Hi. Leading edge wrap - worthwhile??

[avalon]

Hi Guys

I'd like to introduce myself; my name is Neil and I have just purchased & started work on Highlander kit #221, which has been in storage for a year or so. I live in New Zealand.

My kit came with the long range tanks and the upgraded gear legs.

I'm considering the other JA options and would like to know if any of you have any opinion or comment either way on the leading edge wrap (the lift reserve indicator also looks like a good option)?

Thanks

[av8rps]

Welcome to the group Neil.

I've never flown a Highlander with the leading edge sheeting, but I have flown Avid Flyers with and without the smooth leading edge (the Avid and the Highlander have the same airfoil). And honestly, I couldn't tell anything different between the two. Stall was much the same, and so was cruise speed. The only thing I know the leading edge wrap did is add weight. So unless there is something different with the Highlander I am unaware of, I'd skip the wrapped leading edge in favor of keeping the weight down.

[taildrgfun]

I think it's worth it. I put it on my new best Highlander ever that I'm building now.

[rmullins]

Over 50% of the lift generated by a wing is in the first 25% of the cord. It makes sense to me to make that as clean as possible.

[Johnny C!]

Troy says it does help performance.
Speed, I think it was. The wrap hadn't
been conjured up yet, when I built my
wings, or I would have gone that route
myself.

Be safe!

John

[av8rps]

It would make sense that making the wing smooth over the leading edge would help, but Dean Wilson (designer of our airfoil) once told me on the original Avid airfoil the spaces between the ribs actually help to create the effect of a flow fence, which makes it advantageous on a slow, STOL purposed aircraft. But on a faster plane, smooth is everything.

My experience with Avid's equipped with and without was limited to about 60 hours in the smooth leading edge equipped airplane both on floats, skis, and wheels, compared to 1700+ hours in the non-wrapped standard leading edge aircraft. As I said, I saw no benefits either way. Ironically, my Kitfox wing is much faster than the Highlander wing with only a little higher stall, and yet the Kitfox wing is just a modified Highlander (Avid) airfoil. And it doesn't use a leading edge wrap.

I do think when one adds vortex generators to the wing of a smooth leading edge you are likely to see more improvement than you would with VG's on a standard wing. But there again, that opinion is based on what the Avid group found when they added vg's...little to no improvement. In fact, the guy that worked with Riblett on modifying the original Avid airfoil for the Kitfox discovered the best improvement with an Avid wing using VG's came when the VG's were installed on the underside of the wing! That's part of the reason Riblett left the top of the wing alone and changed just the bottom. Granted, there may have been more learned from adding VG's to the Avid airfoil since then (the 90's), but I've not really heard of any real positive results. Maybe a few VG equipped Highlander owners can chime in on what they gained with VG's?

All that said, I'm going to be really interested to hear what Steve Henry reports with his new Highlander wing. I'd trust his judgement on whether or not to do the leading edge wrap, as I recall he said he was going to be very weight conscious with his new airplane. So I can't imagine that he hasn't thought that through. And personally, if you are willing to accept a few extra pounds, I don't think you can go wrong with adding it.

[rmullins]

What you are saying supports my experience. I built my wings with a wrap, and flew it for 6 months before I got around to putting on the vortex generators. I found a dramatic difference in the slow flight after I installed them. Before I was indicating low 30's and was struggling to keep the wings level. After adding them I could fly 5 mph slower and the plane was just sort of wallowing with much less tendency to drop a tip. The kit came with I think 100 VGs, enough to do the wings, but I wanted to put some on the bottom of the horizontal stabilizer also so I bought a second batch. After I installed those, I added what I had left to the original batch and installed all those on the wings. When I flew it to Oshkosh, Troy took a look at the plane and made the comment "sure have a lot of VGs up there". Later after he gave some demonstration flights from the ultralight field, when he landed he said something was different, he could slow down enough to not overtake the ultralights like he normally did. The combination of leading edge wrap and a higher density of VGs improved the slow speed performance from what he was used to.

[avalon]

Thanks a lot for the great information everyone; very helpful. For a couple of pounds additional, on balance, wrapping the edges sounds the way to go.

As a first time builder still undertaking my ppl training it's great to have access to the experience you all have between you. I already read my way through quite a few old topics and picked up heaps of useful tips.

Cheers
Neil

[Dave Krall CFII SEL SES]

It would make sense that making the wing smooth over the leading edge would help, but Dean Wilson (designer of our airfoil) once told me on the original Avid airfoil the spaces between the ribs actually help to create the effect of a flow fence, which makes it advantageous on a slow, STOL purposed aircraft. But on a faster plane, smooth is everything.

<snip>

When I looked at the Highlander airfoil I came to the same conclusion, much to the objection of some other pilots that probably were not adjusting their aerodynamics for the slower speed range we're in.

