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  #21  
Old 06-02-2011, 06:21 AM
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I have been searching for and reading everything I can on wing shape design for future experiments. OK, let me see if I have been reading this material correctly.

Paul, please tell me if this is correct. The problem with the tips are;

1. Too short, do not change the lift distribution or aspect ratio of the wing. Your tips are as long as they are so as to increase aspect ratio and approximate an ellipitical lift distribution.

2. The shape being rounded actually encourages the high pressure on the bottom to remain attached as it spills upward which will increase the strength of the vortex.

Boiled down. If you don't change the AR or lift distribution then you are basically left only with vortex control to reduce drag, sharp corners, end plates, fences,ect.



Paul, do you think your design could be tweaked to a more crescent shape?



Chris your workmanship is incredible.
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Last edited by RV8RIVETER : 06-02-2011 at 07:25 AM. Reason: world's worst typist
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  #22  
Old 06-02-2011, 07:30 PM
elippse elippse is offline
 
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Quote:
Originally Posted by RV8RIVETER View Post
I have been searching for and reading everything I can on wing shape design for future experiments. OK, let me see if I have been reading this material correctly.

Paul, please tell me if this is correct. The problem with the tips are;

1. Too short, do not change the lift distribution or aspect ratio of the wing. Your tips are as long as they are so as to increase aspect ratio and approximate an ellipitical lift distribution.

2. The shape being rounded actually encourages the high pressure on the bottom to remain attached as it spills upward which will increase the strength of the vortex.

Boiled down. If you don't change the AR or lift distribution then you are basically left only with vortex control to reduce drag, sharp corners, end plates, fences,ect.

Paul, do you think your design could be tweaked to a more crescent shape?

Chris your workmanship is incredible.
I think you've got it right. My original intent for designing these tips for Jim was to get him the most span with higher AR to decrease induced drag up high, with the least area increase and its increased parasite drag area down low. But what he got was not only lower induced drag, but his Oswald factor got to 91%, which helped further reduce the induced drag down low to make up for the increased parasite drag. It was a win-win situation. What you'll see when someone flies alongside Jim is that his fuselage is level at 11,000' dalt whereas the other will be nose-high!
I guess that in order to get the most span increase with the least area increase the chord would have to have an inverse shape toward the tip with inwardly-curved LE and or TE. An outwardly curved tip will have more area vs span than a single or double triangular tip.
Please excuse any stupid arguments I sometimes make as I'm undergoing chemo for lung cancer and my mind gets somewhat confused and also I tend to get testy. I probably made at least 20-30 mispells and bad punctuation in writing this and had to go back over it several times to correct it.
I'm not writing this for sympathy, because I'm sure I will beat this thing so please forget what I wrote and don't send any sympathy notes telling me you're pulling for me. I'm sure you are! OK? Thanks.
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  #23  
Old 06-06-2011, 08:41 AM
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What do you all think about the ORIGINAL symmetric RV-7 "sheared" wing tip, with a curved trailing edge, outboard aft tip, extends back further than the wing trailing edge.

I recalled Van's aircraft discontinued the "sheared" tip for the more traditional straight across the trailing edge tip.

Should I leave it or modify it? I understand to get the most out of that tip you need to make a super sharp edge along the length of it. I plan on doing that.
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  #24  
Old 06-06-2011, 08:49 AM
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Quote:
Originally Posted by gmcjetpilot View Post
What do you all think about the ORIGINAL symmetric RV-7 "sheared" wing tip, with a curved trailing edge, outboard aft tip, extends back further than the wing trailing edge.

I recalled Van's aircraft discontinued the "sheared" tip for the more traditional straight across the trailing edge tip.

Should I leave it or modify it? I understand to get the most out of that tip you need to make a super sharp edge along the length of it. I plan on doing that.
I liked the look of those older upswept tips.

I have an untouched pair of the new RV-7/8 "batwing" tips if someone has the older ones they'd like to trade.
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  #25  
Old 06-06-2011, 09:09 AM
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RV8RIVETER RV8RIVETER is offline
 
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George

I have the "old" Hoerners on my kit as well. I think the same, the edge needs to be sharp. I will be sharpening mine, the entire length.

I have attached mine with piano hinge so I can swap out tips for future experiments once flying.
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  #26  
Old 06-06-2011, 12:30 PM
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REHughes REHughes is offline
 
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Default Intersection At The Leading Edge Sweep Change

Quote:
Originally Posted by elippse View Post
Bob, from what I've read, in order to get even the 82% span efficiency with a square tip, the tip needs a sharp edge along the top surface in order to trip the tip vortex as far out on the tip as possible.
The tips fitted to Jim's RV and the older Tailwind tips exhibit a sharp change in LE sweep angle at the tip junction, while the Lancairs gradually curve the sweep of the LE as it transitions into the elliptical tip section.

It would seem that a point of sharp discontinuity of sweep would be a source of vortex initiation, and if so is this a place where a small sawtooth extension at the tip-to-wing junction would better localize the vortex source and reduce drag? Is there an advantage to gradually curving the Leading Edge back into the tip sweep angle like the Lancairs do?

