----- Original Message -----

From: Brent Regan

To: lml@lancaironline.net

Sent: Thursday, January 29, 2009 8:23 PM

Subject: [LML] Re: Alternative Power Plants

Hello Greg,

Thank you for posting the pictures of the 20B aircraft installation you are fabricating. Your pictures and my personal past experience compels me to offer some words of caution.  First, let me say that I have no idea as the the degree and quality of the engineering that has gone into this project to date. I am operating on a worst case assumption so please discard comments concerning issues that you have already addressed. I hope to present these in a self evident fashion. Know that I have been involved in rotary engine development since the late '70s, that I was involved in developing and building a 12A engine that competed and won it's class in the 24 hours of Daytona endurance race,  that I have previously developed high output rotary engines for aerospace applications, that I worked with Charlie Jones at Curtis Wright to help market their SCORE aircraft rotary engine to Cessna and Piper and that I seriously evaluated the Mazda R26B engine (4 rotor winning Le Mans in '91, see SAE paper #920309) for my Lancair IV-P but opted to adapt a Lycoming TIO540.  I flew that airplane, and won, the Denver to Oshkosh race in 1996.  I now have over 1,000 hours on the original engine, including cylinders, pistons, rings and valves.

The Wankel rotary engine we know is actually a compromise from Felix Wankel's original concept. The progenitor engine, designated DKM-54, featured a rotating rotor and housing arraigned such that each had a pure rotary  motion. It was NSU's engineer Walter Froede that came up with the internally geared epicyclic design we are familiar with today.  While this design is attractive due to its high power density and  minimal parts count, it is not without its problems.  One of the greatest problems is the high aspect ratio of the combustion volume. This leads to high percentage of charge quench and therefore poor brake specific fuel economy, high hydrocarbon emissions and high exhaust gas temperature.  The CW SCORE engines attempted to overcome these shortcomings with a heavy fuel direct injection with spark assist. They were moderately successful.

Another problem is the high power density with respect to heat rejection. Nominally 20 percent of the total combustion energy must be rejected to the cooling system. For a 300 Hp engine this heat  flux is more than 100 kW, enough to run 20+ average single family homes. This is divided between the oil and coolant so the oil is at risk of chemical breakdown above 240F (natural oils). I solved this problem on the race engines by adding a tube shell intercooler between the oil and water cooling systems that limited the oil temperature to 230F by allowing the coolant to boil in the heat exchanger, dramatically raising the heat transfer rates. In short, your three biggest problems will be heat, heat and heat.

Comments referencing your photos and subsequent post:

1) Belly mounted cooling system. The engine is VERY sensitive to air in the coolant. You MUST have a de-aeration system mounted above the highest point of the engine. This is a convenient point to place a "radiator cap".

***We have an expansion tank mounted high on the firewall to handle this very issue.  There has been much conversation on the Rotary list about "burping" the engine to make sure there is no air in the system.

2) Oil sump. It appears that you are using a stock oil sump configuration. You will find this insufficient for the anticipated continuos power levels. You need a high volume (12 Qt) remote tank  dry sump system. The oil tank should have a centrifugal de-aeration design with multiple baffles. You should use a synthetic oil that is more tolerant to high temperature operation.

 

***Actually, we are using a dual system.  We are using the stock sump for the engine, and an aux. small tank for turbo and redrive oiling, with a pump designed to return this oil back to the system (modified dry-sump).  We have a large oil cooler in the belly scoop, cooled separately from the radiator.  This system is identical to the P-51 scoop configuration.  We are using AN-10 tubing/hose all the way, with dual large oil filters.  With all of this plumbing and cooling capacity, we figure we have about doubled the oil capacity over stock, dyno and temps will tell.

3) PSRU. It appears that you are using a planetary gear reduction, likely adapted from an automotive automatic transmission. Be advised that this configuration will generate between 1% and 2% of the transmitted power in heat, or about 5Kw at 300 Hp. You need a separate oil circulation and cooling system for this reduction. Prior attempts to use engine oil have been marginally successful, at best. I am also assuming that you have sufficient torsion compliance between the engine and gears to prevent cyclical load fatigue failure.

 

***The redrive is Tracy Crook's design, which has been well tested both on 13B's and 20B's.  It is rated at 450 hp at take-off, then we pull back to 55-70% at cruise.  As I said above, it has a separate oiling system from the engine.

4) Induction Plenum. It appears you are planning single port injection based on mass flow into the intake plenum. It is important that the flow distribution of the plenum be tested, otherwise you may have poor charge and mixture uniformity across the three rotors. Flow testing can be accomplished with a shop vac and carburetor flow gage (balance).

 

***Actually, each rotor is configured with 2 injectors.  One is in the stock location on the block, the other is in the manifold we have built (see picture).  Using Tracy's EC-3, we will map this on the dyno and make the necessary adjustments.  Bob Wirth is one of the best flow bench guys in the State, and with much consultation with Tracy and others, we feel we have gotten close to the optimum design, dyno will tell.

5)  Trochoid Cooling. Stock rotor housings  have poor cooling distribution for high continuos power outputs.  You need to have modified rotor housings and a high output  water pump that is driven at the optimal speed.

 

***Not sure on this one.  We will dyno with the stock pump, and see what happens.  We have even talked about reducing the pump speed, for cavitation issues.

6) High EGT. While having individual exhaust  manifolds to the turbo, to utilize the kinetic energy of the exhaust, is good, these should be fabricated from Inconel to survive the high EGTs without failure. Likewise, the turbo needs to be a high temperature version.

 

***We did schedule 340, because of the tendency of Iconel to need to be at constant hight temps to perform correctly.  With our envelope, 340 seemed the best and cost effective approach.  Again, dyno time and temps will tell.

7) Engine Mount. It is not apparent why the engine mounts are vertical. Thrust loads from the propeller can approach 1,000 lbs. The mounts, as designed, will not respond well to these loads.

 

***We are in the process of beefing the mount now.  We weren't happy with the way this one came out.  The pan plate and front plate were designed to work together, and have been well tested.  No failures to date. 

8) PSRU mount. While I can appreciate that a heavy flat plate is easy to fabricate, it is poorly suited to react the gyroscopic precession loads and moments generated by the propeller.  You would be wise to perform an independent engineering analysis of this design.

 

***Again, this unit has several years and a lot of installations with no failures.  We will keep a close eye on it.

9) Transverse Engine Mount Triangulation.  It is not clear from the photos but it seems like there is insufficient  bracing to react transverse nose gear loads. Ask Skip Slater about this one.

 

***Not sure on this one.  Will do some checking.  It is the stock Lancair Continental bed mount, modified to accept the Rotary, and then we beefed the hell out of it, and intend on adding some additional bracing to it.  We will send pictures of the final mess when we get it mounted back on the firewall.......

10) Reversed slip couplings. The exhaust  slip couplings seem to be reversed. Upstream should be the interior tube.

 

***This is the way Burns configured it.  We will weld tabs and bolts to hold them together. 

The above list is by no means comprehensive. It is simply a free association exercise based on the posted photos. Engine installation design is serious business.  There is a long list of designers that have died behind their engines. Success is in no small part dependent on the ability to understand and allow for the errors of those who have gone before. Remember that almost any engine can power an aircraft. The quality of the engineering and implementation of the installation determines the longevity of the application and, sadly, frequently the pilot.

Fly safe.

Brent Regan