Don't know the steel alloy.  Thickness is doubled where
it exits the engine because of a spring loaded ball joint.
Hopefully that will mitigate cracking.

Yes, it's a p-port.  Ellison tbi efs-3.
Highest rpm, static, with the current prop (95 in pitch, very coarse), about 6200.
Ivo prop went higher, with adjustable twist, but caused major cooling issues.

The pitch is worthless near the hub.  Not much air movement into the cooling intake.

We fixed a long vinyl tube onto the pitot, taped it to a stick and held it close to tape
marks on the spinning propeller, then simply read the airspeed indication
corresponding to the marks, with the engine idling.  All of this led to
the purchase of a new prop.  Fixed pitch, unfortunately, but 1/3 weight of the Ivo.

No cooling issues with this one:

Hopefully, not over pitched for the airframe.  Looking for a 200 mph cruise at 6500 rpm.

Lewis.Bjork

Good point on that IVO prop. Good R&D on the air flow around the hub.

I assume you have K&L wedge diffusers on the inside protecting
the rads from engine heat.


How far is the Ellison from the p-port roughly?
Do You have a intake pipe from the air scope to the Ellison?
If so how long is that? I am trying to determine the tuning.


You are doing a great job Lewis.

Paul Lamar

Thanks.  Your information/expertise has been invaluable.

Wedge diffusers between engine and rads.  Cooling exhausts out gills in the cowl.
Have to look up the intake runner length.  You gave me the numbers..14-15 inches?  That's the tbi just forward of the muffler in this view-- About 4-5 inches from the pport.  Intake runner continues forward (to the left) mounting the air filter.  Total length measured from the forward edge of intake pipe, through the tbi to the rotor face.

Lewis.Bjork

I had some ideas about tuning this morning on the way to the hangar.
Max RPM will be limited to the torque at that RPM. The torque is related
to the manifold pressure. Prop pitch, diameter and efficiency are what ever
you have. Props are expensive and therefore they are hard and costly to change.
It is best to have a ground adjustable pitch as they are a lot less costly
than a constant speed prop.

So how do we tune the manifold for the prop we have. The costly way in terms
of time and money is trial and error on the manifold configuration. A better
way is record the manifold pulses with a high speed data acquisition  system.

The lowest cost data acq system is a small microphone inserted into the
manifold and notebook computer with an audio input. Assuming of course you
already have a notebook or a desktop computer. Then you need a free spectrum
analyser program. That will give you a frequency of the pulses and a qualitative
display of the peak manifold pressure.


A better way is use a $57 Color Maximite and some high speed pressure
sensors. That will detect and record small quantitative peak manifold
pressure changes.

Certain fundamentals are known. Longer pipes resonate at lower
RPM's. Larger volume Helmholtz resonators resonate at lower RPM's.

The ideal is to get the intake system to resonate at maximum prop RPM.
When you make a positive  improvement the RPM and manifold pressure (AKA torque)
will increase and you will go faster. Your fuel burn per HP generated
(AKA BSFC) will be slightly lower.

If you achieve the highest RPM possible you have the best engine tuning
for the prop you have. You need to do this while you are in the air of course.

The Color Maximite is small and portable unlike a notebook or desk top.
It will run off 12 Volts.

The attached PDF explains how to program a Maximite and describes
all the other things it can do. I am not connected with nor make any money
from Maximite sales. I just think it is the best programmable
micro controller on the market.


Paul Lamar

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