Stolspeed VG's

[Rspencer]

Ok. Good to know. I saw his old YouTube video on his 5 wing (very different) and he decided 5% wasn’t good but 7% was. Obviously lots of conversation in this thread alone, but not a real consensus on the 4A wing location. Anyone else agree for 3%. And anything special for the horizontal stab location?

[jaredyates]

If you've seen a different number it is probably worth reaching out to verify. I don't have high confidence in my notes being right.

[Utah-Jay]

Based on my touchdown speeds in my Companion, I think you guys are missing out not using the Hall Brothers VG I am using. I am not the first to use them as the testing was done by a Patrol owner who is not building a Companion.

[Fred Williams]

Based on my touchdown speeds in my Companion, I think you guys are missing out not using the Hall Brothers VG I am using. I am not the first to use them as the testing was done by a Patrol owner who is not building a Companion.

How much difference did they make? What are your stall speeds with and without? Where did you place them. I've got a Patrol but inquiring minds want to know... TIA

[Rspencer]

I saw a YouTube video of a Patrol owner who tried them and Stolspeed. His biased opinion was stolspeed was slightly better for a handful of reasons. Based on that and MANY other Stolspeed recommendations and writings, I went that route. Got them painted tonight. So ready to go on tomorrow.

[Fred Williams]

I saw a YouTube video of a Patrol owner who tried them and Stolspeed. His biased opinion was stolspeed was slightly better for a handful of reasons. Based on that and MANY other Stolspeed recommendations and writings, I went that route. Got them painted tonight. So ready to go on tomorrow.

I've recently received the StolSpeeds for my Patrol as well. Haven't painted them yet but am trying to gather info on where to place them. I'll be checking back here to see if anyone can provide good guidance on where to place them and what it did for the performance of their Patrol. TIA

[Utah-Jay]

How much difference did they make? What are your stall speeds with and without? Where did you place them. I've got a Patrol but inquiring minds want to know... TIA

As per FlySto.net my average touchdown speeds is 38 mph IAS, and that includes all the early landings when I was learning the plane some of which were over 60 mph IAS.

My typical landing nowadays is 35-37 mph IAS.

Slowest was 32 mph and the plane was still flying.

I never flew without the VG’s, never felt the need after I saw the data that Chris sent me. And they were a lot easier to install prior to hanging the wings

[Fred Williams]

As per FlySto.net my average touchdown speeds is 38 mph IAS, and that includes all the early landings when I was learning the plane some of which were over 60 mph IAS.

My typical landing nowadays is 35-37 mph IAS.

Slowest was 32 mph and the plane was still flying.

I never flew without the VG’s, never felt the need after I saw the data that Chris sent me. And they were a lot easier to install prior to hanging the wings

How far back did you place them?

[Utah-Jay]

How far back did you place them?

I can measure tomorrow, they are placed a certain distance from a Rivet line

[Rspencer]

Bearhawk recommends 3-5% in a text with them today for the 4A. What’s everyone thoughts on 3% in front of the ailerons with the tighter spacing, and 5 % on the rest of the wing? Further assist in keeping the ailerons functional during a stall?

[Battson]

How far back did you place them?

I understand that they are best positioned so that when the wing is at the highest angle of attack, the VG is fully exposed to the oncoming airflow i.e. at the highest point of the wing. That's how I arrived at my recommended location for install, and practically it's proved a winner. You can apply the same approach with your aerofoil, all you need to know is the AOA at stall (in landing configuration). You want them at the highest point of the wing, when it's at the stall AoA.

My understanding comes from a lot of pre-reading, watching other guys testing on Youtube, practical experience on my own plane (the modified NACA Bearhawk-A aerofoil), and discussing the Breeden's experience from testing VGs on their Cubs in AK. Bob Breeden reached the same conclusion as I did, highest point on the aerofoil at stall AoA.

I note that the % chord would vary based on the aerofoil. So if Cub guys are saying 12% and Vans guys are saying 7%, that doesn't necessarily mean it would be ideal for the Bearhawk. We know people have tried them further back on the Bearhawk and it yielded poorer results.

You want one straight line across the wing, not a staggered arrangement.

I would follow STOLspeed's recommendation about spacing, and use the templates provided. They specify tighter spacing in the outer section of the wing.

