All I know that on large jet aircraft , ice doesn't stick to the Vgs. I also know that the entire tail is not deiced on most jet aircraft. The engineers do not consider ice on the tail a big factor.


Idaho Supercub

Idaho SuperCub wrote:The engineers do not consider ice on the tail a big factor.

There's a couple of us here who have flown Caravans for a living that might have an issue or two with those engineers!!!!!!!!

Gump

I have flown into Cleveland OH ,and picked up a ton of ice at the OM to the point where I could barely see out a heated windshield. I looked at the aircraft on the ground and it scared the hell out of me when I saw how much ice was on the bird. Thank you Boeing engineers for designing a great aircraft!


Idaho SuperCub

Idaho SuperCub wrote: I looked at the aircraft on the ground and it scared the hell out of me when I saw how much ice was on the bird. Thank you Boeing engineers for designing a great aircraft!

Boeing aircraft are a quantum leap skyward in engineering, power and capability over the lowly Caravan, and it's problems with tail stalls and operations in ice in general. If 737's were literally falling out of the sky in bad weather like Caravans do, the whole US airline industry would be coming to a screeching halt.

Gump

Back to VGs.

A64

Are you saying that Micro VGs are advertising falsely when they say their VGs do not reduce cruise airspeed? Would that not be misleading their customers?

flyer

I finally got a chance to tool around in my new 180 and wanted to chat about my experiences: I did some stalls at different flap and power settings while straight ahead and manuevering. The 180J w/ Robertson STOL, Flap and aileron Gap seals, VGs on wing/stabilizer (vert stab is in box ?awaiting install?) and 80 Gal useable seemed to want to stall at just less than 50mph IAS straight and level and ?55mph with any turning. The empty weight is ~100lbs more than my 182 and add to that 150lbs of fuel. My '59 182 with the Horton would cruise around relatively steady, even in a gradual turn with the airspeed banging on the stop at 40mph IAS and full flaps w/ power to maintain level flight. That was full tanks and 375 lbs of crew w/ 55 gal "useable" on board. This comparison doesn't control for different gross weights, rigging, IAS vs. actual and I will admit that I am a bit ham handed in my flying with the new bird. Perhaps it's the elevator down spring or the mushy feel of the ailerons with the RSTOL, I just haven't developed that perfect feel that I had with the old bird. Hopefully after spending some cash on that Chevron STOL mod (100LL) I'll see some better results.
I also question how much difference I would see if the Flap gap seal was removed. Bub says he did better after he removed his, but how much? Mike V. notes no big change in cruise speed w/ this kit and cited someone who had added it and saw no change, but did this also include STOL / slow flight characteristics?
Mike, I also wanted to question your statement about all the STOL mods functioning at higher AOA - you specifically cited the RSTOL characteristics. I look at the RSTOL as slightly different and why I was happy that the plane I decided to get happened to have the RSTOL.
Leading edge cuff and VGs gain the advantage at high AOA and with no change in the wing camber, this translates to nose to the sky. On a TW aircraft, if you don't have big main tires to point your nose high, this won't help you get off the ground quicker and on landing you'll only plop down tail first and lever the mains onto the ground. On float T/Os you'd be digging in your tails before lift improved - except perhaps climbing onto the step. With the RSTOL, you increase wing camber / upper surface curvature along the entire wing length, generating lift without changing flight attitude to the same degree. I do understand that lowering flaps also changes AOA, but the flap / RSTOL change in lift / AOA seems a better, more functional method for doing this on TW aircraft anyway.
It seems the VGs and leading edge cuff would be more funcional on tri-gear where you can change your ground AOA and on all aircraft for the safety net mentioned by Mike as well as softening stall characteristics.
Just my ramblings,
Matt

Matt,

First, I did NOT state that my flap gap seal didn't create more speed. In fact, the flap gap seals were on my airplane when I bought it. I stated that the flap gap seals somewhat defeat the slotted flap system that Cessna installed, and the lower end of the speed range is what I'm concerned with, not cruise speed. The Flap gap seal may increase cruise speed. If so, I'm betting it's not much, and in any case, I'd prefer to have the slow speed performance instead.

Secondly, you are confusing Angle of Attack with Angle of Incidence. Very different concepts, and not NECESSARILY similar.

a64--The "theory" of VG effectiveness is in their placement. Theoretically, the further aft you place them, the more the relative wind "sees" them at cruise flight attitude.

Place the VGs' further forward, and they start to "hide" from the relative wind, which is separating its flow as it meets the wing leading edge.

