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Gear leg fairing

I have seen Giles Henderson fly that cub in aerobatic competition. He is a champion with it. This was years ago but he screams that thing downhil for his entry speed and I'm sure the clean gear is a big contributing factor. Building a cub gear in the style his airplane has is not difficult and would result in a lot of drag reduction if you just want to fly around grass strips and smooth runways with the 800x4's sporting lower tire pressure. Obviously for exp category only.
 
To the OP, I would make every attempt at streamlining all parts of the landing gear to reduce drag. Even if it doesn't appreciably increase your airspeed, it will reduce your fuel burn and that is always a good thing. Being experimental just makes it easier to be efficient. As you've already discovered, a perfect airfoil isn't required to make a big difference. So make a difference and please post your results.
 
docstory said:
Removal of the bungees, replacing the round tube gear strut braces with streamline tubing, installing symmetric airfoil ribs in the gear legs along with leading and trailing edge extension and the fairings is a lot more than adding fairings. Every part of the landing gear was modified. I was just showing that someone has gone to the trouble of using ribs on a fabric covered landing gear to reduce drag on a cub.
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And I'm just trying to align performance expectations with reality. You can chuck the gear off altogether and it won't result in a 33% reduction in overall drag. Doing all this stuff undoubtedly reduces drag - it just won't affect cruise speed much.

If you tell me that Mr. Henderson is a wonderful guy, champion pilot, with a really cool airplane, I'll believe you. But numbers are testable.
 
sjohnson said:
And I'm just trying to align performance expectations with reality. You can chuck the gear off altogether and it won't result in a 33% reduction in overall drag. Doing all this stuff undoubtedly reduces drag - it just won't affect cruise speed much.

If you tell me that Mr. Henderson is a wonderful guy, champion pilot, with a really cool airplane, I'll believe you. But numbers are testable.
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My last words on this line of discussion are the man made those changes and posted his results.
 
......I'm just glad that the aluminum Husky gear leg fairings will acceptably "cloodge" onto 3" extended Cub gear. :)
 
docstory said:
My last words on this line of discussion are the man made those changes and posted his results.
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Except that he didn't. The rest of the quote included "[FONT=Arial,Helvetica,sans-serif]Should have it completed in a few weeks.[/FONT]"

These were his expectations, not his results.
 
sjohnson said:
Except that he didn't. The rest of the quote included "Should have it completed in a few weeks."

These were his expectations, not his results.
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That wasn't my take on it. He said add, not may or should add. So I read it as not finished but flight testing done.
 
I can't see how fairing the gear would reduce the drag by 1/3, but increasing the power from 75% to 100% does increase the power by that amount, which will increase the speed by 10 to 11%. That seems to be what he said.

Since induced drag decreases with the square of the increased speed ratio, it rapidly becomes insignificant as the speed increases.

The fairing mod itself seems to contribute about 4 mph, which seems reasonable.

People seem to equate engine power with rpm, which isn't the case.
And they equate thrust horsepower with engine rpm, and that certainly isn't the case.
For a given engine power, it is fun to plot how thrust falls off with increasing speed.
 
JimC said:
People seem to equate engine power with rpm, which isn't the case.
And they equate thrust horsepower with engine rpm, and that certainly isn't the case.
For a given engine power, it is fun to plot how thrust falls off with increasing speed.
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So, is engine power the throttle setting alone? Meaning, 75% power is 3/4 throttle regardless of engine rpm?

Your idea of fun, isn't. :nutz:
 
In the example used, increasing the speed from 106 to 121 mph reduces the induced drag by 23%.

No, engine power isn't the throttle setting alone.

I usually work on the flapping flight mechanics and aerodynamics of articulated membrane wings. Now, that's fun :).
This stuff, not so much.
 
I thought he was saying his new IAS was 106@75% and 121@100%. So the only calculation would be that the aircraft flew 11 t0 12mph slower before the mods.
 
Skywagon, no, I meant to say REduces. Remember that Steve's reference in Post #59 was specifically to induced drag.
 
Doc, if he was getting 106 at 75% before, then he would get between 116 & 117 at 100% before. Since he is now getting 121 at 100% after, the fairings are giving him about 4.3 mph at full power. That equates to about 3.9 mph at 75% being due to the fairings.
 
JimC said:
Doc, if he was getting 106 at 75% before, then he would get between 116 & 117 at 100% before. Since he is now getting 121 at 100% after, the fairings are giving him about 4.3 mph at full power. That equates to about 3.9 mph at 75% being due to the fairings.
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To clarify, my interpretation of the numbers was that they are both after the landing gear modification. His after IAS was 106@75% and 121@100%, so his before's would be 93-94 and 108-109 respectively. I don't suppose those figures square with the formulas. I don't design em, I just work on em.
 
