P-factor in high density altitude

[gabez]

this sunday I wanted to see how well the m20K did in high density altitude so went to South Lake Tahoe in the middle of the day about 8500 DA. The plane did extremely well and took off rather quickly with 2 ppl (200 pounds each) and 35 gallons of fuel. 2 things I noticed:

1. there was very little P-factor and actually accidentally applied too much right rudder. 

2. the ram effect took longer to kick in so slight overboost the engine (which is okay up to 43 and 7 seconds) but definitely  something to watch out. 

just sharing some experience

[Slick Nick]

I just had my J into Carson City a couple weeks ago, it was HOT. Could definitely feel the difference in performance. 

Tahoe is a beautiful neck of the woods to fly around. I sure wish I had a turbo. 

[natdm]

20 hours ago, gabez said:

slight overboost the engine (which is okay up to 43 and 7 seconds)

Is this with the intercooler?

[midlifeflyer]

Remember that a prop is an airfoil. At high D-Alt, just like the wings, the prop has less to grab on to.  The visual we used to teach was to think of driving a screw through whipped cream rather than a piece of wood. It's obviously not that extreme, but it can help with the concept.

[gabez]

2 hours ago, natdm said:

Is this with the intercooler?

I do not have one, so still taking off at 40MP

[DavePage]

On 8/5/2025 at 10:51 AM, gabez said:

this sunday I wanted to see how well the m20K did in high density altitude so went to South Lake Tahoe in the middle of the day about 8500 DA. The plane did extremely well and took off rather quickly with 2 ppl (200 pounds each) and 35 gallons of fuel. 2 things I noticed:

1. there was very little P-factor and actually accidentally applied too much right rudder. 

2. the ram effect took longer to kick in so slight overboost the engine (which is okay up to 43 and 7 seconds) but definitely  something to watch out. 

just sharing some experience

I learned to fly 45 years ago at KTRK, not far from South Lake Tahoe, in fact that's where we went to get out introduction to a control tower.

Remember, the engine is Turbocharged, not the propeller or the wings.  The engine will perform like it is at sea level, however the prop and wings are acutely aware of their elevation.   ;-)

[Flyler]

On 8/5/2025 at 1:51 PM, gabez said:

this sunday I wanted to see how well the m20K did in high density altitude so went to South Lake Tahoe in the middle of the day about 8500 DA. The plane did extremely well and took off rather quickly with 2 ppl (200 pounds each) and 35 gallons of fuel. 2 things I noticed:

1. there was very little P-factor and actually accidentally applied too much right rudder. 

2. the ram effect took longer to kick in so slight overboost the engine (which is okay up to 43 and 7 seconds) but definitely  something to watch out. 

just sharing some experience

It would be really interesting to visualize/graph the different p-factors against density altitude.  I wonder if all factors combine in the same direction, or if one is just a really large difference.  Ignoring any inputs, I would assum you would need *more* right rudder as you have less authority with the thinner air.

 

More importantly, how will a CFI be able to comprehend the idea of less right rudder?  This is blasphemy. 

[Pinecone]

One thing to remember is that with a constant speed prop, with lower air density it will run at a higher pitch for the same RPM.  So while prop "indicated air speed" is lower, the angle of attack is higher.