask this because the more people I fly with, I find they have a harder time staying coordinated while trying to perform a shallow bank than they do if they roll the plane over to a steeper bank. Simply put, is it better to get the aircraft turned so you can set up for the decent and approach, or rather take things slow?
I ask this because the more people I fly with, I find they have a harder time staying coordinated while trying to perform a shallow bank than they do if they roll the plane over to a steeper bank. Simply put, is it better to get the aircraft turned so you can set up for the decent and approach, or rather take things slow?
a steeper bank will trade altitude for turning radius. if you are on the runway centerline, you don't want a turn that will put you a mile off to one side, but if you are on a wide downwind when the engine fails then you might want that more shallow bank.
this thing about staying coordinated is a red herring. there is no excuse to be unintentionally uncoordinated regardless of bank angle. we shouldn't set emergency procedures to work around bad technique. we should fix the bad habits instead.
08-19-2010 | 04:02 AM
#14
Gets Weekends Off
Joined: Jun 2008
Posts: 1,398
Likes: 0
From: USAF
banking sharply does not mean that you will gain airspeed. with engine out, you should maintain best glide speed, regardless of bank angle, until you are sure you will make it to your chosen landing site. or until you have chosen a different landing site. and then adjust accordingly to make the field.
a steeper bank will trade altitude for turning radius. if you are on the runway centerline, you don't want a turn that will put you a mile off to one side, but if you are on a wide downwind when the engine fails then you might want that more shallow bank.
this thing about staying coordinated is a red herring. there is no excuse to be unintentionally uncoordinated regardless of bank angle. we shouldn't set emergency procedures to work around bad technique. we should fix the bad habits instead.
a steeper bank will trade altitude for turning radius. if you are on the runway centerline, you don't want a turn that will put you a mile off to one side, but if you are on a wide downwind when the engine fails then you might want that more shallow bank.
this thing about staying coordinated is a red herring. there is no excuse to be unintentionally uncoordinated regardless of bank angle. we shouldn't set emergency procedures to work around bad technique. we should fix the bad habits instead.
08-19-2010 | 04:06 AM
#15
Gets Weekends Off
Joined: Nov 2008
Posts: 826
Likes: 0
Why is this even an issue when six thousand feet above the ground?
Besides that, I'm with mini. If, in an emergency, you keep your head on straight and don't lose control of the airplane reacting to it, you're way ahead of the game right there.
Besides that, I'm with mini. If, in an emergency, you keep your head on straight and don't lose control of the airplane reacting to it, you're way ahead of the game right there.
08-19-2010 | 06:53 AM
#16
Line Holder
Joined: Jan 2008
Posts: 88
Likes: 0
From: AT-301-600G
at a glide ratio of 10:1 you've got 10 miles glide from 6k. even if you loose 1000' in the turn you have something like 8 miles of glide left. of course don't forget the wind when figuring it. if you have an engine failure on takeoff and do the 180, you will be landing with a tailwind.
something to consider: on a lot of airplanes L/D_max (best glide) is better with 5 to 10 degrees flaps. (about the same amount of flap as you can get will full down aileron deflection, or a little less than that) in most training that isn't taught because a little too much flap is a lot worse than a little too little flap.
I suggest that if you fly one airplane a lot get to know that airplane throughout the envelope, not just the normal profiles you use every day. go up high and see how she glides at different speeds, different weights, different flap settings. (or in the sim for the folks flying the big expensive ones)
Last edited by SunDog; 08-19-2010 at 07:26 AM.
08-19-2010 | 07:48 AM
#18
Gets Weekends Off
Joined: Jun 2009
Posts: 317
Likes: 0
Minimum altitude loss would be the bottom of the power required curve, or minimum sink. A speed that occurs approximately 5 knots below best glide (reminder: both change with weight). Since we know the speed we want to fly, we can reverse engineer the bank angle that will give us a stall speed that occurs within a comfortable safety margin of this speed.
For example: Take a 172 with best glide of 65 and a stall speed of 44 clean. Assume minimum sink to be 60 knots.
For maximum performance we'd find the bank angle that stalls us at 60 knots and fly at stall. However, this doesn't seem safe. So let's look for a stall speed of 55:
@57 degrees bank the stall speed is 59.6 knots.
@50 degrees of bank the stall speed is 54.9 knots.
The later technique, using a 5 knot fudge factor, makes flying to maximum performance simpler as well. Since most stall horns trigger at ~5 knots ahead of stall you can simply fly 50 degrees of bank with the stall horn barely audible and be at max performance +5 knot for safety.
Formulas used:
Load Factor (G) = 1 / Cosine (Bank Angle)
Accelerated Stall Speed (Banked) = Level Flight Stall Speed * Sqrt (Load Factor)
08-19-2010 | 10:20 AM
#19
Gets Weekends Off
Joined: Jan 2009
Posts: 350
Likes: 0
From: PA-31/left, LJ31/right
At 6,000 feet this isn't much of an issue IMO. However, there is one technique that does give you the best 180 degree turn performance. In this case performance means maximum rate of turn with minimum loss of altitude.
Minimum altitude loss would be the bottom of the power required curve, or minimum sink. A speed that occurs approximately 5 knots below best glide (reminder: both change with weight). Since we know the speed we want to fly, we can reverse engineer the bank angle that will give us a stall speed that occurs within a comfortable safety margin of this speed.
For example: Take a 172 with best glide of 65 and a stall speed of 44 clean. Assume minimum sink to be 60 knots.
For maximum performance we'd find the bank angle that stalls us at 60 knots and fly at stall. However, this doesn't seem safe. So let's look for a stall speed of 55:
@57 degrees bank the stall speed is 59.6 knots.
@50 degrees of bank the stall speed is 54.9 knots.
The later technique, using a 5 knot fudge factor, makes flying to maximum performance simpler as well. Since most stall horns trigger at ~5 knots ahead of stall you can simply fly 50 degrees of bank with the stall horn barely audible and be at max performance +5 knot for safety.
Formulas used:
Load Factor (G) = 1 / Cosine (Bank Angle)
Accelerated Stall Speed (Banked) = Level Flight Stall Speed * Sqrt (Load Factor)
Minimum altitude loss would be the bottom of the power required curve, or minimum sink. A speed that occurs approximately 5 knots below best glide (reminder: both change with weight). Since we know the speed we want to fly, we can reverse engineer the bank angle that will give us a stall speed that occurs within a comfortable safety margin of this speed.
For example: Take a 172 with best glide of 65 and a stall speed of 44 clean. Assume minimum sink to be 60 knots.
For maximum performance we'd find the bank angle that stalls us at 60 knots and fly at stall. However, this doesn't seem safe. So let's look for a stall speed of 55:
@57 degrees bank the stall speed is 59.6 knots.
@50 degrees of bank the stall speed is 54.9 knots.
The later technique, using a 5 knot fudge factor, makes flying to maximum performance simpler as well. Since most stall horns trigger at ~5 knots ahead of stall you can simply fly 50 degrees of bank with the stall horn barely audible and be at max performance +5 knot for safety.
Formulas used:
Load Factor (G) = 1 / Cosine (Bank Angle)
Accelerated Stall Speed (Banked) = Level Flight Stall Speed * Sqrt (Load Factor)
Good write up, but too much to think about in the heat of the moment. 45 deg will get the average pilot close enough, agreed?
08-19-2010 | 12:52 PM
#20
Gets Weekends Off
Joined: Dec 2009
Posts: 2,115
Likes: 1
From: 127.0.0.1
