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From: Brent Regan <brent@regandesigns.com>
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Subject: Re: Alternative Power Plants
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Greg writes:
<<<Thanks for your comprehensive input below.  You do bring up a couple 
of issues that we have only looked at in passing, and we will look into 
these issues further....>>>

When I evaluated the rotary for my IV-P my comparison categories were 
weight, power, reliability and cost. At an installed weight of 611 
pounds (all accessories), 360 Hp (on the dyno),  a demonstrated 1,500+ 
TBO and a known cost the Lycoming was easy to evaluate. The rotary took 
an early lead due to its high power to weight ratio, low parts count, 
demonstrated high reliability (endurance racing) and relatively low cost 
OF THE CORE ENGINE. The fun started when you begin to add up all the 
support systems. The radiators (four of them, intercooler, coolant, oil 
and PSRU), pumps, tanks, filters, separators, coolant, plumbing and 
fittings, turbo machinery,  scavenging system not to mention the PSRU 
and the weight picture gets pretty bleak.  If you compare the firewall 
to prop weight of the two running engines you will likely find them to 
be quite comparable.

Since the rotary engine needs all of these supplemental systems to 
operate they must be added into the parts count and reliability columns. 
Each of these systems is critical to making power. One failure of a 
fitting, pump, drive, cap or coupling and the whole endeavor goes quiet.

One critical problem with the rotary is the accessory drive in that 
there really isn't one. The original  fan belt system is utterly 
inadequate for the additional power demands of the bigger water pump, 
scavenge pump, fuel pump and bigger alternator. One builder claimed he 
solved the problem by using electric fuel and scavenge pumps. When 
queried where the electricity came from he said proudly "The 
alternator!". Oops.  Serpentine ribbon belts are all the rage but they 
present a significant single point failure opportunity and FOD risk.

The rotary has the advantage in power IF you accept that the rotary will 
live for very long at 150 Hp per rotor.  Ask your engine guys how much 
power you can get for 1,000 or even 500 hours of continuos output. 
Remember that even a race engine is not 100% duty cycle. Even the left 
turn only crowd lifts for the turns. Derate the engine to a more 
realistic 80 to 100 Hp per rotor and the advantage evaporates. I fly my 
Lycoming at 75% power (270Hp) all the time with the exception of the 
climb (90%), the approach (45%) and racing (100%).

Then there is the question of drag. Consider this, as my friend and 
fellow engineer Fred Moreno once observed, thermal transfer rate is 
proportional the the temperature differential of the two materials. In 
an air cooled engine the cylinder heads run about 400 F and the air is 
around 0 F giving a 400 degree F delta. In a liquid cooled engine the 
radiator is running about 200 F so for the same ambient the delta is 200 
F or half of what it is in the air cooled engine. You therefore need 
TWICE the air mass flow to remove the same number of BTUs. Radiators are 
so much bigger than cooling fins because they need to be. Cooling drag 
is a large percentage of the overall drag of our slippery Lancers so 
doubling that drag is bad news in anyone's book. You have the double 
whammy of cowling drag to cool the intercooler and turbo plus the belly 
scoop. One IV I know of that added a belly scoop for an air conditioner 
condenser lost better that 10 Kts. That whole "P-51 scope added thrust" 
story is a myth, IMHO.

You also mentioned a fixed pitch prop. I assume you are using this 
because you don't (can't?) have a propeller governor. How much 
performance will that cost you? (rhetorical question).

There is the matter of being able to use a lower grade of fuel (auto 
gas)  but  how many airports have auto gas handy. Notwithstanding my 
post on auto gas, it presents a logistical problem that makes up for its 
cost.

After adding it all up the rotary and Lycoming come in about even. You 
can argue the minutia, which engineers and builders love to do, but 
there is no elephant in the room that makes the case a slam dunk.  What 
it came down to for me was the simple question of whether I wanted to 
design and build and engine installation or build an airplane and go 
fly. Having already done the engine thing I decided to adapt the 
Lycoming. This only added about 700 hours to the build time. In the 
years since I have revisited that decision many times and have yet to 
regret it.

I am NOT saying that you are doing the wrong thing. If people built 
airplanes only to fly then they would buy rather than build. Builders 
build for the joy of creation. If building a new engine installation  is 
what you want then go for it. I wish you all the best and hope you have 
realistic expectations. If you are typical, when you are done the result 
will both please and disappoint. The empirical evidence is clear. 
Hangers across the globe are replete with failed and abandoned projects 
where hope and enthusiasm tipped the scale until that buzz kill reality 
stepped in and spoiled the party. This does not mean you shouldn't try. 
Every great new accomplishment  is built on a foundation of can't. 
Perhaps you are the one. Good luck.