In any case, VG's could never create LAMINAR flow, but in fact they are specifically designed to create an organized flow, and keep the flow energized over the boundary layer.

Please forgive my grade school verbiage related to this complex subject.

Please also note that I refer to these as "theories". In my opinion, a lot of this stuff is Pure @@3## Magic.

MTV

mtv

Do you think the VGs would affect cruise speed if they were placed as instructed?

flyer

flyer,
At cruise my speed drop is only 4 or 5 mph or so, about half of what it is in full throttle flight.
Ice supposedly dosen't build up far enough back to get to the VG's, I'm allergic to ice, so I don't know about that.
You can't pick where you want to put the VG's, placement is very specific in the STC. Find a placement to where they don't increase drag and you have found a place that renders them inop.
I'm not against VG's, just on my Maule they didn't do as advertised. That is they didn't reduce flaps down stall speed and they were supposed to, and they did reduce cruise speed and they weren't supposed to. I expected the reduction in cruise speed though, I mean look at the things, you honestly can't believe that waxing your airplane or flush rivets will add speed, but VG's won't reduce it?

a64pilot wrote:flyer,
At cruise my speed drop is only 4 or 5 mph or so, about half of what it is in full throttle flight.
Ice supposedly dosen't build up far enough back to get to the VG's, I'm allergic to ice, so I don't know about that.
You can't pick where you want to put the VG's, placement is very specific in the STC.

Wow, I have had VG's on a 210, an RV6 and now on the Scout I have never seen a noticeable change in cruise speed.

A64

I know you do some test flying of the ag aircraft.

How thoroughly did you test fly the Maule before and after the Micro VGs were installed? How closely did you control all of the variables: temp, speed, etc. You seem to be convinced that the Micro VGs reduced your cruise airspeed. I will not install them if that is the case. It is not that I want to go fast but I do not want to go any slower. Would you say that Micro VG advertising is not correct?

I do not want to sell my Maule and buy a Mooney as Charles of Micro VGs suggested.

flyer

I think that there are a couple companies that sell VG's with stc's. When I was researching this, Micro Dynamics seemed to be the preferred one because they located the VG's further forward on the wing, thus getting if further out of te "relative wind" in level flight, thereby reducing the drag in level flight. G

respectfully, you guy's need to look up the definition of relative wind.
I controlled the variables as much as I could. I did not have a test boom or calibrated A/S instrument, nor a test plan etc. My only test point was at 2000 DA and full throttle, really not even any kind of test. Interestingly my cruise speed is the same, but I have to go to a higher altitude to get the speed. I true out at 132 to 136 kts. at 2300 rpm and firewalled of course between 9 to 11,000 ft., My best speed used to be between 7 and 9,000 ft.
There is an article on the internet where a pax river guy did a real test of VG's on a Bonanza, I think. I'll try to find it. My normal cruise speed is only down a couple of knots, the higher you go, the less the difference is. The cross over altitude seems to be about 10,000 ft. above that, I seem to have gained speed? Above 12,000 -7 flap used to slow me down, now I can carry -7 to 14,000.

flyer,
This is the link where I was snivelling about it on the Maule site. http://maulepilots.org/forums/viewtopic.php?t=245 Even Jeremy said the loss in cruise was small, 1 to 3 mph., but I don't think anybody said there was no loss. My gut feeling is that with your shorter wing, you would be happy with VG's. I'm not unhappy really, just think that microaerodynamics should state that there may be a small decrease in cruise, claiming no loss is not really honest, and I think they claim 12% decrease in stall speed? I didn't see that either. Now on a Thrush, I think they are great. They allow you to turn harder and in a tighter radius before you get the pre-stall buffet. I saw no decrease in stall speed on a Thrush either, but seat of the pants it seemed the tail came up eariler and it got off of the ground a little quicker. Anything that get's a Thrush off shorter is good. Now that was seat of the pants and may have really been just a little cooler day.

A64

I read your thread it sounds like you had some rigging issues. I would bet with some more tweaking you could get at least half that speed back.

A half turn on the Scouts strut causes a lot of change in flight.

When I state no noticeable change there are just way to many variables for me to disseminate if it was the air, wind, bugs etc. For 1-3 MPH

They make a huge difference with the 4412 wing on the Scout. I don't disagree there are always trade offs but the + seems to always out way the - where VGs are concerned.

On the RV they allowed a tighter bank much like you noticed on the Thrush, Ayres happens to also use a 4412 airfoil.

Maybe that USA-35B wing in your configuration just doesn't like them.

I bet playing with your wash out/in a bit more will change your speeds.

