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The RENESIS Project

Reader Note:  This page is presented in reverse chronological order, with the NEWEST information at the TOP and the history at the bottom.  If you haven't visited before, you may want to read from the bottom up. 

February 25, 2005: Why no recent updates???    Flight test data is always exciting whether the outcome is good or not so good and I can understand the curiosity in the dozens of calls we get for more results on the Renesis.   Wish there was some blood pumping news to report but the fact is that we have reached the penultimate point in the engine development cycle and every pilots' desire  -  nothing to report.

OK, so that may be overstating it a bit but without going into nitpicking details, that's where we are.  We have about 75 hours on the Renesis and it has a wonderful sameness every time it is started.   Here are the nitty gritty details:

1.   I'm using the same 87 octane fuel that I burned in the 2nd gen. engine figuring that the slight increase in compression ratio from 9.7 to 10.0 would not be significant.   During brief top speed runs near 225 mph I would occasionally hear a single engine miss and feel a slight shudder through the airframe.   Thinking this may be the onset of detonation, I retarded the ignition timing (the EC2 allows this to be done in-flight) by 1.875 degrees.   The miss went away and has not returned.  When time allows, I will bump the timing back up and test with premium fuel.   Mazda does specify premium in the RX-8 but most drivers report better fuel economy on regular.

2.  The removal of the oil filler tower on the Renesis block (done for weight reduction) may not be a good idea.  It may function as an oil-air separator and eliminate the oil mist blown out of the crank case breather hose at RPMs higher than 7000.   Even with the tower, the RX-8 has an elaborate external oil-air separator which was not used for cowl clearance reasons.  At normal cruise and climb rpm the oil mist is not a problem, but after top speed runs the plane's belly is "well oiled".  I have added an oil-air separator to the breather tube and the problem is 95% solved.  A more effective separator is planned when I have the time but I may have to live with the couple of ounces of oil loss during the SUN 100 race in April.

There will no doubt be more ideas to be tried out in the future but now it is time to concentrate on the 20B powered RV-8 project.    The Renesis is *operational*.

November 14, 2004: After a long delay waiting for the flooded Suwannee to recede...

Fortunately there is always a warning before the river floods here, but it was a very frustrating wait while we watched the runway at Shady Bend disappear under water.   It was finally dry enough to use last week and flight tests on the Renesis resumed.  (Editor's Note:  "test flights" have concluded.  Laura took her first flight in the plane since the engine change)

The engine continues to improve with each hour of flight.  The very close tolerances in the new engine require an amazingly long break-in period.  Temps keep coming down although the coolant temp coming out of the block is still higher than the 2nd Gen engine as noted previously.  The oil was changed from Shell Rotella (a very good mineral oil) to Mobil 1 Synthetic at around 5 hours.  This further reduced oil temps to the point that it is no longer a factor under any climate or flight conditions.  If the  OAT is less than 90 degrees, the oil temp is actually too low for optimum efficiency.  180 seems to be the sweet spot and it runs about 20 degrees below this most of the time.  A cowl flap will solve this problem.  Temps too low is the very best 'problem' you can have  : )

The main change tested this week was an increase in intake runner length.   I knew they were well below optimum initially but wanted to see how a short runner performed.  It was better than expected since the lack of tuning was partially compensated for by the very clean configuration of the manifold.

Skipping  several steps, I  went to the longest runners I could fit in the box.  Total runner length is now about 11.25" including the part inside the engine block.  This placed the mouth of the runner fairly close to the far side of the air box and this is the scenario where the teardrop cross-section bell mouth becomes important.  Since much of the air is drawn from the backside of the mouth, it needs a clean smooth path to get there.  

A full evaluation of any significant change requires many flight tests under a full range of atmospheric conditions but it was obvious that the longer runners were an improvement right from throttle up.   Things happen way too fast on takeoff to watch the tach but immediately after rotation the RPM was up about 150 - 200 rpm above previous tests.  This is about where the 2nd gen engine was with the reasonably well tuned dynamic chamber manifold, which is to say - Spectacular!.   

