Engine out glide distance

[jackn]

I've been using the 'glide' ring on my Garmin Pilot app. You plug in the glide ratio from the POH and a fudge factor( suggested 20%), it will give you a ring(cyan) showing how far you can glide. Anyway, I'm always surprised at how much less I can actually glide vs what I had previously thought I could. The photo is just south of JFK at 6k( usual transit altitude). 

Edited November 21, 2017 by jackn

[kortopates]

4 minutes ago, jackn said:

I've been using the 'glide' ring on my Garmin Pilot app. You plug in the glide ratio from the POH and a fudge factor( suggested 20%), it will give you a ring(cyan) showing how far you can glide. Anyway, I'm always surprised at how much less I can actually glide vs what I had previously thought I could. The photo is just south of JFK at 6k( usual transit altitude). 

Do tell what ratio you calculated? Did you enable winds and terrain too? (the latter shouldn't matter over JFK though, but winds would).

But it appears yours is showing 5 nm when we would expect to see (6 * 2.1) * 0.8= 10nm  (using your 20% decrease) no wind. But it looks like it is showing 8-9nm going 180 degrees off your tail and max range about 200 degree bearing off your nose - so I assume you do have winds enabled but still looks short at max range. So what did you use for a number? 

[jackn]

The winds & terrain turned on, the winds where honking from the SW. Thanks. The POH says I have a 10:1 glide. Seemed low to me. 

Edited November 21, 2017 by jackn

[Mooneymite]

I'm not by my POH, but I seem to remember that 2 X your height above the ground/1000 roughly equals your no wind glide distance.  The difference between windmilling and stopped prop is less than I would have thought.

I'm hoping I never have to verify this.  

[kortopates]

35 minutes ago, jackn said:

The POH says I have a 10:1 glide.

Where do you see that? See page 3-13, it shows 2.1 nm per 1000' using that: (2.1nm * 6076 ft/nm)/1000 ft= 12.75 : 1

[FloridaMan]

I've done some tests in my F at near max gross. At 100mph I was descending at 700fpm at 6000msl. I figure 2 miles per 1000ft, keep winds in mind and use the "nearest airports" page on the GNS530. If I had an engine out at altitude and had the choice between deadsticking it to an airport packed in by buildings and/or trees or a farm road/field where I could be less than perfect, I'd probably choose the field. 

 

My engine out procedure in IMC is to dive and come out of the base with as much energy as possible to have as much time as possible to identify a landing location and navigate to it. 

Edited November 22, 2017 by Antares

[N201MKTurbo]

I did some tests about 30 years ago with my M20F. I would sometimes fly long cross countries at 500 AGL or less because I was young and stupid. I wondered how far I could glide from that altitude. So I tried it two different ways. I would fly outbound from a VOR  and at a certain DME I would pull the engine to idle and see how far I could go till I was about 50 ft AGL. I. Don't remember the exact numbers, but it was something like 1.5 miles if I maintained altitude until reaching best glide speed and 2.5 miles if I zoomed up to best glide speed. 

The lesson I learned is if your engine quits, aggressively getting to best glide speed will buy you almost a mile of glide.

[PTK]

There must be a slight variation among the different models. Which airplane are you guys referring to? My POH (M20J) shows 1.8 nm/1000 ft which calculates to a glide ratio of 10.9 : 1.

 

[jackn]

13 hours ago, kortopates said:

Where do you see that? See page 3-13, it shows 2.1 nm per 1000' using that: (2.1nm * 6076 ft/nm)/1000 ft= 12.75 : 1

I don't have my POH handy right now, but I'm sure it came from the performance section, I'll check. Also, years ago when getting my pp, my instructor actually shutdown the engine in the 172. I'm not going to comment whether that was a good idea, but the difference in glide performance was noticeable. 

[Bryan]

I think I have 11:1 plugged into my model in FF for my M20K. I use the ring more as guidance (awareness) than absolute.

[N201MKTurbo]

So Has anyone actually cut an engine to see if they can glide to the ring? To a point in front of them and in back of them. YMMV Can you do the numbers in the book? It probably takes perfect technique. Plus if the point you want to glide to is behind you there is the radius of the teardrop turn. Is that accounted for in the circle? Is the energy loss in the turn accounted for? Is a steep turn better than a shallow turn?

I have been playing with multi-engine planes lately including trying to get them to fly level at their single engine service ceiling. It takes constant perfect technique. The slightest inattention and you are descending. It takes practice to get it right and all planes are a little different. The same is true of the glide in the Mooney. If you don't get it perfect you will not make the circle.

[cnoe]

This topic was discussed in great detail back in March 2016 when I conducted glide tests in my M20J. My findings were that the published glide ratios/distances were overly conservative.