Here's my post about where I installed mine:

https://bearhawkforums.com/forum/flying-and-flight-testing/2251-who-is-using-vgs/page3

[Utah-Jay]

I am a believer in results, here are some real world results with the Hall Brothers VG’s on my Companion. The Flysto.net says I have done 8 touch & go’s, but I have never done a touch and go, so the data is a bit skewed from doing low passes over strips for inspection purposes. The dots in the black circle are some of the so-called touch & go’s, but they are still calculated in the average so the average is higher than actual touchdown speeds.

Debate all ya want, here are results!
IMG_1116.jpg

[Battson]

It would be useful to know the average ramp weight at touchdown, the ASI instrument error at touchdown, and the location of the VGs on the wing, for comparison purposes.

[Utah-Jay]

Battson

I would say my average weight at touchdown is about 1800#’s, that is +/- 25 of accurate.

Location of the VG’s? Further back than the StolSpeed VG’s, all the testing was done by Chris Spira who did the testing on his Patrol. Chris’ testing data is exhaustive!!!! He tested VG location by % of the cord, included aircraft weight that day. He included humidity and DA in the daily testing data. I have a copy of all of his testing somewhere.

I am not aware of an ASI error on my plane, when checking it matches really well with my GS when correcting for my typical DA of 6000’ to 8500’ depending on the time of year (temps)

Hope that helps.

[Battson]

[USER="232"]
I would say my average weight at touchdown is about 1800#’s, that is +/- 25 of accurate.

Location of the VG’s? Further back than the StolSpeed VG’s, all the testing was done by Chris Spira who did the testing on his Patrol. Chris’ testing data is exhaustive!!!! He tested VG location by % of the cord, included aircraft weight that day. He included humidity and DA in the daily testing data. I have a copy of all of his testing somewhere.

I am not aware of an ASI error on my plane, when checking it matches really well with my GS when correcting for my typical DA of 6000’ to 8500’ depending on the time of year (temps)

Hope that helps.

Thanks for that Jay, that is very interesting.

For a long time, I assumed my own ASI error was negligible because, during a casual landing, it always is. Typically one knot or less.
What I’ve since learned, though, is that the error spikes sharply right at the very bottom end of the performance envelope. High AoA is, of course, exactly what we’re doing for these tests at the limits of performance. There really aren’t many fundamentally different pitot designs available, so I think we're all in the same boat here. But extensive testing on very calm days is the only way to know.

This ASI error is especially relevant with Bearhawk flaps. To achieve maximum lift, we must operate at quite high AoA, so when we’re talking about stall speed and the slowest possible landing, the ASI error needs to be investigated before we can fully understand the data.

From repeated testing, I’ve found my ASI error changes sharply with landing technique:

• For a normal 3‑point landing, the error is about ≤1 knot
• For typical STOL landings, it increases to 1-2 knots, but only at the very last moment before touchdown
• In more extreme test cases, using high power and very high AoA, it spikes to 5-7 knots

I can reliably indicate as low as 28 KIAS when the plane is light, but that’s clearly not the true airspeed. At first, I was very optimistic, these days I am more realistic about it. GPS checks consistently show the real speed is about 5-7 knots higher

So depending on landing style, it seems likely we’re all operating somewhere along that spectrum.

What was the absolute lightest landing weight for the data shown in that graph?
(Just pilot, minimum fuel, and the aircraft.)

Looking at the slowest speeds shown in the data - down to 29 knots (34 mph) IAS - that strikes me as unlikely at 1,800 lb for a standard Bearhawk wing with VGs. VGs certainly help, and better designs can buy you a knot or two over poorer ones - but not on the order of eight knots.

For context, in my own STOL testing with an IO‑540 four‑place (same wing and weight), I’m typically around 1,750 lb, an I have 16" extended wings both sides (32" total extension) and STOLspeed VGs right to the tips. On paper, that would make our aircraft reasonably comparable. As I say, the slowest I get is 37 GS which often reads as low as 34 KIAS or even 28 KIAS, but again - it's always 37 GS regardless of IAS.

I think for me, something around 37 kts GS is the best that wing can support at around 1,800lbs. Ultimately, it comes down to weight versus wing area.

I’d be genuinely interested in knowing what weights relate to the lowest speeds reported in that data. If there's ways to go significantly slower, I am going to investigate them.

[jaredyates]

I think there is more opportunity for studying these numbers. Jonathan has additional wing area at the tips, and Jay has a significant density disadvantage. I would have guessed those would be worth a few knots each, but guessing isn't worth much in these contexts.

The other thought that comes to mind is how important weight is. One fellow just completed a build and his empty weight was in line with these gross weights. He's not the only one either.