After climbing to 1500 feet  (less than a minute after starting the takeoff roll) I leveled out to get a reading on temps & pressures.  Everything in the green and stable.  A level acceleration to top speed takes a long time (especially those last 5 MPH) so I typically dive the plane to get to the neighborhood of top speed, level the plane while carefully trimming to zero on the VSI,  then wait for airspeed to stabilize.   This day was not especially good for testing due to some low level shear making for a bouncy ride.  Airspeed indicator was bouncing up and down way too much to get an accurate read.   

Under these conditions I would basically use the airplane as a flying dyno to get a relative indication of HP on the engine.  Since I had good numbers on fuel flow and rpm with the 2nd gen engine, these would have to serve as baseline for this days' tests.   Fuel flow was virtually unchanged from before - about 20.8 GPH at best power mixture.    But it was the RPM that brought a smile to my lips - 7500 rpm,  which was a full 200 rpm higher than the 2nd gen. This was right at my intended target  for the Renesis.

With the turbulence threatening to put my head through the canopy and the ASI bouncing around well above redline I did not spend very long at full throttle and decided to wait for better conditions for further testing.  I was happy.  It was a pretty good result from a relatively minor change.  Landing was normal and post-flight inspection showed that I still had some work to do on the crankcase breather plumbing.   Still blowing a little oil at above 6500 rpm.  I don't think the film of Mobile 1 oil on the belly will make the plane any faster.

Postscript:

Every time I publish fuel flow results on full power engine tests I invariably get a bunch of comments about how thirsty those rotary engines are.   "My IO - 360 only burns 10 GPH!", will be repeated so many times I lose count.  Not that I don't believe them, but the fuel burn of an engine at cruise altitude leaned for best economy has nothing to to with what it burns a full rated power.   It has been well documented that a 200 HP  IO - 360  (or similar aircraft engine) will burn 20+ GPH when making full rated power at standard conditions (Sea Level, 50% humidity, 59 deg F temp, 29.92" Hg MAP).   There is no escaping the simple truth of internal combustion engines -  it takes about .5 lb of fuel to make 1 HP for an hour. 

September 22, 2004:  Following the return of Tropical Storm Ivan and waiting hurricane #4..

The weather finally clears.  Today’s flight test was the first after making several changes.  Yes, I know that it is best to change one thing at a time so the results can be accurately correlated, but that must be balanced against the time available.  It takes me an average of 5 hours to do each preparation/flight test/data evaluation and this does not including the time required to make the hardware changes. 

Changes

Main change was:   Replaced NACA scoop / SCAT duct air inlet with ram-air inlet. 

Other changes included adding an additional coolant temp sensor before coolant passes exhaust ports, cleaner cooling air exit from right rad and oil cooler (result of removing the SCAT duct) and external stiffener on water pump inlet hose (to prevent collapse in the event of negative pressure).

I had intended to just test the pre-exhaust / post-exhaust  coolant temp after installing an added temp sensor, but since weather delayed the flight test, decided to add a ram-air scoop while waiting.  This was a very quick & dirty implementation so don't laugh too hard at the pictures.  The SCAT duct was snaked around the engine compartment and connected to a NACA scoop on bottom right of cowl.  Removing it may have been responsible for some of today’s cooling results.

Test Results 

Cooling

After takeoff, leveled off at 1000 ft to measure coolant temps.  At fuel burn of 5.5 gph the post exhaust coolant temp was 10 degrees higher than pre exhaust.  This would account for almost all the temp rise over the 2nd gen engine.   OAT was 3 - 4 degrees cooler than on previous tests but all temps seemed to be down about 10 degrees. ???   Lower temps may be due to better airflow through cowl as a result of removing SCAT duct.   I'll take it!  

