shark skin for Unlimiteds?

[Gibbs]

Some time ago in a German mag I noticed about adhesive foil (shark skin) for round about 30 percent reduced drag on aeroplanes, as obviously used on some F1 class racers (and others?).

I've never seen this at (photos of) Unlimiteds, why they don't use it

thx,
Gibbs

[AirDOGGe]

Re: shark skin for Unlimiteds?

Perhaps unproven claims? 30% in the lab maybe.

I would think that if an item can really reduce drag by such a huge amount, that we'd see it on passenger airline jets by now. Even a few percent is big news to them.


The issues to still be solved I read about are extra weight, peeling off in high-speed air flows, cost and vulnerability to ultraviolet light.

Plus I read it was tried on a ship and only reduced drag by 5%. I wonder if that's enough to counter the extra mass/weight on the aircraft. And water is a dense medium. I wonder if even 5% can be achieved in thinner air.

[bflynt]

Re: shark skin for Unlimiteds?

Couple things:
Sharks swim in an uncompressible medium and they are comparatively streamlined creatures. Therefore, the majority of the drag on their bodies is from skin friction.

An unlimited racer has lots of bumps, rivets, cooling passages and is traveling well into the compressible regime. Skin friction is still a concern but things like interference drag, compressibility drag, and induced drag are much easier to target for reduction.

As a side note:
I’m not sure how much serious drag reduction work goes into unlimited planes? Most of the work I see is back of the envelope broad stroke ideas (i.e. remove belly scoop and turtle deck). I do know of some work that was done back in ~2006 to better profile Dago Reds wings for wave drag reduction but it is my understanding it was never implemented.

Bryan

[Big_Jim]

Re: shark skin for Unlimiteds?

Just a rudimentary understanding of the idea here...but there is a certain merit to the 'shark skin' texture. It's similar to the idea of why a golf-ball has dimples. We have tried similar things on the hydroplanes in the past to break surface tension on the planing surfaces that are in contact with the water.

However, my understanding is that concept is only beneficial in reducing drag if you have some sort of boundary layer separation. The rough surface causes the air to conform or 'stick' farther along the surface before finally separating.

It works well on a golf ball because it is a sphere, and you get maximum streamlining by delaying the separation point.

IF something like that would work in an aeronautical application, my guess is it would have to be applied similar to a vortex generator or something...find a spot that needs it and apply just the right amount in just the right place to get the airflow to do what you need it to do. I doubt you would get any kind of return covering the airframe with the stuff.

Again, just my rudimentary, armchair aerodynamix observation. Feel free to shoot down in flames as necessary.

[Race5]

Re: shark skin for Unlimiteds?

Just a rudimentary understanding of the idea here...but there is a certain merit to the 'shark skin' texture. It's similar to the idea of why a golf-ball has dimples. We have tried similar things on the hydroplanes in the past to break surface tension on the planing surfaces that are in contact with the water.

However, my understanding is that concept is only beneficial in reducing drag if you have some sort of boundary layer separation. The rough surface causes the air to conform or 'stick' farther along the surface before finally separating.

It works well on a golf ball because it is a sphere, and you get maximum streamlining by delaying the separation point.

IF something like that would work in an aeronautical application, my guess is it would have to be applied similar to a vortex generator or something...find a spot that needs it and apply just the right amount in just the right place to get the airflow to do what you need it to do. I doubt you would get any kind of return covering the airframe with the stuff.

Again, just my rudimentary, armchair aerodynamix observation. Feel free to shoot down in flames as necessary.

The F1 aircraft that was flown by the Swiss team last year made us of it on the aft 1/3 or so of the wing chord. I assume they were using it to keep the airflow stuck further aft like a laminar airfoil does. They claimed it was worth a few mph in testing.

[MARK SHANE]

Re: shark skin for Unlimiteds?

Just a rudimentary understanding of the idea here...but there is a certain merit to the 'shark skin' texture. It's similar to the idea of why a golf-ball has dimples. We have tried similar things on the hydroplanes in the past to break surface tension on the planing surfaces that are in contact with the water.

However, my understanding is that concept is only beneficial in reducing drag if you have some sort of boundary layer separation. The rough surface causes the air to conform or 'stick' farther along the surface before finally separating.

It works well on a golf ball because it is a sphere, and you get maximum streamlining by delaying the separation point.

IF something like that would work in an aeronautical application, my guess is it would have to be applied similar to a vortex generator or something...find a spot that needs it and apply just the right amount in just the right place to get the airflow to do what you need it to do. I doubt you would get any kind of return covering the airframe with the stuff.

Again, just my rudimentary, armchair aerodynamix observation. Feel free to shoot down in flames as necessary.

Nothing here to shoot down Big Jim its a interesting concept and not to go off topic but I just heard on a radio show last week that I listen to that there is talk of building semi truck trailers with the dimples in them to improve fuel economy nothing to do with aircraft I know but I thought I would mention it because the concept is simular.