Glide ratio

[Scott]

An airfoil is intended to create lift with minimal drag. When the airfoil stalls aerodynamically, for all intents and purposes it's creating 100% drag.

As Rob rightly points out, in the case of a prop that has not stalled ie creating both lift and drag, the "lift" also is drag, because all the lift is simply turned into heat by the compression and friction of the engine.

So the question becomes which is less total drag. Generally speaking a turbine, which is what the prop has become, is going to extract much more energy in the un-stalled compared with the stalled state.

Such is the pace of my monday afternoon

[Mike S]

experienced an engine failure on CFCLR

Off topic but I'm curious what caused the engine failure, if you care to share?

[Scott]

The usual... stupidity!
my only defence is
I was lead to believe that there was 30 minutes of fuel left when the float wire reached the red. There's not.
But I was young and should never have put myself in that circumstance in the first place.

Anyway, about 3 miles from home, ran out of gas. Landed on a country road. Local farmer came to see, took me to the local gas station, then after we fueled up, he blocked the road while I took off! I think the farmer enjoyed the whole thing, and I was lucky enough to escape with a bruised ego and feeling like an idiot.
S

[Mike S]

But I was young ...

Youth is wasted on the young!

[1938BF50]

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

I would love to see some numbers for Scotts original question.
I flew this route yesterday in 27599 at 7000’.
About 80 miles of water. I wish I had the time to land at North Fox Island(6Y3),
but didn’t.
Mike

[otrcman]

While the exact glide ratio for your airplane might be interesting, it is by no means the total answer to how far you can travel with an inop engine. As a matter of fact, flight planning with just the still-air glide ratio can lead to some big trouble.

Other factors heavily affect how far you can glide without power. For instance, will you need to change heading to get to your emergency site ? If the emergency field is dead ahead, that's optimum and will not reduce your gliding distance. But what if your emergency site is behind you ? You'll probably give up a mile or so of your theoretical gliding range just changing heading. Then there's the question of a heading change in the landing pattern. Is the runway heading in line with your glide path, or will you need to make another turn to line up with your runway ? Then there's the wind. Do you have a headwind or a tailwind ? What is the height of your emergency landing site ? Just because your altimeter says 5000 feet, that isn't necessarily an AGL number. And then there's the need to arrive over your landing spot with a bit of excess altitude for final maneuvering.

So here we are, sudden engine failure, a bit of confusion and excitement. Scant minutes to get your act together for landing. To take advantage of that famous best glide ratio, you'll need to assume a best glide speed, troubleshoot the failure, pick out a spot, determine exactly how far away your landing spot is, and then do the math. Can you do all that under pressure ? I can't. The best answer for me is to make a best guess while sitting at the kitchen table the night before. Then in flight you will have a calmer, better informed plan to work with. Once actually heading toward my landing spot, I will point my nose toward the objective, establish a best speed, and then watch the spot to see whether it's going UP on the windscreen, or DOWN. If the landing spot is going down, you have it made. If it's going up, you'd better find a closer spot.

So, is the glide ratio totally useless ? No, it does have some value, mostly in the flight planning stage of your trip. If you are contemplating an over water segment to your flight, you can more or less predict how far you need to glide by looking at potential landing sites in a worst case. After you have identified your landing sites, the glide ratio will help to determine how far out you dare go. Start with your planned altitude AGL and your intended cruising altitude. Then reduce your working height by 300 feet for each 90 degree heading change that you will need to make. Then take away another 500 feet for the "startle factor". Then reduce your glide ratio by 20% for each 10 knots headwind that your weather report predicts. News is not so good ? The unfortunate truth is that a 100 MPH light plane flying a low altitude doesn't give you many options if the noise stops.

[PA1195]

This is an interesting thread, not only for the thought provoking what-ifs when flying over water on conventional gear, but also for the obvious concern about the effect of maneuvering and winds during an unplanned descent. I have had those concerns in Alaska while flying on wheels over water, but also to an equal or greater extent while flying on wheels or floats over our land mass for 56 yrs. In most of our State we lack the development rural agriculture and residency have provided some Lower 48 States. Not all mind you especially those with States with mountainous terrain or remote areas. Given a choice I'd rather land prepared on water than on a rocky hillside with wheels, and on floats or skis on reasonably flat but forested terrain. I'm implying degrees of bad here....some are worse than others but none are nice.

One more thing. Keep the engine, prop, and fuel system in top shape, and make damn sure with a carb'ed engine you pay attention to carb icing before it becomes a problem. A manifold pressure gauge can help detect that problem.

Gary

[otrcman]

In re-reading my post of yesterday, I realized that I failed to give Mike (1938BF50) a direct answer to his question about glide ratio. On a still day, at the proper airspeed for best glide, you will realize about 10 feet forward for every foot down. Note that I said "proper airspeed". The correct airspeed for your airplane will vary depending on the calibration of your ASI. Also, the exact speed will very with the weight of the airplane at that moment.