Started slowly adding power and trimmed airspeed to 120 mph.  Measured pre/post exhaust coolant temp deltas between 25% and 90% engine power as computed by EM2.  Power was limited by engine speed (fixed pitch prop) and MAP at test altitude.  Delta went from low of 10 degrees F at 25% power to high of 16 deg at 90%.  Post exhaust temp reached a high of 222 F at 100%   

Side note:  Remember those much lower EGT temps on the Renesis?  It is now apparent that part of that exhaust heat is now going out via the coolant.   Bummer.  I had hoped that it was all going out as HP at the crankshaft.

Oil temps reached a high of only 190 F.  This was significantly lower than on 2nd gen engine under similar conditions.  Could be due to ceramic coating on rotors, better cooling inlets, better thermo efficiency on Renesis, or (your guess here).  Since oil cooling is the critical number in the rotary, this was an especially welcome result.

Cooling Conclusions

The extra heating of the coolant by the exhaust is real but of no significant impact.  Only critical coolant temp is when it is flowing over the combustion chambers of the rotor housings.  It is not significantly higher here than it was on the 2nd gen engine.  Not a scientific test but I did not sense the slight fall-off of power in the Renesis that I did on the 2nd gen when coolant temps went above 180F. 

You may be asking yourself why a 16 deg F coolant temperature rise is of no significant impact.  Fair question.   Since the source of the heat is transfer from the  exhaust ports, it does mean that the coolant temps are going up before it goes to the radiator but it doesn’t mean that the critical combustion chambers are getting hotter.  Here’s the key point:   The higher coolant temp makes the radiators more efficient (i.e. it transfers more heat to the air going through it) and this means that the coolant coming out the outlet is not significantly hotter than it was when the inlet temperature was lower.  I know this sounds somewhat counterintuitive but it really does work that way.  The only real down side is that the under cowl air temp (air after passing through rads) is hotter.  Only impact of this is that we must pay more attention to temperature of electrical components under the cowl like coils & alternator.  May want to have cooling blast tubes on these parts.  (note to self:  Measure ambient air temp around these parts)

Why the 10 deg F overall reduction in coolant temps  with only a 3 deg reduction in OAT is still not explained.  Possibly the SCAT duct removal or the water pump inlet stiffener.  Not likely, but it could even be due to the additional cooling air outlet area from the butchered cowl around the ram-air inlet.

Ram Air Inlet Results

This is the really good part.  The added power was evident from the moment of throttle up on take-off.   ROC felt like the old RVotter again!  After temp testing was complete, a WOT run was made at altitude of 4000 msl.  On initial throttle up, full atmospheric pressure was indicated on MP gauge and MP increased as aircraft accelerated to 221 TAS indicating that ram-air recovery was in-fact happening.  Did not have time to make multiple runs to accurately measure how much recovery there was.  Inlet and diffuser is in very crude form so will refine this plumbing before doing careful tests.  Cooling stayed within limits during test.

Overall Impression was that peak power on Renesis even in its crude state of tune had now equaled the 2nd gen at the height of it's refinement.  The 2nd gen had a slight edge in ROC when the engine was at lower rpm in climb.  I could feel the Renesis start to come 'up on the pipe' as revs increased at higher airspeeds.

Why the Big Difference?

Now it is time to revisit the results of the test with the SCAT duct removed from the throttle body.  In retrospect, the slight improvement in manifold pressure would not be expected to make much improvement in power.  It was only about 1.5” Hg.   On the other hand, the 80 deg F increase in air temperature SHOULD have hurt power noticeably, and it didn’t.   My guess at this point is that the air temp didn’t go up that much.  Why?   Because the air must have been heating up going through that long SCAT tube more than I could ever imagine.  I could verify this by removing the ram-air scoop, putting the SCAT duct back on and installing an air temp sensor just ahead of the throttle body.  I won’t do it though.  Life is too short and there are more rewarding experiments waiting to be done.

Now it's time to start tuning that intake manifold.  The runners are near their minimum length right now.

September 21: 2004: THREE hurricanes later..

