My 1968 Cessna Cardinal

Performance

 

When I initially bought the aircraft, it had no performance modifications on it at all. It had a great climb rate, but the prop was not suitable for cruise as it was revving too high and no performance.

I flew the plane back from San Antonio, TX to my home base of Torrance (KTOA) in California. I had to file IFR coming in to the LA basin as the weather was marginal.

 

My initial speed estimate was a cruise speed at around 108-110KTAS. The power setting was around 65% at 2500rpm.

 

I contacted a company in Canada called Maple Leaf Aviation. The specialize in Cessna modifications, especially the Cardinal. The modifications are developed by a man called Roy Sobchuk, and he has done a great job on the Cardinal.

 

There are a few things on the earlier Cardinals that Cessna could have done a lot better. Most of this is in the cowling area.

 

 The cooling inlets are too big

 

 The exit is too big, and poorly designed as air is also entering through the exit and reducing the pressure differential and thus reducing cooling.

 

 The exhaust stub is poking out from the cowling and creating a lot of drag.

 

 The air inlet for the carburetor is located in an area that does not provide good ram air recovery.

 

 The wheel pants are poorly designed and they don't really reduce the drag.

 

I called Maple Leaf and ordered the fixed cowl flap and the exhaust fairing. I had my mechanic install it and sign it off.

While my mechanic was installing the modifications, I had the propeller sent off to a prop shop for re-pitching. The original pitch was 56 per turn. I had it re-pitched to 60.

 

I had everything installed and flew the plane and the speed had increased about 8-9ktas. My cruise was now at 118-120ktas at 2500rpm (65%).

 

I knew that I could get more out of the plane and continued with the modifications.

I bought a used set of wheel pants from a 1975 C172. I fixed them up and I also bought what is called the Fancy pants from Maple Leaf. It is the nose gear strut cover.

I also ordered the brake cover fairings for the new wheel pants.

 

I had all these installed and test flew the aircraft. The drag was reduced but now I had run out of prop pitch again as the engine was over revving. I had the prop removed again and sent it off for another re pitch. This time I had it pitched to 62-63. It worked fine although I am considering another re pitch to 65 since I can still over rev the engine and in order to get 75% at 8000ft, I need to rev the engine to 2650 or so, which I am not too happy about.

I think 65 would do the job.

 

At present time, my cruise speed at mid weight and 7500ft, is about 125ktas at 2550rpm. This is about 65-70% power depending on temperature.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

My goal is to re pitch the propeller a last time and to get 135ktas at 75%.

 

Most aircraft in this category are not optimized for performance. They are to the most part designed to be manufactured with reasonable ease.

 

The cooling drag of a typical Cessna or Piper is around 30-35% of the total drag of the aircraft.

Any improvement in this area will make quite a difference in performance.

The Maple Leaf modifications, together with re pitching the propeller yielded a net speed increase of 15ktas, which is a 13.6% overall increase in speed using the same power setting. Not too bad at all.

Having the propeller re pitched again, might yield a speed increase to 135ktas at 75% power, which is a 22.7% increase.

 

Climb rate

The interesting thing is that my rate of climb has not changed much with the re-pitching of the prop. On a standard day, 2 people and full fuel I usually get 1000-1100ft/min at around 80kias.

 

 

 

Updates will follow as I do more modifications.