VGs /split from new owner engnd spec talk

[Bruce Fenstermacher]

Well, I sort of agree with both sides of the VG question. I have VG's on my airplane, and I would never install them again. I approached this with the idea that they are cheaper than a Sportsman, which I also have extensive experience with.

The VGs did alter the stall characteristics of the airplane. They turned an already mellow stalling airplane into a slightly more mellow stalling airplane.

All the stall speed decrease hyped by everyone did not accrue from my installation, and yes, I've done multiple runs before and after, using GPS, etc. At best, there may have been a 1 to 2 mph decrease in stall speed. That's positive, but not worth the bother, in my book.

The Sportsman, on the other hand, does present a significantly lower stall speed, in my experience. It is more expensive, but I think the additional expense may be warranted by the better performance.

Wing covers: I use mesh wing covers, and I agree that the VG's aren't a total disaster when using wing covers. They are sort of a pain in the neck, though. Not bad ugly, but a significant increase in hassle. Understand that using wing covers itself is a hassle, so you're making the hassle worse, which isn't fun.

The worse problem I've seen is potential for pilot damage while fueling the plane. In icy, wet conditions, I've slipped a couple of times (okay, so I'm a klutz), and ripped a pretty nasty little gouge in my forearm with a VG. Frankly, it doesn't stretch my imagination to envision being out in the boonies somewhere, and precipitating a major bleed after a slip. That may seem unlikely, but.

A lot of folks also sit on the wing to fuel from cans (a practice I don't condone in any case). I wouldn't advise that with VG's, unless you are already contemplating hemorrhoid surgery.

As noted, I've got VG's, but I wouldn't do it again on a Cessna wing. On a Cub, yes, on a Scout, yes. On a Cessna, no. The minor benefits (and there are some) aren't worth the hassles, and there are clearly (to me) better STOL kits available for the Cessna wing.

Mike

Gee Mike I'm surprised you only saw a 1 to 2 mph drop in stall speed. My B model stalls so slowly and at such a ridicules angle I know the airspeed indicator isn't working. It's usually indiating between 0 and 30ph.

Can’t say how much but that’s way more than 1 or 2 mph. And there is improved aileron authority all the way to stall and beyond.

Will I fly an approach at the ridicule sly slow stall I know have with Vgs. No, but I will easily do the book numbers and beyond with out a thought.

Mike, Did you see any improvement in aileron control?

[zero.one.victor]

On my ragwing anyway, my approach speed isn't so much governed by stall speed as by aileron effectiveness. I had some bootleg flap-gap seals installed (Ok they were fashioned out of duct tape,so what!), which did decrease stall speed. However, I could not take advantage of the lower stall speed to make slower approaches, as my ailerons were mushier a the lower speed than I felt comfortable with. So I would end up with a lot of float due to approaching at too much over the stall speed. I removed the gap seals, and now I can make shorter landings in spite of a higher stall speed, due to the lack of float.
For the ragwing at least, I would be looking for increased control effectiveness over slower stall speed. Mike, which would you say gave better low speed control, the Sportsman cuff or the VG's?
This is all just hypothetical for me anyhow, neither cuffs or VG's are available (STC'd) for the ragwing 170.

Eric

[Doherty]

Can you help me find the sprotsman stol webpage?
This is a must, still undecided about the VG's and the engine.
As far as floating with gap seals, this is simply just carrying to much speed. Try controlling roll with the rudder when slow and see if that helps.

[mvivion]

Try http://www.dandtaircraft.com for some info on the Sportsman.

If you've seen one of the new Lancair production aircraft, you will notice that the leading edge of the outboard section of the wing is drooped and extended. This is precisely the same cuff as the Sportsman, and accomplishes similar results. Lancair needed to keep their stall speed below the 61knot certification requirement for single engine airplanes, and this cuff was the way to do that on a pretty laminar flow airfoil.

I don't think Quackenbush has a web site for the Sportsman kit. Locally, Northland Aviation sells the kits. You can reach Jon at 907 474-0948. He also sells the Micro Aerodynamics VG kits, by the way.