After several more flights I noticed that the coolant temps were coming down a little with each hour added to the hobbs .   My guess is that the new engine is breaking in and frictional losses are coming down.  Power is also slightly improving  but still disappointing since it still felt weak compared to the 4 port 2nd gen.   I am beginning to fear the Renesis swap might be a mistake. 

The low power and higher observed coolant temps are really starting to get to me.  I’m pacing around the shop without accomplishing anything and not sleeping well at night.   In desperation, I decide to at least verify that the cause of the low manifold pressure is the long SCAT duct.  The SCAT duct is removed from the throttle body so the engine will be breathing hot air from under the cowl.  A brief flight test is made in this configuration and the results are not at first conclusive.  The manifold pressure comes up some but the power is not improved.  I am at first disappointed but as I think about it and evaluate the results,  I realize that the power was not adversely affected as it should have been by the high inlet air temps (about 160 - 175 deg F).   

While pondering this,  I also realized that I had not been properly evaluating the results of my temperature data collected on the first flight.  I made the assumption that the coolant flow rate was much reduced (compared to the 2^nd gen engine) because of the higher coolant temp delta between radiator inlet & outlet and the pressure drop seen at the water pump inlet when the rpm was increased from idle to 5800 rpm.

The problem with this theory is that it did not explain the higher AIR temp delta from cooling air inlet to behind the rad.  This temp delta was also higher than it was before (90 / 140 on 2^nd gen vs. 90 / 170 on Renesis).  If the coolant flow rate was lower, the air temp delta should ALSO be lower.  The only factor which would properly explain ALL the observed data was that there was more heat going into the coolant on the Renesis than on the 2^nd gen 13B.  This is a conclusion I did not want to see and it did nothing to improve my mood or sleep.

Why would the Renesis put more heat into the coolant?  This question haunted me until I came up with a possible answer.  The main difference between the two engines is the side exhaust ports on the Renesis.  These ports are in-fact longer than the 2^nd gen peripheral exhausts and there are twice as many of them.  Could these be the source of the heat? 

 My coolant temperature sensor is located in the engine block outlet after the coolant has passed over the combustion chamber side of the engine and then back through the other side of the engine where the exhaust ports are located.  Nothing else on that side of the engine adds any significant heat to the coolant.

There is a convenient spot to install an additional temp sensor in the block which is after the combustion chambers but before the exhaust ports.  This is the car heater port which I had plugged.  I installed a sensor at this location and connected it to one of the unused auxiliary inputs on the EM2 engine monitor.   The difference in coolant temperatures at these two locations should show the heat added by the exhaust ports.  I wait impatiently for the weather to improve so a flight test can be made.  Blasted hurricanes!

September 20,  2004:  Two hurricanes and 1 vacation later.....

Still convinced that the high coolant temps were due to lower coolant flow rate,  the water pump inlet plumbing was completely revamped to reduce the restriction in this path.   As a bonus, the change also reduced the weight about 1 pound.   Only down side was,  after 20 hours of work and $160 in hardware and supplies,  a brief flight test showed no change in coolant temps.  Power still sucks.  I am beginning to get panicky.  

August 15: World's FIRST FLIGHT of a RENESIS powered Aircraft!  (and perhaps as significant, Tracy paid me$500 for winning the bet!)

OAT 88 – 90 deg             Humidity 90+%

 Pilot Impressions

Take off  done with engine warm (~ 155 F) but water temperature  was 207 on first check after rotation.  Reduced throttle and orbited Shady Bend for 64 minutes at ~ 1000 ft  MSL.  Engine very smooth with low cockpit noise level.  Water temp slowly fell to 195 – 197 at fuel burn of 5 – 5.5 GPH.  Engine RPM was 4300 – 4700 during flight.  Very brief full throttle run yielded only 5800 rpm and engine did not feel strong.  MAP appeared to be limited to 28.5” Hg. Water temp immediately climbed to ~ 205 and power was reduced.  Oil pressure continued to read 100 PSI (full scale on instrument) as it has during ground tests.  Engine builder used 3^rd generation  pressure regulator and it has been my assumption that this was normal for it. Reset oil pressure high limit on engine monitor to 102 PSI to get rid of flashing alarm.  Oil temps were stable at 185F during entire flight.  Normal landing with engine temps falling rapidly during final approach.