Scout,
I had the front struts swapped left to right. putting them back right of course put the aircraft back into rig. I'll live with it. If I were experimental, then I would only have the VG's in front of the ailerons and on the tail. They do incease both roll and pitch authority, which is nice. Again, I have only lost speed down low, when travelling if winds allow, I always go high both for the speed and decreased fuel burn.
I think some things just work better on some models of aircraft than others is all. If I wax the C-210, I'll pick up a couple of knots. Wax makes no difference to the Maule.

And, I think that once again pretty well summarizes the VG situation. Some airplanes they do some positive things with. Some, they are sort of neutral, and maybe some they offer a couple of negatives.

I have no doubt that they could reduce cruise speed. The original NASA research on VG's found optimum stall speed reduction at something like 12 % chord. Most of the Micro kits install at somewhere around 3 to 5, I believe. The problem with situating them at 12 % is that there is a significant reduction in cruise speed that far aft. This is NASA research, NOT Micro.

Micro makes all sorts of claims, but in fact their stc's are granted based on an assertion to the FAA that the VG's do not induce any adverse effects on the aircraft. That is a lot different than what Robertson did back in the day with their kits.

MTV

MTV & A64

I agree with both of you.

The advantages or disadvantages of the Micro VGs vary from aircraft to aircraft.

Micro's advertisment shows specific aircraft like the Maule with specific numbers for stalls, etc. They also say NO Decrease In Cruise Airspeed.
It appears that they did no testing on Maules. Who knows where they got the very specific numbers. We assume when we see their Maule advertised speeds that they had done some testing on the Maule.

It is interesting that the FAA would award an STC without adequate testing.

I tried to get more information from Micro. Like I said, Charles statement was "If you want to go fast, sell your Maule and by a Mooney".

I was just trying to find out the facts. I guess he did not have a good answer.

flyer

Looks like all the discussion is about the Micro VG's. What about the ones that Cub Crafters sells? I believe they used to be marketed as Boundary Layer Research, don't know what CC calls them.

Flyer,

I think you are missing the point regarding the definition of the term "Flight Testing" when it comes to certification.

I have no doubt that Micro did "flight testing" of their VG's on a Maule, and every airplane that they make VG kits for. The point is, the "flight testing" they are required by the FAA to do essentially only requires that they demonstrate that the modification does not create any ADVERSE flight characteristics. Going a little slower is perhaps undesireable, but certainly not an "adverse" flight characteristic by FAA definition. So, they do fly the things, both to demonstrate no adverse flight characteristics, and to determine what appears to be an optimum location for the VG's.

Now, consider the Robertson STOL mods. Robertson went through complete flight test, including all aspects of the flight testing protocol for modifying the airplane. They issue a flight manual supplement for the modified aircraft which specifies significantly lower stall speeds. THOSE speeds are now part of the airplane's operating limitations, and have been documented using a calibrated test boom, etc, and during a full flight test program.

Take a look at ANY of the modern "STOL" kits (Bush, Sportsman, Micro Aero, BLR, etc) flight manual supplements. When it comes to airspeeds, they are either silent, or simply say that the kit creates no adverse flight characteristics (or words to that effect). They do not provide lower stall speeds IN THE FLIGHT MANUAL SUPPLEMENT than stock. If they did (as Robertson did) they would have to complete full flight testing that proved that reduction in stall speed.

Now, as far as advertising goes--you can advertise anything you want, and you don't have to prove it or document the proof that the information is accurate. It's called "Buyer Beware". So, next time one of these outfits tells you their kit will reduce the stall speed by 4 knots or whatever, ask them to provide flight test data to support that claim....

But, also realize that, just because it hasn't been thoroughly flight tested, doesn't mean it DOESN'T reduce the stall speed either. Point is, there's no documented proof, based on very controlled and corrected flight test data.

The BLR kits (the BLR stc for the Cub is now owned by Cub Crafters) were designed by a fellow named Bob DeRusche (sp). He and Charles White were partners early on in the development of VG kits, but split over differences of opinion. I believe De Rusche was a flight test engineer for Robertson at one point.

In any case, they have taken slightly different approaches to the application of VG kits. Micro appears to take the approach that ANY wing will benefit from a set of VG's. BLR has stuck to more rigorous flight testing, and modifies airplanes that they seem to feel benefit MORE from VG's. Frankly, I don't know which is more accurate, but I'd stand by my statement that different airplane designs respond differently to the application of VGs, and I think the discussions here would suggest the same.

As always, your mileage may vary.

MTV