You should know that the weight of your airplane does not in itself affect the glide ratio. Wing loading has nothing to with glide ratio, it just affects what airspeed you need to fly for best glide. Remember the story of the "Gimlie Glider", the 767-200 that ran out of fuel and made a dead stick landing ? That airplane weighed about 200,000 pounds, and yet its glide ratio was about 20:1. Why ? Glide ratio is a function of the aerodynamic shape of the machine, not the weight. Weight (really wing loading) determines the best gliding speed, not the angle at which it comes down. If you want to get really technical, higher weight usually makes a small improvement in glide ratio due to the higher Reynolds Number. But that's such a small effect that you won't be able to see it over the range of weights that a Taylorcraf flies.

[3Dreaming]

Competition sailplanes use water ballast to bring their weight up to gross weight for flights. They do this so their best glide speed is higher for better penetration. This allows for less time between areas of lift, and less time in sinking air. They will also sometimes take the higher sink rate and fly a speed that is faster than best glide to get through the sinking air faster.

That brings up another point, in that how far you can glide may be effected by the weather conditions. Right now over the great lakes you have almost zero rising air because you have warm air over cold water, but in the winter I have seen 500 foot per minute lift forecast over the lakes, because the water is warmer than the air above. 500 foot per minute lift is almost enough to keep the Taylorcraft in the air, and certainly enough to help the glide.

[Robert Lees]

Further to the sailplane analogy **, you have to remember that best glide speed does not mean best forward penetration (think of descending at 65mph into a 65mph headwind). Sometimes it's worth practicing at a higher airspeeds for better "reach" to your chosen destination.

Also consider turning immediately downwind, if possible and not already doing so. Flying downwind with a dead donkey gives more landing opportunities, but factor in another turn to land into wind (if needed). I practice landing downwind, to a full stop, regularly (on both hard and grass) up to about 15mph of tailwind. It uses a lot of real estate!

** Thread drift: a few years ago a competition sailplane ran out of lift and landed out on one of our long-grass runways at my local airfield. We went out to manoeuver it to a better spot, but the pilot said "you won't, it weighs a quarter of a ton".
He added that with full water ballast (he having already dropped it miles away) said it weighs over a ton with full water. Some 15metre or 18m class single-seater. They found a tug and launched home.

[Mark Bowden]

The Dick's comments are spot on but I suggest that the sailplane gross weight trick isn't fully relevant if one were "engine out" in the Tcraft. It's kind to like getting from lift to lift areas, getting through down drafts with minimum loss of altitude, opposed to max glide.

Best glide distance is at max L/D (lift/drag) ratio for the wing. At gross weight the speed you fly is faster than at lighter weights, but you will go the same distance.

Minimum sink rate is slower than maximum glide distance speed. Sink rates are higher at higher gross weights and higher altitudes, glide distance is the same at the proper airspeed. Sink rates are not relevant. But as Tom mentioned weather matters and maybe finding a good thermal on the way down to buy some altitude back.

The prop must be feathered or stopped to achieve the best possible glide distance.

Charlie Precourt did a good article about an year ago on this in Sport Aviation. You can find it yourself by flyting Test Card 8 in the EAA Flight Test Manual. If you fly the test card you will find the indicated air speed for your bird even if the ASI isn't in "calibration". lol.

Our focus for best glide when the engine is out, is the indicated airspeed for L/Dmax at the gross weight we are at.


Question, has anyone every done any of the Test Cards in the EAA FTM for the Taylorcraft?

[3Dreaming]

The Dick's comments are spot on but I suggest that the sailplane gross weight trick isn't fully relevant if one were "engine out" in the Tcraft. It's kind to like getting from lift to lift areas, getting through down drafts with minimum loss of altitude, opposed to max glide.

The sailplane gross weight trick as you called is relevant, in that the heavier you are the faster you best glide speed will be compared to lighter weights.

[Miguel]

By my information, the Glide Ratio of Model B is 11-1

[woodmw]

Miguel.... I have to ask. What is the source of your information?

[Hank Jarrett]

Having learned to fly gliders in an old SGS 2-22 (glides a lot like a BC-12 with no engine) the most important consideration when the engine fails for gliding distance is not the glide ratio, it is finding lift to stay up! The Taylorcraft is actually a decent training glider. Not a "real" sailplane by ANY MEANS, but she will stay up in light lift. The down side (no joke intended) is finding lift over open water is kind of hard. If you ever get the chance to fly a 2-22 JUMP ON IT!! It is a blast and you learn a lot about getting max range with no power (or you learn how to take a 2-22 apart and put it on the trailer, which WILL NOT make you popular with the glider club.