Wing-tip comparison

The triangular wing-tips Jim Smith has mounted to his RV-6 have not only increased his speed above 8000' dalt, but also down to at least 4000' dalt. He's getting 2 mph more at 4000' dalt, 3 mph more at 8000' dalt, 5 mph at 10,000', and 7 mph at 11,000'. To demonstrate in a significant manner to all of you folks how dramatic this is, I would propose the following demonstration. I would like one or more of you with 150HP RV-6s, as is Jim's, with no engine enhancements, (he runs on mogas), or even 160 HP, to volunteer to do some side-by-side runs with Jim on at least two separate two-way, GPS-measured runs at 8000' dalt, where Van's gives his speeds, calling out your ground speeds along the way. We might even get some higher speed planes to accompany them and verify their ground-speeds to keep it on the up-and-up. Since the 160 has a 2.2% speed advantage over a 150HP at the same rpm, we can adjust the speed of the one of the planes for HP and RPM to normalize the results. If we can get some planes within 400 miles of Jim's home in Wichita, then each of them could fly a little over and hour to a meeting place.
I'm sure many of you have heard of the Oswald efficiency factor which gives the percentage of a wing span that is truly effctive. On a typical rectangular or tapered wing with a square tip and a well-shpaed tip it can get to 82%; a rounded tip like a Cub drops it to 75%. However, an elliptical wing is 100%. If you can reshape the end of the wing to bring it closer to the elliptical ideal, you can go beyond the 82% and approach the 100%. In my number-crunching of why Jim's tips performed better than I predicted, I found that his wings are running 91%! That's why he's even seeing an improvement below 7000' where I told him that hiis speed would drop slightly due to more wing area. Not only is his speed better, but he lands slower and takes-off and climbs faster, due to the reduced induced drag!
I sure hope we can get some takers in the months before Oshkosh.

C'mon! Aren't there any of you interested in finding out more about the speed improvement by use of different tip designs? We need to get some volunteers to step up!

Well, this is essentially the same thing that was done on the Wittman Tailwinds back in the day. The problem is the W-8 was twitchy and had a decently high wing loading. It also suffered from Steve's lack of any dihedral in the design. The later W-8 and W-10 wing use an tapered elliptical style tip which increases wing area, top speed, and stability...

The RV's already have enough wing though, so the way to make this truly effective is to clip the wing a little before adding a longer wingtip... not an option on a built airplane for most folks.

The tapered wing design that was used on the F1 rocket decreased the effective CG range, weighed more, and was only marginally faster.

The racing guys have found that down low, flat cap or shorty tips have been more effective because the ratio between induced drag and parasite drag is weighted differently down low.

So the main benefit for these would be people who do lots of high cross country work... Many of those folks aren't so concerned in a couple knots here and there, which might explain the lack of resounding interest. I don't have a built RV yet. But if I was truly that concerned about high altitude performance, I'd probably have bought or built a different airplane.

could be that the 150hp RV-6 guys with their FP props are perfectly happy with the setup they are running....or 5mph isn't worth the extra work.
If he was closer I'd race him.....I mean.... run along side for comparison. But not likely a fair comparison. 180+hp, RV-7 C/S prop.

I'll be cruelly honest.

Paul, I'm sorry to have to say so, but those tips are ugly! I'd rather have a couple MPH slower airplane that's purty!!

Kinda like the guy who's married to a trophy wife who's a biatch.

Best,

Ahhh the wisdom of the Elders..

pierre smith said:

Paul, I'm sorry to have to say so, but those tips are ugly! I'd rather have a couple MPH slower airplane that's purty!!

Kinda like the guy who's married to a trophy wife who's a biatch.

Best,

Click to expand...

I appreciate your posts Pierre, there is always truth and practicality in your advice. But better yet, us lister's also get some humor

I've always wondered why nobody has come up a set of fiberglass elliptical shaped wingtips for the RV wings. They'd look pretty good and I'd reckon you could probably sell quite a few sets.

Paul, I fly over to Jim's strip often and would not mind going flying with Jim. I'll get a hold of Jim and set up a time to go fly (I look for any excuse to fly). I have a O-320-H2AD with a Fred Felix prop, with a max RPM of approx 2680 at 8k.

