Thoughts on VG's

[a64pilot]

Specifically the Micro Aerodynamics ones, STC # SA00170SE. Has anybody else done any performance comparsions between before and after? I installed them exactly IAW the STC of course, the only deviation I made was to strip the leading edge of the wing, glue them to bare metal and prime and paint the leading edge and VG's at once. I needed to strip my leading edge to remove the 3M tape that had been applied that had yellowed, split, and had mildew growing inside of it.
Anyway my airplane would indicate 160mph firewalled, level flight at 2,000 DA. and cruise 120 kts IAS at 22 squared. Which made it a decent cross country machine for a STOL airplane.
Installed a three blade prop for smoothness and because the two blade had been inadvertantly modified with Q tips. Full throttle IAS at 2,000 DA dropped about 2 mph to 158. I had been forewarned of this and considered it a decent trade. It took a little more power to cruise 120 IAS, 23 and 22 respectively. I could still true out at 130 kts true at between 8 to 11 thousand feet.
So I installed the VG's, being told in writing by Micro aerodynamics that they wouldn't hurt cruise at all. Being a pessimist and knowing that you can't produce a vortex without some drag, I figured I would lose another 1 or 2 mph, but hoped the elimination of that nasty 3M tape from the leading edges would compensate some.
Flew it for the first time yesterday. It lost eight mph when firewalled and it now takes 23 squared to indicate 120 kts.
Eight mph is huge, and I'm not sure it's worth it. I'm not sure that much of anything is worth eight mph. Previously I had a 600 nautical mile range with a comfortable reserve. I haven't cruised at a decent altitude yet, I can only hope the less dense air will lessen the reduction of cruise speed.

[maules.com]

I've been fitting VG's for years since inception by Micro and never seen more than a tiny change, hard to measure one, two or three mph. Something else must have been affected, paint drft to pitot, temperature, etc. It is dificult to paint VG's already installed as the gun causes vortices of paint which will cause uneven paint surfaces and thickening of the vanes. Just fishing here.

[Hottshot]

No kiddin' 8 mph is very weird that's a new one on me

[a64pilot]

No the paint is close to perfect, except for some trash from a not too clean booth. I did have the struts off to strip and repaint them. I'm going to check rigging, maybe somehow I swapped sides with the struts ? I do have to hold more right rudder now, I assumed it was because of the slower speed. The eight mph is at full throttle, the speed reduction is less, the slower you go. Slow flight, just tooling around with the windows open, it's not noticable at all. I would have thought pitot, static leak except the GPS verifies the speed.
The elevator requires more up trim at take off, would this indicate incorrect washout?

[Hottshot]

Yep rigging sounds like the issue....

[a64pilot]

Yep rigging sounds like the issue....

I'll start from scratch Saturday.
I'm afraid I wasn't clear, the eight mph is cumulative from both the prop and the VG's. Two from the prop and the rest from the VG's. I was wanting to hear that my speed loss wasn't typical. I was starting to believe that I had screwed up a good airplane with these "improvements".

[donknee]

I still have the two blade prop, 8:50's, with the micros: 162 mph true airspeed @ 6000ft. Improved slow speed performance. Even stall characteristics.

[Jet-A]

I have a similar situation where I bought the airplane without VGs and I installed them (via A&P) and I noticed a slight charge of approximately 2 or 3 kts in cruise, but at altitude it was only about 1 kt. But that was the ONLY thin I changed externally. Your prop, with it's increased weight, might me more of a culprit than you are assuming in addition to the rigging..? Dunno - just fishing like Jeremy here.

The safety improvements were far greater of an advantage than the cost of the cruise. Before, full stick back, full flaps, and no thrust (after a gentle deceleration) would produce a significant wing drop and a rotation towards a spin. NOW she just waffles in the air back and fourth at 32 kts (per the GPS) and a 500 fpm decent rate. Additionally, the improved handling below 60 mph indicated is terrificly improved. Loads of confidence!

[a64pilot]

The prop was done a year or so ago. I am leaning towards rigging being the issue. The struts went to sandblast and I think they may have removed the tags I had on them marking location and replaced them incorrectly. Who knows? I did have to make a rather large adjustment on the right rear strut because she was rather left wing heavy. I always record any adjustments I make, so it will be easy to un do.
Believe me no one wants to have egg on my face worse than me. I want to find that I screwed up, because then it can be fixed. The more people tell me that they got little if any difference in speed, the better I feel.
I knew the M-5 would probably be faster because the wings are shorter, but I didn't think it would cruise at 140 kts at altitude. Maybe I need an M-5
So far I have seen very little improvement, even in a stall. The only way my airplane will actually stall, except for an acclelerated stall, is with little or no flaps. With power off, it's a clean break, doesn't drop a wing and will self recover easily. Power off, full flaps it has always just "mushed" around 45 mph IAS or so. It's not really stalled, it has run out of elevator authority is all. Now if the CG were moved far enough aft, of course it would stall.

