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Hi Bill,
Here is my viewpoint on the topic - concerning injector size and Renesis
Power. PRIMARY INJECTOR SIZE CHOICE The yellow 360 cc/min (presumably at 56 psi) would give (derated for 43 psi)
approx 310 cc/min * 2 = 620 cc/min *60 = 37200 cc/hour = 9.8 gph *6/0.55 = 106 HP (approx). Failure of the secondaries on take off would obviously
create a huge pucker factor - at the very least. In some aircraft (the RV
for example), a 106 HP might be sufficient to keep you airborne (depending
on density altitude and weight), but I certainly would not count on it.
Now I know the EC2 can handle 550 cc/min injectors on the old 13Bs. So IF
IT were ME and a Renesis, I would go for the blue injectors ( 500 cc/min) in
both primary and secondary. Derating the 500 for 43 psi gives approx 430
cc/min *2 = 830 cc/min * 60 = 51600 cc/hour = 13.6 gph * 6/0.55 = 148 HP
(theoretically) on just the primary injectors along. Now 148 HP will do as
adequate (if not sterling) with an RV even on a high density day. Now the
only down side I can think of is you have to have 4 of the blue injectors
(you probably already have 2) and the idle MIGHT not be quite a smooth as
the smaller injectors (probably depends a lot on how well you tune the idle
end).
So my personal opinion is that I would rather put up (at most) with a bit
rougher idle and have essentially full power available from either injector
pair. But, again, that is just my preference. RENSESIS POWER
1st I think we all know that the initially somewhat optimistic RX-8 HP
claims were later reduced by Mazda from around 250 to around 225 HP. Even
then you need to climb into the 8500 -9000 rpm range to get even that
(assuming no boost). Here is a range of rpm and power (based on 12.56:1
air/fuel ratio) that applied to the Renesis and older 13B. I'm using a Ve
of 98% for the volumetric efficiency of the induction system - which is
probably considerably better than the average induction systems we make. Sea Level standard day.
RPM HP Fuel Flow
5000 144 HP 13.1 GPH
5500 155 HP 14.5 GPH
5800 164 HP 15.3 GPH
6000 170 HP 15.8 GPH
6500 184 HP 17.1 GPH
7000 198 HP 18.4 GPH
7500 212 HP 19.7 GPH
8000 226 HP 21.0 GPH
Remember this is ALL at SEA LEVEL and assumes you have a Ve of 98% and so is
an undoubtedly optimistic estimate for most of us. Also normally the VE
decreases as losses rise at higher RPM, so a Ve of 98% at 7500 is probably a
bit higher than it should be. Also if your Air/fuel ratio is less than 12.56
then you are producing less power.
The point is, I just wanted to present what a well set up and tuned 13B
might be capable of as a baseline. Naturally the Renesis is more likely to
get to 75000 + rpm than the older 13B - so IF you can get there or operate
there you will be producing more power. However, these numbers are likely
to be maximum obtainable rather than the norm for our installations. The
norm is likely to be less - how much less, well that depends {:>)
Now as to additional power being produced by the Renesis -- since I don't
have one, hard to comment on - but, I will {:>). Given that the Renesis and the older 13B are essentially the same engine
(other than the exhaust side ports) as far as being an air pump, then the
only three reasons to expect the Renesis to produce (significantly) more
power than the older 13B are:
1. The 10:1 compression rotors is going to add a small amount of power over
the older 13B
2. The timing of the ports (now that there is no overlap between intake and
exhaust) MIGHT add a bit more power - or might just be a wash-or it might
actually cost a small amount of power).
3. Higher RPM (due to lighter rotors and different seals) - This is the most
significant factor in the Renesis producing more power.
So from that perspective, the Renesis is only going to produce noticeable
more power (than the older 13B) due to the higher rpm. Ergo, if you are not
getting into those rpm regimes then you are not going to make much (if any)
more power than the older 13B. Sorry, but at the lower rpm it would seem to
me that the Renesis really only has the higher compression rotors going for
it.
WHERE'S THE POWER, SCOTTY?
