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Thread: Glide ratios in a Super Cub

  1. #1

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    Glide ratios in a Super Cub

    Attached is an article I wrote for our local EAA chapter. I hope it can provide a practical tool to selecting an emergency field. While I developed the idea in my Cub, it can be used in pretty much any aircraft.

    Dan
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    courierguy's Avatar
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    As one who has done a fair bit of dead stick ridge soaring, (in a RANS S-7S, not a SC) I'm going to hazard a guess: 7 to 1? Work calls, I'll read your article tonight.
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    frequent_flyer's Avatar
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    Quote Originally Posted by Dnh98221 View Post
    Attached is an article I wrote for our local EAA chapter.
    Makes my eyes and head hurt so I gave up trying to read it. How did you manage to make a PDF so fuzzy?
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    gdafoe's Avatar
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    Oh wow, I really want to read it too. Is there a way you can send it or a link to it that works for my old eyes.?
    Gerald

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    cubdriver2's Avatar
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    I always was told radius below looking at horizontal jury strut brace was a quick guide

    Glenn
    Last edited by cubdriver2; 01-03-2022 at 10:53 AM.
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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    Ooh, sorry about the pdf. It looked good on my computer when I sent it. Let me see I I can fix it.

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    It's amazing how much drag a windmilling propeller creates. NACA did a test many years ago on a PA-18-95 using it in a glider configuration (propeller removed and the engine cowling opening all closed over) and recorded a 10:1 L/D or glide ratio.
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    mvivion's Avatar
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    First, look right under you. THEN, if nothing there, look VERY close to the plane.

    Do you KNOW what the wind is at altitude? Do you know what the wind is on the surface?

    If you try to stretch a glide, either of those, and a dozen other variables can bite you.

    And, sometimes, the best solution is right under you.

    MTV

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    JP's Avatar
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    Simple. Jury strut on the side, and out the front that spot that isn't moving away or towards. That is as far as you will make it.
    JP Russell--The Cub Therapist
    1947 PA-11 Cub Special

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    Colorguns's Avatar
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    In my -12 it is the top of the cowl as I look out set for VY, I will hit that spot not above it but the spot or short.
    Easy way to see where you can go.

    Doug
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    Quote Originally Posted by JP View Post
    Simple. Jury strut on the side, and out the front that spot that isn't moving away or towards. That is as far as you will make it.
    Perhaps important to distinguish between "as far as you will make it" and "as far as you can make it". At any speed and with any airmass motion there will be a spot that doesn't move. Doesn't mean that spot is a far as you could glide if you flew best glide speed for the conditions. POH best glide speed is for max gross, zero wind, and zero airmass vertical motion. These are not usually the conditions that exist when the engine stops.

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    To confirm what MTV wrote: I took a Forest Service check ride out of Missoula 50 years ago. The inspector suddenly said “Engine failure!” I rolled the 206 sharply to the left. There was a strip right under me! End of emergency.
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  13. #13

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    Most light planes we fly have a glide ratio around 7 to 1 + or- Boeing 747 ratio is 15 to 1 +.

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    A friend of mine took a check ride in a 747 sim. They flew under the Golden Gate Bridge. He was admonished to fly very low: “Do you know how high your tail is!” Then the inspector pulled all four engines to idle. “What are you going to do now!” The plane had enough speed and glide ratio to return safely to SFO.
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    Quote Originally Posted by Farmer Hank View Post
    They flew under the Golden Gate Bridge. He was admonished to fly very low: “Do you know how high your tail is!”
    I knocked the tail off an MD-11 doing the same. (Lots of time in sim cabs doing engineering development and there was sometimes time to play)
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    Quote Originally Posted by frequent_flyer View Post
    Perhaps important to distinguish between "as far as you will make it" and "as far as you can make it". ....... These are not usually the conditions that exist when the engine stops.
    All good considerations. This is as far as I could make it. Established best glide (55 for the 11) while picking best spot upwind and uphill within a 45 cone, and down we went. Right on the spot.

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    JP Russell--The Cub Therapist
    1947 PA-11 Cub Special
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    Quote Originally Posted by JP View Post
    Right on the spot.
    It must be nice to have options like that. Where I fly in AZ a Cub is very seldom in glide range of a spot as nice as that. The places that the locals call airstrips aren't even as nice as that.
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    mvivion's Avatar
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    As suggested earlier, you MAY have to make a turn into the wind, once you get to your chosen landing site. A tailwind on landing off airport can cause a LOT of damage…..to the occupants. How far you can glide in a straight line is just one PART of an engine out emergency.

    MTV
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  19. #19
    JP's Avatar
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    Quote Originally Posted by frequent_flyer View Post
    It must be nice to have options like that. Where I fly in AZ a Cub is very seldom in glide range of a spot as nice as that. The places that the locals call airstrips aren't even as nice as that.
    For this practice session I was in luck; 5 minutes prior I was over the endless woods and headed towards even more, and had just left a small, tight strip on the edge of a lake with lots of lovely obstacles.