I did what I consider pretty thorough testing on my 170 with and without the VG's. Indicated airspeed is totally irrelevant, for the very reason that at high alpha, you are measuring differences in pitot mast angle errors, NOT differences in actual airspeed. That's why in test programs, they use specially designed pitot masts.

I ran the four cardinal directions, on a very calm day, and measured on my GPS the speed at which I achieved a buffet from airflow separation in each of those directions. I then descended a couple thousand feet, and did the same drill again. I made sure that the weights of the before and after tests, as well as the ambient temperatures being the same.

My results were at best about a 2 mph decrease in stall speed with the VG kit. I could stretch it to make you feel better to three, but that would be a real stretch.

A similar test done on a 180 with a Sportsman yielded a 6 to 7 mph reduction in stall speed.

I'd really like to fly a Boundary Layer kit on a Cessna wing to see what they do. They are not approved on the 170, however.

Note that Micro Aerodynamics (and Sportsman) makes all sorts of claims on their advertising about stall speed reductions, but they only tell the FAA that the kits do not induce any adverse effects. If they claimed to the FAA that they reduced the stall speed of the airplane, they'd have to prove it via flight test. That's expensive, and might not yield the results you'd really like to advertise.

Note that Robertson STOL flight tested and certificated EVERY airplane they equipped with a RSTOL kit. On the 185, they reduced the stall speed (and this was flight tested and certified by the FAA) from 56 knots to 37 knots with that kit. Now, that's not advertising hype.

I am a firm believer in aileron gap seals. The Sportsman kit comes with aileron gap seals, and aileron effectiveness is significantly improved by that kit. I saw some improvement in aileron effectiveness with the VG's, but only a very little. The difference accrued by the Sportsman is much more significant, in my opinion.

Again, even for the additional money, if I had it to do again, I'd have a Sportsman kit installed, not the VG's.

One issue that is worthy of note, however: It is possible to change the angle of incidence of a Cessna wing. My airplane has the wings cranked up for maximum performance. As a consequence, it's a slow cruising airplane. It also stalls slow to start with. The way your wings are rigged will certainly affect how any STOL kit performs, but I'm not sure how that would work. Just thinking out loud here.

Mike

[Bruce Fenstermacher]

That's very interesting Mike. Of course as I said earlier I knew my airspeed indicator was not registering correctly. Next time I go out I'll pay more attention to the GPS and see if I can determine my stall speed and see how it compares to stock numbers. I won't at this point be taking off my VGs for comparison though.
BTW I didn't pay for them but won them as a door prize so I have no vested interest in them working.

Mike, just looked at the website you linked in your post.

Did you find increased climb and cruise speed with the sportsman stall kit as they claim?

[Roesbery]

Something you folks haven't been addressing is the rigging of the ailerons. You might want to play with them and see the difference they make. I did some a lot of years ago and found that drooping them gave a shorter ground run (180hp) but decreased cruise speed, and if drooped enough the stall became a sharp break, instead of the gentle drop or high sink you normally get if it is entered slow enough. Running them up increased cruise and ground run and made it hard to get a break in the stall, just a high sink. A high sink as opposed to a sharp breaking stall probably has something to do with me still breathing as opposed to some of the people I used to work with. Some food for thought.

[GAHorn]

mvivion wrote: "My airplane has the wings cranked up for maximum performance."

I believe tweaking the wing angle of incidence is the epitome of too much spare time on your hands.
The mid-range of the eccentric bushings was designed as the ideal from the standpoint of drag, and the bushings are for the purpose of correcting wing-heaviness (as we all know, of course.) The farther from the mid-point of incidence the greater the drag (in theory) of the fuselage, and the tailplane (which must make up for the changed incidence), and that is the very reason such tweaking is an excersize in self-deception. (Simply loading one's airplane fore/aft with pax and baggage will obviate any advantages imagined by the tweaking anyway.)
All of which becomes a moot point in 50 year old airplanes that have been wrecked and repaired in the field 3 times by now. (I knew you were all holding your breath until I chimed in on this subject.)

[mvivion]

George,

This may irritate the dickens out of you, but I fully agree with you, except for one thing: cranking the wings up with the eccentrics does change the stall on these airplanes. I'm not saying it's better or worse, and it I should have noted that the previous owner is the one done it to my airplane, not me.