My experience indicates there are several reasons (assuming no major errors
in the installation, auxillary systems and engine set up):
1. The engine is an air pump - air is the limiting element in producing
power (you can always pump in more fuel).
2. The engine can not/will not pump more air than the most severe
restriction in the induction/pump/exhaust system. That could be an over
restrictive air filter, muffler, throttle body, intake, etc. 3. Engine Load - since we do not have a gear shift, we are stuck with one
gear ratio from idle to top speed. You can over-prop the engine such that
it simply can never get past a certain point where the engine power at that
rpm is matched by the power required by the prop. Now if you have a
variable pitch prop - you have even more variables to deal with.
Now you have to optimize thrust produced by the propeller and power produced
by the engine.
IMPORTANT. I know of one accident where the pilot decided that maximum
rpm = max power, so far so good. However, he set the prop to produce max
engine rpm (Not so good) - he never lived to understand his mistake. While
the engine was shrieking (not a rotary) on take off and he was undoubtedly
producing gobs of rpm - the prop pitch was set so fine that he was only able
to develop sufficient thrust to get airborne in ground effect. Could never
climb out of it and crashed into a tall cactus on his first and final
flight.
So what you really want (at least on take off) is maximum thrust at whatever
engine rpm prop pitch will give it. Max engine RPM IS NOT the sole
determining factor. 4. Assuming your engine airflow is all it needs to be, then the next things
I would look at are:
1. Appropriate fuel for the engine operating conditions 2. Ignition timing
I would say that 50% of the time, the situation is unrealistic expectations
of power for the conditions (rpm/load) combined with indeed less than
optimum air flow conditions (probably 80% of the cause) for the engine.
The main reason I continue to fly with my older 13B (other than the
cost/time and effort required) rather than convert - is that as nice as the
Renesis is, it would simply do nothing for the way I fly (or glide {:>)). I
want max power at take off and have tuned my intake to provide that - I
seldom ever fly top speed - just too much fuel and $$$$. At 6000-6200 rpm
(my static with 2.85 and 74x88 prop), I doubt there is any significant
difference in power between the two engines. No question the Renesis will
produce more power on the top end - but, that's where I don't fly {:>). Finally, I know of no magic formula (wish I did- think of the $$$$ {:>))
other than to tinker, tune, test,and tinker some more with your
installation. Check the set up of others who are demonstrating (talk is
easy {:>)) more power with their set up and try to determine why they are
and you are not. IF you have the resources there is always the dyno route -
which Al has shown can be a great help in tuning your engine and getting to
know what it will deliver.
Hope this helps
Ed
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
http://www.andersonee.com
http://www.dmack.net/mazda/index.html
http://www.flyrotary.com/
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.rotaryaviation.com/Rotorhead%20Truth.htm
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Bill Bradburry
Sent: Wednesday, June 24, 2009 9:13 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: 88HP vice 130 HP. [FlyRotary] Re: 295cc vs 495 cc
Renesis Test[FlyRotary]
Ed,
I really don't know what to make of this. I need someone to brush the
cobwebs out for me.
It would seem that most or all of the Renesis folks are not getting the
power the engine is capable of, and at least a couple of us get an empty
sleeve(no response) when we hit the last 1/3 of the throttle movement.
I don't understand why we are not reporting going lean or causing the engine
to quit at those conditions like Dennis did on only the primaries. I think he is correct about the yellow/blue being the best combo for us. If you lose the secondaries on takeoff you are still in deep kimshi because
at about 107HP the best you could do is maintain altitude, you wouldn't be
able to climb. If you lost the primaries you could make about 150 HP, so
you would be ok. If either happened at altitude, you would just fly to the
nearest, no prob JoBob.
I am pretty sure that Tracy is in Colorado, so hopefully someone here(you?)
could have an opinion about the best way to set up the EC-2 with the
yellow/blue combo. The difference is about 29-30%. Tracy's instructions
say that if the difference is over 50%, you should use the "large secondary
differential", mode 6? To correct for it. So would it be better to cancel
that and work with the MAP table around the staging point, or go with the
big secondary setting. You would still have to correct around the staging
point.
Bill B
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