Vortex Generators

[GrassStripFlyBoy]

42 minutes ago, AGLyme said:

Do they decrease top end speed ?

thx 

That is a curiosity of mine as well, I looked into VG's a while back and remain a bit intrigued with playing with them - being experimental I can easily venture in this direction.  I am not too excited about having them in the way for washing / waxing.  Was thinking of a hybrid plan of maybe the first 8' of inboard wing area and not running full span.  There are already those 'square blocks' on the leading edge - anybody know the story on them?  I suspect these are sort of a VG device to achieve the LSA stall speed?  Ultimately I've become comfortable landing the plane and base approach speeds according to loading, but greater safety margin is always a desirable thing. 

[Tom Baker]

The blocks on the wing are more about controlling the air that flows over the stabilator.

[FlyingMonkey]

2 hours ago, AGLyme said:

Do they decrease top end speed ?

thx 

Typically no.  Maybe on some very high speed airplanes, but the drag effect is usually so minimal that it's imperceptible. 

BTW, those thinking about this might also want VGs on the underside of the stab.  I have a friend who did that (not on a CT) and he said the effect was much higher control authority at low speed.  The stab is basically an upside-down wing with the lift vector downward to produce down force to counter the main wing, which is why the VGs go on the bottom.

[AGLyme]

4 minutes ago, FlyingMonkey said:

Typically no

No brainer then, thanks FM.  And thank you to Madhatter and the pioneers on this project.  I live near FD USA (Woodstock), happy to use my plane as a guinea pig if it helps the "FD approval" cause.

[Madhatter]

The VG's will also be on my stabilator to keep it flying at low speeds. 

[FlyingMonkey]

1 hour ago, AGLyme said:

No brainer then, thanks FM.

Yeah, VGs are one of the few "zero cost" (in performance, not dollars!) mods for most airplanes.  The only downsides are in proper setup and the fact you occasionally lose a VG and have to replace it.

[AGLyme]

45 minutes ago, FlyingMonkey said:

The only downside

don't forget the blood on the wing(s) during waxing... ; )

[Tom Baker]

1 hour ago, FlyingMonkey said:

Yeah, VGs are one of the few "zero cost" (in performance, not dollars!) mods for most airplanes.  The only downsides are in proper setup and the fact you occasionally lose a VG and have to replace it.

They make the airplane a pain in the ass to wash.

[FlyingMonkey]

44 minutes ago, Tom Baker said:

They make the airplane a pain in the ass to wash.

Fair point!

[Madhatter]

Micro AeroDynamics vg's are low profile compared to others and I have never had a problem washing. Just can't use a sponge over them. 

[Mike Koerner]

VGs are not free. They certainly increase drag at high speed. It may not be much, maybe not enough to notice... I don't know. But for low drag you want to maintain laminar flow as far back along the wing as possible. Consider high-performance sailplanes; they go to great lengths & expense to avoid perturbations on the wing, especially from the leading edge and back along the top surface.

FlyBoy, you might consider putting the VGs on the outboard portion of the wing instead of the inboard portion. You want the inboard portion to stall first so you maintain aileron effectiveness. In fact, I had assumed that's what the leading edge block was for, since our wings don't appear to have any washout.

Mike Koerner

[BravoFoxtrot]

7 hours ago, Mike Koerner said:

You want the inboard portion to stall first so you maintain aileron effectiveness. In fact, I had assumed that's what the leading edge block was for, since our wings don't appear to have any washout.

Your are correct. If you google "Stall strips" that is the explanation they also give.

[JDB]

I think this may be the supplier referenced with the video above.  I found this some months back wondering if there were any vg's for LSA...

https://www.stolspeed.com/aircraft-using-stolspeed-vgs-testimonials

[okent]

That's the one

[Jacques]

not exactly    the ones in the video are  from Italy

http://www.veleriadedalo.com/vortex-generators-eng/

the StolSpeed from Australia are very common in America  and get inpressive results

that's the one I have experience with  

[Madhatter]

All VG's are pretty much equal in performance. I have always used Micro Aerodynamics as I prefer certified quality and they are aluminum. The advantage is that Micro AeroDynamics will help in the determination of vg location based on their 35 yrs of engineering and test data. There is no specific airfoil data that I can find for the CT and any help will save me a lot of time. I should  start working on the baseline flight data prior to installing the VG's in a few days, hopefully there will be significant result.  

