Bobby,

 

When you say “drive losses” are you referring to the energy to turn the supercharger?  Or are you referring to the PSRU?  If it is the SC, I wonder if anyone knows what it costs in HP to run the PSRU?

 

Bill

 

 

Bill,

 

After a closer review of the Eaton MP90 performance charts I believe my actual super charger losses are less than I originally thought. 5000 crank rpm is about 8000 rpm for the super charger.

 

5000 rpm / 30” MP at 8000 ft.   150 HP – 10 for temperature rise and 10 for drive loss nets 130 hp. That’s a BSFC of .40 at 8.6 gph.  At 9.1 gph it would be .43 BSFC. I suspect my fuel flow may be off by .5 gph.

 

At 6800 engine / 30” MP at 8000ft.  Base HP of 215 – 12 for temp rise and 23 for drive losses nets 180 HP. A BSFC of .5 would be 15 gph and .53 would be 15.9 gph. Very close to the 16 gph I see in this configuration.

 

Bobby

 

 

 

Bill,

 

Without an intercooler I don’t operate in the low rpm / high MP setup. I’m MP limited to about 32” for cruise depending on altitude.  I don’t lean the mixture below 14.3-14.5 in the 32-34” range.  I do run 38-40” for takeoff and initial climb. F/A at 12.5-12.0 with water injection for extra margin.  Takeoff roll at 2450 rpm and then reduced to 2100-2200 for climb. MP drops some with the lower climb rpm but my water injection stays on above 33”.  My peak HP is with F/A around 13.5-13.7. 

 

At 5000 rpm / 30” MP at 8000 ft I estimate a loss of 12HP for air temperature rise and 23 HP for drive losses.  With a base HP of 150 -35 = 115 net HP. That would be 8.6 gph at a BSFC of .45.  Is the 23 HP drive loss costing me 2 gph? An IO540 should see a maximum 197 HP at this altitude / 118 HP at 60% power.  

                           

I’ve managed to shave a little weight off but I’m still around 1590- 1600 pounds. 

 

Bobby

 

 

 

Bobby,

 

The Renesis has a 10:1 compression ratio.  Are you sure you are not getting detonation at high (30-40) manifold pressures and low (1700 prop) rpms?  These considerations and the fact that I just don’t have room to squeeze it in are the reasons that I decided against a turbo.  The stock (car) engine has a knock sensor, but we don’t have any way to monitor it and with the noise and headsets to cancel it out, I doubt that we would ever hear detonation unless engine parts were flying past our ears.  :>)

 

I would like a little more power, but for me, it would be easier to install a 20B than to switch to a turbo.  I have enough room behind the engine that a 20B would set on my existing motor mount.  All I would have to do is make up a mount plate for the 20B that has the mounting ears in the positions of the 13B ears.  I could even use a little more weight in the front for W&B, so the extra weight would also probably work well also. My plane is heavier than a RV6/7 by about 500 lbs, so I could use the HP on takeoff and same for cruise as well.

 

I briefly touched on this mount plate idea a year or so ago with the Cozy Girrls, but they didn’t seem to be interested in making the mount plate although it would be pretty simple to leave 13B as well as 20B ears on a 20B mount.

 

The rotary HP is really a factor of the rpm.  When you dial it down in rpm, the HP drops to that level.  I am not certain what effect the turbo would have on this number, but for NA engine, 5K rpm is about 160 HP, 6K=180, 7K=200, etc.

This is pretty close to the same on all the Dyno graphs that I have seen.  Pretty much no matter how “souped up” the engine is, it still follows that same HP curve.  This becomes a problem for those of us who want to develop 200HP but run at 5K rpm.  That aint gonna happen with the two rotor engine.  :>(

 

Bill

 

 

Charlie,

 

This configuration is my sweet spot. Efficiency declines rapidly with faster rpm.  I can also run the same prop rpm at a lower manifold pressure 24-26 “and see almost the same fuel burn at 150 mph TAS. Increasing the manifold pressure to 30 or a little higher increases speed but the fuel burn barely increases. At the other extreme with prop set to 2350-2400, 30 -32” MP I see a top speed of 190 mph but the fuel burn shows 16 gph. Not good. The lyc RV10’s are way more efficient at this speed. I suspect the super charger drive losses are a big factor at the high power settings.  Possibly up to 2 gph?   It’s possible the fuel flow is not accurate in the high power configuration.  I’m not comfortable running the engine that hard for very long so calibration verification is not possible.  I’ve been reconsidering a turbo but still not convinced the renesis exhaust ports are up to the abuse. Although a looser turbo may eliminate the housing damage that has occurred in the turbo RX8’s.   I wonder what intercooled, 38” MP at 1900 rpm would do for speed and fuel burn?

 

Bobby

 

 

 

 

Hi Bobby,

Those are pretty good numbers for a 4seat plane, even a -10, at that fuel flow. Have you checked it at around 11gph?

Thanks,

Charlie


On 05/14/2012 03:26 PM, Bobby J. Hughes wrote:

Cruise rpm is typically 1700-1825 prop \ 4850-5200 engine. The low rpm may influence my EGT’s. In this configuration I see 160-165 MPH TAS at 8-8.5 gph at 6000 foot. It does a little better up high.

 

Bobby

RV10

 

Bill,

 

I see around 1650F max. At cruise altitude running less than 30”MP I can lean to about 1475F.

 

Bobby