Has anyone experimented with placing small VGs on the leading edge of flaps. The guys at Sherpa did this with great success as I am told. They used lip stick cameras to video tuffs on the back side of the flaps before and after VGs. Before the VGs the flow was turbulent and after it was laminar. The Sherpa uses a fowler flap that has a slot to energize the flow over the top of the flap, I am not sure if it will work on the Cub flap. Perhaps Jerry has done some testing on this.
VGs on the flap?
- Thread starter ksecub
- Start date
AkPA/18
MEMBER
Big Lake Ak
Hey Doug
Jerry posted a tuffted wing showing the aileron bay with quite a bit of disturbed air---some even flowing fwd over the top of the wing. I am not sure if he has tested the vgs in the flap and aileron bay. Very cool pic if you can search and find it.
Good Holidays to you
Mark
Jerry posted a tuffted wing showing the aileron bay with quite a bit of disturbed air---some even flowing fwd over the top of the wing. I am not sure if he has tested the vgs in the flap and aileron bay. Very cool pic if you can search and find it.
Good Holidays to you
Mark
Mark,
I was just looking at those pictures and that is why I posted the question. I am trying to spark Jerry's interest if he is lurking, I am sure he has some insight on this.
Congratulations on your thrust line STC. It seems like it is very popular, at least everyone is talking about it. I know of three people down in my area that are on the verge of ordering your STC. Believe it or not, Byron brought it up the other day he might be coming around. He is impressed by how short my airplane gets off the ground and is wondering what effect the thrust line change has on it's performance. I hope you are able to recover your investment in engineering and certification and are able to make a couple of bucks. I have a couple of ideas that I would like to put on the market, but I don't think they would appeal to the masses like your STC does. You need to sell a lot to recoup your initial investment as I am sure you know well enough.
Doug
I was just looking at those pictures and that is why I posted the question. I am trying to spark Jerry's interest if he is lurking, I am sure he has some insight on this.
Congratulations on your thrust line STC. It seems like it is very popular, at least everyone is talking about it. I know of three people down in my area that are on the verge of ordering your STC. Believe it or not, Byron brought it up the other day he might be coming around. He is impressed by how short my airplane gets off the ground and is wondering what effect the thrust line change has on it's performance. I hope you are able to recover your investment in engineering and certification and are able to make a couple of bucks. I have a couple of ideas that I would like to put on the market, but I don't think they would appeal to the masses like your STC does. You need to sell a lot to recoup your initial investment as I am sure you know well enough.
Doug
Jerry Burr
MEMBER
Sedro Woolley, Washington.
Flap V.G.
Hi. Sorry to be so slow. V.G.'s don't work on Cub flaps. They work fine on Byrons setup as he has great flow through the flap slot. The Cub doesn't. I tried them on all parts of the flap and inside the false spar, everywhere they would stick and not get in the way. The main problem is that the Cub flap deployed in excess of 30deg is an air dam and not a lifting device. It simply forces air over the front of the wing enhancing lift. And there is no high energy flow in the flap area. Jerry.
Hi. Sorry to be so slow. V.G.'s don't work on Cub flaps. They work fine on Byrons setup as he has great flow through the flap slot. The Cub doesn't. I tried them on all parts of the flap and inside the false spar, everywhere they would stick and not get in the way. The main problem is that the Cub flap deployed in excess of 30deg is an air dam and not a lifting device. It simply forces air over the front of the wing enhancing lift. And there is no high energy flow in the flap area. Jerry.
Two thoughts:
1) The flow aft of the vg's isn't laminar; when they are working, it is turbulent attached as opposed to turbulent seperated. If not working, the vg's are not protruding through the boundary layer into an area of high energy (and/or an area of high energy doesn't exist), and the flow aft of the vg's remains turbulent seperated.
2) I fly a J-3, so haven't looked at cub flaps. I presume that Jerry is correct re the low energy flow through the cub slot (he has a great track record, and I listen to him. In that case, in order to get flap vg's to work on a cub, one would likely need to redesign both faces of the slot including the leading edge of the flap itself to provide a high energy location for the vg's that wouldn't cause interference between the flap and the wing as the flap opens and closes. It might also be possible to enhance the flow through the stock cub slot by placing a fixed gurney flap on the trailing edge of the stock cub flap. My hunch is that would increase the maximum lift coefficient of the flapped portion of the wing by perhaps 20%. Caution, it would also increase the potential for tipstall, reduced aileron performance, and squirrelly stall/spin characteristics and recovery. It would also load the flap support mechanisms and the rear spar more heavily.
All the best,
JimC
1) The flow aft of the vg's isn't laminar; when they are working, it is turbulent attached as opposed to turbulent seperated. If not working, the vg's are not protruding through the boundary layer into an area of high energy (and/or an area of high energy doesn't exist), and the flow aft of the vg's remains turbulent seperated.