I'd never waste the time to do it on my airplane, but I'm also not about to waste the time to re-rig it, either. That's how important I think it is. I think its pretty silly, frankly, but you see it all the time. And it does make some difference when you compare apples to apples, but not huge amounts. My point is that it can muddy the waters on these sorts of discussions. The wings are adjustable, after all.

As to the claims of added climb performance or cruise speed, no I haven't seen those "benefits" of the Sportsman. It is worthy of note that Quackenbush hasn't put his cuff through the rigorous flight documentation either that would unequivocally answer these questions, so this "data" must be viewed as advertising.

Mike

[ak2711c]

I put the Sportsman Cuff on my 170B. Regretfully I did not take many before numbers. However I did get a 1-2 mph increase in cruise. I am pretty sure the rate of climb is slightly better. Stall speed is way lower and the AOA at stall is much steeper. I think the cuff is a great mod that gives you a good boost in performance. However having said that, take the numbers that they give you in the brochures with a grain of salt. They are a bit overly optimistic. A couple of draw backs to the cuff is it is permanent and it takes over 40 hours of labor to install.
Shawn

[GAHorn]

Anybody (everybody) ever notice how prototype airplanes go through flight testing with a long "unicorn" pitot probe on them? There are plenty of special instrumentation mods on aircraft that are being fight tested for performance documentation. The reason is because the cheap....er....inexpensive....uhm......less expensive instruments that the production aircraft ends up with cannot accurately measure aircraft performance, especially at the extremes of the envelope such as top speed, and stall. (As the airplane is brought to the stall, the angle of attack becomes so extreme that the standard pitot does not allow the full impact of undisturbed relative wind to enter the tube, and the gauge itself is suffering from the most errors due to internal frictions and other errors at it's upper and lower ends.) That's why we frequently see airplanes with stall warnings screaming and airspeed indicators showing "zero" yet the airplane has not quite yet stalled.
So,....imagine that an airplane is in or near that regime of flight when the super-duper kit is installed and it's owner then makes the observation that his stall speed has decreased by 2 knots, or top speed has increased by 2 knots.
The likelihood of an accurate assessment of the performance changes imparted by the super-duper kit is very low when using standard instrumentation....comparing flights on different days....with all sorts of other unnoticed differences in the flight tests existant. An example: If the aircraft previously stalled with it's standard ASI quivering near it's lowest point of readability...will the same airplane 50 lbs lighter...on a day 2 degrees cooler....and a barometric pressure .02 mm HG greater....demonstrate a higher or lower indicated stalling speed?
The 2 points I'm wishing to make is the phenomenom that we all experience: The relative merit of many modifications is directly proportional to the expense and inversely proportional to the permanence of the mod....and....you never hear a pilot publicly criticise his latest wife or airplane modification when either is within earshot. (And in any case, it's most likely a relative opinion anyway.)

[mvivion]

George,

True, for the most part. You will hear me knock the VG kit, though. As noted, I wouldn't do it again.

As to the Sportsman, it is a good kit. The fact that the Lancair folks used a virtually identical cuff on a go fast machine suggests that at the very least it shouldn't reduce cruise speed.

In any case, one of the reasons I have always liked the Robertson STOL kits is that Robertson instrumented, flight tested, and certificated all data on their kits. They also provide a flight manual supplement, which spells out different procedures and speeds for the modified airplanes.

If Micro Aerodynamics' VG kit reduces the stall speed so much, why doesn't the FAA require them to produce and provide to the pilot a Flight Manual Supplement?

There's a couple simple answers to that one.

