Airfoil tail

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Re: Airfoil tail

Postby AV8R Paul » Sun Dec 18, 2016 1:58 am

Round tube versus airfoil shape. Around bar like in the horizontal and vertical stabilizer 9 times more drag than an airfoil shape. An old video but it get across the point.
https://youtu.be/ftq8jTQ8ANE
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Re: Airfoil tail

Postby av8rps » Sun Dec 18, 2016 10:37 am

That is most definitely a good video to demonstrate what we are discussing.

But if you go back to the video where he is first accelerating the fan, freeze the video when airspeed hits the 100 mph mark on the scale. Then compare what the scale shows and you will see that the drag at 100 mph is only 1/4th of what it is at 210 mph. That was my point in my previous post, our slow planes are less affected by streamlining than a fast plane.

But the video does prove that a cable 1/10th the diameter of a streamlined airfoil tube produces the same drag, so that pretty well proves that streamlining the cables would be just as effective as streamlining the tail with ribs. Maybe more?

Of course doing all of the above would do the most to reduce drag, but we are still probably only going 100 mph'ish...

Now don't get me wrong, you will save fuel and increase climb by streamlining assuming you gain at least a few mph. But don't expect a huge increase. Our planes are too far at the low speed end...
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Re: Airfoil tail

Postby AV8R Paul » Sun Dec 18, 2016 11:15 am

If you compare the size and length of the tubes tha make up the horizontal & vertical stabilizers to that if the cables tha hold the empennage without a doubt the empennage would have more effect. The square bar support the Proffessor showed is probably a 1/16 larger than tha cables, but compared to the round it was surprising to me that the round caused so much drag. I personally would opt for a symmetrical airfoil shape for the empennage and use airfoil shape struts for the empennage. It should give the plane a lot more control authority and result in a lot less drag. I concur it will produce significantly less resistance at 100 mph versus 210, I was going to recommend that Slow flight speed of 100 MPH should be used as the unit 1, I need to go watch again to see what the actual resistance would be.
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Re: Airfoil tail

Postby AV8R Paul » Sun Dec 18, 2016 4:16 pm

I did Screen Captures at as Close to 100 MPH and set the load .3 = 1 for the Airfoil at 100 MPH.
Drag Chart.png


Here is the Screen Capture of the Rod the Same Diameter as the Airfoil.
Drag@100Rod Same diameter as AirFoil.png


I can only attach 2 photos, but the chart shows the results. The Top Row is his initial Drag Factor at 200 MPH. The second & 3 Rows using .3 = a Factor of 1, and the calculations for the remaining configurations of the experiment. The Rod that is the diameter of the Airfoil still shows to be the highest factor or load. I will attach all photos
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Re: Airfoil tail

Postby AV8R Paul » Sun Dec 18, 2016 4:19 pm

Here is a screen capture of the Airfoil into the wind at 100 MPH
Attachments
Drag@100AF.png
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Re: Airfoil tail

Postby AV8R Paul » Sun Dec 18, 2016 4:21 pm

Here is the Airfoil backing into the 100 MPH Wind
Attachments
Drag@100ReversedAF.png
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Re: Airfoil tail

Postby AV8R Paul » Sun Dec 18, 2016 4:24 pm

Here is the Rectangular Mounting Rod. Note this one the screen capture was eith about 80 MPH or 120 MPH, that was the best I could get.
Attachments
Drag@100Square Rod.png
Last edited by AV8R Paul on Sun Dec 18, 2016 5:08 pm, edited 2 times in total.
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Re: Airfoil tail

Postby AV8R Paul » Sun Dec 18, 2016 4:26 pm

Here is the Round Rod the same diameter at the airfoil thickness.
Attachments
Drag@100Rod Same diameter as AirFoil.png
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Re: Airfoil tail

Postby AV8R Paul » Sun Dec 18, 2016 4:31 pm

Here is the 1/10 Diameter of th Airfoil that would represent the Drag Wire.
Attachments
Drag@100Rod Same one tenth the diamter of the AirFoil.png
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Re: Airfoil tail

Postby AV8R Paul » Sun Dec 18, 2016 4:32 pm

The Math leads me to the conclusion that the Airfoil Shape for the Empennage would reduce the load. However you would need to look at the Linear feet of Empennage & Linear Feet of the Guide Wires to do a Calculation of which would result in more load.
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Re: Airfoil tail

Postby av8rps » Sun Dec 18, 2016 10:34 pm

Wow Paul! Awesome work with screen captures and formulas. I've learned even more from looking at them.