Hey Paul,

Just MHO, but I'm not sure a side-by-side test using two different airplanes is a very effective test (too many variables). Carefully controlled before and after tests (same airplane, swap tips) would seem a much more effective measure of effectiveness and performance for the "tri-tips" (sorry, couldn't resist...it is BBQ season after all! ) (Edit, just saw Curtis's post above, and was not commenting on it...will be interested to see what kind of data it yields).

Interesting note from Steve about clipping the wing to start...hmmm...I just happen to have clipped wings. They were built shorter to decrease the bending moment of the wing, to allow standard g limits at the higher gross weight associated with the big engine...or so the theory goes. I recall a post in an earlier thread discussing these tri-tips, that more or less stated that adding these tips would be the quickest way to turn your RV-6, 7 or 8 into an RV-9. That is not to disparage the wonderful RV-9, but the additional wing area would likely reduce the g limits and perhaps remove the ability (or recommendability) to do acro.

For me and many others, that becomes a deal-breaker. These tips may be awesome for X-C, and may even have an applicability for racing AirVenture Cup when its west to east and run high; but methinks mainstream "Total Performance" RV flyers probably don't want to swap tips for various missions. Heck, ya never know when your going to be jumped by someone and have to fight your way back to friendly country!

All that being said, with those clipped wings of mine, and an interest in AVC, if ya wanna build me a set, I'll come down to SMX and test them at all altitudes, SL to wherever you want. I'll even buy the famous Santa Maria BBQ when we're done. Bet we could get a couple other stock 6, 7, and/or 8 builders that would be willing beta testers too. We could post the results, and those tri-tips might start to look purtier, if the results are that significant! I know that you are not trying to sell these, but rather want to advance knowledge and effeciency among the community, so I doubt that is something on the table...but I'm a willing tester if you ever want to go that route!

And Pierre...I think the guy with the pretty, but slightly slower RV is much happer than the guy with the TW/B that you speak of...eh amigo!

Cheers,
Bob

The tapered wing design that was used on the F1 rocket decreased the effective CG range, weighed more, and was only marginally faster.

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Well I do have quite a bit of time in this wing and so I will comment on the above "facts"
I can carry the same load with my tapered wing as I did with the standard wing. The stick does have a lighter feeling fully loaded but that it has not affected how I use the aircraft. I have often carry 250 pound + passengers in the aircraft.

Yes the wings are heavier, about 60 pounds, that is a negative, but the increased lift has negated any performance decrease due to the extra weight.
I can still carry a full load with a gross of 2050 lbs

As for speed I will let the SARL results speak to that issue. In the last race of 2010 I was close to 15 mph,12.75knots, faster then the next closest rocket. At the slow end the stall speed is 5 to 10 knots slower.

PLUS, and this is a big plus; My wife, who suffers from motion sickness, has for the first time in 25 years been able to share my love of flight. We have travelled from coast to coast with this wing. The added stability of the tapered wing has made all the difference in the world for her.

I guess it is easy to see that I am a Big fan of the EVO wing and I hope that Mark Fredrick will be able to get his new wing into production so that more people can share the rewards that I have received from this design.


As for the wing tips I would like to try a set with my plane. I think that the tapered wing could benefit from a properly designed elliptical tip. I would give up a bit of lower speed for an increased altitude speed AND an even lower stall speed that would result from an increased wing area. I am in agreement with Pierre in that esthetically I to not care for the triangular shaped tips. However I must say that it is easy to say that you are not interested in two or three knots until your buddy slides past you by two or three knots!

Tom Martin said:

........PLUS, and this is a big plus; My wife, who suffers from motion sickness, has for the first time in 25 years been able to share my love of flight. We have travelled from coast to coast with this wing. The added stability of the tapered wing has made all the difference in the world for her. .......

Not being an aerodynamicist (hope I spelt that right!), I am very curious why a tapered wing would work better in turbulence? What would Barnaby Wainfan say???

..... However I must say that it is easy to say that you are not interested in two or three knots until your buddy slides past you by two or three knots!

Ain't THAT the truth!

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Always looking to learn something new.......