Thanks very much,
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  #27  
Old 06-06-2011, 03:28 PM
elippse elippse is offline
 
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Quote:
Originally Posted by REHughes View Post
The tips fitted to Jim's RV and the older Tailwind tips exhibit a sharp change in LE sweep angle at the tip junction, while the Lancairs gradually curve the sweep of the LE as it transitions into the elliptical tip section.

It would seem that a point of sharp discontinuity of sweep would be a source of vortex initiation, and if so is this a place where a small sawtooth extension at the tip-to-wing junction would better localize the vortex source and reduce drag? Is there an advantage to gradually curving the Leading Edge back into the tip sweep angle like the Lancairs do?

Thanks very much,
Jim did some tufting of his wingtips when approaching a stall and all of them from the break to the tips stayed straight back except the one that went over the outer aileron gap which lifted slightly.
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  #28  
Old 06-06-2011, 07:38 PM
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Quote:
Originally Posted by RV8RIVETER View Post
George

I have the "old" Hoerners on my kit as well. I think the same, the edge needs to be sharp. I will be sharpening mine, the entire length.

I have attached mine with piano hinge so I can swap out tips for future experiments once flying.
Great comment... I had "old Hoerners" on my RV-4, but to be clear, the ORIGINAL symmetric RV-7 "sheared" ("batman") wing tips were not of the Hoerner design, like was on all the classic RV's preceding, including early RV-8's.



I have the one on the left, the non dash-1 (which came out first).... My question is should I make mine a dash-1, aka straighten the aft curved edge. Just from looks, I have mixed feelings about the swept curved trailing edge. I assume Van dropped it because it did not add anything, but then again he may have not tried the SHARP edge detail?

However you refreshed my memory, very sharp edge, got it! Thank you.

Do you have details on how to make the edge (outer most tip, chord wise edge) sharp? Do you file existing fiberglass material down or add something to shape it? Where does the edge start, just aft of the front corner Nav lights? I assume that sharp edge needs some "span", needs to start at some % cord? I was thinking a very thin metal strip embedded into the edge, micro ballooned in.... even make it razor sharp to keep people away at air shows?

So SHARP I WILL! However that "sheared"/"batman" trailing edge, I might just change for aesthetics.


I found this interesting:
From the Sonerai group there is an article comparing wing tip styles. The big point is the Hoerner increases effective span the most, which might be a good thing to tame the short wing RV-6.
...............


In simple terms as I understand it the smaller the vortex, the smaller the less energy wasted, the more efficient. How you do that varies. The wing of a RV is not tapered in chord or thickness.... There is only so much the wing tip can do: end cap, end fence, Hoerner, symmetric..... winglet...... We have seen very one of these on RV's, factory GA and commerical aircraft. Fighters tend to have no wingtip but flat, since the wing is so radically tappered towards the tip; they don't need things poking up to get radar return or kocked off. Also when you have big thrust, afterburners you don't need to reduce nits of drag.
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Last edited by gmcjetpilot : 06-06-2011 at 08:31 PM.
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  #29  
Old 06-06-2011, 08:16 PM
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RV8RIVETER RV8RIVETER is offline
 
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Quote:
Originally Posted by REHughes View Post
It would seem that a point of sharp discontinuity of sweep would be a source of vortex initiation, and if so is this a place where a small sawtooth extension at the tip-to-wing junction would better localize the vortex source and reduce drag?
As Paul indicated with the tuft testing the vortex is not initiated by the start of the sweep.

"If a vortex wake were shed from the trailing edge, one could compute the change in local onset flow at every point on the airfoil. However, the streamwise vorticity actually develops along the chord, so that the full trailing vorticity is reached at the trailing edge"
From;
Ilan Kroo, DRAG DUE TO LIFT: Concepts for Prediction and Reduction



Some interesting reading:
http://www.dept.aoe.vt.edu/~mason/Ma...DevicesS04.pdf

http://folk.ntnu.no/vebjort/Master/L...ced%20drag.pdf
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  #30  
Old 06-06-2011, 08:41 PM
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RV8RIVETER RV8RIVETER is offline
 
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George

About your wingtips, good question, and got it, I assumed the early -7 tips were the same as my early -8 being the same wing. I have not read any detailed info about the Hoerner or sheared design details and have seen both trailing edges used, so your guess is as good as mine. Raked and crecsent tips seem to be the favorite these days and both have extended trailing edges. Does that mean anything? Would it make any measurable difference? Perhaps someone else can offer an opinion?

Man all this experimenting is sure making me wish I could have finished my aero degree.

As for the edge, I have been thinking thin metal strip embedded in flox would be easiest way to accomplish the task. Been too busy working on my cowl exit right now to finish the wingtips, so haven't attempted the mod yet.
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Last edited by RV8RIVETER : 06-07-2011 at 07:55 PM. Reason: clarify
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