For me personally, I set the (wind corrected) glide distance rings on my moving map (Foreflight) to a ratio of 14.4:1 or 2.37 nm/1,000' agl. In the event of a power-off event I want to know ALL of my options, not just the ones that Mooney's lawyers conjured up for me. Of course I'd look for the closest acceptable landing spot, but I wouldn't put it into a hole in the trees if my calculated glide range would allow me to fly beyond them. 

I believe that a CONSERVATIVE figure (for MY plane) is 14:1 or 2.3 nm/1,000' agl. Your numbers may vary; you'll never know unless you practice this.

My personal testing was done with both "power on" and "power off" (i.e. mixture pulled to ICO) with the prop control pulled fully out. The difference between "idle" and "off" was less than you'd expect.

Somebody may flame me for flying around with my engine off but it's really no big deal. I also have no issue running a tank to empty if the flight scenario requires it (though it rarely does).

All the details are found under a previous post titled "M20J or glider". This link may get you there: https://mooneyspace.com/topic/17978-m20j-or-glider/?tab=comments#comment-261924

cnoe

 

[cnoe]

21 minutes ago, N201MKTurbo said:

It probably takes perfect technique.

The same is true of the glide in the Mooney. If you don't get it perfect you will not make the circle.

I didn't find that to be the case. I'm anything BUT a pilot with "perfect technique". Anything within a 5 knot range around 88 kts should buy me 14:1 in my J.

[Mooneymite]

This is all great information and we can all learn from this thread.  However, in an actual engine out situation, the last thing I want to do is try to strectch my glide unless absolutely necessary.  I would rather have to dissipate energy in an area I know that I can make than to hit houses because my glide computations were just a "little shy" of a runway.  Once the engine quits, I'm flying the insurance company's airplane.

[AH-1 Cobra Pilot]

There is a HUGE difference in glide performance depending on a few things. 

1.  Is your engine barely running?  If so, it will not provide thrust, but may allow you to feather your prop.  Anyone who flies twins can attest to what happens when you change your prop pitch in flight.  Most twins have the prop set to go to feather if the engine fails in flight; singles do not.  (In fact, most singles' prop systems fail to the max rpm mode.)  It also makes a big difference how many rpm your engine still has.  Some rpm is the zero-drag-point, with higher rpm producing thrust and lower rpm producing drag.
2.  Is your prop stopped?  Big difference in drag between windmilling and stopped.
3.  If your prop is windmilling, throttle open or closed?  Less engine resistance with a full-open throttle reduces drag.

If you really want to give us all some good numbers from your experience, please test all of these and let us know.

[Hank]

@Ah-1 Cobra Pilot There are precious few Mooneys whose props will fully feather, or even approximate a feathered position. But if the prop is turning and the engine still has oil, pulling the prop control will move the blades and reduce drag. Haven't heard that tidbjt about WOT if the engine is dead.

Even my own aged Owners Manual has different Best Glide speeds and descent rates for "prop windmilling" and "prop stopped." Yes, the latter us both slower IAS (100 vs 105 mph) and longer range (12.3:1 vs. 10.7:1 glide ratio, I forget the miles per 1000' for stoped but it's 2.3 windmilling, the most common type of engine failure),

An awful lot of it comes down to "know your airplane!"

[cnoe]

10 hours ago, Ah-1 Cobra Pilot said:

There is a HUGE difference in glide performance depending on a few things. 

1.  Is your engine barely running?  If so, it will not provide thrust, but may allow you to feather your prop.  Anyone who flies twins can attest to what happens when you change your prop pitch in flight.  Most twins have the prop set to go to feather if the engine fails in flight; singles do not.  (In fact, most singles' prop systems fail to the max rpm mode.)  It also makes a big difference how many rpm your engine still has.  Some rpm is the zero-drag-point, with higher rpm producing thrust and lower rpm producing drag.
2.  Is your prop stopped?  Big difference in drag between windmilling and stopped.
3.  If your prop is windmilling, throttle open or closed?  Less engine resistance with a full-open throttle reduces drag.

If you really want to give us all some good numbers from your experience, please test all of these and let us know.

You do have some good points. Pulling the prop back makes a BIG difference IMO. You can see this in most any landing approach by getting stabilized then pulling the prop back to the stop.

I also agree that if your prop is "stopped" you'd gain even more, but from all accounts you have to slow to near-stall-speed to get the prop to stop in the J. Unless you were really high I'd be hesitant to waste all that energy just to get the prop to stop windmilling. I WOULD like to know how much difference it actually makes and may do that someday; if I do I'll report my findings back here.

The "throttle position" brings up some interesting questions as well. Once the prop starts "pushing" the engine, manifold pressure increases dramatically. My biggest concern would be the consequences of my engine coming to life at WOT while preparing for an engine-out landing. It should be a non-issue if handled quickly but it could also prove startling in a critical phase of flight. 

