I commented on here recently about how I took a cross- country flight to Walla Walla from Everett, Wa recently and was only seeing 140-150 mph cruise at 11,500 feet. It got me to thinking- I was getting about 6200 rpm on the engine which is 2175 at the prop. So, I'm a little overpropped/ underpowered.

 

So, there's the old chestnut about how you can get a few more knots from an airplane in cruise if you go a little above your cruise altitude and then descend to your cruise altitude, thereby getting "on the step" . Some pilots swear by this, others dismiss it. I have a theory- if I climb to a cruise altitude and stay at full throttle while doing so, I will only get the engine to run up to a certain RPM and therefore a certain hp will be achieved, and no more and so the airplane will settle into an equilibrium at a certain speed- say at whatever hp/speed - 140 mph at 6200 rpm- lt's say x hp.

 

Now, If I were to descend to my cruise altitude in a shallow dive, I will be acheiving a higher rpm and hence horsepower, say 6800 rpm and horsepower will be x + 9%x for a hp of 109% of the hp achieved at 6200 rpm, so I should be able to achieve and maintain a higher cruise  speed if I descend to my cruising altitude. ( I picked 9% arbitrarily for the sake of argument) .

 

Anyone want to shoot me down on this one?

 

This is just an theory, If I want to go faster first I have to clean up my drag. My cooling scoop is effective, but obviously draggy. And It needs a flap on it. That's a project for this winter.

 

Brian Trubee