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vortex generators
Russell Knowles
- Russell Knowles
- ICS BOD member
- Posts: 12
- Joined: Mon May 26, 2008 7:15 am
Re: vortex generators
Jay
PA 30 N7702Y
Jay- ICS member
- Posts: 473
- Joined: Tue Sep 30, 2003 10:59 pm
- Location: Portland, Oregon
Re: vortex generators
Best, Don
Don Nelson- ICS member
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- Joined: Mon Nov 10, 2003 5:57 pm
- Location: Burlington, Washington; KBVS
Re: vortex generators
Russell
- Russell Knowles
- ICS BOD member
- Posts: 12
- Joined: Mon May 26, 2008 7:15 am
Re: vortex generators
Our laminar flow wings are very efficient, and I'd be concerned about whether there would be a speed penalty. That said, on my 182 they are very effective at improving low speed handling in both pitch and roll. Stall speed reduction is difficult to measure as the difference between CAS and IAS widens at higher angles of attack. I can tell you that stall speed on my 182 is reduced, but more important is the crispness of the controls at low airspeeds.
I did my BFR this year in my highly modified 182. The instructor doesn't know me very well but knows that I fly often, generally well over 300 hrs per year so I think he was feeling pretty relaxed. When he asked me to demonstrate a short field landing I asked him if he wanted a true short field landing or just a kind of short field landing. I think the question left him a bit perplexed, but he asked for a short one. Well, in my modified 182 that involves indicated airspeed on short final of 50 MPH with the stall warning blaring. Well, I saw him tense as I plopped her down and could have stopped in the first 500 ft of runway. In the interest of the brakes I coasted to the 1,000 ft turn off. He was rather surprised and asked if that was how I always fly my short fields. I answered yes, when I do a short field it's a short field.
Anyway, my point is that they are highly effective in the low speed envelope in a 182.
T210DRVR- ICS member
- Posts: 117
- Joined: Sat May 03, 2008 4:31 am
- Location: So. Oregon
Re: vortex generators
Russell
- Russell Knowles
- ICS BOD member
- Posts: 12
- Joined: Mon May 26, 2008 7:15 am
Re: vortex generators
I can say that it took me longer than a day to install the VGs as I went very slow to ensure I placed each VG exactly where it was supposed to be and cleaned the excess epoxy with a swap after each VG install to minimize the clean-up. Also, I found the most difficult portion of the install was getting the rudder template to line up correctly.
If you have any questions about the install call or email me.
Scott
N7610P
PS from looking at the knots2u website, I suspect the knots2U VGs are actually the ones from microaero. www.microaero.com. These are the VGs that I put on my plane.
- Scott R Morris
- ICS member
- Posts: 21
- Joined: Fri Aug 06, 2004 8:53 pm
Re: vortex generators
That said, does anyone have any performance figures or experience on a counter rotated, PA30 Robertson with VGs ? I talked to the VG people at Anacortes, Washington about this,and they had none to offer. I was surprised that it would be legal to install VGs on any airiplane without extensive testing and numbers approval by the FAA, but they showed me a copy of the STC for the PA30 that approved VG installation with a rather wide open proviso that it in essence left it up to the pilot to test and accept the compatibility of VGs with any other modifications on the airiplane. (!!)
I like my airplane with its current mods, but I would certainly like to know what the numbers would look like if I added VGs.
Al Powers ICS 2978
- SLIMDREDGER
- ICS member
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- Joined: Sat Aug 05, 2000 6:20 pm
Re: vortex generators
It's kinda of a dark secret of STCs that it's up to the "operator" to determine STC compatibility. You can legally "stack" most STC'd mods to your hearts content, but you get to be the test pilot.
The only STC's I can think of offhand with conflicts are those that increase gross weight. For example, if you have the Robertson STC you get a 200 lb gross weight increase. But if you put on the Osborne (Brittain) tip tanks, any weight above 3,650 lbs must consist of fuel in the tip tanks. In other words, you can't get the Robertson 200 lb increase and then the Osborne 150 lb increase on top of that for a total gross weight of 3,950 lbs.
It does make a certain amount of sense. If an STC applicant had to test his STC in conjunction with every other STC that an airplane could have it would make an already difficult process impossible.
Jay
PA 30 N7702Y
Jay- ICS member
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- Location: Portland, Oregon
Re: vortex generators
Charles Allen
- farmer
- ICS member
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- Joined: Mon Nov 08, 2004 3:47 am
Re: vortex generators
The ROC and speeds were determined by their pitot boom recording barograph. With the barograph temporarily mounted on the right outboard wing, I was handed a temporary airworthiness certificate by the FAA at the event.
Being temporarily experimental, I mounted my own vortex generators using double back tape. Their shape was like a 1/2 delta wing offset at 15 degrees to the airflow at the skin splice at the spar (40% chord). Empty weight of the plane was around 2850 pounds.
The results were: ROC was about 1850 fpm, top speed was 213 mph, and minimum speed was 59 mph. The minimum speed was a bit scary. Full power, gear down, flaps down, and the nose waaaay up. It took full right rudder to keep the ball centered. I might have gotten a little more out of it, but I was worried that if a stall occurred, the plane would go into a spin.