Post Flight Engine Check (engine still hot)

Significant data

Analysis

Coolant Temperature

High coolant temperature was very disappointing as I had expected much better cooling with the improved diffusers.   Reasons for the high temps can be surmised by delta temps above.  The high air temp delta would indicate one of two things:

1.  Higher coolant temps indicating more heat rejection    OR

2.  Lower airflow through radiator

The coolant temp was higher but only marginally (10 deg after stabilized at 195)  This would not account for a 30+ deg increase in air delta.  This leads me to believe that reduced airflow is the cause.   The diffuser on this radiator cannot possibly (?) be worse than before so my guess is that the greatly extended duct divider that separates the oil cooler duct from the radiator  duct is having an adverse effect.  Oil cooling was not a problem and delta was in normal range so it was not hurt by the divider and may even have been improved. 

The water temp delta would indicate that the water flow rate is less than half of the previous value when deltas were in the range of 10 – 12 F.   Two possible causes come to mind.

1.  The coolant manifolds I made are too restrictive.

2.  The water pump design is less effective than the 2^nd gen engine.

Item one  was a concern even while I was building them.  I thought they would be adequate because the coolant outlet arrangement does not appear to be any more restrictive than the previous setup.  OTOH,  the inlet setup could be significantly worse than before.  It has 90 degree fittings which could be a problem.

The water pump design is the same as the 3^rd gen 13B, which looks crude by comparison to the 2^nd gen,  but has evidently been adequate in the auto racing environment.  It may require a much cleaner coolant path in order to achieve adequate circulation.  Or, conversely, the 2^nd gen pump may be much more tolerant of restrictive coolant paths.

A later observation supported my suspicion that the water pump inlet was restricting coolant flow.  The coolant pressure (measured at the pump inlet) dropped from 10 psi to 0 (lower limit of instrument, could have been negative).

Oil Pressure

The 100 (+?) psi oil pressure is a concern after learning from the engine builder that the 3^rd gen oil pressure regulator (presumably equipped with a Renesis regulator spring)  is supposed to give pressure in the range of 70 – 85 psi.  This would indicate that the pressure is being regulated not by the rear regulator but the front pressure relief regulator which does not become active until 150+ psi.    As I write this, I decided to check the Racing Beat Tech manual for info on oil pressure.  According to their chart, the 93 -95 rear pressure regulator is set at 110 PSI !.  This leaves me with no firm conclusion about the oil pressure readings.  

Engine builder later confirmed that he had pressure spec wrong.  3^rd gen is specified as 110 psi.  A 3^rd gen car racer also said that his oil pressure runs 85 – 95 psi hot.  Off scale when cold.  Have canceled tentative plans to pull the engine for this problem.  I would still prefer to have a lower pressure regulator and will do this if I have another opportunity.

Low MAP

This problem is probably due to the relatively long and tortuous path between the NACA inlet and throttle body.  There is over 4 feet of 2.75” diameter Aeroduct (SCAT?) between the two.  I was concerned from the start that this stuff would cause a pressure drop.  It will have to go.  Many more hours of fiberglass work required to fix.

Did prop pull-through test of engine ‘feel’ and it was same as earlier tests prior to flight test.  Compression of engine when pulled through in reverse is impressive.

Confirmed that the air temp sensor behind right rad was accurate.  In view of this I have decided to cut the duct divider back to near its original position and re-test.   My assumption is that the higher air temp delta is due to reduced air-flow volume through the rad.  I’m flabbergasted by the idea that all my careful duct work resulted in WORSE airflow.

