REFLECTOR: Prop

[Pat Shea]

Rene,

I agree with Scott. Engines have RPM limits, props
have RPM limits, and Engine/Prop combinations can have
RPM limits, etc. In spam cans, the standard 2700 RPM
limit is usually due the the mass of the metal prop. 

Your best bet is to find a engine builder with lots of
experimental engines (including your model) in the
field, including race/aerobatic applications. They
should be able to give you the skinny on your specific
engine as it relates to higher RPM's.

Ken, the owner of Lycon, is the best source I've
found:

http://www.lycon.com/

Pat


--- Scott Derrick <scott at tnstaafl.net> wrote:


---------------------------------
    Rene,

The redline limits can be a confusing issue.  There
are airframe limitsand there are engine limits.  

Most folks are familiar with airframe limits, thats
whats in the POHand on the RPM gauge in a type
certified airplane. This number isderived from the
airframe/engine/prop combination. Some
combinationshave limits within the overall range,
usually because of a harmonicissue between the engine
and prop.  These limits are conservative bynature.

The engine limitations by themselves are usually wider
than airframelimits. They are also debatable if you
talk to the racing crowd.  I'vebeen told by many that
I could operate my old IO360 up to 3,000 rpmbecause I
had a wood/composite prop on it. Most Catto props are
ratedto +3000 RPM.  I did have the engine up to 1850 a
few times duringtesting but ran it below 2750 during
cruise which was the Lycoming setlimitation.

Wood tends to dampen vibrations vs a metal prop which
tends to enhanceand make a vibration worse.  Thats a
general rule and not inviolate.  Also some engine
limitations are because of the type of counter
weightson the crank shaft, the theory being that
higher rpm will wear them outfaster.

Since your engine is experimental and you own the
airframe you can setthe RPM limits.  I would contact
folks who race IO540's and see whatthey say about your
particular IO540 version, the D4A5.  

Scott



Rene Dugas wrote:            
Mounted andflew AeroCompositeprop 2.5 hrs of 5 hr fly
off this weekend.  Gained 300 fmp climb at 25squared
and 8 knts in 23/23 cruise from 172 knts indicated to
180 knotsIASwithout the spinner on.  Workmanship is
beautiful but mounting hardwarefor spinner is now over
a week late in delivery.  It was left out
oftheshipping container with the spinner.   Prop was
two months later thanpromised but it does look and
work very well.  
  
Question: The AeroCompositehas a rpm limit of 3000 and
an overspeed limit of about 4000.  I wasthinking of
increasing my engine rpms up from the 2700 of the MT
to2800 oreven 3000.  That is still very low rpms and
should get better climb outontake off.  Thoughts?
  
Rene’



 
____________________________________________________________________________________
The all-new Yahoo! Mail beta
Fire up a more powerful email and get things done faster. 
http://new.mail.yahoo.com