How VG's effect R182 performance

[scottrsellers]

Here is text exchange between Dan Wood(260hp R182 with VG's) and Mike Pattison(300hp R182 with VG) discussing how VG's impact performance of their airplanes:


Hello Dan - R182 type club co-founder Mike Pattison copied here is interested to know how your VG’s effect performance. His R182(300XP) also has VG’s. Thanks *****

Scott,
Thank you for the intro sir.

Mr.Dan,

I hope you’re enjoying Oshkosh! Your R182 is beautiful. As Mr.Sellers mentioned regarding VGs, I’m on the fence removing my VGs. Scott’s airplane flies fantastic without and I know no other operators with them.. I would love your input.
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Much better elevator authority with them and better slow speed aileron control. We have a Sportsman cuff so we can land at slow speed on grass etc. We are very satisfied with ours. We experienced an elevator stall on landing prior to installing them so I can’t imaging going back.
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How do you feel about top end performance? I have a rather slow airframe and with rigging I’m trying to make it as slick as possible
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We really don’t care. I would have bought a 210 or a bonanza if I wanted to go fast. We are extremely happy with what we have.
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R182 power! Love it
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With the new Air Plains 260hp engine, we’re getting about 155 true. Air Plains claims 158. So maybe we are a little slower but not significantly.
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Roger that.

[AnthonyL]

What approach speeds are you gents using with the VG’s, I vary mine depending on landing weight. Book says 64 knots for short field and at light weights I still feel that’s fast.

[mpatt]

Well, Unfortunately, my airplane has been down for months for maintenance but ill definitely let ya know when its up and running! I'm still on the fence about keeping them on.

MP

[mpatt]

I recently removed all VGs on the airplane and associated placard.

Testing has shown a solid 5 knot increase in cruise speed. Don't forget the 337 due to the change! Low speed handling qualities didn’t seem noticeable.

Most came off easily with a razor blade.

[Gilbenl]

I have a 300HP IO540 conversion on my ‘78. I think I’ve discussed this very topic with many in this group. While I’ve never flown my plane without them, I’ve come to believe they don’t make as much of an impact on top end as compared to rigging, paint quality/dirt, door mounting (flush or not), cowls etc. In fact, I’m not convinced they make any difference.

The amount of surface area they add is minuscule and if I understand the physics, they’re only really relevant to airflow at low speeds and high angles of attack. I feel that at the relatively low speeds our planes are capable of, the tiny bit of drag they add is irrelevant. For cruise speed, I think taking them off is tantamount to exchanging some rivets for flush.

I used to buy the rumored 2kt impact, but it doesn’t make sense to me given their combined surface area and lack of impact on the airfoil at cruise. In fact, I’d venture that at cruise speed, the boundary layer doesn’t even interact with the VGs due to the shape of the leading edge.

Would make a cool wind tunnel experiment.

[mpatt]

funny,

I also have a IO540 300 HP, this all started with my airplane running slow.

Airplains says 165 True all day long.

Fastest I've seen is 155.

Myself, Scott stellers and Paul new having been trying to get to the bottom of the issue for awhile.

The airframe has been investigated, on to the powerplant and prop.

[Gilbenl]

That’s because the plane can’t do 165kTAS unless you go into the yellow or in a very narrow window of conditions. Let’s butcher some math and make definitive conclusions on broad assumptions!

Yellow line is 140 KTS IAS. I’m going to assume IAS=CAS.

Assuming you could achieve and maintain 140kts IAS at all these altitudes:

At 12,000ft, you’d need an OAT of 5F or greater.

At 10,000ft— OAT 45F+

At 8000ft—OAT 80F+

At 6000ft—OAT 125F+

I don’t have my POH with me but since we’re normally aspirated, power is going to peak in the 6K-8K range if I recall…but let’s say we can maintain 100% power at 10k. I also don’t recall the OAT at which the engine makes peak power.

So despite my ignorance of the exact best performance conditions, let’s stumble on and figure out what sea level conditions would make the 45F OAT reasonable at 10k. Using the 3.5F per 1000ft estimation, the sea level temp would be around 97F.

This is all very much back of the envelope and there are a lot of assumptions, but you can see that in order to hit that 165kTAS, you’d need a very hot day with unusually stable air. Those of us who have flown in places where it gets into the upper 90s know that those temps and calm air don’t often go together.

If we repeat all of this with a goal of 155 kTAS, it all becomes very achievable, which mirrors what most of us have experienced.

I’m sure AirPlains hit 165 kTAS in a perfect plane, on a perfect day, with a 115lb pilot and tanks filled with hopes and dreams a just a hint of 100LL. In the real world though, with full tanks and this 200lb gorilla at the controls, I’m very content with 155 kTAS.

Disclaimer: I’m not an engineer or mathematician or physicist or even that good looking. I’d be very interested to see if someone can make the 165k TAS possible under broader conditions.

I used the sports E6B app, which best I can tell, uses the formula discussed here to get the estimated TAS— https://aviation.stackexchange.com/que ... 20air%20Ts

Best—

N Gilbert