Regards
Brent Regan



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<font face="Arial">Greg writes:<br>
&lt;&lt;&lt;</font><strong><font size="2">Thanks for your comprehensive
input below.&nbsp; You do bring up a couple of issues that we have only
looked at in passing, and we will look into these issues further....</font></strong><font
 face="Arial">&gt;&gt;&gt;<br>
<br>
When I evaluated the rotary for my IV-P my comparison categories were
weight, power, reliability and cost. At an installed weight of 611
pounds (all accessories), 360 Hp (on the dyno),&nbsp; a demonstrated 1,500+
TBO and a known cost the Lycoming was easy to evaluate. The rotary took
an early lead due to its high power to weight ratio, low parts count,
demonstrated high reliability (endurance racing) and relatively low
cost OF THE CORE ENGINE. The fun started when you begin to add up all
the support systems. The radiators (four of them, intercooler, coolant,
oil and PSRU), pumps, tanks, filters, separators, coolant, plumbing and
fittings, turbo machinery,&nbsp; scavenging system not to mention the PSRU
and the weight picture gets pretty bleak.&nbsp; If you compare the firewall
to prop weight of the two running engines you will likely find them to
be quite comparable. <br>
<br>
Since the rotary engine needs all of these supplemental systems to
operate they must be added into the parts count and reliability
columns. Each of these systems is critical to making power. One failure
of a fitting, pump, drive, cap or coupling and the whole endeavor goes
quiet. <br>
<br>
One critical problem with the rotary is the accessory drive in that
there really isn't one. The original&nbsp; fan belt system is utterly
inadequate for the additional power demands of the bigger water pump,
scavenge pump, fuel pump and bigger alternator. One builder claimed he
solved the problem by using electric fuel and scavenge pumps. When
queried where the electricity came from he said proudly "The
alternator!". Oops.&nbsp; Serpentine ribbon belts are all the rage but they
present a significant single point failure opportunity and FOD risk. <br>
<br>
The rotary has the advantage in power IF you accept that the rotary
will live for very long at 150 Hp per rotor.&nbsp; Ask your engine guys how
much power you can get for 1,000 or even 500 hours of continuos output.
Remember that even a race engine is not 100% duty cycle. Even the left
turn only crowd lifts for the turns. Derate the engine to a more
realistic 80 to 100 Hp per rotor and the advantage evaporates. I fly my
Lycoming at 75% power (270Hp) all the time with the exception of the
climb (90%), the approach (45%) and racing (100%).<br>
<br>
Then there is the question of drag. Consider this, as my friend and
fellow engineer Fred Moreno once observed, thermal transfer rate is
proportional the the temperature differential of the two materials. In
an air cooled engine the cylinder heads run about 400 F and the air is
around 0 F giving a 400 degree F delta. In a liquid cooled engine the
radiator is running about 200 F so for the same ambient the delta is
200 F or half of what it is in the air cooled engine. You therefore
need TWICE the air mass flow to remove the same number of BTUs.
Radiators are so much bigger than cooling fins because they need to be.
Cooling drag is a large percentage of the overall drag of our slippery
Lancers so doubling that drag is bad news in anyone's book. You have
the double whammy of cowling drag to cool the intercooler and turbo
plus the belly scoop. One IV I know of that added a belly scoop for an
air conditioner condenser lost better that 10 Kts. That whole "P-51
scope added thrust" story is a myth, IMHO.<br>
<br>
You also mentioned a fixed pitch prop. I assume you are using this
because you don't (can't?) have a propeller governor. How much
performance will that cost you? (rhetorical question).<br>
<br>
There is the matter of being able to use a lower grade of fuel (auto
gas)&nbsp; but&nbsp; how many airports have auto gas handy. Notwithstanding my
post on auto gas, it presents a logistical problem that makes up for
its cost.<br>
<br>
After adding it all up the rotary and Lycoming come in about even. You
can argue the minutia, which engineers and builders love to do, but
there is no elephant in the room that makes the case a slam dunk.&nbsp; What
it came down to for me was the simple question of whether I wanted to
design and build and engine installation or build an airplane and go
fly. Having already done the engine thing I decided to adapt the
Lycoming. This only added about 700 hours to the build time. In the
years since I have revisited that decision many times and have yet to
regret it.<br>
<br>
I am NOT saying that you are doing the wrong thing. If people built
airplanes only to fly then they would buy rather than build. Builders
build for the joy of creation. If building a new engine installation&nbsp;
is what you want then go for it. I wish you all the best and hope you
have realistic expectations. If you are typical, when you are done the
result will both please and disappoint. The empirical evidence is
clear. Hangers across the globe are replete with failed and abandoned
projects where hope and enthusiasm tipped the scale until that buzz
kill reality stepped in and spoiled the party. This does not mean you
shouldn't try. Every great new accomplishment&nbsp; is built on a foundation
of can't. Perhaps you are the one. Good luck.<br>
<br>
Regards<br>
Brent Regan<br>
<br>
<br>
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