August 14, 2004:  The RENESIS started. What a beautiful sound it is!!! Flight testing scheduled for next week (or as soon as all these tropical storms & hurricanes depart the area). 

The engine was started for the first time on Wednesday 8/11 - one month and 1 day from the time that Tracy  took the old engine off the plane.  And yes, it did start on the first try.  I was in Atlanta for the big event (I feel like I missed seeing my child's first steps!) but he ran it up for me to hear a few minutes ago.  I do not think it is any quieter than the 2nd Gen 13B (I thought it was, T), BUT the tone of the exhaust note is mellower and easier on the ear than the 2nd Gen.  

I'll let Tracy fill in the details.  He mentioned that he really needs to work on the low end tuning.  To the untrained ear, it sure sounded GREAT at high throttle.  The RVotter was literally quivering with anticipation and wanted to take to the sky. See photos below.

August 8, 2004: No Noise from the Engine Yet (and no $500 either)

Parts keep going back on the engine (how long can this possibly take??) but after renovating the inlet on one side, Tracy decided to do the same on the other side.  This led to a change in the oil cooler air scoop.. which led to a new bracket .. which led to.. well, you get the idea. Last night he did the fiberglass for the bump required for the oil filter.  The only good thing about this is that it matches on the bump on the other side of the cowl so at least it is symmetrical. Finn Lassen wanted to know why he didn't leave the oil filter on the firewall where it has always been.  Seemed like a good idea to me, but Tracy  wasn't willing to pass up the 4 pounds of weight reduction gained by using the modified stock oil filter mount so the cowl gets butchered (again). 

July 30, 2004:  Update from Laura and Photos/Captions  from Tracy

The big news of the day is that Tracy is FINALLY turning his wrench in the "ON" instead of the "off" direction.  Those of you who have seen Tracy's cowl are not going to believe this but - now sit down - the cowl has once AGAIN been modified!  Yes, ladies and gentlemen, the "mud dobber" nest on the top has been unceremoniously sliced off with a hacksaw blade and a NACA scoop will be  installed on the lower cowl instead.  It is a good thing that the cowl is removed at air shows because it truly is an abomination.  New photos follow:

July 24, 2004: Update from Laura and Photos from Tracy. (Laura WON the Bet (why do I feel like I lost??)

No Oshkosh for Tracy this year - there is just too much to do and too little time.  No amount of 3 am work days can make this come together so Oshkosh is off.  I guess I'm $500 in the green but it is not a joyous victory.  He has made very good progress - below are some recent photos:

July 18, 2004:  Update from Laura

My $500 bet money is closer, unfortunately.  Tracy worked all last week until 3:00 am every night, but there is a LOT more to do.  The engine mount had to be modified (that is completed) but the fabrication of the exhaust is quite a challenge.  Of course, we'd also promised EC2s, EM2s and gear drives to customers so that cannot stop either.  There are no problems with the project - it is just a tremendous amount of effort.  I'll see if I can run down to the hanger and snap a couple new photos.  It won't look like much yet - the parts are all OVER the hangar.

July 10, 2004:  Update from Laura

Tracy is - literally - up to his elbows in engine oil.  Last night he removed the 13B from the RV-4. I guess this means he really believes he will get this thing flying at least a week prior to Oshkosh.  (I'm still counting on the $500)

June 19, 2004:  Update from Laura

Tracy continues to ASSURE me that "great progress is being made" on the Renesis and he still plans to have it ready for Oshkosh (we have a $500 bet on that.. I'm planning how to spend the money).  His current focus is on the intake system.  He won't say much about is except that it is a totally different way of looking at intakes.  All I REALLY know about it is that is a veiled reference to "flying wainscoting" (for those who don't know - we used to fly a hair spray can and we upgraded that to rock maple when the EFI was installed.  I can't determine if wainscoting is an upgrade or downgrade).  Tracy also said this intake experiment will either revolutionize the future approach to intake systems for the rotary (in which case he will produce them for sale) OR be a complete and dismal failure (in which case we will burn the wainscoting).  The only photos he allowed me to take are below.  

