Corsair2
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Glide Distance

Mon Jun 20, 2005 11:28 pm

What is a good rule of thumb for glide distance with an engine failure in a Cessna 172 as a function of altitude? 1000 ft per mile?
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KFLLCFII
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RE: Glide Distance

Tue Jun 21, 2005 4:26 am

Quoting Corsair2 (Thread starter):
What is a good rule of thumb for glide distance with an engine failure in a Cessna 172 as a function of altitude? 1000 ft per mile?

Appx. 1.5 NM per 1,000 feet at best-glide speed (68 knots). This, of course, will depend on total weight, flap setting, a windmilling propeller, and zero wind. Source: C172R Information Manual, Section 3, Figure 3-1 Maximum Glide.

(Edited for source)

[Edited 2005-06-20 21:34:24]
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Corsair2
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RE: Glide Distance

Wed Jun 22, 2005 1:36 am

Also, what FAR's apply to the crossing of water in single engine airplane. I remember one about minimum equipment needed but can't remember which one it is to refer to it?
"We have clearance Clarence. Roger, Roger. What's our vector Victor?"
 
KFLLCFII
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RE: Glide Distance

Wed Jun 22, 2005 9:32 am

There is no equipment requirement regarding the crossing of water in a single-engine airplane unless that aircraft is operated for hire:

Sec. 91.205 Powered civil aircraft with standard category U.S.
airworthiness certificates: Instrument and equipment
requirements:

(b) Visual-flight rules (day). For VFR flight during the day, the
following instruments and equipment are required:

(12) If the aircraft is operated for hire over water and beyond
power-off gliding distance from shore, approved flotation gear readily
available to each occupant and at least one pyrotechnic signaling
device. As used in this section, ``shore'' means that area of the land
adjacent to the water which is above the high water mark and excludes
land areas which are intermittently under water.


In reading a required-equipment regulation farther down part 91, one may confuse this next regulation as applying to all airplanes:

Sec. 91.509 Survival equipment for overwater operations.

(a) No person may take off an airplane for a flight over water more
than 50 nautical miles from the nearest shore unless that airplane is
equipped with a life preserver or an approved flotation means for each
occupant of the airplane.
(b) Except as provided in paragraph (c) of this section, no person
may take off an airplane for flight over water more than 30 minutes
flying time or 100 nautical miles from the nearest shore, whichever is
less, unless it has on board the following survival equipment:
(1) A life preserver, equipped with an approved survivor locator
light, for each occupant of the airplane.
(2) Enough liferafts (each equipped with an approved survival
locator light) of a rated capacity and buoyancy to accommodate the
occupants of the airplane.
(3) At least one pyrotechnic signaling device for each liferaft.
(4) One self-buoyant, water-resistant, portable emergency radio
signaling device that is capable of transmission on the appropriate
emergency frequency or frequencies and not dependent upon the airplane
power supply.
(5) A lifeline stored in accordance with Sec. 25.1411(g) of this
chapter.


Sound convincing for all small single-engine airplanes? Sure. But when you take a step back and check the applicability of the subpart having authority over this regulation (Subpart F), you will note this:

Subpart F_Large and Turbine-Powered Multiengine Airplanes and Fractional
Ownership Program Aircraft

Sec. 91.501 Applicability.

(a) This subpart prescribes operating rules, in addition to those
prescribed in other subparts of this part, governing the operation of
large airplanes of U.S. registry, turbojet-powered multiengine civil
airplanes
of U.S. registry, and fractional ownership program aircraft of
U.S. registry that are operating under subpart K of this part in
operations not involving common carriage.


Hence, this regulation ALSO does not apply to all light single-engine airplanes.

So, if you are in a light single engine airplane for private use, there is no over-water equipment requirement. These regulations only apply to aircraft operated for hire, or are large, turbojet-powered multiengines, or are operated under a fractional ownership program.
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atct
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RE: Glide Distance

Wed Jun 22, 2005 9:35 am

I believe the Bahamas require overwater equipment. I dont know the reg offhand, but I believe they have one for aircraft doing the FL-Bahamsa hop.
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PlainSmart
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RE: Glide Distance

Wed Jun 22, 2005 3:05 pm

The best glide distance for a power off prop happends at the L/Dmax. This is the speed where there is the lowest drag between parasite and induced. As airspeed goes up so does parasite drag. On the other hand, as airspeed goes up, induced drag ultimately goes down. For each airspeed one can calculate what the total drag for an airplane is. At one point though, there will be a smallest total drag number. The airspeed that corresponds with this total drag value is your best glide airspeed.

