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Date: Sun, 11 Oct 2009 21:14:33 -0400
From: cbeazley <cbeazley@innovista.net>
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To: flyrotary@lancaironline.net
Subject: where's the missing power?
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Hi Mike;

Before you start chopping up / swapping out that very nice installation...

One quick and dirty thing you can try to "get over the hump" is porpoise 
flying.
The idea is to intentionally dive and "overspeed" your engine allowing 
it to achieve a higher rpm and HP output before smoothly levelling out 
and hopefully maintaining the higher rpm.
There are also reduced drag related reynolds number effects that may 
assist you here.  In cruise, you may need to repeat this periodically.
This can work depending on the prop/engine/airframe combination.  There 
are, of course, prop, engine VNE limits to respect.
In your case, the engine rpm is not the limiting factor as long as the 
prop efficiency is not falling off due to transonic diameter effects.
What is your prop make, diameter and pitch?

The part throttle position, giving max HP, may create additional 
turbulent mixing and fuel atomization resulting in higher HP.

Any sort of drag reduction will also help you out.

BTW, I hope that JBWeld in the intake is mechanically secured somehow.  
I've heard of more than a few bad days due to JBWeld ingestion.
Although the intake is probably subjected to less thermal cycling than 
other parts of the engine block.

Cheers
Cary

> Mike,
>    You may have hit on the reason..............With the 2.17 redrive 
> you may be limited by the
> prop...........Let us say you are seeing 5500 rpm at 
> speed............At that rpm you are only
> able to develop xxx hp and your prop is absorbing it even though you 
> are only at 3/4's of
> your throttle travel............Now let us say you now have the 2.85 
> redrive and now seeing
> 6500 rpm and the resulting xxx+ hp is also absorbed by your prop but 
> you are now able
> see the extra power at full throttle.............Just a "WAG" on my 
> part...............
> --
> Kelly Troyer
> "Dyke Delta"_13B ROTARY Engine
> "RWS"_RD1C/EC2/EM2
> "Mistral"_Backplate/Oil Manifold
>
>
> -------------- Original message from "Mike Wills" <rv-4mike@cox.net>: 
> --------------
>
>> Bill/all,
>>  
>>  Thanks for the feedback. Most of your comments line up with my 
>> understanding/thoughts. I didnt go into installation details when I 
>> wrote this for a couple of reasons. One, I've said it before, and 
>> two, many of the details now are pretty vague because my exhaust and 
>> intake systems came together about 6 years ago. I'll recount what I 
>> recall:
>>  
>> 1) The engine is a Bruce Turrentine built. Turbo housings and high 
>> compression NA rotors. No porting.
>>  
>> 2) The exhaust is a true 2 - 1 header with equal length primaries. 
>> I'm a little sketchy on dimensions but my recall is 1 3/4" primaries, 
>> 32" long and equal length into a Burns merge collector  2 1/2". 
>> Muffler is 4" behind the collector, 2 1/2" inlet and outlet, 28" 
>> long, 4 1/2" diameter. It's a spiral flow design, homebuilt, with a 
>> relatively large straight tube through the middle. I dont believe it 
>> presents any significant restriction. Internals are Inconel and it 
>> was in good shape when I had it off the airplane a couple of weeks ago.
>>  
>> 3) The intake starts with a modified 88 Mazda NA lower manifold with 
>> all the excess metal cut away and port matched to the turbo housings 
>> (blended with JB Weld). I used the first part of the upper manifold 
>> to make the 90 degree bend over the top of the engine and from there 
>> welded on aluminum tubes (1 1/4" primaries, 1 1/2" secondaries, about 
>> 10" long. Plenum at the end of the tubes is small. Hard to describe 
>> so I'll try to find a picture. The throttle body is as described 
>> previously - a hacked Mazda tb with only 2 of the 3 original inlets.
>>  
>> I guess what really shocked me is how much throttle was still 
>> remaining when I reached max power. I guess the real question is, is 
>> my prop load limiting power output, is there some dip in the power 
>> curve and my engine cant push the prop load "over the hump", or is it 
>> simply a matter of a restriction in the system somewhere that is 
>> limiting the airflow? As I said previously, I'm not too worried about 
>> it because the airplane performance is pretty good. But who doesnt 
>> want more, especially if you suspect its there and accessible with 
>> hopefully not too much effort?
>>  
>> Mike