Engine failure best glide speed descent rate

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RMarkSampson
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Re: Engine failure best glide speed descent rate

Post by RMarkSampson »

one into the Pacific approaching the shore on a low IFR approach after a long day into Crescent City
Interestingly, that fatal Diamond accident was a rental plane out of my home airport. The FBO operator (previous one, not the current FBO) had recently purchased it and the person renting it decided to fly from Florida to Oregon without any sleep ending up in extremely bad weather, IFR and turbulence. Spoke to the owner about it - If you could do every thing wrong, that guy did it. They never found the plane - just a few things that floated. I know conspiracy theories should be only blogged in the Hangar Talk forum, but I had this vision that the pilot and the plane ended up in South America with an unknowing ex-wife still residing in North America - but the FBO guy said they did find a few items that were identifiable (serialized?). Anyway, the insurance company paid out - but the FBO did not have adequate insurance and the they never bought another Diamond to replace that one.

So bottom line for this Engine Failure discussion - that engine ran perfectly fine right up until the pilot's total disregard of risk caught up with him. Sad....
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Re: Engine failure best glide speed descent rate

Post by yl472401 »

astaib wrote:And remember that a 180 turn will make a loss of 500ft
Thanks for the input, but that number doesn’t seem to match what was mentioned previously as 838 ft/min gliding with propeller windmilling and 713 ft/min with propeller fully stopped. Considering the standard turn will last one minute.
What could be the cause of discrepancy here?


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Re: Engine failure best glide speed descent rate

Post by Rich »

yl472401 wrote: Fri Sep 25, 2020 8:47 pm
astaib wrote:And remember that a 180 turn will make a loss of 500ft
Thanks for the input, but that number doesn’t seem to match what was mentioned previously as 838 ft/min gliding with propeller windmilling and 713 ft/min with propeller fully stopped. Considering the standard turn will last one minute.
What could be the cause of discrepancy here?


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Pretty simple. You do not want to use best glide speed (which gets you as far as possible for a given loss of altitude) or standard rate turn for most of that turn. Something like minimum sink speed (possibly even below) gets you turned around in less time and with less distance to cover to the runway. Unfortunately, minimum sink speeds are routinely not published for powered aircraft.

BTW, not all power losses are total. many leave you with quite a bit of power. But there's a minimum altitude to even think about this in any case. A SR22 fatal accident in May illustrates the point.
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Re: Engine failure best glide speed descent rate

Post by yl472401 »

Rich wrote:
yl472401 wrote: Fri Sep 25, 2020 8:47 pm
astaib wrote:And remember that a 180 turn will make a loss of 500ft
Thanks for the input, but that number doesn’t seem to match what was mentioned previously as 838 ft/min gliding with propeller windmilling and 713 ft/min with propeller fully stopped. Considering the standard turn will last one minute.
What could be the cause of discrepancy here?


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Pretty simple. You do not want to use best glide speed (which gets you as far as possible for a given loss of altitude) or standard rate turn for most of that turn. Something like minimum sink speed (possibly even below) gets you turned around in less time and with less distance to cover to the runway. Unfortunately, minimum sink speeds are routinely not published for powered aircraft.

BTW, not all power losses are total. many leave you with quite a bit of power. But there's a minimum altitude to even think about this in any case. A SR22 fatal accident in May illustrates the point.
So, a good estimate is 500 ft per 180* turn for Diamond DA40 with complete power loss?
I saw the news about a recent fatal and baffled by the calculation for the ideal descending control in the power loss situation. Want to be prepared for the worstImage


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Re: Engine failure best glide speed descent rate

Post by Rick »

The EAA just had a great webinar that covered this topic. It was geared toward turning back to the airport following an engine failure shortly after takeoff, via a 180-degree turn, and had lots of advice about how to make that turn with minimum sink, etc. The video also pushes pilots to make some in-flight measurements and report the results to the EAA to help them design a tool called "Takeoff Advisor". This tool would calculate the best course of action if your engine fails on takeoff, based on your aircraft performance, current weather conditions, departure airport, takeoff weight, etc. I was skeptical at first, but after watching the video I believe such a tool could be quite useful - even if only to get pilots thinking about their options before taking the runway. The video is 90+ minutes, but most of the meat is in the first hour.

