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11/92 - Flight in Comanche N829P - Reprinted from the Comanche Flyer



As I wrote in a previous article, Dave Pratt lent me his Comanche, N8294P, to fly home after a forced landing in mine. 94Pop is the Prototype Comanche that sports the new APP cowl STC'd for the Comanche 180/250/260.

Dave and I go back a long way together. When he was the SE Tribe Chief, he anointed me the SE Tribe Door Prize Chairman for the duration of his reign. I'm familiar with Dave's airplane as he came to fly-ins through the years and at other times around the local area.

Now, honestly folks, when it comes to speed mods I'm as skeptical as the rest of you. I delight in flying with pilots in their Comanches and Bonanzas, demonstrating the true airspeed course, as printed in the June '85 AOPA Pilot and shown on ABC WIDE WORLD of FLYING video, both authored by Barry Schiff. Time and again we prove the airspeed indicator is honked up, and the airplane actually flies within one or two miles per hour of book speed. Please don't tell me how fast your airplane is, let's fly it to discover what the numbers really are.

No Comanche pilot wants to admit that there is an airspeed calibration chart for the airspeed indicator. Yep, it's right here, Piper Part number 760-705. In general, in cruise configuration, subtract 5 miles per hour from your indicated airspeed to find calibrated airspeed.

When I see ads in the Flyer exclaiming 6 mph increase for a poop-de-scoop, I want to say "Prove it". Put it on my airplane and if it actually gives me 6 mph, then I'll pay for it. If not, I won't. Chances are I'm going to write a letter to the Flyer about the product, either way.

Furthermore, when I write about a product, I call it like I see it. For almost all the products there is a good and bad side, whether it's stainless steel brake discs, aileron gap seals or "Slick 50". I'd be happy to discuss my findings with anyone, just give me a call.

Dave's Comanche was recently painted in a tastefully beige scheme, (I beg your pardon, moondust mist) but he always kept it touched with good paint. It has the late model half fork landing gear and dorsal fin cooling scoop. As for speed mods, It has aileron gap seals, rudder gap seals, after market wing tips with enclosed nav lights, a flush marker beacon antennae, leading and trailing edge wing root fairings and tight fitting aileron-to-flap and aileron-to-wing tip seals. All this was on before the new cowling.

In the high drag category, the airplane still has plenty of antenna's hanging off of it and a big rotating beacon on the top side. Their's no change to the spinner, nor the stabilator to fuselage gap, areas I always thought produced a lot of drag.

The day I flew 94Pop home it was a bit dirty with bugs on the leading edges. Fuel tanks were Full. On the ground it seemed to feel heavier during taxi, maybe because it sits lower than mine. My struts are pumped up to 4\". After takeoff, climb is sprightly, belying the heavy perception on the ground. In flight the ailerons feel a bit heavy, maybe due to the gap seals or possibly the higher speed. I've flown some Comanches that have a feather light touch on the yoke. All other flight characteristics feel standard Comanche.

I operated 94Pop with the greatest of care at power settings I generally use; cruise power setting of 2300 RPM, full throttle at 7500 ft., which equals about 22\" MP. The manifold pressure gauge in 94Pop is more sluggish than mine, but you can't argue full throttle position. I have no idea how the rest of the gauges are calibrated.

The airspeed indicator showed this airplane to be every bit of 15 to 20 MPH faster than mine in cruise with the exact same engine. This speed was verified by the DME and Loran which were within 4 knots of each other. As if I had any doubt, I looked out the window at the ground and clouds rushing by. Finally, gear up to landing time was somewhat shorter for the trip home.

Close examination of the wing in flight reveals that this airplane flies at a flatter pitch attitude than mine does. Lowering the induced drag of the wing could be the key to crossing the airspeed barrier. How did Dave achieve this? I'll have to guess that the wing cleanup and the lower drag of the cowl design put it right on the edge of the lift / drag curve.

Did you ever notice as you begin a descent out of a higher altitude, that by lowering the nose slightly, the airspeed takes off as though you released the brake. This is the effect of reduction in (pilot) induced drag. Continued flight at this lower pitch attitude maintains the higher airspeed, while almost holding altitude. This is often incorrectly termed, "getting on the step", when lowering the nose actually reduces the angle of relative wind and ultimately lowering induced drag.

At low altitudes, you just pour on the coal to get past the best lift/drag speed, but at higher than optimum altitude there just isn't enough power to maintain altitude at this configuration. Sufficient pitch attitude is maintained to sustain lift, and as a result places the wing on the back side of the lift/drag curve where it flies slower. At any rate, there's a bit of technical discussion as to when, where, and why some airplanes just plain go faster.

Someday, I'd like to fly 94Pop at 16,500 ft. where I often fly my Comanche to compare the characteristics higher up. I'd like to know at what altitude it stays ahead of the lift/drag curve? Need it delivered to Oshkosh, Dave?

On the return flight to Melbourne, the plane was full of gas with a tool box, case of oil, cylinder assembly, and various other baggage on board. I wished I had the time to wash the plane but I was busy getting parts for my own Comanche repair. After take off I used the power settings that I remember Dave using, 2400 RPM and full throttle at 6500 ft.

Holy Shit, Batman! This thing really screams along! I can't ever remember climbing a Comanche at 160 MPH indicated. It pushed 200 MPH TAS in the early morning glass smooth air, so I let it fly, IAS in the yellow arc. Yep, at that setting it's a full 20 to 25 MPH faster than mine, again backed up by the DME, Loran and view out the window. On descent it out ran a twin approaching the airport. I had to pay attention to airspeed to slow it down before lowering the gear.

Well, I'm not sure of exactly why this airplane is so fast,…..but it is. Dave says it's mostly in the cowl. If it is the combination of the cowl and wing cleanup, all this is available for your Comanche, and mine too. It's really a treat to see a Comanche 250 cruise so fast, especially after all my doubts. Personally, I think it's time to start setting new FAI speed records with this airplane to demonstrate how fast it really is.


Mike Dolin CFII, ICS 0698 "