The 172 is 68 KIAS This is the speed that you will incur the least amount of drag possible. I do not know the L/D max of the 172 although a very close cessna I worked the numbers and the L/Dmax is 10.33 which means for every NM f altitude, the airplane will travel 10.33NM. About 85 kias at sea level.
 
Corsair2
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RE: Glide Distance

Fri Jun 24, 2005 5:49 am

Thanks KFLL CFII. I didn't realize that the equipment requirement was for commercial operations.

The trip I had in mind (Apostle Islands in Lake Superior) involves a short crossing of water (4-5 miles). Now I realize that all I need to do is fly >3000 ft and use some reasonable caution based on the wind conditions that day.

If I were wanting to cross all the way across Lake Michigan (> 60mi) it would be wise to get a life preserver even though it is not required. Not a pretty situation to be stuck in the middle of Lake Michigan!
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KFLLCFII
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RE: Glide Distance

Fri Jun 24, 2005 6:30 am

Quoting Corsair2 (Reply 6):
If I were wanting to cross all the way across Lake Michigan (> 60mi) it would be wise to get a life preserver even though it is not required. Not a pretty situation to be stuck in the middle of Lake Michigan!

Not at all! For that trip I would also recommend renting a life raft (if such a service exists in your area), a flare gun with an adequate supply of flares, and a hand-held transceiver packed in a waterproof case with many sets of spare batteries. Prepare for the worst, hope for the best!
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B744F
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RE: Glide Distance

Fri Jun 24, 2005 10:49 am

Pilots practice water landing procedures but most know going down in water means almost certain death. There are life preservers and rafts on airplanes but they do little good unless you are just having a lucky day.
 
KFLLCFII
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RE: Glide Distance

Fri Jun 24, 2005 12:05 pm

Quoting B744F (Reply 8):
There are life preservers and rafts on airplanes but they do little good unless you are just having a lucky day.

Adding to that, the best type of life preserver is the inflatable "vest" type, which can be worn in flight with little interference. Should you have to make an emergency egress into the water, you already have it donned, and all that's required is a tug on the CO2 cord to inflate. But you are right regarding the raft; They can be bulky, and can be difficult to get out of the plane if it's rapidly sinking. However, I'd rather have one onboard with the chance I may or may not be able to utilize it than not having one at all.

PS - 300th Post!
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sccutler
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RE: Glide Distance

Sun Jul 03, 2005 7:32 am

Quoting B744F (Reply 8):
Pilots practice water landing procedures but most know going down in water means almost certain death. There are life preservers and rafts on airplanes but they do little good unless you are just having a lucky day.

This may well be true for large, transport category aircraft, but in general aviation aircraft, nearly all ditchings are survivable, and the aircraft usually remains afloat for long enough to get out and into such flotation gear as you may have. I hope never to provide the proof myself, but I know people who have ditched and survived to tell all.
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DH106
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RE: Glide Distance

Sun Jul 03, 2005 8:13 am

Quoting PlainSmart (Reply 5):
The 172 is 68 KIAS This is the speed that you will incur the least amount of drag possible. I do not know the L/D max of the 172 although a very close cessna I worked the numbers and the L/Dmax is 10.33 which means for every NM f altitude, the airplane will travel 10.33NM. About 85 kias at sea level.

Min Drag Speed = Min sink/Max Duration
Max L/D = Max range

As PlainSmart quotes, for a C172, 68KIAS give you min sink/max duration and 85KIAS gives max range achievable albeit in less time. So when your engine stops, an assessment of how terminal it is will dictate which of these to adopt.
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Corsair2
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RE: Glide Distance

Mon Jul 18, 2005 10:40 pm

Thanks for all the good posts on this. I have always wondered too when flying along Lake Michigan (within glide distance of shore) how easy it would be to get out of a Cessna 172 if it went down in the water. How would one get the door open in the water and then get out given the possibility of the high wing being an obstacle. Water evacuation is something not practiced in our training but would be worth knowing how to do.
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