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.