I guess I'm somewhat puzzled by the tag that these tips are ugly; I always thought beauty was in the eye of the beholder. Just becuase someone holds that OPINION it doesn't mean it's true, just an opinion. If true, I guess that means that my Lancair with its similar tips, or Peter Garrison's Melmoth, or the Katana, or the Xenos are all delegated to the stack of planes with improved performance that shouldn't be seen in company with more orthodox planes. 'Course they won't be, because they are faster and leave the orthodox behind.
Really, I'm not trying to sell anything here. I just thought that some of you who will spend thousand$ to get a little more speed might want to see a demonstration of a different technology that really produces results. 'Seems to me wing-tip experimentation is something that a lot of you do!

Slightly elliptical tips

These are kind of elliptical. Need a view from overhead to show a little better. I don't know what, if any, performance affect they'll have, but I like the look a lot more then the stock tips. At the very least though they took off about 10 lbs.

elippse said:

I guess I'm somewhat puzzled by the tag that these tips are ugly; I always thought beauty was in the eye of the beholder.
Really, I'm not trying to sell anything here. I just thought that some of you who will spend thousand$ to get a little more speed might want to see a demonstration of a different technology that really produces results. 'Seems to me wing-tip experimentation is something that a lot of you do!

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Can you post some pictures (from different angles) of the plane with these tips on, or direct us to some place on the web that pictures are. I can't figure out if they are ugly or not just from people saying they are ugly.

I spoke with Jim yesterday and he said that the tips come off with 17 screws each and he can put the old tips on the same. He thinks he can change out the tips in less than an hour so it would be no problem doing the test by changing the tips as someone suggested. For this the test would need someone with at least a 180 HP to fly alongside and verify the two GPS ground-speed runs. 160 HP would not keep up at the two higher density altitudes. By doing the test at 7000', 9000', and 11,000' density altitudes this should cover the typical range of density altitudes covered in the summer when the density altitude is about 1500' to 2500' higher than the baro altiudes of 5000', 7000', and 9000'. The shape of the tips is not important as long as it brings the lift distribution close to the elliptical ideal. The Wittman design with the LE coming back to the 25% chord and the TE going forward to the same point is just as good as Jim's swept LE triangular.

elippse said:

I spoke with Jim yesterday and he said that the tips come off with 17 screws each and he can put the old tips on the same. He thinks he can change out the tips in less than an hour so it would be no problem doing the test by changing the tips as someone suggested. For this the test would need someone with at least a 180 HP to fly alongside and verify the two GPS ground-speed runs. 160 HP would not keep up at the two higher density altitudes. By doing the test at 7000', 9000', and 11,000' density altitudes this should cover the typical range of density altitudes covered in the summer when the density altitude is about 1500' to 2500' higher than the baro altiudes of 5000', 7000', and 9000'. The shape of the tips is not important as long as it brings the lift distribution close to the elliptical ideal. The Wittman design with the LE coming back to the 25% chord and the TE going forward to the same point is just as good as Jim's swept LE triangular.

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Paul,

Since I'm the one that suggested the before and after tests, I'd be happy to chase Jim, if we can find a good location to meet, if a closer candidate is not available.

I'd also like to get your take on Chris's tips. Pls see pic above and comments below.

Cfrisella said:

These are kind of elliptical. Need a view from overhead to show a little better. I don't know what, if any, performance affect they'll have, but I like the look a lot more then the stock tips. At the very least though they took off about 10 lbs.

Click to expand...

Chris,

At the risk of thread creep, I'd really like to see more pics of those tips installed, from different angles. They kind of look like my flat tips, but with the center portion pushed (or bulbed) out to a pseudo-elliptical shape.

I'm also interested in your treatment of the aileron outboard ends. Do you have more pics of that, from various angles? They kinda look like EVO tips (just the aileron covers...but that is a potentially draggy area on an RV. Have these tips flown yet? Wondering if any handling anomalies have been noted.

Pretty neat stuff...I saw your posts when you were fabbing them, but hadn't seen them installed. Very cool look!

Paul,

Whattya think of those? Could sharp edges on the outer part (near the wing connection), combined with the elliptical center portion be a performance-enhancing combo of high Oswald Factor and increased elliptical wing area? I'd pull the lights for a racing tip, but wondering about the overall design. Thoughts?

Cheers,
Bob

Removable Tips

It seems like some people want to optimize the wing for one thing OR another. Rather than play with trade-offs, removable wingtips would allow the wing to be optimized for multiple missions. For example, one could build a drastically shorter wing (as high a wing loading as they felt comfortable with) that's optimized for racing. Between races, they could use a different wingtip that returns the wing to stock area and tip.