So in thinking about all this more, I do want to remind everyone here that the leading edge of the tail is not the equivalent of a round tube going through the air, as it's the back side of the round tube that is where most of the drag comes from. Having fabric covering on the back side of the round tube (as in tailfeathers) changes everything. It would be really interesting to see that same test comparing a non ribbed flying surface vs a streamlined flying surface. I would speculate the unribbed piece would be only 25 to 35% more drag, but that is purely my speculation / guesstimate.

The point of all that is that with 8 separate flying wires each essentially the same length as the leading edges of the tailfeathers, the wires represent more length, therefore more drag overall. Or at least the same drag as the rest of the tail. I have my horizontal stabilizer struts on my Kitfox streamlined nicely, and have the horiz stab and elevator ribbed, and have a really fast Model 4, even when on floats. So something is working.

Anyhow, just trying to stimulate minds of those contemplating modifications to their airplanes. Thanks again for all that research Paul.
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Re: Airfoil tail

Postby SheepdogRD » Sun Dec 18, 2016 10:44 pm

av8rps wrote:I have my horizontal stabilizer struts on my Kitfox streamlined nicely... ...and have a really fast Model 4, even when on floats. So something is working.


How did you streamline your struts, Paul?
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Re: Airfoil tail

Postby AV8R Paul » Mon Dec 19, 2016 1:24 am

av8rps,
No problem, the screen captures are pretty easy, even the math is easy. Since I fly a Kitfox I have the flying tail with ribs. I'm cogitating building a SuperSTOL, and one change would be to make it with a flying tail. The flying tail would have a thicker cross section than the rod diameter, but I still believe the flying tail would offer less resistance.

Paul Z


av8rps wrote:Wow Paul! Awesome work with screen captures and formulas. I've learned even more from looking at them.

So in thinking about all this more, I do want to remind everyone here that the leading edge of the tail is not the equivalent of a round tube going through the air, as it's the back side of the round tube that is where most of the drag comes from. Having fabric covering on the back side of the round tube (as in tailfeathers) changes everything. It would be really interesting to see that same test comparing a non ribbed flying surface vs a streamlined flying surface. I would speculate the unribbed piece would be only 25 to 35% more drag, but that is purely my speculation / guesstimate.

The point of all that is that with 8 separate flying wires each essentially the same length as the leading edges of the tailfeathers, the wires represent more length, therefore more drag overall. Or at least the same drag as the rest of the tail. I have my horizontal stabilizer struts on my Kitfox streamlined nicely, and have the horiz stab and elevator ribbed, and have a really fast Model 4, even when on floats. So something is working.

Anyhow, just trying to stimulate minds of those contemplating modifications to their airplanes. Thanks again for all that research Paul.
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Re: Airfoil tail

Postby moving2time » Mon Dec 19, 2016 1:20 pm

The tail wires can be replaced with modified wires but the connection points would need to be modified to accept the threaded thimbles. I think they are very important on the Highlander specially since the Highlander/SS both use four cables. It would be best to get rid of the cables completely, which I have studied, but the width at the mounting points on the frame are very narrow. It would be tough to create the stiff connection needed to get rid of the wires but it would make installing an airfoil shaped tail more feasible. The simplicity of tube and fabric tail feathers is hard to beat and they do work very well for what they are. They just are not the fastest or most efficient cross section through the air. When it comes to flight everything has a trade off in speed, efficiency, performance or cash!

However, I don't think the thickness of the Super STOL wing is slow. The Zenith 650 airfoil is probably even thicker and cruises 130 MPH or more with the Rotax. Considering the point made earlier, at the speed that these planes are flying the thickness of the airfoil is not that big of a detriment to cruise speed. It is the accumulation of all of the drag that slows down the Highlander and Super STOL way less than the thickness of the wing. I think flying tail feathers would improve slow speed control but I haven't been able to devise a light simple solution but I do like to think about it now and then. Joe b
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Re: Airfoil tail

Postby dkshow » Mon Dec 19, 2016 4:50 pm

These are quite draggy airplanes. I think the best way to make a SS go faster would be to take the shocks and the gear off... All those round tubes hanging out there in the breeze pulls incredibly hard in the wrong direction. Unfortunately, we sort of need the gear for the landing part unless you only plan on doing it once. Try this, drive down the road at say 65mph, now stick a broom stick out the window and see how tough it is to hold it. Just the struts alone is a lot of drag. I'm not sure the best way to reduce it but I think you could pick up a bit of the top end by working on losing some of that drag. Didn't Troy say in the beginning that the SS wing was 10 slower and 10 faster than the Highlander? That could have been before the SS gear I suppose. I think horsepower and the right prop is the key to a faster SS honestly. Everything is a trade off, do you want to go fast or leave the ground fast.

I'd love to have the best of all worlds, something tells me I don't have enough money.
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