[FlyingMonkey]

On 8/11/2020 at 8:39 AM, Tom Baker said:

The blocks on the wing are more about controlling the air that flows over the stabilator.

I was under the impression those existed to ensure the wing stalls first at the root rather than out toward the tip.

[Tom Baker]

2 hours ago, FlyingMonkey said:

I was under the impression those existed to ensure the wing stalls first at the root rather than out toward the tip.

That is true with traditional stall strips. Traditional stall strips are also typically placed closer to or below the center line of the leading edge.

[Madhatter]

I have completed the vg tests on the CT and I have the results 

Prior to installing the vg's I made several flights to get baseline accurate numbers on stall speeds with different  flap configurations. Stall speeds were done by using accepted  methods, (initial entry speed, one knot per second) etc. The vg's were installed at 6%, 4%, and 2% chord of the wing and flown several times in each configuration. The stabilator vg's were placed at 8% chord of the stabilator. 

In all the flight tests there was no reduction in stall speed in any configuration, however the plane had no tendency to drop out of a prolonged flair, which was my main complaint about the CT. In talking with Micro AeroDynamics the consensus was that the stall strip initiated the stall and the vg's became ineffective at that point, they had seen this before. Eliminating the stall strip would change that but it's not something I would ever do or recommend. 

At this time I am going to continue to test the vg's on the the stabilator for better landing characteristics without the wing vg's which are ineffective. 

[GrassStripFlyBoy]

Interesting find on the results, I think I could tolerate these on the underside of the stabilator.  Keep us posted.

[AGLyme]

well done MadH...

[GlennM]

You will need a stall fence to stop the burble from progressing outward, if that is the case.

[Madhatter]

Not something I am going to do, that gets into some serious testing and fabrication issues.  There are still some flight tests I have to do. Stabilator VG's are usually always combined with wing VG's as there are sometimes issues with aileron effectiveness if none are used. I have noticed some possibly positive characteristics even with no reduction in stall speed. Time will tell.

The CT is a great plane without changes, my goal is to make the landing characteristics better. In the end I may not change anything but at least I will have some answers and will learn a lot from Micro AeroDynamics.

[Madhatter]

An update on vg's

So far I have been able to reduce the power off stall speed by 8 to 10% based on 15° flaps

Easy take off speed at 30 kts

Made landings with 30° flaps with intentionally high flair and I have positive stabilator control all the way to touchdown,  no tendency to drop out. 

Min airspeed, level flight , no descent at 20 kts indicated at 2000 ft.

The main issue with the CTSW is stabilator boundary layer control. It's a difficult issue to resolve,  I have done several changes on % chord and lots of flight tests.  I have one more test to do and that will be to try Stolspeed vg's on the stabilator.  They are 1/2 inch in height vs 1/4 inch on Micro AeroDynamics and might be able to get more bite in the boundary layer which might be partially blanked out with full up elevator,  who knows.

Installing vg's on an aircraft that hasn't been done before takes a lot of work, I am sceptical of the other CT that tried it as there were no specifics reported and his % chord definatly does not work on mine, not even close.

After all the vg tests then all vg's will be removed and flight tests are done again to reverify the difference prior to final vg installation. All this is the way it's done even for certified aircraft, just takes time.

[Mike Koerner]

Hatter,

Is the reduction in power off stall you report with the Micro AeroDynamics vg's at 8% cord on the stabilator only?

Before removal you might also want to measure wide open throttle airspeed at a fixed altitude… If there was a noticeable change in high-speed drag with either your 310 or cub.

Mike Koerner?