Most new sailplanes have removable wingtips that allow the pilot to race in both 15m and 18m classes (nearly a 10ft difference in span!). Winglets may usually be added or removed depending on the weather conditions. It only takes a minute to swap the tips.

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. What I'm mainly referring to is an elliptical or semi-elliptical planform to get as close as possible to the elliptical lift-distribution. What is looked for is to bring the lift gradually to zero at the tip so that the upper-lower pressure gradient disappears with no vortex. The typical wing tries to generate lift almost to the tip with its resultant high top-bottom pressure gradient which causes flow from the bottom to the top around the tip, which is the vortex. That's why with a sharp edge you try to tip the flow, whereas with a rounded edge the flow around the tip is actually enhanced by Coanda effect.
That's exactly what my propeller design with its elliptical lift distribution does which is why my props generate no noise as proven in an anechoic chamber by Northwest UAV. No tip vortex, no turbulence, no noise, no energy loss, high efficiency.
'Appreciate your offer, Bob, but Jim is in Wichita which is about 1300 statute away from Reno.

Smith, Jim
[email protected]
316 776 9912

As Bob reguested

Thanks Chris...they sure look sharp! I'm gonna ask Paul, you and others following this thread a few questions...but please don't take them as criticism...its all geared towards tip development and educational discussion.

Here goes:

In looking at Chris's tips, I believe I see the following:

1. An edge around the circumference of the tip, that is somewhat sharp, but slightly rounded.


If Chris had made these tips flat, they would look very much like my flat racing tips (just way nicer!), shown here:


2. An elliptical-ish extension from the middle of the tip, almost like an extrusion, or a bulbous (not the best word to use) push-out of the tip. The shape is biased towards the leading edge a bit, especially if the aileron is included in the tip chord calculations.



3. An aileron end-cap of sorts. It looks as though there is still a space between the aileron and the cap, as there is at the trailing edge of my tip. However, Chris's aileron cap obviously moves with the aileron, as opposed to my fixed trailing edge (of the tip).

Questions:

- In a true elliptical tip, would it be better to not have that edge lip? In other words, have the top and bottom of the wing and the top and bottom of the tip be flush...then perhaps taper slowly to the outer edge of the elliptical tip.

- Or is this a beneficial combination of a sharp-edged tip (higher Oswald Factor, longer attachment of the vortex) plus an increased wing area in an elliptical shape to reduce the overall vortex that remains?

From Paul's earlier statements, these two characteristics may be in opposition, but ya never know...it might be a little "discovery". (Chris, did you engineer any of this with these things in mind?)

Would the elliptical shape be better if it was centered along the chord line, and included the aileron portion as well? That would be harder to fabricate with enough strength to extend alongside the aileron, since there is no support back there. Just mulling over the difference in a full-chord elliptical tip versus one that only covers the wing chord, and not the aileron (like Chris's).

Chris, does the aileron cap have a gap between it and the aileron, and if so, how is it attached? (Just hard to see that part.)

Any controllability issues with capping the aileron like this that anyone can think of? I've heard reports of winglet-like end plates loading up ailerons and making the contols stiff, but nothing about caps like this. The EVO wing looks a lot like this in the aileron area (just smaller), but this may be a different aileron design, so just wonderin'.

Along those lines, any concerns of aileron flutter when adding a cap to the outer edge of the ailerons? I know some folks have filled the tip rib outboard of the aileron, but I don't know if anyone has filled the gap in the aileron, or has capped it. These look very lightweight, but just thinking about all issues, since its a departure from plans (not a bash there!). Thoughts?

Chris, they really look sharp...just beautiful work sir, so these are just experimentin' questions. I'd love to hear Paul and others' thoughts about these versus Jim's tri-tips, and other designs (and don't use too many 5 syllable words on me now Paul! )

If Jim heads anywhere near my way, I'll meet him Paul. Or maybe do it en route to a race later this year if we don't get another taker (I think one stepped up earlier).

Fun discussion!

Cheers,
Bob

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.

RV8RIVETER said:

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.

Click to expand...

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.

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.

gmcjetpilot said:

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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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.

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.

Intersection At The Leading Edge Sweep Change

elippse said:

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.

Click to expand...

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,

REHughes said:

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,

Click to expand...

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.

RV8RIVETER said:

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.

