Cooling Ideas for review

[LargePrime]

A very interesting post on the canard-aviators group.

 

Graham Shevlin's post on problems cooling his Long is a source of some frustration. It's been close to 30 years since this design hit the runways and yet I continue to see repeated posts dealing with high temps. Wayne's generous effort to help Graham is not his first. He and others before him have addressed this issue repeatEdly over

these many years. So why does this issue persist?

 

I've never seen the results of any tuft tests on the belly or the Long or the Ese but I am growing more and more convinced that any attempt to cool the engine from below the cowling is fraught with trouble. Granted, many have made it work but the costs in time, frustration and experimentation appear to have been high. And they

only go to prove that if you work hard enough you can make damn near anything work to some degree.

 

It had to be at least 15 years since I spoke to John Rontz about this issue and while I do not remember his exact words, I do remember him saying something like: "Here. Take a close look at this and you'll know where to put your inlets".

 

I examined the color printout he handed me and I immediately saw an air pressure distribution profile of the Long with red being the high pressure areas and blue the low or negative ones.

 

It will come as no surprise to anyone of you to know that the front of the canopy and the leading edges of the wings and winglets were bright red as were other parts like the nose of wheel pants and main gear bow. The bottom of fuselage aft of the speed brake had relatively low pressure. It wasn't at the aft (deep blue) end of the pressure gradient spectrum but it was obvious that in terms of pressurizing a cooling inlet, this wasn't the place!

 

My eyes were drawn to another bright red area of high pressure. I pointed to the forward part of the cylinder blisters in the top cowling, "Here?"

 

I do remember John smiled and nodded his head.

 

I've reported this any number of times at the old C-A site over the years.Some of you likely remember it. Some of you immediately wrote and asked for a copy of the data John gave me. Sorry crew. That data was lost many years ago. Perhaps if one of you knows how to reach John, you can convince him to make it public again.

 

Not that it's vital for I am confident that any of you standing in front of a Long and looking down the "Barrel" of it's fuselage will immediately verify what John asserted a long time ago. Those blisters dominate the profile drag in that area and promise to provide the best cooling where it's most needed: cylinder heads and exhaust

manifold.

 

Armpit scoops may prove better than what the Long has now but located as far aft as they are suggests that the air must do a 180 to get back to the cylinders.I am not convinced that's the best solution.

 

Maybe this will help some.

 

Have a wonderful holiday and safe year!

 

Art Bianconi

aka

"Laughing Jaguar"

http://groups.yahoo.com/group/canard-aviators/

[John Slade]

Interesting stuff, Art.

Unfortunately (or fortunately, depending on how you look at it) I don't have cowl blisters. My cowl for the turbo 13B rotary goes straight back along the fuselage, so I don't have that high pressure area.

 

I'm hoping that the NACA, enticed by a couple of vortex generators, will do the job.

[LargePrime]

As, I think, many are. But Art has a neat point about flow reversal, No?

[Jim Sower]

Actually, it seems like more and more of the EZ speed merchants are going with downdraft. It's not difficult to imagine that the cowl cheeks will be a high pressure area. It follows that ducting that into a cooling plenum will not only reduce parasite drag but enhance cooling (not to mention greatly simplifying baffling). If there were cowl cheeks on the bottom, they would be even higher pressure and that is one reason for armpit scoops. But it seems to me that downdrafting from the front of the cowl cheeks, even if it doesn't reduce profile drag, has to put a lot of that drag to work for you so you don't have to add to it with cooling drag elsewhere.

 

I aim to do that on my EZ when I put it back together and will be downdrafting my Velocity (even though the inlet is on top of the turtleback in a low pressure area) just for the simplified baffling. An added advantage of downdrafting is that you don't have a red hot exhaust system pre heating your cooling air. IMO that's a big plus. Of course downdraft cooling from inlets anywhere above the wings lends itself nicely to better diffusers and plenums which produce better cooling and less cooling drag.

 

Burt had this thing about updraft cooling that Ihave never understood - even on the front engine of the Defiant. I have had what I fancy to be more than my fair share of problems with updraft cooling and all the associated baffling and bullshit.

 

I'll never updraft nothing, no more, never .... Jim S.

[LargePrime]

pressure pics

[LargePrime]

and another

[LargePrime]

It would seem that a scoop just under the wings would make more sense than the belly scoop?

[No4]

Aren't the colours as described by Art the wrong way around?

It looks to me as if the red is low pressure, and the blue is high pressure.

The tops of the wings are red, whilst below is yellow.

It's hard to read the scale but it seems to say coefficient of pressure with 1 being dark blue and pink being -1.

[LargePrime]

yep

Blue is high

Red is low