Mike

[GAHorn]

I"m not a fan of VG's myself, but the really simple answer to the question as to why the FAA doesn't require a supplement is because the kit doesn't increase stall speed....i.e....there's no penalty with the kit from a safety standpoint regarding reduced stall speed claims. VG's certainly do help keep boundary air attached, as demonstrated by lots of aircraft that have had the performance claims properly documented. As for the benefits accrued to the 170 however, it's a waste of time/money in my opinion.....the stock airplane will already get into places too short to get back out of.
The same sort of claims are made by VG mfr's in multi-engine aircraft...namely that stall and Vmc speeds are reduced. So what! The critical speed in a multi-engined airplane (for the benefit of non-MEL rated pilots present) is NOT stall or Vmc...but Vyse/Vxse....which is always higher than either stall or Vmc. In other words, if one doesn't wish to give up the safety of multi-engine capability (i.e. continued flight with single-engine performance) then one shouldn't fly the airplane below Vyse or Vxse anyway...so what in the world does a VG mod do for you? Nothing worth the trouble and price, in my opinion. (or the cut forearms and uglyness)

P.S.: Not to be argumentative, but it's like apples & oranges to compare a cuff's performance on a Lancair airfoil with that same cuff on the C-170A/B NACA 2412/symmetrical airfoil. The two simply aren't the same, so it's not a valid comparison. (not to mention the lack of comparison of the cuff's angle of incidence to the airfoils in question.)

[Doherty]

Gahorn, I am watching these post very carefully, as I am trying to decide what mods to do, or not to do to my 170B. I would however, like to correct you on the use of VG's on multi engine aircraft. The first benifit you get by lowering the VMC on is twin is not ending up dead if you loose an engine with low airspeed. If your VMC is lowerd, you can maintain heading controll until you accelerate towards blue line, or best angle (s.e.). Most twins are approved for a higher gross weight take-off with the use of VG's and most pilots (me included) notice a big impact on stall speed, especially if the top of your wing has suffered from contaimanations, like freezing drizzle, for example. I relize this post may seem as if my finger is poking you in the chest, I am not. I am simply offering my advice that on twins, the rersults of VG's can be very significant. As for the C-170B, it looks as if the jury is still out, but the guys who like them seem to be loosing ground to those who don't.

[GAHorn]

Gahorn, I am watching these post very carefully, as I am trying to decide what mods to do, or not to do to my 170B. I would however, like to correct you on the use of VG's on multi engine aircraft. The first benifit you get by lowering the VMC on is twin is not ending up dead if you loose an engine with low airspeed. If your VMC is lowerd, you can maintain heading controll until you accelerate towards blue line, or best angle (s.e.). Most twins are approved for a higher gross weight take-off with the use of VG's and most pilots (me included) notice a big impact on stall speed, especially if the top of your wing has suffered from contaimanations, like freezing drizzle, for example. I relize this post may seem as if my finger is poking you in the chest, I am not. I am simply offering my advice that on twins, the rersults of VG's can be very significant. As for the C-170B, it looks as if the jury is still out, but the guys who like them seem to be loosing ground to those who don't.

No offense taken, Doherty! For the sake of discussion:
1) Can you tell me a common, legitimate (non-training) reason to be at/near Vmc in flight other than when just above the runway for the purpose of landing? (And since landing, Vmc will not apply because the power is considerably less than the Vmc definiiton, and the aircraft is not likely in the takeoff configuration either.)
2) When near Vmc and wishing to accelerate with one engine failed, can you tell me what the NEW Vmc is? ....(since Vmc is related to the sudden loss of power in the critical engine in the take-off configuration.....then what possible explanation can a conscientious pilot have for being at/below Vmc, in flight, .....and attempting to accelerate? The only reasons I can think of is: He didn't plan his takeoff VS his available field length,...in which case the takeoff wass illegal to make per the regs anyway. If the pilot has not achieved Vxse or Vyse then not much possibility exists for acceleration for climb purposes, in which case the only remaining option is to land regardless of remaining runway.
No multi-engine aircraft I'm aware of have any procedure for use of full power on one operating engine at or below Vmc, for very good reason. Lowering that (Vmc) speed with the use of VG's does not make the aircraft more capable of achieving a climb, ...in fact it worsens the situation because the aircraft would then be even FARTHER below it's climb speeds (Vxse/Vyse) and therefore less likely to succeed in any such attempt.
VG's will not improve a multi-engined airplane's climb performance regardless of what it does to Vmc or stall speeds.... two speeds which do not apply to climb performance. (I have approx. 8,000 hours in multi-engine airplanes including a few hundred hours in Cessna 414 and 421 aircraft with RAM VG kits and they are mammaries on a boar hog, in my humble opinion.)
VG's have quite a bit of value at high speed however. Witness their extensive use on certain jet aircraft to prevent boundary seperation at high mach numbers.

