With my MT electric prop at cruise settings any rpm setting above 2100 slows me down. The difference between 1900 and 2100 rpm is about 8 mph but a lot more fuel. I believe Mark Steitle can report similar data.  I use 2400 rpm for takeoff and initial climb. Yesterday with 35 gallons of fuel, 39” MP, 50F OAT and trimmed for 95 mph I was seeing a solid 1600 fpm climb. Not too shabby for a little engine in an RV10.

 

Bobby

N416AS

SC Renesis

 

 

 

 

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Thursday, December 22, 2011 7:42 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: off topic, propeller carving and paint

 

Not quite that simple, Andrew.

 

While more rpm (air mass flow) + more fuel = more power is basically correct,   there is more to matching prop load and engine than that. 

 

 I know of an indivdual who was a very smart individual when it came to electronics (converted auto CPUs for aircraft usage), but did not understand the relationship between rpm, prop pitch and thrust.  He tuned his adjustable pitch prop to get maximum rpm - He took off and discovered (sadly too late) that he had very little thrust.  He had sufficient thrust to get airborne but could not fly out  of ground effect - contacted a catus off the end of the runway and died.  Maximum rpm is not the answer.  The answer is maximum thrust (at least for take off).  The key is balance -- if you have too little prop load (too little pitch for example) , you get great rpm - but little thrust.  If you have too much prop load (too much pitch or diameter or chord), you reduce the rpm the engine can obtain, therefore your power and thrust.  So the key is balance. 

 

I run an older 13B with the 2.85 and an 74x88x5.25 prop - I get 6000-6100 rpm static at WOT.  However, if I take the prop off (no load), my engine will turn 5000 rpm at the idle setting.  So rpm is not the sole criteria.

 

Ed

 

 

 

From: Andrew Martin

Sent: Thursday, December 22, 2011 5:39 AM

To: Rotary motors in aircraft

Subject: [FlyRotary] Re: off topic, propeller carving and paint

 

whats with assuming max rpm is 6000, I intend to use a CS prop with Tracy's 2.85 drive so I can rev the renesis out to 7500rpm when needed and dial it down when not, correct me if I'm wrong but doesn't more rpm + more fuel = more power. Ernest's drive should be able to withstand 8500-9000 rpm. Way to go! up there in Lynn's league.

 

 

Andrew

On Thu, Dec 22, 2011 at 4:08 AM, Bill Bradburry <bbradburry@bellsouth.net> wrote:

That is true, but if I was going to go with something else, I would try to
find something that will turn my prop close to the 2700 that most props are
designed for.  That means that I would look for something in the 2.2-2.4
ratio range, not 3.17.  That ratio will mean your prop will never get more
than 2000 rpm with the rotary.

Bill B

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On

Behalf Of Ernest Christley
Sent: Wednesday, December 21, 2011 2:26 PM
To: Rotary motors in aircraft

Subject: [FlyRotary] Re: off topic, propeller carving and paint

Bill Bradburry wrote:
> Tracy's PSRU ratio is either 2.17 turning backwards (A,B) or 2.85
> turning forward (C) I think??
>
>

And it is a good product; but, it's not the only PSRU in the world.


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