Commander glide ratio

[mrogers641]

ForeFlight has a great new feature that gives you your estimated dead stick glide path if you have your ACs best glide speed and ratio. My POH gives best glide speed as 82-65 kts depending upon load so I picked 75kts as a middle load range. But I can't find anything on glide ratio. Does anyone know those numbers. I would assume it would be different based on the different wing length out there.


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[Commander91gm]

Re: Commander glide ratio

There is a chart in the POH. For mine it shows a little under 2 miles per thousand feet.

 

[mrogers641]

Re: Commander glide ratio

So if you were 5,000 ft agl you would have 10 miles. I know Commanders are not gliders but that's pretty bad. Am I calculating that correctly?


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[mrogers641]

Re: Commander glide ratio

Might have answer my own question if my calculations are correct. If 2 miles per thousand feet works out to a ratio on 10.5:1 Not too bad Mooneys are about 12:1?


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[proppilot]

Re: Commander glide ratio

I have FF set up with an 8:1 glide ratio with best glide (Vbg) at 85 knots. I see others are using 8 as well as it may go to 9 but I like to set expectations low and push it IF I need to !

 

[Airotto370]

Re: Commander glide ratio

I have FF set up with an 8:1 glide ratio with best glide (Vbg) at 85 knots. I see others are using 8 as well as it may go to 9 but I like to set expectations low and push it IF I need to !

Ditto

 

[gmores]

Re: Commander glide ratio

There was discussion about this previously and I believe Scott Sedam did some testing. A search should find it. But if I recall it seemed that 9:1 was considered a safe number for those of us with the regular wings. The TCAs and 112Bs with the longer wings should be better but I don't know if anyone has done any real-world testing.

 

[Commander91gm]

Re: Commander glide ratio

The attached is in the emergency procedures section of the POH.
Do you think the numbers were calculated, or actually derived from flight testing?

 

[davidnusca]

Re: Commander glide ratio

I am using 9, but maybe 8 is more realistic and safer.

 

[mrogers641]

Re: Commander glide ratio

Thanks Joel. From your chart for the TCA wing it does look like 9:1 ratio and 75kts. I'll look again for my chart I'm sure I have it.


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[proppilot]

Re: Commander glide ratio

My thoughts are that the number should be conservative to drive your decision making process IF you are actually in a position that you are now making a decision based on that glide circle so I would prefer 8 to account for my lousy reaction as I get over the WTF factor and realize I need to land and knowing that I have a bit of wiggle room with 9 being the actual

It reminds me of the joke....

A student and flight instructor are up doing a night flight and the student asks the instructor 'what do we do if the engine fails ?'. The instructor replies that you put the airplane in best glide and when you are 200 feet off the ground, turn on the landing light. The student asked 'what if I don't like what I see !! ??' to which the instructor replies 'turn off the landing light'.....

 

[mrogers641]

Re: Commander glide ratio

My chart is showing 8.5:1. With 82kt heavy and 66kt light. I hope I'll never need it but it's a nice feature in FF.


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[proppilot]

Re: Commander glide ratio

In Joels chart it shows 10,000 feet of ground for 18,000 feet of air so that would be 8:1 ?

 

[Airotto370]

Re: Commander glide ratio

Yup, that will certainly account for some time and altitude lost.

 

[mrogers641]

Re: Commander glide ratio

I think 8:1 is a good conservative number. I was cross referencing 5280 Ft - 1 mile to miles of glide. In reality I'm with Tony I'm looking for a good place far inside that FF glide circle.


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[jukelemon]

Re: Commander glide ratio

To me, it is a whole lot easier to use a different ratio and that is miles per 1000ft. 1.5 miles per 1000 ft is a lot easier for me to figure in an ER situation and is a conservative number against the POH numbers.

At 10k ft, you have 15 miles. At 6k ft, you have 9 miles. Etc.

Moreover, the POH is at 0 wind...when is that ever the case?

So, 1.5 feels safe to me.

 

[mrogers641]

Re: Commander glide ratio

The POH numbers are great but try putting 1:5 into Forefight for the glide ratio, doesn't work and my POH only goes to 12,000 and I usually fly much higher. So I'm sticking with 8:1 and 75kts knowing that if I'm heavy I need to be a little faster. And hope never to use it.


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[jukelemon]

Re: Commander glide ratio

The POH numbers are great but try putting 1:5 into Forefight for the glide ratio, doesn't work and my POH only goes to 12,000 and I usually fly much higher. So I'm sticking with 8:1 and 75kts knowing that if I'm heavy I need to be a little faster. And hope never to use it.


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Fair point. I just prefer having a quick calc at hand as opposed to relying on an app during an ER situation.

 

[cschuler123]

Re: Commander glide ratio

I think 8:1 is a good conservative number. I was cross referencing 5280 Ft - 1 mile to miles of glide. In reality I'm with Tony I'm looking for a good place far inside that FF glide circle.

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Yep, from dead stick experience, you set up for glide speed and find directly in front of you, what you believe will work. My plane dropped like a rock at about 100 ft or so above ground, from what I can remember anyway. . I'm glad she dropped where she did....but flying her, I did not believe she would drop at all. I thought for sure I would get another 50-100' feet of glide out of her no problem. Not the case though.

 

[mrogers641]

Re: Commander glide ratio

You just didn't have much time Clint. The Forefight guides won't even show up until your at least 200 ft agl so no value. But what is good to know is how strong an airframe we have. Safe flying.


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