Click to expand...

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.

REHughes said:

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?

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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/Mason_f/WingtipDevicesS04.pdf

http://folk.ntnu.no/vebjort/Master/Literature review/20 - ARFM - Lift induced drag.pdf

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.

X-47B Tip Shape

I ran across some drawings that I believe reflect the latest tip planform for the X-47B Carrier Suitability test vehicle.

The shape could be easily adapted to the RV wing, and might enjoy some advantages by limiting any imposed twisting loads on the wing.

http://www.richardcyoung.com/terrorism/x-47b-unmanned-combat-air-system-ucas/

REHughes said:

I ran across some drawings that I believe reflect the latest tip planform for the X-47B Carrier Suitability test vehicle. The shape could be easily adapted to the RV wing, and might enjoy some advantages by limiting any imposed twisting loads on the wing. http://www.richardcyoung.com/terrorism/x-47b-unmanned-combat-air-system-ucas/

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I think you just wanted to post this for the fun of it. There is no info on wing tips... I sat through the video and read the article. The wing is highly swept and it's a tailless design, so not sure the applicability to a low speed RV, verses transonic swept flying wing UAV. I suspect the wing tip shape and the two sharp angles is for stealth.

BTW auto-land on carriers is not new... The carrier pilots don't go around saying they have autopilot that can get them on deck, so a UAV is not going to be a big deal. It is pretty clear pilots in fighters will be a thing of the past in the near future... well the future is here.

Easy tip mod

Continuing the subject of wingtip mod, I just wanted to report an easy way to mod the std Hoerner tips to be sharp, for anyone who may be interested.

I found some 3/32 pieces of balsa wood at the local hobby shop. I cut an about 1/2" deep groove (went deeper in about 4 spots for more hold) in the tip with a cut-off wheel. Then soaked the wood in epoxy, filled the groove with flox and set the blasa strip in to set, and backfilled the edges with micro. It has turned out to hold a nice sharp edge and the balsa fibers resist chipping. The balsa is also light and more importantly holds the nice straight line of the wingtip.

I am sure Prof Hoerner would be happy now, as the stock edge was very rounded indeed.

RV8RIVETER said:

Continuing the subject of wingtip mod, I just wanted to report an easy way to mod the std Hoerner tips to be sharp, for anyone who may be interested.

I found some 3/32 pieces of balsa wood at the local hobby shop. I cut an about 1/2" deep groove (went deeper in about 4 spots for more hold) in the tip with a cut-off wheel.

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I assume the balas was 3/32 thick. You used a cutoff while and just by hand to put a grove in the wing tip? Is it even 1/2" thick any place? I was thinking going in 1/32" not 1/2"?

Then soaked the wood in epoxy, filled the groove with flox and set the blasa strip in to set, and backfilled the edges with micro. It has turned out to hold a nice sharp edge and the balsa fibers resist chipping. The balsa is also light and more importantly holds the nice straight line of the wingtip.

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Any pictures you care to post?

I am sure Prof Hoerner would be happy now, as the stock edge was very rounded indeed.

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I am sure he would be. Have you done any A/B flight test comparison before after?

That is a great idea. How is a sharp edge critical on the Hoerner tips? I thought it was uber critical for the symmetrical / sheared tips. Sorry if the question is old news.

I had the Hoerner tips on my old RV4 but the RV7 has the symmetric and I do plan on sharping up the edge. I was going to use a thin strip of brass like the insert in old fashion school rulers and using it like you did with balsa I image. I like your idea better, lighter and easier to bond to. I was thinking metal to hold a very sharp edge.... but it would be a pain to work with and get to fit. Balsa is a nice former.

gmcjetpilot said:

I assume the balas was 3/32 thick. You used a cutoff while and just by hand to put a grove in the wing tip? Is it even 1/2" thick any place? I was thinking going in 1/32" not 1/2"?


Any pictures you care to post?


I am sure he would be. Have you done any A/B flight test comparison before after?

That is a great idea. How is a sharp edge critical on the Hoerner tips? I thought it was uber critical for the symmetrical / sheared tips. Sorry if the question is old news.

I had the Hoerner tips on my old RV4 but the RV7 has the symmetric and I do plan on sharping up the edge. I was going to use a thin strip of brass like the insert in old fashion school rulers and using it like you did with balsa I image. I like your idea better, lighter and easier to bond to. I was thinking metal to hold a very sharp edge.... but it would be a pain to work with and get to fit. Balsa is a nice former.