For everyone's viewing pleasure I'm attaching 2 pics of my JPI data (manifold pressure, RPM, and EGTs) for a "simulated" engine-out (idle speed only = ~860 rpm) vs. a "true" engine-out (ICO position = ~663 rpm). The RPM difference between those 2 scenarios is approximately 200 RPM in my plane.  Note: The JPI quickly shuts down once the engine quits making significant power which truncates the graphs somewhat. 

As stated before, in my plane 14:1 or 2.3 nm/1,000' is a conservative glide expectation either power-off or idling. For me these are good numbers. Your mileage may vary.

cnoe

[bradp]

I use 11:1 in foreflight as a conservative figureI   

l like the glide ring feature on takeoff - it gives you a pretty decent idea of when the impossible turn becomes possible.  

[amillet]

On 11/22/2017 at 2:51 AM, PTK said:

There must be a slight variation among the different models. Which airplane are you guys referring to? My POH (M20J) shows 1.8 nm/1000 ft which calculates to a glide ratio of 10.9 : 1.

 

I have also input 11:1 into ForeFlight extrapolating from the POH chart.  I’m surprised there is not a more precise glide ratio published for the J model.  I haven’t done the in flight cross check like @cnoe, but it is comforting to know the POH is a conservative number.

[cnoe]

I use 11:1 in foreflight as a conservative figure 

Happy Thanksgiving everyone!

The last thing I want to do is come across as a know-it-all (because I’m not) but I want everybody to consider making a brief flight or two to determine their “actual” glide ratios.

Consider that at an altitude of only 5,000' AGL you would be looking for a landing spot within 9 nm (no wind). If you don’t see an airport on your iPad within that distance you’ll be aiming for the best visible terrain (which may or may not turn out to be hospitable).

Meanwhile if my engine stops I’ll see a glide-ring with a diameter that’s FIVE MILES larger than yours. Now I have 415 square nm in which to find an airport (or other landing site) while you are limiting yourself to only 254 square nm. That’s 39% less available landing area.

All I’m saying is that in my M20J the published glide ratio is excessively conservative. With today’s incredible technology (iPad w/glide ring) and a simple 30 minute test flight I’ve increased my engine-out landing options by 63%! That’s one of the best safety return-on-investment I could imagine.

cnoe



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[steingar]

A fun thing to try if you don’t need to get anywhere. Put yourself at 4K feet over an intowered airport, hopefully with no one in the pattern. Pull the power.  Land with no engine power in the first third of the runway. It’s actually a bit harder than it sounds.  Good way to safely explore energy management in your airplane.

[Mooneymite]

Just now, cnoe said:

....All I’m saying is that in my M20J the published glide ratio is excessively conservative....

 

I'm glad to have your empiracle data.  It's great data...for your aircraft.  However I'm not a test pilot.  My career has been spent keeping as much as I can "by the book".

I am skeptical that Mooney's numbers are "excessively conservative".  They may include factors mandated by real world flight test experience.

 

[PTK]

2 hours ago, amillet said:

I have also input 11:1 into ForeFlight extrapolating from the POH chart.  I’m surprised there is not a more precise glide ratio published for the J model.  I haven’t done the in flight cross check like @cnoe, but it is comforting to know the POH is a conservative number.

I have in the back of my head the nice round number of 10:1. 

I know if I’m at 6k ft (1 nm) no wind I have a 10 nm horizon.  And then up or down from there. At 12k ft I have 20 nm and 5 nm at 3k ft.

[cnoe]

I’m not suggesting that anybody do anything risky here. It’s as simple as (on a calm day) setting up a 5 nm straight-in final at 3,000' AGL and pulling the throttle to idle and the prop knob out. Keep your configuration “clean” and pitch for 88kts/100m ias.

If your glide ratio is truly 11:1 you’ll cross the threshold at ~250'. If you cross at ~850' then your glide ratio is closer to 14:1. Either drop the gear and land or go around.

It may be counterintuitive but IMO it is less safe to fly with one’s Glide Distance Ring set up inaccurately, thereby significantly limiting your options in an engine-out.



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[TargetDriver]

CNOE,

I apologize for taking this thread sideways for a moment, but I've bought the JPI 830 and its waiting for me to get home and get it installed (might try it myself) in a couple weeks. My K Model is all virgin with the Silver Crown stack so this will be its first modern upgrade.  I've seen guys posting their graphs as you have.  Where are you getting that software? Does it come with the 830 and is loadable to read the downloaded data?  I've done a lot of engineering flight testing but not in the GA world so looking forward to having this amount of data from my plane.  Thanks