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Dead Stick!

Here is the raw data. EDIT: 68 C-180H Two pilots, 1/2 fuel, 2330 lbs. CG 38.6
80 degree summer Florida day. Done from 5 to 3 thousand MSL. 88 inch Black Mac prop.

Throttle closed, Mixture rich, Propeller low pitch, Flaps up
IAS, Rate of Descent, (or altitude lost /minute, this is more accurate), Distance over ground/minute
100
90 1200 FPM
80 850 FPM
70 800 FPM
60 700 FPM
50
Throttle closed, Mixture rich, Propeller high pitch, Flaps up
IAS, Rate of Descent, (or altitude lost /minute), Distance over ground/minute
100
90 910 FPM
80 825 FPM
70 700 FPM
60 550 FPM
50
Throttle closed, Mixture idle cutoff, Propeller low pitch, Flaps up
IAS, Rate of Descent, (or altitude lost /minute), Distance over ground/minute
100
90 1300 FPM
80 1000 FPM
70 780 FPM
60 900 FPM (aircraft stalled and sinking)
50
Throttle closed, Mixture idle cutoff, Propeller high pitch, Flaps up
IAS, Rate of Descent, (or altitude lost /minute), Distance over ground/minute
100
90 1300 FPM
80 1100 FPM
70 800 FPM
60 900 FPM (again, stalled and mushing)
50
Propeller stopped, Flaps up

Could not get the prop to stop down to 50 mph in coarse or fine pitch. Weather was closing in so we stopped there.

Surprisingly, the prop pitch had little effect on a windmilling, dead engine.
Here is what the POH shows.

1968 C-180 POH

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FWIW the difference in gliding range between coarse and full fine in a Pitts is dramatic. In full fine the Pitts feels as if it is carrying out an auto rotation :)


Sent from my iPhone using SuperCub.Org
 
High pitch / low pitch terminology always confused me.
Judging from the sink rate results,
I'm assuming "low pitch" means fine pitch (blue knob pushed in),
"high pitch" means coarse pitch (blue knob pulled out)?
 
You assume correctly!


High pitch / low pitch terminology always confused me.
Judging from the sink rate results,
I'm assuming "low pitch" means fine pitch (blue knob pushed in),
"high pitch" means coarse pitch (blue knob pulled out)?
 
I did some math with the new numbers in red. The best average distance and time from 5000 feet is at 60 mph with the engine idle and high pitch.
With the engine shut down it is 70 mph and low pitch. It is interesting that perhaps with the engine shut down there are not enough rpms to produce enough oil pressure to move the prop to high pitch.
I also figured the numbers for 85 mph since that is Cessna's suggestion.

Here is the raw data. Two pilots, 1/2 fuel, 2330 lbs. CG 38.6
80 degree summer Florida day. Done from 5 to 3 thousand MSL. 88 inch Black Mac prop.

IAS, Rate of Descent, (or altitude lost /minute, this is more accurate), Distance over ground/minute

Throttle closed, Mixture rich, Propeller high pitch, Flaps up
IAS, Rate of Descent, (or altitude lost /minute), Distance over ground/minute
100..............Time from 5000'......distance in miles
90 910 FPM.........5.49 minutes........8.24
85 867 FPM.........5.77 minutes........8.17
80 825 FPM.........6.06 minutes........8.08
70 700 FPM.........7.14 minutes........8.33
60 550 FPM.........9.09 minutes........9.09
50
Throttle closed, Mixture idle cutoff, Propeller low pitch, Flaps up
IAS, Rate of Descent, (or altitude lost /minute), Distance over ground/minute
100..............Time from 5000'......distance in miles
90 1300 FPM.......3.85 minutes........5.77
85 1150 FPM.......4.35 minutes........6.16
80 1000 FPM.......5.00 minutes........6.67
70 780 FPM.........6.41 minutes........7.48
60 900 FPM (aircraft stalled and sinking)

Propeller stopped, Flaps up

Could not get the prop to stop down to 50 mph in coarse or fine pitch. Weather was closing in so we stopped there.

Surprisingly, the prop pitch had little effect on a windmilling, dead engine.
Here is what the POH shows.

View attachment 44527
Not being able to stop the prop is not surprising, as the aluminum prop with it's good flywheel characteristics is very efficient. You would likely have to zoom climb at just above stall speed to get an extra low speed to get the prop to stop. Then when you picked up just a little speed it may start turning again. You would likely sacrifice time and altitude in the effort for a net loss in a real emergency. It would be an interesting experiment though.

As a point of interest I tried this with a 727-200 once from 10,000 to sea level with the engines idle and 250 knots. It went 41 miles, twice the distance of a 185 per Cessna.

I would suggest that if in a real situation that you trade some altitude for more speed when almost down. This will give you enough speed to flare, arresting the rate of descent for a smooth landing. That may be the reason that Cessna is recommending 85 mph?
 
I did some math with the new numbers in red. The best average distance and time from 5000 feet is at 60 mph with the engine idle and high pitch.
With the engine shut down it is 70 mph and low pitch.