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Hey George

Yes the sheets, about 6" wide I think, are 3/32 thick.

I started the groove with a body saw as it was easiest to make a straight cut along the edge. Then made a pass along the line with the cut-off wheel.

As for thick, can only speak about the old style Hoerners I have. They are over 1/2 thick at least 80% of the length. I had to go over 3/4 in a few places to get all the way thru. I went that deep because most of it is gel coat and I didn't feel comfortable bonding only to the gel coat. I probably could have gone more shallow since the 4 cuts thrus are bonded to the inside fiberglass, but deeper made me feel better.

No data as I am still building. I think as long as I am still working a part I might as well make sure it is the best it can be. The original edge was pretty rounded, at least a 1/4" radius. Searching for Heorner data found that the sharp edge is one of the critical design components, along with the flat top surface, straight thin trailing edge, and convex lower surface, IMIC.

ADDED: Sure, I can post a picture, but will have to wait until Wednesday, as I will not be able to get to the hanger until then.

RV8RIVETER said:

. They are over 1/2 thick at least 80% of the length. I had to go over 3/4 in a few places to get all the way thru. I went that deep because most of it is gel coat

ADDED: Sure, I can post a picture, but will have to wait until Wednesday, as I will not be able to get to the hanger until then.

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Gelcoat.... ha ha! I forgot about the Vans Gelcoat... it can be thick.

Yes thanks, I'd appreciate it. I am interested, a picture would be nice!

I think that's the right way to go, get'er done right, be done with it.

Later you could swap tips out with stock ones for flight test comparison (which you probably won't). It's just the engineer in me that likes data. I'm pretty sure it's a very good worth while mod, even if you can't measure the difference by it self. You'd need smooth air and subsequent flights in identical conditions. Trying to resolve stall speed or top speed to a MPH for a small single Mod is almost impossible. I'm sure it will be an improvement. Top speed might increase, stall decrease? It might be more than a MPH or two? Who knows; I don't. I'm guessing. Hard to predict the effect. There is no math for it.

However when you get her all flying and the overall performance is above par, as I suspect it will be, it will be due to attention to detail like this. Cheers

Just comments

This is the fastest of 5 configurations I have made for my plane so far:



I look at the tips people put on their airplanes looking for some kind of performance gain I assume, then they stick on the nav lights and strobes naked in the breeze - That can't be a good thing.

Bob Axsom

Bob Axsom said:

This is the fastest of 5 configurations I have made for my plane so far:

I look at the tips people put on their airplanes looking for some kind of performance gain I assume, then they stick on the nav lights and strobes naked in the breeze - That can't be a good thing. Bob Axsom

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I think part of the gain is you clipped the wing a tad, reduced wing area... good fore a little higher speed but (if noticable) higher stall?

Can I ask how much faster and what else did you try, may be you have a thread... sorry if it's old news. I know people have used end plates with some degree of sucess.

I gather van has done all kind of test. I suppose the stock ones are pretty good, but the edge mod (sharp) seems to be the hot ticket. I see yours are rounded.

I agree nav lights in breeze on wing tip (or any where) can't be good.

Here you go George. Took some pictures as I did the trailing edge of the last tip today. Still work in progress.

Yes, I do intend to experiment, by the way. I have my wingtips attached with hinges so that I plan to try other tips later on when valid speed data can be gathered. Wanted to make it easy to change for racing tips when it is time to race.

RV8RIVETER said:

Here you go George. Took some pictures as I did the trailing edge of the last tip today. Still work in progress.

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Awesome pics Wade... Thanks a million... That looks sharp (pun intended). You will have to put a sign up at air show, to keep a passersby clear, so they don't cut their self .... Ha ha! That baby will cut through the air~!

That is great news you have them removable and might do some testing... love the data!

Unrelated curious question, what is the small tab at the trailing edge with a screw?

gmcjetpilot said:

Unrelated curious question, what is the small tab at the trailing edge with a screw?

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It is the hinge pin acces cover. I wanted the entire exposed side of the tip flush and smooth so easiest way to get to the pins was to make this removable corner cover. The only way it can come off is to slide back. The pins are then a simple straightline push/pull and they are guided all the way.