April 3, 2004: Update from Tracy 

With all the preparations required to get the RVotter ready for the upcoming Sun 100 race I haven't had time to do much updating of this page.  Just to give you an overview of testing results so far, I'll paste a few email messages I wrote to various people.  (That's why it will sound kind of choppy as you read it). 

I'm just now starting on my Renesis evaluation.  First I wanted to compare it to the earlier rotary (89 vintage) so I installed the RD-1C  2.85 : 1 drive and larger prop (intended for the Renesis).  Things are different enough that it will take at least 20 hours to evaluate.  I'll be posting detailed reports on the website. 

On the second flight test of this configuration I had planned to do a maximum performance takeoff to see how it compared.  I was fully aware that the P-factor would be opposite (prop turns right instead of left) but I was unprepared for the magnitude of it.  With full right rudder the plane was still veering left.

Things happened too quickly for me to be exactly sure of what happened next but I think when the tail wheel lifted off, the plane turned sharply to the left and I was certain that I was going to crash into the fence that borders the runway.  No one was more surprised than I when the RV-4 lifted off and cleared the fence (barely!).   

There were lots more interesting differences (most of them good) but it will take several pages and more time than I have right now to explain them. 

My first recommendation when using the -C drive and a big prop is Feed in power gradually on takeoff until rudder is fully effective.  A bit of right offset in the engine mount might also be in order (mine has none)

Wish I had more carefully documented fuel burn vs airspeed on the -B drive & old prop.  But from the few well documented points that I have, it looks about the same at 6.0 GPH (sea level) IAS, 143 - 148 depending on OAT, humidity, etc (its amazing how much conditions affect things).  This is the only point I've had a chance to compare so far.  I have not built the prop blade cuffs that I feel will be necessary to get best performance from this combination.  Clark at Performance Props was very honest about the difficulty in getting the proper pitch at the blade root (out to ~ 3" past the 13" dia. spinner) with pitch this high.  This being the case, I'm very happy with the results so far. 

Other conclusions are that anything less than 74" L prop is a waste on the -C drive.  More would be better but that's as long as the -4 prop clearance would allow. 

I can't measure static rpm (plane wants to skid on grass and/or nose over) but climb RPM is at 6200 at 120 mph (up from about 5200 with -B drive) and VSI is pegged (hard!).  Only did very brief test of WOT in level flight and engine hit 7050 rpm.  IAS was still climbing at 215 mph.  Oil cooling has suffered due to stalled air around prop hub and reversed spiral of airflow due to RH prop.  Erased several years of tweaking inlet shapes.

Most unexpected finding so far is the radically improved glide at idle setting.  Have no clue why.  Would have expected worse instead of better.

The following was a response to a question about whether a customers used B drive could be concerted to a C version.

The -C drive has very different internals but I will look at the feasibility of reworking the -B housing to receive the -C guts.  I think it can be done.   Yes, the -C bolts right up to the same adapter plate.  I think you are right about the 2.85 becoming the preferred ratio, but only if you can handle the longer prop.   You nose draggers have the advantage here.

The more I fly it the better I like this setup.   The higher rpm was very disconcerting at first but I acclimated rapidly.   And now that I have  digested the fact that the actual rpm difference at normally used throttle settings is only about 5%, I absolutely love it. Another good sign is that the manifold pressure is now more than 5% lower at any given airspeed that I've tested so far.  Even if the wear rate is up 5% or so it would be a non issue. 

One more plus for the 2.85 is something I hesitate to mention.  It's kind of like the "engine making oil so I have to drain some out" thing, kind of unbelievable.   It makes sense that there would be less prop noise but I'm also getting less engine noise. 

I was getting tired of the increased noise with the Hushpower II muffler and was almost ready to put the Spintech back on even though it costs at least 5 - 6 mph in drag.  But with the -C drive things have quieted down substantially.  I think part of the credit for this goes to the difference in RPM moving the vibrations away from the resonance point of the sheet metal panels in my RV-4 but even observers on the ground have mentioned that the engine sounds quieter.