With the consistant reports of improvement with the addition of micro VGs on the top side of the Highlander airfoil combined with your report of demonstrated improvements when added to the underside, it is logical that micro VGs on BOTH sides together could yield the most superior results in stall peed reduction and slow speed flight characteristics.

[danerazz]

I hate making indirect quotes, but I will say that after talking to some factory folks, especially Troy, he did say that rmullins plane really did slow way down. The general consensus seems to be that a LOT of VGs on top of the wing, with obviously close spacing, seems to make quite a difference. The VGs on the bottom of the stab just ahead of the hinge line should give better elevator effectiveness with larger deflections at low speeds.

As for the wing-bottom VGs, I can only say I am skeptical but interested in some actual test data on that one. There is generally clean airflow over the bottom of a wing, especially at high AOA, that I just can't imagine VGs being particularly effective there.

[moving2time]

Dave
I think you missed something in the discussion above. Rick did not add VG's to the bottom of his wing. He added VG's to the bottom of the horizontal stabilizer which can help with elevator control authority durring slow flight. VG's would have a detrimental effect on lift if they were added to the bottom of the air foil.
Joe B

[danerazz]

That's what I thought, but I think he was referring to the earlier post about the Avid by av8rps. I agree though, bottom of wing SHOULD not really help.

[Dave Krall CFII SEL SES]

Dave
I think you missed something in the discussion above. Rick did not add VG's to the bottom of his wing. He added VG's to the bottom of the horizontal stabilizer which can help with elevator control authority durring slow flight. VG's would have a detrimental effect on lift if they were added to the bottom of the air foil.
Joe B

Joe,

Nope, check paragraph 3 of av8rps's post above -truth is stranger than fiction!

I could see where it could be possible that the micro VGs on the underside of a wing could enhance Newton's Law effects by organizing turbulent airflow under the wing, thereby increasing lift more than drag.

It will have to be flight tested to be sure.

[av8rps]

That's what I thought, but I think he was referring to the earlier post about the Avid by av8rps. I agree though, bottom of wing SHOULD not really help.

That was me talking about VG's on the bottom of the wing. I got that information from a guy who in the 90's had done pretty much everything he could to his Avid Flyer, and after installing a turbocharged Subaru in it and flying it at altitude on long distance trips, he was looking for more cruise speed (Not a slower stall). So he contacted Harry Riblett, who computer analyzed the Avid airfoil to learn that the faster you go the more drag gets created by the undercamber of that airfoil shape, which ends up slowing you down considerably. So Ribblett added a sharper edged plastic extrusion to the existing round aluminum tube leading edge, then redesigned a rib that removed most of the undercamber, and finished off the new airfoil by adding a flapperon with a wider chord, and tucking it up closer to the trailing edge so as to create the effect of a fowler flap when it was fully deflected. The end result of the redesign was so good that Kitfox adopted it (after Avid passed on it), and has been using it ever since on their airplane. The wing compared to the old wing was significantly faster (20%+) and the stall was about 95% as good as the old one, so they lost very little while gaining speed.

Ok, now that I explained all that I need to go back to what Ribblett told Chuck to do with his Avid...install VG's on the bottom of the wing about 1/3 of the way back from the leading edge. The idea was to use the VG's to break up the huge bubble that forms under the wing as the speeds increase on that airfoil. If one could reduce the size of the bubble, the drag would decrease significantly, and would therefore stand the best chance of increasing the cruise speed on an existing Avid airfoil wing. I don't specifically remember what the results of that were anymore, but I seem to recall that it did help. I'll dig through my old Avid Flyer stuff and see if I can find anything on it just to verify.

In the meantime, maybe someone wants to try that on their Highlander? Wouldn't it be cool if we could increase our cruise that easily?

[av8rps]

Dave
I think you missed something in the discussion above. Rick did not add VG's to the bottom of his wing. He added VG's to the bottom of the horizontal stabilizer which can help with elevator control authority durring slow flight. VG's would have a detrimental effect on lift if they were added to the bottom of the air foil.
Joe B

Joe,

Nope, check paragraph 3 of av8rps's post above -truth is stranger than fiction!

I could see where at LOW airspeeds, it could be possible that the micro VGs on the underside of a wing could enhance Newton's Law effects by organizing turbulent airflow under the wing, thereby increasing lift.

It will have to be flight tested to be sure.

I should have been clearer...

Way back then people discovered that the VG's on the top of the Avid wing did almost nothing to improve slow speed handling (because of the flow fence effect coming from the ribs sticking up???).

The VG's on the bottom of the wing were recommended by Ribblett to increase CRUISE SPEED (by decreasing the drag created by the undercamber)