Previous to the event, I experimented with the vortex generator placement, including tufting the wing. My reduction in stall speed in the normal flight configuration was about 6 mph lower at a modest power setting. Since the vortex generators were at 40% chord, my speed reduction was minimal, since that is the location where the airflow turns turbulent anyway.
And yes, they do work in reducing the stall speed. The current STC configurations I have seen place the vortex generators on the leading edge, and in that configuration, cruise and top speed will suffer a bit since the forward section of the wing should be in laminar flow, and with the generators, turbulent flow is introduced. The difference in drag between laminar flow and turbulent flow on wings is 5 to 1.
In the intervening 22 years, more improvements have been made to the plane, and I now normally cruise at 208 mph (180 knots) in smooth air at altitude, provided the plane is clean.
Hansmeister- ICS member
- Posts: 802
- Joined: Thu Jun 27, 2002 5:44 pm
- Location: Kah-li-forn-yah
Re: vortex generators
Thanks for the factual comments and data points. Your cruise speeds are impressive.
I assume my Robertson cuff destroys the laminar flow characteristics of the unmodified Comanche wing????? I felt I lost 3 mph +/- when I had the mod done. Subsequent Lopresti and Knots 2U have regained the speed I lost.
I converted to Robertson back in the days that PA30 VMC demos were frequent and fatal and I had experienced a 1/2 turn spin with an instructor demonstrating VMC to me.
If I added VGs on top of the non laminar flow Robertson wing, do you think I would still lose 5 mph or so on the top end cruise?
Any thoughts on what VGs effect on the stall speed would be? Currently with counter rotated props Vs is 63 mph.
Warm regards, Al Powers
- SLIMDREDGER
- ICS member
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- Joined: Sat Aug 05, 2000 6:20 pm
Re: vortex generators
PA-39 N8934Y
ICS 268
John Fuller- ICS member
- Posts: 11
- Joined: Fri Jul 30, 2004 12:37 am
- Location: Minden, NV
Re: vortex generators
Very interesting report! Did you actually stall it with the extreme eccentric thrust on the engines?
Having experienced (as a passenger) a fast 1/2 to 1 turn spin before I bought my airplane, when the demonstrator pilot feathered one and had normal cruise power on the other engine to show me what VMC was, I am impressed that your VGs apparently allow you to prevent a spin.
After I bought my airplane, there were a number of fatal training accidents resulting from pulling engines on takeoffs and the PA30 reputation suffered. I was concerned about the problem and when the Robertson mod appeared I flew their demonstrator and was impressed with the ability to fly out of below VMC spin entry. "Push the nose down and stand on the opposite rudder" worked. My airplane was the second or third to receive the Robertson mod.
What loss (if any) of speed was there on yhour cruise speed?
Warm regards, Al Powers ICS 2978
- SLIMDREDGER
- ICS member
- Posts: 306
- Joined: Sat Aug 05, 2000 6:20 pm
Re: vortex generators
Yes, I stalled it with one engine at cruise power at 9,500'. Plenty of rudder and even some aileron required, but vmc is clearly below stall speed at that power setting. Nothing dramatic at all. I got my multi back in 1968 in a Twin Comanche when all the hoopla was going on and stalls (with both engines running) were a lot more dramatic in that plane. VG's do seem to be magic.
I'm sure I lost a knot or so in cruise speed with the VG's, but it's hard to tell since I put them on while I was having the engines overhauled. I still see about 163 kts plus or minus at 9,500' depending on weight (my paint is very rough but I have lots of speed mods - and tip tanks).
I had the Robertson STOL kit put on an Aztec I had once. Very impressive improvement in already good runway skills, I was also hoping for an improvement in single engine performance.
John
PA-39 N8934Y
ICS 268
John Fuller- ICS member
- Posts: 11
- Joined: Fri Jul 30, 2004 12:37 am
- Location: Minden, NV
Re: vortex generators
at 10,000 ft,after the paint job, I picked up and additional 3-4 knots true airspeed over my previous flight with the old paint. Mind you that speed mod was one
of the most expensive Here are the stats of my flight home at 10000 ft, airspeed indicator indicating 176 knots true at 65% power, fuel burn 15.9 gallons per hour, running 50 degrees rich of
peak.
Gary
- md11flyer
- ICS member
- Posts: 330
- Joined: Tue Mar 24, 2009 3:48 pm
Re: vortex generators
Thanks
Jim
- MULEFLY
- ICS member
- Posts: 900
- Joined: Tue Jan 25, 2000 1:34 am
- Location: Wisconsin
Re: vortex generators
Please tell us more about your paint job on a different thread. I would like to here more. What was good, bad, what you would do different, etc.
Thanks,
Jeff
- jeffrey aryan
- ICS member
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- Location: Chino, CA (So-Cal)
Re: vortex generators
Gary
- md11flyer
- ICS member
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- Joined: Tue Mar 24, 2009 3:48 pm