Engine failure best glide speed descent rate
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- Rick
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Re: Engine failure best glide speed descent rate
It seems like the best configuration will be the one with the lowest rate of descent, won't it? The glide distance will always be affected by the wind relative to the direction of travel. But your rate of descent at best glide should be constant and independent of wind direction, so once you know that, you can look at ground speed and altitude AGL and know how far you will go (in that direction) (assuming winds don't change on the way down).
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Re: Engine failure best glide speed descent rate
My idea was to calculate the 8.8:1 or 10:1 value of my plane.Rick wrote: ↑Thu Oct 01, 2020 5:10 pm It seems like the best configuration will be the one with the lowest rate of descent, won't it? The glide distance will always be affected by the wind relative to the direction of travel. But your rate of descent at best glide should be constant and independent of wind direction, so once you know that, you can look at ground speed and altitude AGL and know how far you will go (in that direction) (assuming winds don't change on the way down).
Arnaud
DA40 Star 180 / 40.026 / 2001
Wingtip, landing and taxing LED (Whelen)
Skitube
GNS430 NON-WAAS
Steam gauges
Non certified ADS-b
DA40 Star 180 / 40.026 / 2001
Wingtip, landing and taxing LED (Whelen)
Skitube
GNS430 NON-WAAS
Steam gauges
Non certified ADS-b
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Re: Engine failure best glide speed descent rate
"It seems like the best configuration will be the one with the lowest rate of descent, won't it?"
Depends on whether you want maximum range or maximum time. Minimum sink rate and best glide ratio are not the same speed.
As usual, Bold Method does a good job on the subject. They say, "Minimum sink is always slower than best glide, because it's the point on the power required curve where the least amount of power is required. Keep in mind, though, you're going quite a bit slower than your best glide speed, and that can significantly impact your glide range." https://www.boldmethod.com/learn-to-fly ... -to-do-it/
On a graph of L/D vs. speed, a little fast is better than a little slow. The L/D drops off more steeply on the slow side than on the fast side. That means if you can't hold speed perfectly, 5 kts faster will penalize your L/D less than 5 kts slower. Speed is reserve energy. If it looks like you are going to land short of your chosen field you can convert some speed to distance. If you are going to overshoot you can drop flaps and/or side slip.
Minimum sink is pretty slow. Trying to hold a speed just above stalling while troubleshooting and maneuvering to an off field landing runs a risk of getting distracted and stalling.
Best L/D in an avgas plane is with throttle forward and prop lever back. Not sure if the position of the power lever would make any difference in a diesel. Anything in the POH about that?
Depends on whether you want maximum range or maximum time. Minimum sink rate and best glide ratio are not the same speed.
As usual, Bold Method does a good job on the subject. They say, "Minimum sink is always slower than best glide, because it's the point on the power required curve where the least amount of power is required. Keep in mind, though, you're going quite a bit slower than your best glide speed, and that can significantly impact your glide range." https://www.boldmethod.com/learn-to-fly ... -to-do-it/
On a graph of L/D vs. speed, a little fast is better than a little slow. The L/D drops off more steeply on the slow side than on the fast side. That means if you can't hold speed perfectly, 5 kts faster will penalize your L/D less than 5 kts slower. Speed is reserve energy. If it looks like you are going to land short of your chosen field you can convert some speed to distance. If you are going to overshoot you can drop flaps and/or side slip.
Minimum sink is pretty slow. Trying to hold a speed just above stalling while troubleshooting and maneuvering to an off field landing runs a risk of getting distracted and stalling.
Best L/D in an avgas plane is with throttle forward and prop lever back. Not sure if the position of the power lever would make any difference in a diesel. Anything in the POH about that?
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- Boatguy
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Re: Engine failure best glide speed descent rate
The Power/RPM curve in the AFM suggests that having the power lever set at 20% would be the most "feathered" position. This is not marked on the console and obviously would have to be established with the engine running, then marked by the owner.
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Re: Engine failure best glide speed descent rate
I'm not about to try and second-guess the AFM on anything about based on tests with the engine at idle. In that state, you're still putting a certain non-zero amount of energy into the system. For minimum sink, though, I consider it reasonably valid to seek the IAS at which the minimum power is required for maintaining altitude (at a specific weight, of course).
For calculating the geometry of sink rate at best glide, consider this; It's really a matter of ground speed, not indicated airspeed. What does that mean? Even in the simple case of no wind, ground speed is true airspeed derived from calibrated (not indicated) airspeed adjusted for density altitude. According to the airspeed calibration graph in the AFM, for a DA40-180 with flaps up, 70 KIAS = 74 KCAS. At 4000 ft. DA, that works out to 79 KTAS. At 6000 ft DA it's 81 KCAS. The angle is unaffected, but your vertical speed will be higher than if you used 70 as the speed and even higher as DA increases.
For calculating the geometry of sink rate at best glide, consider this; It's really a matter of ground speed, not indicated airspeed. What does that mean? Even in the simple case of no wind, ground speed is true airspeed derived from calibrated (not indicated) airspeed adjusted for density altitude. According to the airspeed calibration graph in the AFM, for a DA40-180 with flaps up, 70 KIAS = 74 KCAS. At 4000 ft. DA, that works out to 79 KTAS. At 6000 ft DA it's 81 KCAS. The angle is unaffected, but your vertical speed will be higher than if you used 70 as the speed and even higher as DA increases.
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Re: Engine failure best glide speed descent rate
On landing in Lake Michigan
The thought of making a water landing in a fixed gear airplane scares me. The thought of sinking inverted inside the DA40 canopy and fumbling for the red rear door hinge release handle and climbing into the back seat to get out sounds very challenging as well.
I’m often fly fishing for Steelhead in Michigan in a river just east of the narrow point in the lake and I’ve told myself that I’d fly around the bottom of the lake rather than at the “waist” if I ever try flying from LA to Michigan.
Even in summer Lake Michigan is cold away from shore. Very cold
The thought of making a water landing in a fixed gear airplane scares me. The thought of sinking inverted inside the DA40 canopy and fumbling for the red rear door hinge release handle and climbing into the back seat to get out sounds very challenging as well.
I’m often fly fishing for Steelhead in Michigan in a river just east of the narrow point in the lake and I’ve told myself that I’d fly around the bottom of the lake rather than at the “waist” if I ever try flying from LA to Michigan.
Even in summer Lake Michigan is cold away from shore. Very cold
Sold 2002. Powerflo, Hartzell composite two blade, 530W/430, 345 transponder.
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Re: Engine failure best glide speed descent rate
Today I confirmed what I've seen before. In my plane at idle power and 60 KIAS the RPM is ~1350. Whether the prop control is full forward or back makes no difference in this RPM nor does it produce any perceived change in the glide path. Remember moving the prop control does not directly affect the propeller pitch. It merely changes the RPM set point. In this case the above RPM is below the minimum RPM limit hence it doesn't change. I daresay with a non-firing but freely rotating engine I wouldn't expect the situation to be any different.
I have the MT with a Woodward governor. With a different setup YMMV, but it does illustrate that you may or may not be able to rely on getting any benefit in glide angle with prop adjustment in this situation.
I have the MT with a Woodward governor. With a different setup YMMV, but it does illustrate that you may or may not be able to rely on getting any benefit in glide angle with prop adjustment in this situation.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5