    AZ is stunning and I hope to get back at some point.
    JP Russell--The Cub Therapist
    1947 PA-11 Cub Special

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    Steve Pierce's Avatar
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    PDFs uploaded here get fuzzy for some reason. Might email it to SJ and see if he can post it.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

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    courierguy's Avatar
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    The S-7, with 29" tires, dead stick performance probably about the same as a SC. 1 notch of flaps, indicated speed about 55 mph I think. https://youtu.be/PkxFzQE2gEo

    On short final, it was looking about right to continue the dead stick to a landing, which I've threatened to do on my strip but haven't yet, I'll save it for when I need it. Plus I'm scared.

  22. #22

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    I've kept a PA-18A-150 up with the engine shut down (and tow rope) for over a half hour from 2000'. I even outclimbed one of the 2-33s that had a student in it. Supercubs glide pretty good considering.
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  23. #23
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    Flying over cold water that will kill you if you take a swim will cause you to set reasonable glide ratio expectations. I use 1 mile of glide per 1000 ft of altitude.
    Keeps the thought process simple. If I cross between two islands I try to cross at half the distance times 1000 ft. A 16 mile water crossing means cross at 8000 ft. It gives me time for all the stuff that will happen when the engine gets quiet.

    Jerry
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    Quote Originally Posted by cubflier View Post
    Flying over cold water that will kill you if you take a swim will cause you to set reasonable glide ratio expectations. I use 1 mile of glide per 1000 ft of altitude. Keeps the thought process simple. ....
    Good thinking.
    Cessna indicates about an 8:1 glide ratio,
    so about 1.5 miles per 1000' of altitude.
    Of course, that's if you are right on the mark for the best glide speed *at your actual weight*,
    and doesn't account for time spent turning to a new course, stabilizing your airspeed, etc.
    So your 1 mile:1000' is probably a lot closer to reality.
    Cessna Skywagon-- accept no substitute!

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    mvivion's Avatar
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    Quote Originally Posted by cubflier View Post
    Flying over cold water that will kill you if you take a swim will cause you to set reasonable glide ratio expectations. I use 1 mile of glide per 1000 ft of altitude.
    Keeps the thought process simple. If I cross between two islands I try to cross at half the distance times 1000 ft. A 16 mile water crossing means cross at 8000 ft. It gives me time for all the stuff that will happen when the engine gets quiet.

    Jerry
    You must be getting old like me Jerry! I can remember vividly many crossings of Shelikof Straight, wishing I could get a bit higher, like ten thousand feet higher….but I was young then, and perhaps not quite as…..er bright?

    Good advice, in any case.

    MTV
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    Quote Originally Posted by mvivion View Post
    First, look right under you. THEN, if nothing there, look VERY close to the plane.

    Do you KNOW what the wind is at altitude? Do you know what the wind is on the surface?

    If you try to stretch a glide, either of those, and a dozen other variables can bite you.

    And, sometimes, the best solution is right under you.
    This is sage advice. I've spent a fair amount of time flying high-drag aircraft, and have learned that the only place that you are absolutely, positively sure you can make is that which is directly below you, or nearly so. That's where I always start! If you have to start looking farther and farther away, your chance of success diminishes pretty quickly.
    Joe

    Fortis Fortuna Adiuvat
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    Click image for larger version. 

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    Some places there are no good options.


    Sent from my iPhone using SuperCub.Org mobile app

  28. #28

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    Where were you guys when the discussion was single engine along the coast from Seattle to Anchorage? That run scared me looking at it from a jet at 35,000 feet! Talk about cold water and no beach . . .
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  29. #29
    mvivion's Avatar
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    There is a balance between stupid and trusting your engine. I had an engine failure in a very inhospitable place. I landed a place that was more hospitable, but I guarantee nobody here would land there intentionally. Pretty well used up the plane. That evening I went to dinner with Gina and relatives of hers she hadn’t seen for years. I’m sure they figure Gina married a wino.

    You just have to walk, or crawl away. You can get another plane. Land slow, and Use the plane up and it’ll likely save you.

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    MTV

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    BC12D-4-85's Avatar
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    Mike, didn't the plane do a full rollover coming to rest upright?

    Gary

  31. #31
    mvivion's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    Mike, didn't the plane do a full rollover coming to rest upright?

    Gary
    Gary,

    Yes, it tumbled. Toe of right float hit a tussock....big one. The area was the only one around not covered with trees, because it'd recently burned. But, as you know, all that country is tussocky.

    MTV
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    Bill Rusk's Avatar
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    A very simple adage……just toss your car keys out…… That’s where you’re going to land. LOL


    Bill
    Very Blessed. "It's not an obsession, it's a passion"
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    BC12D-4-85's Avatar
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    Mike owes PK floats and Cessna for building durable stuff. Amazing.

    Gary
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  34. #34
    mvivion's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    Mike owes PK floats and Cessna for building durable stuff. Amazing.

    Gary
    Never questioned that for one second. And happy to get right back in another.

    MTV
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