Here is a link to the webinar: https://eaa.org/Videos/Webinars?playlis ... 3816644001

Has anyone filled out the "test cards" for their DA40 yet?
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Re: Engine failure best glide speed descent rate

Post by Rich »

Rick wrote: Sat Sep 26, 2020 12:13 pm The EAA just had a great webinar that covered this topic.
It's amusing that it took all this analysis to realize a disqualifying criteria for whether you could make it back: The angle of climb vs. your best glide angle. If you climb at an equal or more shallow angle than your best glide angle, you have no shot at making it back to your lift-off point. A decent headwind on takeoff alters both in your favor and might be enough. But failing that, just forget it in a straight-out departure scenario. Density Altitude will cut into your climb relative to sea level. So what you can pull off departing KSQL you might not at KABQ.

There are some other density altitude effects that are ignored. Granted, they are second-order, but TAS will be higher than the speeds at which you maneuver. All other things being equal, then:

-Turn rate is somewhat slower, hence turn time is greater.
-Turn radius will be larger.
-Altitude loss in the turn will be greater.

FWIW, the documented glide ratio in the POH is about 6.56 degrees. 1000 FPM at 70 KTAS is 7.8 degrees. but 1000 FPM at 90 KTAS is only 6.37 degrees. Rate of climb alone is not the solution.
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Re: Engine failure best glide speed descent rate

Post by Rich »

Ran some what if stuff for a 180-deg turn. The numbers I plugged in assume a willingness to make a coordinated turn close to stall speed for a non-NG DA40. It also excludes the startle/denial delay. The altitude loss rates are sort of extrapolated from the bast-glide loss rate, though the 60-Kt number is in line what I've seen at medium weights. Note that, generally, a steeper bank overcomes the necessity to use a higher airspeed. This is largely a consequence of the fact that rate of turn is proportional to the tangent of the bank angle and the turn radius/diameter is inversely related to the tangent. Note also that the tangent approaches infinity as the angle approaches 90 degrees. This supports the "wingover" approach promoted by some. :D
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Re: Engine failure best glide speed descent rate

Post by Rich »

The video does present a valid condition. Some airports don't have attractive off-airport options nearby. Most of us could come up with examples (I'm lookin' at you, LDJ). So we have to recognize when we're rolling the dice.
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Re: Engine failure best glide speed descent rate

Post by gtmize »

I've been curious about Glide Ratios so I went up Monday in my DA40 and did two test glides @ idle / no flaps and got

1) 6 nm descending 2,000' @ 70 kts ( best glide) ~ 13:1
2) turned 90 degrees - then 3.5 nm descending 2200' same config ~ 9.5: 1
...better than I expected but Cross and Tail winds I'm sure factored in

Plan on doing a few more extended glides to test GR but for time being 8.5:1 seems conservative .. I'll be assuming 10:1

Having a good fix on glide ratio is important for me in practicing Power Off Landings - my current focus
holding 70 kts at Idle the rate of descent is high of course .. 800 f/m.... so the holding that ROD to flare is a challenge/scary
So next step is to try a few more Power Off landings adding ( and holding) 200 -300 RPM at 70kts to achieve a lower descent rate around 500'/min
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Re: Engine failure best glide speed descent rate

Post by astaib »

gtmize wrote: Wed Sep 30, 2020 1:14 pm I've been curious about Glide Ratios so I went up Monday in my DA40 and did two test glides @ idle / no flaps and got

1) 6 nm descending 2,000' @ 70 kts ( best glide) ~ 13:1
2) turned 90 degrees - then 3.5 nm descending 2200' same config ~ 9.5: 1
...better than I expected but Cross and Tail winds I'm sure factored in

Plan on doing a few more extended glides to test GR but for time being 8.5:1 seems conservative .. I'll be assuming 10:1

Having a good fix on glide ratio is important for me in practicing Power Off Landings - my current focus
holding 70 kts at Idle the rate of descent is high of course .. 800 f/m.... so the holding that ROD to flare is a challenge/scary
So next step is to try a few more Power Off landings adding ( and holding) 200 -300 RPM at 70kts to achieve a lower descent rate around 500'/min
Very interesting tests, I will do it too, but how to be sure that there is no wind that will influence the result? Maybe make it 3 times at the same place/same altitude but with a heading of 120° different each time. What altitude did you start? The higher the better?

Personnaly I do all my "integration and landing" in my home airport (and sometimes elswhere) with a "power off configuration": Overhead/1500 ft above the ground/Idle/pump/full rich/Pitch lever push/70 kt. Flaps only when I'm sure to have the runway. I indeed noticed a vario of -800fpm.

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