Subject: [FlyRotary] Re: Power on a cold day was Re: [FlyRotary] Re:Some turbo thoughts from a pro ....

<... density change is proportional to the change in absolute temp, so 10F is about  2% ...>

True.  But that 2% increase in power is ALL EXCESS THRUST (over and above what it takes to hold exactly what you've got - say 90 kts and 1000 fpm climb).  Two hp would be 66000 #'/min which with a 2000# airplane produces 3300 fpm rate of climb - ABOVE what you started with !!  Of course not every spec of that extra power gets to the prop, but you can see how what appears to be a modest power increase can produce results that are apparently way out of proportion to change in power.
Just a theory .... Jim S.
 

Al Gietzen wrote:

Rusty, the rotary engine (for what ever reason) just LOOOVVVVVEEEESSS those cooler days.  I have had fuel flow of over 20 gph on take off when OAT was 28F.  That calculates out to over 200HP, static RPM was 5800 rpm vice a nominal of 5200 on a "normal" day.  I've never said anything about it because 1.  Who would believe me 2.  Who would believe me? and 3. Who would believe me?   Anytime the OAT is below 65F or so my static RPM increases about 200 rpm for ever 10F further temp drop.

Ed;

The only problems with this is 1. I don’t believe it, 2. I don’t believe it; and 3, I find it hard to believe J.

The air density change is proportional to the change in absolute temp, so 10F is about  2%.  Maybe 3 hp?  Gee, we don’t really need to turbo because the adiabatic temp drop with altitude will overcome the loss of power due to altitude J. Could there be some other effect going on here? Fuel density is also changing.  How are you measuring fuel flow. 

One problem with hp inferred from fuel burn is that we know that the rotary’s don’t burn all that fuel to make power.  Fuel is burning right on out into the exhaust pipe, and the amount of unburned fuel varies with a lot of other factors. 

Al

--
Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T