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

From: M Roberts

To: Rotary motors in aircraft

Sent: Wednesday, November 14, 2007 7:43 PM

Subject: [FlyRotary] Thick vs. Thin...ED is trying to scramble your brain like an egg

RESIST!

 

It's a sinister plot to keep us all from working on actual airplanes! There are too many people completing rotary powered airplanes. Ed is trying to side track us!!

 

Really tried to remain silent, but all those drugs the dentist used have lowered my resistance......

 

I've had more thermo and fluid dynamics than I wanted, and have had to apply it in the real world. You guys are on a great big snipe hunt. The only way to fairly compare this is take a core that is say 4 units thick. spread that exact core out so it is only 1 unit thick. Now run the numbers both ways sizing the inlets, diffusers, and nozzles and core area, for the same heat rejection rate and hot side mass flow....All assuming same efficiencies for diffuser and nozzle (not necessarily valid, but do it anyway). No rigging the efficiencies or saying this core is better than that one etc. You can't just assume a cold side DeltaT. You have to calculate it. Both must be a cross-flow exchanger etc, etc, etc. You will need a heat transfer book, and a thermo 1 and 2 text. Before you do this you might want to have a little light background reading in calculus 1, 2, and 3 and probably fluid dynamics, You will get real familiar with a lot of funny non dimensional numbers named after dead German guys. On second thought just go get a mechanical engineering degree because you will already be so deep in this junk by then.

 

Then if you avoid any math errors you will find out the magic theoretical advantage one radiator might have over the other.

 

We are flying too slow and reject too little heat to use the black magic voodoo Meredith effect....so just put that out of your mind if that is in any way steering your thinking on this matter.

 

If this sort of thing floats your boat you can spend hours and hours with spread sheets and equations. and in the end........ sailboat fuel....turd polishing....snipe hunt.

 

Trade studies for both designs for given airframe and mission are all that matter....and in the end testing.

 

Packaging/weight/structural  constraints will trump some minor theoretical heat transfer advantage every time. 

 

I guess you can argue with the pocket protector set in heat transfer lab after it's all said and done...but it sure won't get you any dates (or at least not ones you'd want ;-).

 

All the while you toil, earthbound, in vain, Ed will be flying overhead with a loud buzzing sound overlain with evil, maniacal, laughter.

 

Monty