Hi Al,

THEORY vs EXPERIMENT

I've been studing the development of the rotary for 30+ years.  I also had the dubious priviledge of working on NSU Ro80s in the early '70s.   Nothing that ever came out of the NSU Factory ever worked (for long).  MTBF of the engines was  around 15,000 - 17,000 miles!!!  All good German Engineering Theory that didn't EVER work (for long) in practice. 

Leon; I love you, man; BUT, I think you miss my point.  It is:

THEORY AND EXPERIMENT!

Without the theory there would not have been the rotary that would go the 15,000 miles.  You do the theory; you do the experiment; you do some more theory; experiment etc.  It wasn’t the experimenter who did the metallurgy; the heat balance, etc; all the stuff needed to get in the ballpark. Nor could the theory advance without the tests of what worked and didn’t work, and trying new ideas.  Theory is born out of observation; which then models and leap-frogs to what the next observation should be.

Try going to moon by trial and error.

I would never say that putting a oil/water heat exchanger in the oil pan wouldn’t work.  Why; Paul Lamar proposed that years ago. But is it the best way?  The most reliable?  For example; you can try a half dozen  fin/tube heat exchangers in the oil pan trying to find the optimum configuration; and maybe get close; or you can combine it with some analysis and maybe get there in two. 

I would never say an EWP wouldn’t work in an airplane.  But, for other than configuration reasons, is it a more efficient and reliable way to go.  No one has proven that yet.  But it’s true for most of us here; we do things by experience and experiment – we don’t usually have access to sophisticated analytical tools.

Anyway; enough of this – I need to get out in the garage and try out some things and see if they work.

All the best,

Al

For sure,  the NSU Ro80 chassis itself was a magnificent road car (thanks to Audi knowhow),  but the powerplant and drivetrain was a mobile (more often than not IM-mobile) mechanical disaster from day 1. They were NEVER able to satisfactorily fix it.   Many a divorce and many a heart attack was caused by these infernal contraptions. 

It also took Mazda several years to get it right.  By 1974,  with the intro of 3mm steel seals,  different alloy in the rotor housings,  and proper teflon/silicone water seals,  most of the problems were fixed.  But it was mainly by trial and error,  and observation,  and sheer dogged perseverence. The exercise nearly sent Mazda broke too.  In the end,  it was what worked in practice that mattered.  Bugger the theory!!

By 1974,  Mazda had fixed most of the basic intractable sealing problems. Looked after,  the engines would go well over 250,000 miles between overhauls. Now,  with the REW powered RX7s,  the motors are so reliable  that Mazda don't even have an engine reconditioning facility in Oz any more.  However, I still get ignorant people coming up to me telling me that rotary engines are no good because the "seals blow". (But that is another issue) .. I do digress ....

SUMP MOUNTED HEAT EXCHANGERS

Back to the matter at hand.  Personally,  I can't see what oil flow rate has to do with convective flow/heat transfer,  at least in the application I'm proposing.  Maybe I'm like the bumble bee that is too ignorant of physics to know what can't work??  As it happens,  the flow I've used is a kinematic inversion of a normal oil/water heat exchanger !!!  

The coolant is INSIDE the tubes) of the heat exchanger,  and is at normal block pressure (15-22 PSI). The hot oil is passing over the EXTERNAL fins of the heat exchanger,  so it will experience TURBULENT flow. Really good for convective heat transfer,  or so they tell me!!

The HOT oil actually enters from the top and flows (drizzles - depending on engine RPM)  down to the bottom of the pan over the fins and is continually removed by the pick-up,  which is below the heat exchanger.  Bulk oil flow rate will depend on engine RPM.  As Mike Wynn said,  if the oil dwells on the fins a little,  so much the better.  There's (relatively) cold water running through the tube(s), taken from the cold side of the rad, so it is just going to cool the oil a bit more ... 

The flow of cooling water can be controlled either by a thermostat,  a manual heater tap,  or an electronically controlled EBP.  (Electronic Booster Pump - shock horror Batman!)  In cold climates,  you want to be able to warm the oil quickly,  and keep it at near water temp when running hard.

As I mentioned in a previous post,  the best heat exchanger unit I've found is something like a Hayden auto tranny oil cooler.  See attached pic. The one on the right is about the G_O.  Also see:

http://www.powerdemon.com/Transaver.html

Different sizes are available,  and depending on the heat rejection capacity required, (and available space),  often it is better to run 2 or 3 small ones in parallel rather than one giant one.

So to summarise,  COLD water passes through the tube(s),  and the oil flows over the outside fins.  NOT expensive,  NOT heavy,  and really easy to engineer,  and a lot more compact than an oil/air heat exchanger,  AND no high pressure oil hoses to spew hot oil at 70+ PSI all over your pristine engine bay and canopy!!

Cheers,

Leon