2) I fly a J-3, so haven't looked at cub flaps. I presume that Jerry is correct re the low energy flow through the cub slot (he has a great track record, and I listen to him
. In that case, in order to get flap vg's to work on a cub, one would likely need to redesign both faces of the slot including the leading edge of the flap itself to provide a high energy location for the vg's that wouldn't cause interference between the flap and the wing as the flap opens and closes. It might also be possible to enhance the flow through the stock cub slot by placing a fixed gurney flap on the trailing edge of the stock cub flap. My hunch is that would increase the maximum lift coefficient of the flapped portion of the wing by perhaps 20%. Caution, it would also increase the potential for tipstall, reduced aileron performance, and squirrelly stall/spin characteristics and recovery. It would also load the flap support mechanisms and the rear spar more heavily.All the best,
JimC
ground loop
Registered User
Anchorage
Are vg's on the flaps the antithesis of gap seals?
bob turner
Registered User
Aren't gap seals for high speed cruise, and counter-productive with flaps extended?
Hey, Jerry - we had flaps that went to what looked like 60 degrees (since restricted per type certificate, with performance degradation). The thing was a real performer (with Micro VGs) in that the "flare speed" was so slow one could walk beside the aircraft as it hovered. How far down do your flaps go?
By the way, not all wing mods work well together - we tried the Sportsman kit and Micro VGs together on a 180 - gut feel is that it was better with the stock cuff and no VGs.
Hey, Jerry - we had flaps that went to what looked like 60 degrees (since restricted per type certificate, with performance degradation). The thing was a real performer (with Micro VGs) in that the "flare speed" was so slow one could walk beside the aircraft as it hovered. How far down do your flaps go?
By the way, not all wing mods work well together - we tried the Sportsman kit and Micro VGs together on a 180 - gut feel is that it was better with the stock cuff and no VGs.
AkPA/18
MEMBER
Big Lake Ak
Thanks Doug
Too bad you could not have done a before and after test. I am sure you are curious also. But what are you going to do when you are rebuilding and want to incorporate these mods as you build up. In reading your posts it sounds like your AC has the characteristics of the TL mod making an influence. How are the landings---carry less power and floating more in ground effect??? And how is your cruise speed?
It depends on the mod as to what the investment will be. This was a mjor modification in the eyes of the ACO--and rightfully so--very costly. Talk to your local ACO and get their opinion---it might be less than what you think. Hate to see new ideas just sit there!
You might see if your buddies want to get together and get the best measuring cub of the three and just install a TL mod. We still are not taking any money until the customer decides he likes it. On the cubs that have measured good pre install. we have not had one mod returned (about 40 flying). We are measuring them all pre install now as we have come up with the AOI range that we know works with the TL. It would give you guys a firsthand look--Byron included --- as to what it does before and after.
Glad your Cub is working out so well and hope to see pics posted of it with the 35s!!!
Mark
Too bad you could not have done a before and after test. I am sure you are curious also. But what are you going to do when you are rebuilding and want to incorporate these mods as you build up. In reading your posts it sounds like your AC has the characteristics of the TL mod making an influence. How are the landings---carry less power and floating more in ground effect??? And how is your cruise speed?
It depends on the mod as to what the investment will be. This was a mjor modification in the eyes of the ACO--and rightfully so--very costly. Talk to your local ACO and get their opinion---it might be less than what you think. Hate to see new ideas just sit there!
You might see if your buddies want to get together and get the best measuring cub of the three and just install a TL mod. We still are not taking any money until the customer decides he likes it. On the cubs that have measured good pre install. we have not had one mod returned (about 40 flying). We are measuring them all pre install now as we have come up with the AOI range that we know works with the TL. It would give you guys a firsthand look--Byron included --- as to what it does before and after.
Glad your Cub is working out so well and hope to see pics posted of it with the 35s!!!
Mark
Jerry Burr
MEMBER
Sedro Woolley, Washington.
Stuff
Hi Groundloop. V.G.'s on a flap like Byrons will work as it is a lifting device. And it has no gap seal. As far as the Cub wing is concerned it has to do with the speed you are talking about. If you pull the flaps on at 50mph there is enough pressure to have some effect on VG's. At 25 or 30 it just isn't there. Hang a 6 foot long piece of yarn about half chord on the bottom of your wing and go fly with the flaps down. The yarn will not go through the slot it will hang about 4 inches below the lowest point of the flap. As I stated before beyond 30deg it's simply a air dam. It will work as a slightly better dam with a solid gurney but not a heck of a lot. The yarn will hang 6 inches below the flap. The best thing that I have seen for the Cub flap is the stock gap seal. Up to 30 deg it holds the air on the flap leading edge and beyond that it doesn't matter anyway.
Hi Bob T. Gap seals on a Cessna will give you speed and performance. But you have a fowler type flap. Piper nada. If you have droop ailerons you have to have a top seal to make them work, but you have a different false spar to deal with. My flaps are about 58 deg and the ails about 24deg. And yes I agree with you. In ground effect that combination is neat. I call it the parachute effect as that is what it feels and acts like. I also agree with all mods not being compatable. I have never had anything to do with a 180, but ALL MODS should be given close consideration. Especially as to weight, benefit, and cost. Also the mission of the airplane. For Crash it's Moose. For me it's fish. And a neat way to get where I want to go.