[a64pilot]

OK, Friday I checked the rigging. The front struts had indeed been swapped. I put them back and re-adjusted the right rear strut back to where it had started. I was now exactly where I was rigging wise before the VG's. I tried hitting the test points, but it was hot, 98F and air quality was terrible to say nothing about 2,000 DA being underground.
Saturday morning early when it was still cool and air quality was perfect, I repeated my test points. 151 or maybe 152 at full throttle, but only a speed reduction of 2 or 3 mph at cruise power settings. A power setting of 23 in and 2200 RPM which used to give me 120 Kts now give 118 Kts or so. There is a definate increase in drag that is not linear. I started looking around the internet and bumped into this http://web.usna.navy.mil/~dfr/flying/Vg ... e_wide.pdf This is comparing apples to oranges, Maule to Bonanza and the manufacturer of the VG's wasn't even the same. I.E. His testing is more precise and returned the opposite results from mine, less difference as speed increases where I got more difference. I can live with the decrease in speed I guess, the airplane seems to climb at a steeper angle, I think it will land slower although the limiting factor in at least my airplane is a lack of elevator authority most likely the result of a foward CG.
In all I would have to think that BD built a pretty good little airplane, and My attempts to improve on it can be viewed as not being improvements, depending on what you are after. This does re-affirm my belief that there is usually no free lunch and if you improve one aspect of an airplane, it usually will reduce the performance somewhere else.
It would be interesting to have been a little more precise in the testing, but the airspeed boom that I have will not fit a Maule, and I don't have calibrated A/S indicators either.
P.S. if an M-5-235 will really cruise at 140 Kts true, then I may be in the market for an M-5. I don't think they give up much in the STOL category compared to my M-6 do they?

[Hottshot]

P.S. if an M-5-235 will really cruise at 140 Kts true, then I may be in the market for an M-5. I don't think they give up much in the STOL category compared to my M-6 do they?

Fly before you buy......

[Kirk]

My M5 is pretty clean and I get about 125 kts at 55-65%, 130 kts maybe 135 at 75%.

Not real sure about 75% numbers since the high MEAs in my area usually push me up to 8000' or so.

[Jet-A]

Simple fact is that we all bought the "Jeep" of airplanes. I am reminded of that fact everyday that I drive my Jeep TJ (aka "Wrangler") that it's not made for the concrete. When I get airborne in my Maule, I realize right away that she climbs like a homesick angle, but cruises like a Jeep.

As far as "BD got it right the first time", I believe that he was, like any other person producing a product, in it to make money and survive. As a producer, he would have to draw a line in the sand and say, "this is it". The FAA makes it near impossible due to time and expense to make changes following certification. Therefore, it's not going to be perfect and we have the opportunity to improve it to suit our needs. That's a good thing in my book.

The VGs are the perfect example of this concept. It's like putting a 4" lift on your Jeep. It will give you better clearance when you need it, but robs you at the gas pumps the rest of the time. But when you need that clearance to get over those rocks, trees, whatever - it's nice to know they are there.

CHEERS!

[a64pilot]

OK, I've put about 70 or so hours on them in the past couple of weeks and have some more impressions.
The higher the power settings and the lower in altitude, the greater the decrease in speed. Above 6,500 MSL or so, full throttle and 2300 there isn't any noticeable decrease in speed. I would true out via the trusty Garmin E6B between a low of 132 kts to a high of 136 kts. at altitude or 152 mph to 157 mph for Jeremy and the other MPH folks. Which is awfully close to what she has always trued out at before. Or at least since David Wright rigged it properly. At higher altitudes, say between 10K and 12K there seems to maybe even be a slight increase in cruise speed.
She used to be fastest around 7,000. It now is fastest around 9,000. The speed is about the same, just at higher altitudes the fuel burn rate is lower, so if I cruise at higher altitudes, I should have slightly increased range.
The break even point for me as far as the reflexed flaps used to be about 12,000. That is at altitudes above 12,000 the negative flap setting would actually slow me down. With VG's it is now 14,000. I flew quite a bit this trip on O2, but not above 15,500.
If there is a decrease in minimum flight speed at full flap with the power at idle, then it's so little as to not be noticeable to me. Jeremy pointed out that there is more decrease in stall speed with partial flap settings, I don't have data points for that, but seat of the pants, I would agree with him. The stall break at 0 flap is more pronounced, but there is more aileron authority in the stall now. There is more elevator authority in the flare with the VG's than without though and that has been the limiting factor for me in the slow and steep approach before, not as much now.
There is more aileron and elevator authority at all airspeeds now and that is nice. I am still at a loss to understand the M-6's supposed lack of aileron authority, maybe it's because I have so much rotary wing time and aren't opposed to use my feet as I guess most airplane guy's are. I have found to have crisp roll response and keep it in trim you have to lead the ailerons with the rudder, if you don't then you aren't keeping it in trim, you are correcting an out of trim condition from the adverse yaw from the ailerons.I have never really found it to be a problem, but the roll response is greately improved. I think if the M-6's came with VG's from the beginning there wouldn't have been a perceived lack of aileron authority.
The limiting factor on which airfield is usable and which is not for me is what I can get out of and not what I can get into. At DA's of say more than a couple of thousand and a few hundred pounds of fuel and junk I can land in less room than I can get out of, even with the 235. Sea level DA and an empty airplane, minimum fuel then I can get out shorter than I can get in, but what can you do with an empty airplane?
The VG's do seem to have a crisper control response when you are down real slow especially and there is more control authority in both the elevator and aileron.
The stall angle of attack is higher with the VG's than without. The way I know this is that I adjust the stall warning to come on at 5 mph before stall with full flaps. I had to bend the stall warning tab down quite a bit to keep the 5 mph constant, indicating that the stall now happened at a higher AOA than without the VG's.
The net effect of the VG's seem to be about the same as increased wing length would have done. There seems to be more lift at a given situation as evidenced by my max speed altitude moving up almost 2,000 ft., the neg flap working for an additional 2,000 ft. and last but not least if you believe in the no free lunch aerodynamic theory the increase in drag and the speed penalty at low DA's and high power settings.

[SkyMaule]

I put on the VG's. I like em. slow speed mushiness much better. loss of three knots at cruise. Less above 9,000 feet. I like em.