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View Full Version : pirep on Micro VG equipped PA-18: "lousy teaching platf



JMBreitinger
03-26-2006, 05:22 PM
This has probably already been beaten to death, but two friends have asked me about the efficacy of VGs within the last week so I thought Id share my experience.

This week I finally had a chance to do a full stall series in my new Cub which is equipped with Micro vortex generators. This is the only way that I could really figure out how much they improved its handling characteristics.

I went with Chris Napier, a friend who is a very gifted instructor with a ton of tail wheel and aerobatic time. He loves teaching this stuff. His day job is flying a 767 for UPS. He is one of those increasingly rare pros who actually loves to fly. It probably has a lot to do with the fact that he still flies rag and tube airplanes. He actually arranges layovers in Alaska so that he can use his rest time flying moose meat off gravel bars for a pall of his in a Maule.

My airplane is a pretty light (1,150 pound) wide body with a 160 HP O-320 and an 80-40 wood Senseich propeller. It has a 2,000 lb kit. With two of us and full fuel, we were at about 1,850.

We started with a series of Dutch rolls, lazy eights and wingovers. There was nothing special about the handling here except that the airplane is exceptionally true and well rigged.

The next thing Chris did was to try to trick me into a moose stall by having me set up for slow flight, then do steep turns both ways while he pointed out stuff on the ground. He is sneaky this way. It takes a lot of power to maintain altitude and airspeed in a steep bank while slow (we were at 55 MPH). This induces a lot of yaw because of the very high angle of attack. The plane was pretty stable, while turning very tightly, never any trouble. In my old stock Cub this trick worked.

Then we did a series of power-off stalls, first straight ahead, then while turning, both coordinated and uncoordinated in slips and skids. These were pretty benign. Prior to the VGs, the airplane would roll into a classic base-to-final spin if stalled from a skidding turn. We would typically loose at least 500 feet in this maneuver. Now it has pretty good elevator authority right into the stall.

We also did some actual spin entries. They required quite a bit of aggravation. Chris had me stall the airplane 1,500 RPM and giving it a lot of left rudder right at the stall. It will go in but it takes a big shove. The recovery was so fast though that I never got more than a quarter of a turn. We never lost more than 150 feet. The wing really wants to fly.

In the interest of full disclosure, Chris did this with my partner Keith the next day and really aggravated it with more power. It snapped in much more abruptly. Keith said they lost 400 feet in that recovery. Power is obviously a bad thing in a spin. I remember Rich Stowell saying: "throttle forward, spin fast, throttle closed, spin slow".

The biggest surprise was that we could not induce an accelerated stall. We set it up in a coordinated steep turn at 60 mph and then loaded up the wing in order to exceed the critical angle of attack. I have done them in nearly every airplane that I have ever flown. We tried them at 60 mph, 70 mph and 80 mph. With very steep turns and abrupt full elevator, the plane would just not quit flying. We did not try them at any higher airspeed.

Chris complained that this airplane did not fly like any other Cub that he had flown. He is teaching Keith to fly it and getting him over the insurance requirements. He said it is a lousy teaching platform because it gets off the runway before a guy can get into trouble, it lands so slow that exposure is similarly limited and things have to be so aggravated to cause trouble in flight that it is almost absurd.

flynlow
03-26-2006, 07:35 PM
Thanks for the excellent write-up. I recieved my Micro VG's a couple days ago but havn't had time to get em on.

Did you do any tests on takeoff distance or climb rate?

I am looking forward to testing my own Cub and always wanting a excuse to fly!

JMBreitinger
03-26-2006, 07:57 PM
[quote="flynlow"]Did you do any tests on takeoff distance or climb rate?
quote]

Yes and no. We did test all of this stuff. I think that the thrustline mod, the lighter weight, the longer gear legs, more power, new wood prop, etc. have affects that can't really be separated out. I don't attribute it all to the VGs.

The stall / spin characteristics, though seem more attributable to this change.

The honest answer is that I don't know how much any one of these things affects any particular flight characteristic. I sure like the combined affect though.

bsantana
03-28-2006, 12:53 PM
John, do you have the VGs below the horizontal stab just forward of the elevator as well as on the wing?

JMBreitinger
03-29-2006, 05:34 AM
John, do you have the VGs below the horizontal stab just forward of the elevator as well as on the wing?

Yes.