Glide ratio

[Scott]

Hi all
getting ready for Osh and looking at flight planning options. My usual route takes me down the western shore of Lake Superior and a left turn at Silver Bay. There is about 20nm of open water to cross at that point.

I generally use 1.5nm per 1000' as a glide ratio which I believe is conservative. I do a cruise climb for the first half and usually end up at about 5000' which gives me 7.5 miles i.e. a little shy of the shoreline! I guess that's a statement of my risk tolerance with life jacket on board.

I've looked through the manuals, including the L2 flight manual and the only data I can find is 60mph as the specified engine out speed, but no information on glide ratio performance.

Anyone know of any data for glide ratios at 1200lbs?

[Robert Lees]

Just my view:

I'm quite used to water crossings, living on an island! I regularly used to cross the English Channel to France (72 miles between Southampton and Cherbourg) well below the altitude required to glide to land.

I also once crossed the North Sea between Texel in Holland and Norfolk in the UK at 50 feet, 125 miles total over-water distance, on the basis that ANY height in a Taylorcraft was not going to allow me to reach land. The visibility and horizon reference was fantastic! If the donk quits, why worry about the inevitable longer than necessary?

I have also flown for about 200 miles along the Gibraltar Strait (in sight of both Spain and North Africa) but out of gliding range of both.

I have also flown across vast tracts of the USA and northern Scandinavia where there would be little hope of survival if the donk quits (the "jungles of Pennsylvania" being a typical example). With water, you know it's flat (on the whole); you know its elevation; there are no big surface obstructions.

I'd rather ditch into water, than into trees or the rocky deserts of Utah or Nevada. Canada must be similar? I trust my engine; if it gives up at that exact point, so be it. Sorry for the fatalistic viewpoint, but life's too short to worry about glide ratios! Just enjoy the flight!

Rob

ps Scott: The OI are in a similar place to two years ago; maybe a little south, out in the open, just the other side of Lindberg. The Brit contingent won't be there, but please go and make your presence known; you will be welcomed, as before.

Rob

[Scott]

Thanks Rob
Lake Superior is rarely calm and rarely above 50F so I maintain a Healthy respect. I've crossed it many times, have confidence in my engines, but there's a pucker factor none the less!

I was more curious about the number. Most aircraft publish some form of distance vs altitude guidance. Not surprised that Taylorcraft didn't but curious just the same.
S

[Lisa]

My copy of AN-01-135-DA lists the ratio for a 1280 pound L-2 at 10:1, a Cessna 172 (even heavier) POH says 9:1. A-700 says the BG can be converted to a BL and vice versa, so this is really conservative. 6000' is roughly one nm. Playing it safe 8:1 is 4800/6000 or 1.33 nautical miles per 1000 feet of altitude. Keep in mind till you get half way you just turn back. So 1000 feet AGL per 2.66 miles of open water.

Lisa

[Scott]

Seems like more of a brick than I expected. My 172m manual shows about 15 statute miles from 9000' .

I would have expected the Taylorcraft, with lower wing loading and lower glide speed, to do better than the Cessna...?
S

[Lisa]

Seems like more of a brick than I expected. My 172m manual shows about 15 statute miles from 9000' .

It's not a brick at all, your IP was 1.5 SM per 1000 or 1.30 NM. Pretty close to my very conservative 1.33 NM. When I fly south from Menominee I usually cross Green Bay to the Door Peninsula avoiding GRB's controlled airspace: 20 miles of cold water.

I'm not planning on ditching should the fan quit. But rather landing along the shoreline. I enjoy having options. B's didn't come with more than a card. But the heavier Army model has a dandy book that says 10:1 (1.67 nmi per 1000), halving that is 6000' AGL, 6600' at mid point over the bay.

I would have expected the Taylorcraft, with lower wing loading and lower glide speed, to do better than the Cessna...? S

6.9 vs 12.8 (depending on models of each) Yeah, a lot less. IIRC Cessna never built factory 172 gliders. Heck, coming across Lake Michigan you might be able to make MTW (122.8) in a glide. (I should try that some day, it could be fun.)

Lisa

[PA1195]

Prop turning vs not might make a difference. Try it sometime. I went to HS in Sturgeon Bay Door County. Lots of nice water all around. Now live in Alaska where nothing's flat except water.

Gary

[Edwin Otha]

I had one engine out, pulled it back to best glide and it sunk like a stone. When the prop windmills, glide is improved.

EO

[PA1195]

Another opinion: https://www.aviationsafetymagazine.c...stop-the-prop/

Gary

[Edwin Otha]

I'm talking about practicing with the throttle at idle. Engine out, stop the prop it has less drag. Prepare for a high sink rate at best glide.

EO

[PA1195]

Here's some more opinions> https://aviation.stackexchange.com/q...ller-in-an-eng

I don't have one based upon personal experience.....and experience trumps theory most days.

Gary

[Scott]

I have experienced an engine failure on CFCLR, back in the 80s, before restoration. The prop initially wind milled but eventually stopped. Can't say that I noticed a difference in glide ratio at that point as I had other priorities!
S

[PA1195]

I suppose the difference can depend on prop pitch and diameter another factors. Most of my time is in a CS prop plane with some compression. Pull the prop control out before the oil pressure fades as a demonstration and it does make a difference when in coarse pitch.

Gary

[Robert Lees]

I apologise if I'm grinding the same old grindstone, but a windmilling prop from a dead piston engine requires energy from which to rotate, so as to overcome the energy of compressing the air in the cylinders of the now-defunct engine.
That energy comes from an increased rate of descent.

There is an argument to open the throttle fully upon complete engine failure (in a carburetted engine) so as to allow maximum airflow through the induction system and hence reduced rate of descent).

Big vehicular trucks use compression in their engines to slow down on hills; I'm sure the principle is the same.

[PA1195]

That open throttle is a good point Rob to remember. Things like this used to be reviewed during training....like what to do if the engine stumbles or quits. Always suspect and try to prevent carb icing. I note here how often light aircraft with small Continental engines "crashed under unknown circumstances". Ice formed during pre-takeoff or during flight can be a problem.

Gary