If both sets if numbers are after, then there is either about a 4 mph discrepency in the airspeeds, or he was flying at about 67% power at 2300. If both sets of numbers are after, then there is no way to extract the fairing contribution.
 
JimC wrote:
Gordon, I'd be interested in seeing your math.
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Jim, Nothing fancy - With zero drag the prop would simply screw itself into the air a distance equal to its pitch each revolution. So 42in/rev * 2400 rev/min gives 100,800 in/min. That converts to 95.5 mi/hr. I actually see about 90 mi/hr at 2400 RPM with 82-42 Borer prop. So my actual speed is about 5.8% less than the zero drag speed, which implies the roughly 5% slippage.

Interesting discussion!
 
cgoldy, yeah, you have em. A beastie called Mythunga comes to mind (I don't remember where in Australia it was found). There are others as well.

I don't work much on bats. Here's a photo of one of the little critters I do work on. The camera cropped off the outer ends of his wings, so he's bigger than he looks in the picture. You can get an idea of scale from the man standing on the ladder by his head. Wingspan is a little larger than a PA-18.
 

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Gordon, that isn't how props work. The designated pitch is simply the geometric pitch at 75% of the semi-span (usually). It has no real significance other than that. Blade planform, spanwise blade twist distribution, and spanwise airfoil section distribution all vary substantially between different prop blade families though they are fairly constant within a single family. The pitch number doesn't translate to (and isn't intended to translate to) how far the blade would travel forward in one revolution if there were no 'slippage'. It isn't even possible that there be no slippage because of the effect of the airfoil section on the zero lift angle of attack (how negative the prop AOA is at zero thrust coefficient). Isn't related to zero drag either.
 
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JimC said:
Gordon, that isn't how props work. The designated pitch is simply the geometric pitch at 75% of the semi-span (usually). It has no real significance other than that. Blade planform, spanwise blade twist distribution, and spanwise airfoil section distribution all vary substantially between different prop blade families though they are fairly constant within a single family. The pitch number doesn't translate to (and isn't intended to translate to) how far the blade would travel forward in one revolution if there were no 'slippage'. It isn't even possible that there be no slippage because of the effect of the airfoil section on the zero lift angle of attack (how negative the prop AOA is at zero thrust coefficient). Isn't related to zero drag either.
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Interesting - I knew some of that but not all of it. Now you have my curiosity piqued, to do some studying!
Thanks -
 
Drag bad, less drag good.

What in the hell is that critter JimC? You messing with us?!

Never mind, I googled it, I want one.
 
Here's me out in my front yard with the left humerus from one of them. I'm holding the shoulder joint in my right hand, the elbow in my left.

This one was cast from the Quetzalcoatlus northropi found out in in the Big Bend National Park in southwest Texas a few years back. The northropi in the ladder photo is a full scale skeletal replica that we worked up to hang in the lobby of the Texas Memorial Museum in Austin.

The thing stood 14 feet tall (a big giraffe is 17 feet). It could stand flat footed on all four feet and reach the tip of its snout 23 feet in the air -- a pretty respectable flying machine. Perhaps the largest animal that ever flew.
 

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P.S. I've got enough of these things (of different species, some still unnamed) floating around my house that my wife threatens to run me and them both off.
 
It is no wonder that there were so few humans in existence during those times, they were used as hors d'œuvres.
 
These things mostly ate fish. In the case of northropi, rather small ones even though its head was about 8 feet long. northropi didn't even have teeth. Others did, but they mostly ate fish too. They were killed off by the Chicxulub asteroid impact about 64.8 million years ago, so they didn't interact with us. Wouldn't have been dangerous if they had. One minor irritation would have been that they had tiny digestive systems, processed oily foods very rapidly, and were known to have assembled in flocks (little pterosaur up in the sky, you did something in my eye).

Here's a small, toothed, Anhanguera piscator skull (about 2.2 feet long) that my grandson had out to play with. It's a medium sized juvenile from Brazil with a 16 foot wingspan. The second photo is of the piscator in the Atlanta Fernbank Museum, cast from the same mold as mine. The toes on its front feet are positioned incorrectly (ouch).
 

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Back to faired gear legs. I'd like to see someone adapt a thinned, decambered, stretched GAW-1 section to a Cub gear leg. Fabric would be lower drag than aluminum if not overloaded with too many rib sections.
 
JimC,
What does the 42 stand for, if not inches of pitch? Gordon's math is pretty close, considering the pitch number doesn't have anything to do with anything.
I've always used pitch X RPM X .00095 and it goes to the same ballpark as Gordon, which is pretty close to what the airplane does.
My Pitts has a 60 pitch prop X 2700 RPM X.00095 = 153.9MPH, which is pretty damn close.
 
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