Blessings and Happy New Year to all. Sincerely. Jerry.
Hi Groundloop. V.G.'s on a flap like Byrons will work as it is a lifting device. And it has no gap seal. As far as the Cub wing is concerned it has to do with the speed you are talking about. If you pull the flaps on at 50mph there is enough pressure to have some effect on VG's. At 25 or 30 it just isn't there. Hang a 6 foot long piece of yarn about half chord on the bottom of your wing and go fly with the flaps down. The yarn will not go through the slot it will hang about 4 inches below the lowest point of the flap. As I stated before beyond 30deg it's simply a air dam. It will work as a slightly better dam with a solid gurney but not a heck of a lot. The yarn will hang 6 inches below the flap. The best thing that I have seen for the Cub flap is the stock gap seal. Up to 30 deg it holds the air on the flap leading edge and beyond that it doesn't matter anyway.
Hi Bob T. Gap seals on a Cessna will give you speed and performance. But you have a fowler type flap. Piper nada. If you have droop ailerons you have to have a top seal to make them work, but you have a different false spar to deal with. My flaps are about 58 deg and the ails about 24deg. And yes I agree with you. In ground effect that combination is neat. I call it the parachute effect as that is what it feels and acts like. I also agree with all mods not being compatable. I have never had anything to do with a 180, but ALL MODS should be given close consideration. Especially as to weight, benefit, and cost. Also the mission of the airplane. For Crash it's Moose. For me it's fish. And a neat way to get where I want to go.
Blessings and Happy New Year to all. Sincerely. Jerry.
ground loop
Registered User
Anchorage
Jerry, Thanks for the explanation. Can you or anyone else explain the positive and negative attributes of creating an air dam?
Jerry,
Thanks for the insight. Can you explain the gap seal you use on your ailerons or better yet, post a picture? I have droopy ailerons and do not have a gap seal, I only have the stock aileron false spar. I really like the droopy aileron system Wayne put on my airplane, I would highly recommend this system to anyone.
Thanks for the insight. Can you explain the gap seal you use on your ailerons or better yet, post a picture? I have droopy ailerons and do not have a gap seal, I only have the stock aileron false spar. I really like the droopy aileron system Wayne put on my airplane, I would highly recommend this system to anyone.
Jerry Burr
MEMBER
Sedro Woolley, Washington.
Darn Dams
Hi Groundloop. Try this. Cut 9 or 10 2" pieces of yarn or string and get some tape and tape them on the bottom of your wing under the gas tank in front of the flap. Spread them all around. Fire up the Cub just sitting there. The tufts will all wiggle and stream back toward the rear of the wing. Then pull on full flaps. They will all just die and hand loose on the bottom of the wing. Where did the air go? Well a portion of it is now going over the top of the wing instead of under it. I don't want to get in to circulation theory here, but on the ground or in the air the dam increases circulation around the wing. ie: lift. You can look at your 60deg flap as a huge Gurney flap on the bottom of your Cub wing.
Ksecub. I haven't figured out the new picture upload process. When I get home this week-end I will send you a pict. I think I have your address. Jerry.
Hi Groundloop. Try this. Cut 9 or 10 2" pieces of yarn or string and get some tape and tape them on the bottom of your wing under the gas tank in front of the flap. Spread them all around. Fire up the Cub just sitting there. The tufts will all wiggle and stream back toward the rear of the wing. Then pull on full flaps. They will all just die and hand loose on the bottom of the wing. Where did the air go? Well a portion of it is now going over the top of the wing instead of under it. I don't want to get in to circulation theory here, but on the ground or in the air the dam increases circulation around the wing. ie: lift. You can look at your 60deg flap as a huge Gurney flap on the bottom of your Cub wing.
Ksecub. I haven't figured out the new picture upload process. When I get home this week-end I will send you a pict. I think I have your address. Jerry.
Gurney's work by increasing circulation, which increases lift (and drag). Essentially, they create an area of increased pressure on the underside of the wing immediately in front of the gurney, and that in turn shifts the stagnation line. The net effect is that the direction of flow of the air exiting the trailing edge is directed more downward, so that lift is increased. The extra drag comes from the work required to redirect the flow.
As an aside, notching the gurney's will decrease the drag increment, but it may also decrease the lift increment (more on that below). It is possible that an unnotched gurney with less height might have the same overall effect as the taller, notched gurney, but I suspect that the vortices coming off the notches might help entrain the flow over the top of the wing, lowering the exit line and giving enhanced lift with a milder drag hit. T.J., Jerry, have you tried the notches in practice yet?
JimC
As an aside, notching the gurney's will decrease the drag increment, but it may also decrease the lift increment (more on that below). It is possible that an unnotched gurney with less height might have the same overall effect as the taller, notched gurney, but I suspect that the vortices coming off the notches might help entrain the flow over the top of the wing, lowering the exit line and giving enhanced lift with a milder drag hit. T.J., Jerry, have you tried the notches in practice yet?
JimC
