Over-water glide calculator

flyingcheesehead

flyingcheesehead

Touchdown! Greaser!
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iMooniac
Well, on a whim yesterday, I whipped up this spreadsheet for calculating over-water glide distance and such.

I guess it was mainly because I finally tested the glide performance of both the 182 and my favorite Archer. The 182's Vg is 80mph. If you pull power and put the trim all the way nose up, it holds 80mph amazingly well all on its own. With me + Kate + my big-ass flight bag aboard, we were getting 1000fpm descent. In the Archer with just me and the bag, 76 KIAS Vg resulted in a 750fpm descent, though holding Vg took a bit more work in this plane and the trim was not all the way back.

Anyway... You enter your best glide IAS, the descent rate at best glide, your cruise altitude (MSL), the level of the water you're crossing MSL, your cruise speed, the distance across water on your course, and any headwind/tailwind component.

The spreadsheet will then tell you your glide ratio (the 182 has a rather brick-like 7.04 to 1!), your glide range forward on course, your glide range backwards (for returning to shore behind you), the distance and time you'll be outside of gliding range to either shore, and the minimum altitude you'd need to fly at to have zero exposure time.

Enjoy! :)
 

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  • Best Glide.xls.zip
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the nice thing about gliding over water is that you dont usually have to worry about slowing down in the lift and speeding up in the sink. dont forget to add half the wind speed for a headwind, and slow down a tad for a tailwind.
 
flyingcheesehead said:
With me + Kate + my big-ass flight bag aboard, we were getting 1000fpm descent.

the 182 has a rather brick-like 7.04 to 1
Click to expand...

What was your true airspeed and GPS indicated ground speed?

Calculating glide ratio based on VSI FPM descent probably isn't a very accurate. Did you crosscheck the VSI by seeing if you actually went down 1,000 ft in a minute? It'd be better to do it with your GPS and altimeter. You'll also want to pay attention to your ground speed versus true airspeed as that will skew your numbers drastically as well.

Also as Lance mentions where was your prop set? Prop forward is going to really screw your glide ratio in a complex bird.
 
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flyingcheesehead said:
...
I guess it was mainly because I finally tested the glide performance of both the 182 and my favorite Archer. The 182's Vg is 80mph. If you pull power and put the trim all the way nose up, it holds 80mph amazingly well all on its own. With me + Kate + my big-ass flight bag aboard, we were getting 1000fpm descent. In the Archer with just me and the bag, 76 KIAS Vg resulted in a 750fpm descent, though holding Vg took a bit more work in this plane and the trim was not all the way back.
...
Click to expand...

My 235 drops at 1000fpm at best glide with only my big ass on board...or mine with a CFI.
 
Mythbusters took on gliders made of concrete last night....
 
Ken Ibold said:
I saw that a while ago. Jaime could have whipped Adam's butt if he hadn't make a poor throw. They should have used identical launch methods.
Click to expand...

Nah, it was a balance issue. Had Adam not added the proboscus to the front, all would have been well.
 
lancefisher said:
Was that 7:1 with the prop in coarse or fine pitch? IIRC a 182 will do closer to 10:1 with the prop knob pulled all the way out.
Click to expand...

I just left it at 2200 RPM where it was already.

Isn't 9:1 about average for the GA fleet? The 182 is a very draggy airframe. I can't say I was overly surprised at the ratio.

I'll go up again and try it with the prop all the way back. I'm also now very curious to see what the ratio is with prop forward and full flaps (landing configuration).

I was just playing around with it at first... Maybe I'll improve on it by correcting for true airspeed, correcting airspeed for glide angle, and adding a place to put in winds aloft at the various altitudes to calculate a more accurate turn-back point.
 
jesse said:
What was your true airspeed and GPS indicated ground speed?
Click to expand...

I was just playing around for the heck of it... Didn't note anything else.

Calculating glide ratio based on VSI FPM descent probably isn't a very accurate. Did you crosscheck the VSI by seeing if you actually went down 1,000 ft in a minute?
Click to expand...

I thought about timing the descent to crosscheck the VSI after I'd already dropped about 3,000 feet. :redface:

It'd be better to do it with your GPS and altimeter.
Click to expand...

That would be affected by winds aloft, though.

You'll also want to pay attention to your ground speed versus true airspeed as that will skew your numbers drastically as well.
Click to expand...

Skew, yes... Drastically, I doubt it. I'd bed that correcting for true airspeed and then correcting for the vertical component of the airspeed would nearly cancel each other out.

OK, now I've done it. I've let a bunch of pilots analyze something...

So, next time, I'll go up to 13,000 feet or so, have the autopilot hold heading perfectly still, and every 1000 feet on the way down I'll record:

IAS (should be consistent 80)
OAT
Ground speed
Ground track
Elapsed time
Actual distance covered

Then, for the entire experiment, I'll record the altimeter setting and forecast winds aloft.

With that data, I should be able to calculate true airspeed, actual winds aloft, and the actual glide performance. Am I missing anything?
 
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flyingcheesehead said:
Hehe... Yeah, you got me. Guilty as charged. :D

Actually, I'm just interested in getting to know the bird really well. :yes: Next time I cross the lake I should be able to calculate a more accurate turn-back point.
Click to expand...

sometimes ignorance is bliss...
 
A couple of rules of thumb I've heard:

- Each degree of pitch is worth 100 ft/nm.. So at 10 degrees nose low, you're doing about 1000ft/nm.

- Airspeed in miles per minute (Indicated Mach Number) x Degrees of pitch change relative to level flight = VVI
So at 0.6 Mach, a 1 degree pitch change = 600 FPM up or down
 
Patch said:
A couple of rules of thumb I've heard:

- Each degree of pitch is worth 100 ft/nm.. So at 10 degrees nose low, you're doing about 1000ft/nm.

- Airspeed in miles per minute (Indicated Mach Number) x Degrees of pitch change relative to level flight = VVI
So at 0.6 Mach, a 1 degree pitch change = 600 FPM up or down
Click to expand...

so what mach does a 182 fly at?
what aircraft is that a ROT for?
 
ok thought about it more, makes sense.
 
Patch said:
It's all about the math. :D
Click to expand...

isnt everything?

my HS geometry teacher had these posters with quotes all over his room. one was "Mathematics is the language with which God has written the universe"
 
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