I decided to try Micro AeroDynamics VG’s alone on my P-Ponk’d 1959 model year C180B, as I was interested in decreasing landing speed at my fairly rough grass strip. I didn’t want to go with the Sportsman, at least at the present time, because of the additional hit on payload. My current empty weight of 1715 lbs with a gross weight of 2650 lbs, leaves me with 935 lbs useful load, but that’s not counting oil (22.5 lbs) and the 50 lbs I keep in the aft baggage compartment (case of oil and spare parts) to decrease the forward c.g., nor the 20 lbs of tools, chocks, rudder block and ropes I carry. With 74 gallons of full fuel (23 gallons in Flint aux tanks), I only have 205 lbs of payload after I climb in the aircraft.

In order to get a good idea of cruise performance before and after the modification, I used Foreflight track logs and the 3 leg GPS method outline here:

http://www.kilohotel.com/rv8/rvlinks/ssec.html

To measure cruise speed, I flew three stable legs 120 deg from each other at a stable temp and pressure altitude at various power settings as determined using my CGR-30P, and then took the mean magnetic course and true airspeed of 10 measurements from the track log once stabilized on a direction, and plugged those values into the Excel spreadsheet described above. It’s possible to derive a drag coefficient and Oswald efficiency factor from the TAS and %Power from that data by plotting the data as shown here for the flight with the VG’s on:



Donald Crawford’s “A Practical Guide to Airplane Performance and Design” was used to calculate those parameters, and they in turn can be used to predict aircraft performance at standard altitudes:



Based on the data, there’s negligible difference in full throttle at sea level, but up to 3.5 KTAS loss in TAS at 14,000 ft. At 7,000 ft, only about 1.4 KTAS is lost at full throttle.
Stall speed was measured by averaging the indicated airspeed of three stalls per flap setting at the same temp and pressure altitude; that data, along with the onset of the stall warn horn, corrected to gross weight and reported as mph:




The full flap stall speed was hard to determine with and without VG’s because the airspeed indicator was very near the zero indication and the airplane just quit maintaining altitude without a detectable buffet to initiate recovery, both with and without the VG’s.

At 0 deg flaps, the data appears to show about a 14% decrease in stall speed, and at 20 deg only a 2% decrease in stall speed. I suspect that the truth is somewhere in between as the indicated airspeeds were measured at very low indications on the airspeed dial, and as mentioned above getting a firm airspeed corresponding to a stall buffet was essentially impossible at full flaps.

So, how does it fly? Aileron and elevator control feel more precise without being fidgety at low airspeed. The conventional short field takeoff on a smooth surface with the control wheel held back until the aircraft lifts off no longer has a wallowing feeling and the lift-off is definitely more positive. The tailwheel will get beaten up if I use that technique at my home strip, however, a tail low takeoff with rotate at 40-45 mph achieves a positive rate of climb with just of touch of stall warning vs. 50-55 before. Previous landing speeds using a tail-low wheel landing (not 3 point) landing technique at my rough-surfaced landing strip used to be 70 to 75 mph IAS depending on gross weight, but are now flown at 60 – 65 mph IAS, with the stall warning coming on in the flare/power off. Takeoff and landing distances appear shorter, perhaps 15% or so.

Overall, probably worth it. Lost a touch of cruise speed, but gained improved control and a slower takeoff and touch down speed with negligible weight and balance change.

Now thats a pirep! Thanks for the time you spent gathering all of this data and posting.

Kurt

De nada!

Wow! Talk about thorough! Impressive detail--and far beyond my ability to understand beyond your summary paragraphs.

FWIW, several years ago at OSH I spent some time chatting with Anni Brogan, president of Micro AeroDynamics, mostly about the community of Anacortes, her home which is a town Mah Woman and I really like (it's where we have gone to charter boats for cruising the San Juans and Gulf Islands), but some about their VGs. She was very honest in our conversation not to guarantee significantly lowered stall speeds for many airplanes, although as she said, most airplanes will have slightly lower stall speeds--and some have a distinctly lower stall speed. But she emphasized that at low airspeeds, the VGs will improve low speed handling on all airplanes.

Of course, their advertising seems to make percentage claims for lowered stall speeds, but I suspect that comes under the umbrella of "puffing" from a legal perspective.

I came away from our discussion concluding that I didn't want to spend the money, since I already have pretty crisp low speed handling due to the droopy Madras wingtips my airplane has, but that VGs would be a worthy addition if I had stock or near stock wingtips.

Cary

I think it is very airplane specific, I had a maule m-5-180 and they made a huge difference in control at low speeds, on a 206 I couldn't tell a difference at all. A buddy of mine took them off a 206 on floats, he said they made take off run longer. The cool thing is that they are so cheap, in aviation terms that to give them a try doesn't really hurt.

I found that on my 172M they did not make any noticeable difference in speeds, top/cruise or stall. What I did see and feel was a huge increase the control at lower speeds.

jrc111 wrote: 50 lbs I keep in the aft baggage compartment (case of oil and spare parts) to decrease the forward c.g.

Why carry a case of oil in the aft baggage? If it is to keep an aft cg, why not carry water. It will do you more good in an emergency and for the same weight it takes up less space.

Tim

But what if I need oil?

jrc111 wrote:But what if I need oil?

If you need that much oil then I am guessing you have 6 cylinders as part of your spare parts.

Tim

Gosh, I've always carried oil, too--1 quart. Hard to justify carrying a case, unless I got a heckuva deal on it and was taking it home. I carry about the equivalent weight, in a really complete survival kit that includes 4 quarts of water. That's potentially a whole lot more useful than a case of oil.

Cary

Thank you for the thoughtful presentation of data.

This question is so often asked/debated and you have a very well presented case study.

Ironically the focus will now shift to a debate over whether you should have certain items (water instead of oil) in your plane and not how you loaded it to obtain a CG and load configuration.

Your plane is vertible flying dump truck compared to some bush planes. I say bring water and spares/tools and oil if you've got room and capacity (within reason).

Thank you!

Great info and data. I appreciate you doing the before and after research.

So, if you had to spend the 2k again, would you?

Yes, I believe so. If I flew out of 3000 ft prepared strips all the time, I wouldn't bother, however, decreasing the takeoff and landing speed with increased control authority makes it very useful on short rough strips. Two things I forgot to mention is that side slips seem more effective, probably making crosswind capability at least as good despite the slower airspeed. Also, it's easier to push the tail up off the ground at the start of the takeoff roll.