(I would not purchase VG's for the explicit purpose of improving my chances with a "contaminated" wing due to icing. Even Airplanes approved for flight in icing conditions shouldn't initiate a flight in an attempt to be flown with a contaminated upper wing surface, and if already in flight anti/de-icing equipment should be used to keep the wing clear (and the upper surface will not become contaminated in flight anyway.)

[Doherty]

Ok, good. It may be more appropriate for us to discuss this in a multi engine board, but if we keep this to the pros and cons of VG's, then we should be OK. Interestingly enough, we have about the same time in twins. I have 14,000 total with 8,000 of that in Cessna 402C's, F-406 (unpressurized conquest) and Captain in the BE-1900C. I am also current in a Grand Caravan and a flight instructor and check airman (part 135) in all of the above except the BE-1900C. (its kind of fun to post a resume on a message board, isn't it?) I operate all of these aircraft in Bush Alaska operating on gravel, or snow/ice covered runways. Or mud, should it be spring. Your response that you have to have a balanced field length to take-off per the FARs is not accurate. You only need to meet accelerate stop, or accelerate go in aircraft that carry more than 9 passengers, excluding crew. This means, that you may see the end of a 2,200 foot long strip quickly approaching and all you need to do is get out of the mud to be safely on your way. This will be achieved by horsing the twin off the runway sooner than any best performance climb, but after VMC. If your VMC is at a slower speed, you can lift off (safely) at a point before the runway ends, and fly into a non-obstacle departure route, waiting for best rates. The above example answers your first question that you wanted a legitament reason to be near VMC without being in a training environment. You did say however, near
VMC for landing, you are correct, VMC is the speed at which you loose directional control with the most rearward CG and at gross weight at take-off power on the non critical engine. Your second question seems to be similar to your first. I am not talking about operating at a speed lower than VMC, I am saying, that because VMC is lowered with a VG kit, you can still operate above VMC, but at a lower airspeed than the original VMC. This is mostly for take-off reasons except when landing on runways that have little to no braking action. When you are landing on braking action nil runways, you have to land as slow as possible, then use full aerodynamic
forces to slow down. This may mean going to one mag, per engine, or using beta or reverse. Cross controlling the rudders and ailerons work well, as this will put you in to a sideways slip (on the runway) therefore increasing your drag, mostly due to the fuselage being expose to the slipstream. In short, speed does matter, and it matters allot. A lot of twins are operated commercially, and the increase in gross weight the VG kit gives you has a HUGE economic gain, even if the performance was not changed. Dam Gahorn, I have to argue with your icing statement too!
On several occasions, while in flight, I have had airframe icing so bad that it ran past the boots, jumped the aileron gaps and froze as icicles on the trailing edge of
the wing! These same events had ice on the entire upper wing area, all within one minute of first being in the icing layer. So upper wing contamination can be a problem, even if you are conforming to all of the FAA regs. You say that VG's will not increase a twin engines aircraft climb performance, I will agree to that. My big question, is will it better the take-off roll, no obstacle of a C-170B? As I said
before, the evidence is not real strong in that area. It does appear to me that the first upgrade (after a flat prop) should be a sportsman stol kit for the 170. I have flow 185's with both Robison and Sportmans kits (part 135) on them and I always liked the sportmans better. I wish I was able to provide this board with reasons why, but that was just my opinion, when I used to fly those planes. Since we are on the topic of performance, do you know if there are any 84" inch props out there that meet the O-300c bolt pattern? I found out at P-ponk.com, that I may need a prop longer than the 80" I have now, to get the best % mach number for maximum thrust efficiency? All I want to do is get in my 170B and get off as short as possible. I am on this board to find out what the best way to do that is. I hope you can provide me with other ideas that may promote shorter take offs, light weight is ok, I can just ferry items to a longer nearby spot for the long haul home.
Thanks!