I better shut-up now, this is starting to sound too good to be true.

  (This was written in response to a wise crack from Finn Lassen saying "Guess Paul Lamar was right all the time about the higher ratio being the best choice" )

OK, OK, rub it in, but before you guys get carried away, consider the following:

The prop limitation was always my only reservation about using the higher ratio.  I must emphasize that in order for this to work, the prop must not only be long but has to have a good profile as far down toward the root as possible with the MUCH higher pitch.  I worked with Clark at Performance Props and emphasized this.  It required a thicker than standard hub to get close to what was needed.

If you don't do these things, all you get is significantly higher rpm,  less performance, higher fuel burn and higher wear.  Look at the numbers from previous users of the 2.85 drive.  

Did I mention the three spinners, various spinner bulkheads, prop bolts that were now too short and other various things that went wrong  during the effort to make this work right?

As I accumulate more hours I clearly see the trend.  Huge advantage at low speeds (acceleration & climb) but advantage diminishes as speed approached maximum.   With the IVO prop (72" dia) I saw the same thing but the advantage diminished to zero at about 140 mph and then became negative above that.   

 I still have not run the new drive & prop to top speed.  I attempted to yesterday evening but the dreaded SAG (Sparkplug Attention Getter as Ed calls it) struck as I was approaching 220 MPH.   My best guess is that the zero point (same performance as with -B drive) is right at this speed.   Things may improve after I get the cuffs built (today's project).

(Ha!  "today's project" has taken 6 days and still counting)

Stay tuned, more results to come after these prop cuffs and several other 'tweaks' are finished.

March 20, 2004:  Flight testing of the new prop and RD-1C gear drive combination began this week.  It has been interesting to say the least. We also test drove an RX-8 last night.  Details to follow SOON!

March 14, 2004:  The new prop arrived last Monday.  Tracy installed the RD-1C drive on the plane Friday and worked all day today modifying a new  spinner to fit the new prop (we are holding the original spinner in reserve in case we need to switch back to it).

For those who don't know, the original plan was to re-power the RV-4 with the Renesis prior to Sun n Fun.  Various delays made that goal impossible, so Tracy decided to put the RD-1C (2.85:1) drive and the new prop on the OLD engine.  We have no idea what kind of performance this might produce, but regardless of the outcome it will be useful information for all those who bought the RD-1C with the goal of using it on the 13B.  If all goes as planned, the test flights will start this week.

March 3, 2004:  Tracy's new Renesis engine arrived , personally delivered by Bruce Turrentine of East Coast Rotary.  Of course, nothing ever goes as expected.  When Bruce assembled the engine, he used a 3rd gen 13B e-shaft which according to the information available, met all the requirements for the four port Renesis. (Remember, Mazda has published virtually no technical data on this engine).  All was well until the engine was completely assembled, when Bruce realized the E-shaft  seemed to be too short! The front pulley would only engage about 60% of its bore when bolted in place.  So...  he ordered a real Renesis e-shaft to be shipped overnight to Shady Bend on Friday.  It arrived, and after dinner, the break down and reassembly  began.  There were dumbfounded looks all around when the Renesis shaft turned out to be exactly the same length as the 13B shaft.

A mad frenzy then ensued to determine what was going on.  Skipping all the head scratching and calculations, the bottom line is that Mazda decided that 60% engagement was acceptable.  The whole exercise looked like a Chinese fire drill except for one small detail we noticed during the head-scratching.  The front main bearing oil hole on the Renesis shaft was moved about .150" forward.   This resulted in a mismatch between the oil hole and the main bearing oil groove.  Using the original 13B shaft may have resulted in insufficient oil to this bearing.  

Laura has been waiting to use this line a long time so she summarized the episode as:     Bruce was shafted and Tracy got the shaft!

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