That's the biggest surprise of the big engine experiment. I don't see any speed or altitude where the 20B RV-8 burns more fuel than the Renesis RV-4. (until the speed exceeds what the RV-4 is able to fly).
It should be said that the RV-8 is said to be cleaner than the RV-4, and I worked harder on lowering the cooling drag on the -8. Then there is the factor of increasing the wing span on the -8. That probably reduced the TOP speed but it increased the efficiency at speeds less than that. Since the top speed is still well over Vne, the longer wing is pretty close to a free lunch. The only thing it gives up is some of the G rating of the airframe. I arbitrarily reduced it to 4.4 G. The longer wing is especially helpful at high altitude where it can fly at a lower AOA and have a lower Cd.
Stuff for Marks spreadsheet:
RV-4. Renesis, 74 x 88 Performance 2 blade prop, 1850 hrs. Shoe box intake manifold. RV-8. 20B, extended 26' wing, James Aircraft "holey cowl", 72 x 104 Catto 3 blade prop, 56 hours, shoebox intake manifold. Failed 2 RX-8 coils at 50 hours.
Somebody asked if EC3 had to be reprogrammed for the coil change. Yes, dwell time is very different between RX-8 and LS1 coils. Due to some space constraints, I used a mixture of D580 and D585 coils. Also took this opportunity to try out the new idle strategy in the software. Still evaluating and optimizing that.
Inspected the flex plate without removing it and see no cracks so far. I paint all parts like this a light gray to make crack detection easier.
Tracy
Sent from my iPad Tracy,
Did you secretly swap out the 20B for a Renesis without telling anyone? Those numbers look fantastic. They look like what I would expect to see from a 2-rotor. Maybe I need to start flying higher. How do they compare to your lower altitude numbers?
Mark
P.S. Can you provide the missing info for my spreadsheet? Prop, mods, significant events
On Sun, Aug 14, 2011 at 4:12 PM, Tracy <rwstracy@gmail.com> wrote:
Got the coils changed out from RX-8s to a mixture of LS2 and LS1 coils and installed in an improved air box. Coils much cooler now.
Ran with auto pilot on to hold altitude steady during tests so I think they are pretty accurate. I was mainly interested in fuel economy and speed at various fuel flows. All these results were at 14,000 feet. I'll do some at 18,000 where the results should look even better next time. I forgot to dress warmer because the temp on ground was 94 F. OAT during test was 39F. Speeds are TAS.
6.0 GPH 169 mph. 28.1 mpg 7.0 GPH. 180 mph. 25.7 mpg 8.0. GPH. 200 mph. 25 mpg 10.0 GPH. 224 mph. 22.4 mpg
The manifold pressures sounded a bit unrealistic during test but 2 different instruments agreed so I think they are right. The only one I wrote down was at 7 GPH where it was at 13.9" Hg and rpm was 5174. The sweet spot seems to be very close to 8.0 GPH. I think that is where the rpm gets into the area where the fuel charge is stratified by the centrifugal force at around 5400 rpm and the mixture can be aggressively leaned.
The goal is to get 30 mpg at 200 MPH at 18000 ft. If I can get there I can fly non stop from FL to CO with only a small aux fuel tank.
Tracy
Sent from my iPad
Who's flying one (P-ported *Renesis*), & does it meet *both*
criteria?
Clarification: If I read correctly, the question was about complex
intake vs adding a supercharger & using it to 'normalize' only
back to the output of a properly done intake. My point is that a
manifold like Tracy's is very simple to build (much simpler than
anything for an aftermarket supercharger), and the power (and
efficiency) is there with much less weight & much higher
reliability. Higher *output* & high altitude benefits are still
there, but that wasn't the question.
Obviously, after the P-port is done the intake is simpler (by 2
tubes), but not that many homebuilders have the resources to do the
P-port mod, which makes the manifold look like child's play.
Charlie
On 08/14/2011 10:02 AM, Mark Steitle wrote:
Charlie,
Maybe you meant "...best power of all side ported
rotaries". I'm pretty sure that a p-ported 13B would easily
produce more power than a side port motor, assuming they do a
good job on the intake and exhaust. The nice thing about a
p-port motor is the intake is simpler and easier to build than
a side port intake.
Mark S.
On Sun, Aug 14, 2011 at 8:34 AM,
Charlie England <ceengland@bellsouth.net>
wrote:
On the subject of
Renesis intake complexity, take a look at Tracy's intake
(pic from his web site).
<mime-attachment.jpg>
http://www.rotaryaviation.com/renesis_engine.htm
Can't get much simpler, & as far as I know, he has
the best power numbers and the best efficiency numbers
of anyone flying. His intake tubes are now longer than
in this shot, but as you can see from the pic, adjusting
tube length (retuning) is pretty straightforward.
Charlie
On 08/14/2011 06:36 AM, Ed Anderson wrote:
Sam, As you find in this
"hobby" there are always trade offs. First,
technically there is no reason you could not do
what you propose - however, you will add weight
and complexity. A poor intake affects both N/A
and forced induction - its just with forced
induction you are paying in a different way to
overcome any defficiencies in your intake.
If going that route, I
personally would prefer the centrifugal type
belt/gear driven blower over the roots type which
has historically had the poorest efficiency. On
the other hand, if you are not going to "boost"
above ambient pressure - then I think I would
concentrate on getting a good N/A intake.
Good luck on your project
whichever decision/approach you take. Super and
Turbo chargers have both been used successfully.
just my $0.02\
Ed
Sent: Sunday, August 14, 2011 1:01 AM
Subject: [FlyRotary] Renesis Question
I think my brain has had a meltdown: I am thinking
about "supernormalizing" the Renesis engine. Is this
even possible. The idea is to use a by-passable
positive displacement type blower (roots
type...probably an eaton m90) fed to an intercooler
that then sends air to the engine. If my thinking is
correct, and it probably isn't, this would eliminate
the complex N/A intake, while not over-boosting the
Renesis engine. Also, the supercharger being a
positive displacement blower would in theory produce
more boost than is needed by the engine at all rpm
levels, eliminating the "peeky" torque of boosted
engines. The excess (above standard intake) pressure
would be controlled via an automatic or manual
waste-gate. Please shoot my idea down if it is insane,
but i would like some constructive criticism if it is
available.
Sam
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