The accuracy of the data needs to be considered. Physics says that for a given configuration as speed increases from stall the sink rate will reduce and glide ratio will increase until reaching lowest sink speed. Then the sink rate will increase until best glide ratio speed. Then the sink rate will increase more rapidly and glide ratio gets worse. The data doesn't show that, perhaps to do air currents or other factors that couldn't be controlled. ...something to consider when planning glide distance, you may not get what you planned for.

19.jpg

As a point of interest I tried this with a 727-200 once from 10,000 to sea level with the engines idle and 250 knots. It went 41 miles, twice the distance of a 185 per Cessna.

Airliners are very efficient, as is necessary for any high speed aircraft. The result can be very good glide ratios and typically will be if the wing aspect ratio is high enough, even if the sink rates are high.
 

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Just a thought....I remember reading a Berry Schiff article years ago where he suggested in some situations trimming to "minimum sink" airspeed might be better than trimming to "best glide" speed. The idea was to have more time in the air to sort out a problem, call ATC, whatever...
 

Curious what year POH that's from.
The owners manual for my 53 model doesn't have best glide info,
nor does the 1956 owners manual that I have.
Somebody was kind enough to send me this scan of the best glide chart from their later model POH, not sure what year though.
There's a significant difference in glide ratios -- 7.9:1 for my chart & 11:1 for yours.
FWIW I see the best glide speed for your is 85 & mine is 80.

C180 glide ratio.png
 

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...FWIW I see the best glide speed for your is 85 & mine is 80.
I assume that you have a 180? Eddie has a 185. Different gross weights. Also Eddie's flight test was done at less than maximum gross. I assume that Cessna's manual was based on maximum gross weight.

This may account for the differences you are seeing.
 
What's this "sink rate" thing about? You come down when the engine quits?! https://www.youtube.com/watch?v=8J9v433C0nM 5:00 in for the shutdown.

Ha, no ridge with a good breeze blowing into it I'm guessing, lousy luck! I ridge soar with one notch of flaps, 45-55 mph, glide seems to be about 7-1, twice as good as my first few hang gliders anyway. Sink rate about 750 FPM. I like to think my time spent engine off will help in a real emergency dead stick, but who knows until it happens for real.
 
I assume that you have a 180? Eddie has a 185. Different gross weights. Also Eddie's flight test was done at less than maximum gross. I assume that Cessna's manual was based on maximum gross weight. This may account for the differences you are seeing.

My question / comment is only about the POH best glide graph.
I believe Eddie has a C180H.
Different gross weight, correct.
May be why it shows 85 mpg glide instead of 80.
That's a pretty dramatic difference in glide ratio though.
 
Can you post a scan or photo?
Or give us a example--
for example, Eddie's chart shows 20 miles of glide from 10,000'.
 
My A185F manual shows a ground distance from 10,000 feet of 13 nautical miles or 15 statute miles. The best glide speed varies dependent on gross weight. 3350#-75 knots, 2650#-67 knots and 1950#-58 knots

For comparison, when on EDO 2960 floats the distance from 10,000 feet is 12.5 nautical miles. 3320#-75 kias, 2820#-69 kias and 2320#-63 kias.
Interesting that when on EDO 2790 amphibs the difference is just the speeds and weights. 3265#-75 kias, 2865#-70 kias and 2465#-65 kias.
 
My plane is a 69 180H. The chart I posted is from a 68 180 POH.

I assume that you have a 180? Eddie has a 185. Different gross weights. Also Eddie's flight test was done at less than maximum gross. I assume that Cessna's manual was based on maximum gross weight.

This may account for the differences you are seeing.
 
The two 185 graphs are the same as mine.
Maybe the one I have is from a 185?
Can't recall who sent me the scan,
as neither of the early 180 owners manuals I have (53 & 57)
have any engine out / glide info or procedure at all.

Like I said though- pretty drastic difference in glide ratio.
 
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I used to think "dead stick" meant loss of propwash makes the stick kinda dead, but its really from when all props were wood. Years ago a Luscombe pilot rigged up a microswitch that touched a wire that went thru a tube and touched the back of the prop flange. The axial play was enough to trigger the sw when the power was pulled just below zero thrust. No risk dead stick practice.
 
4000 feet probably seems pretty high (can't remember getting there) until you want to glide. Using the 185F chart that's about 6 miles without smiles. I'd guess that 6 miles is shorter than you may think.
I've seen this before, from which I've always appreciated knowing that as long as I can glide better than 1:14, I've got a fighting chance:

"A glide ratio of 20:1 might be appropriate for an Eagle riding the wind while a 1:14 ratio is similar to the glide capability of a brick."

http://www.csgnetwork.com/glideratiocalc.html



I like looking at the time factor. According to that calculator, at 500 AGL in a supercub in a stabilized 6:1 glide, you have 30 seconds before touchdown, depending on your choice of speed. I doubt a bush wheel equipped supercub would have much better than a 6-ish:1 ratio.
 
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Interesting technical discussion with some good information.I am curios though.How many still routinely fly closing the throttle abeam your proposed touchdown point and land the airplane?The bulk of my landings are done this way.
 
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