Hi Mike,

Sorry for the ambiguous post.  

Regarding this O-200 powered KR2S:
https://youtu.be/k5kWkv-Es_s <https://youtu.be/k5kWkv-Es_s>

The prop pitch was (in my opinion) set at too many inches travel forward per 
rotation.  This may also be referred to as high pitch or coarse pitch, over 
prop-ed or cruise pitch - as opposed to climb pitch.   

The engine only made ~2300 rpm static.  The climb performance was less than I 
expected with two 170lb passengers and 10 gallons gas giving about 700fpm 
(though this is probably much better than Cedric’s KR2S will be with the VW).  
However the cruise performance was undeniably good - 175mph @ 3000rpm.   
(Justin is a mechanic for a Reno Racer and it shows.)  

The engine instruments indicated very high temps (well over 430F!).  

I would not fly at those temps (or RPM for that matter on an o-200) and this 
became my major focus.

I believe those temps were due in part to an incompletely tuned cooling system 
(needing better baffling?, more air in? more air out?), too lean a mixture, and 
in large part due to high back pressure on the engine leading to greater heat 

The engine installation was new, so it could also just be pre-seated rings or 
bad/uncalibrated instrumentation readings (but I don’t think so).

Of course, I could be totally off base.  I only had a short look-see of the 
airplane.  It was/is and very interesting airplane and Justine’s work on the 
engine installation was fantastic.  

The airplane was later sold to Andrew Angellotti? and then appeared in Sport 
Aviation as the platform for flight instrumentation development with lots of 
probes mounted on the wing.  He’d be a great one to ask.  I placed that article 
here in the files section of the Yahoo group KRaircraft:

Your experience with RPM vs Oil Temps is interesting.   

I wonder if the key is in the latter section of your post where you state that 
with the course pitch your engine can not “accept” full throttle, so you do not 
give it full throttle.  In essence, you are not running at full power when slow 
- the most critical heat phase of flight.  Less power = less heat.  Later at 
high cruise you go full throttle and do not have temp problems, but you are now 
high (cool) and fast (lots of air).  

Cedric’s HAPI VW has the small top oil cooler but he is planning on installing 
the lager Revmaster style bottom mounted oil cooler before flight.  Its often 
very hot here in the summer.


> On Dec 14, 2017, at 9:01 AM, krnet-requ...@list.krnet.org wrote:
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> Today's Topics:
>   1.  Prop pitch (laser...@juno.com)
> ----------------------------------------------------------------------
> Message: 1
> Date: Wed, 13 Dec 2017 11:50:55 -0800
> From: <laser...@juno.com>
> To: krnet@list.krnet.org
> Subject: KR> Prop pitch
> Message-ID: <aabpddbfuagwy...@smtpout02.vgs.untd.com>
> Content-Type: text/plain; charset=iso-8859-1
> Owen said, 
> "He had it pitched for high speed cruise.  It was a pretty efficient
> combo but the high pitch seemed to be loading up the engine making  quite
> hot."
> I'm wondering if Owen means it was pitched to allow the engine to turn up
> at a very high RPM, thus causing the plane to go faster, thus "high speed
> cruise"?  If so, then the resulting heat - the hot engine - would be the
> result of internal friction - parts turning against each other (friction)
> inside the engine.  The faster the engine turns, the more friction is
> generated.  More friction = more heat.   If this is what Owen means, the
> prop was set to a flat pitch.
> Owen's second sentence refers to "loading up the engine" however.  This
> would imply the prop was set to a sufficienty coarse pitch to limit the
> engine's ability to turn at its optimum RPM.  In this case one could say
> the engine was "over propped" - the coarse pitch "loading up the engine".
> This would not cause the engine to get hot since at the lower RPM
> friction would be low.  With such limited RPM however, the plane would
> not be capable of "high speed cruise.".  
> Perhaps Owen would clarify which it was.  What do you mean Owen with the
> phrase "loading up the engine"?  Your two sentences seem to contradict
> each other in meaning.  This is a very interesting subject with lots of
> variables and I'd like to comment, but to do so I'd need to presume what
> you meant and I'm a lousy mind reader.    
> ****************
> Regarding my own plane, when I first got it I had a heck of a time
> keeping oil temps down and eventually learned I had a glitch in my
> electrical system that caused the gauge to read high.  In the process of
> figuring things out however, and in the process of finding a prop to do
> just what I wanted - these two objectives running in parallel - I was
> enormously impressed with how easier it was to keep my oil temperature
> down by going to a coarser prop, one that allowed me to run at WOT at
> cruise altitudes (anything above 8 thousand feet) at the cruise RPM I
> wanted ( ?3100).  Why 3100?  Initially it was to keep my tip drag at an
> ideal speed but the immense improvement I got from reduced oil
> temperature as a result of lower engine RPM's was a very welcome
> secondary benefit.  
> With my GP 2180 w/Ellison EF-2 and a Sterba 52 x 56, my engine operates
> right on the edge.  That is to say, when starting the take-off roll the
> engine is slightly overpropped.  I have to pull it back slightly since
> the engine cannot accept that last little bit of throttle.  Once underway
> however, once the prop is unloaded and I am in the climb phase and
> especially once in the cruise phase, the engine can accept full throttle.
> At the higher altitudes I normally curise at on cross-country flights,
> the air is less dense and I've found a prop that turns 3100 WOT at 5
> thousand feet will turn 3200 WOT at 12 thousand feet while using less
> fuel.  I attribute this to the air being less dense, thus less drag. 
> It's the same phenomenon that allows the plane to go faster for a given
> amount of thrust, the higher it goes.  For my plane there is an optimum
> altitude where power and drag are at their respective optimum points. 
> It's 12-13K for my KR-1?.     
> One advantage of using the Lycomings and Continentals over the VW is
> their rated power RPM of 2700 is much lower than the VW's rated power RPM
> of 3500.  Although props are longer for the certified engines, RPM is so
> much lower that mach tip speed limitations are of no consequence as far
> as I know.  
> Mike
> ____________________________________________________________
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