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  #71  
Old 08-23-2007, 02:03 PM
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F1Boss F1Boss is offline
 
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Fellas:

Seems to me we are swimming upstream here: why continue to try to optimize the exit into a high pressure area?

Fact: the entire bottom of the plane is a high pressure area.

So, let's investigate channeling our exit or exits to a low pressure area.

Fact: Most of the upper surface of an airplane is a low pressure area.

If we can't re-locate our outlets to a low pressure area, let's at least move the outlets to a lower pressure area, instead of the center of the belly, where pressure would be the highest. I will submit that the cooling air exits should at least be at the outer corners of the bottom of the cowling (there IS a reason why Columbia and Cirrus do this), with the sides of the cowling being lower pressure yet, but this location can cause a bit of a mess down the side of your ship... One fella I worked with, who set many altitude and time to climb records, did try the side outlets,, but he related that at high alpha angles, the flow thru the inlets would stop, and the sides became inlets to the still open bottom outlet. Of course this didn't provide the most optimal cooling!

Shop tip: if you're going to experiment with side outlets, you're gonna have to close off the bottom, as much as practical.

Go back and look at the picture of the Yak, and maybe Rear Bear too: their outlets (and many other relatively high tech piston engine ships) are not on the bottom/high pressure area...

A fixed panel used as a side outlet (look at the Yak again, and a Sea Fury too) could have a very effective cowl flap -- easy to manufacture and actuate, and tough as nails (= very little maint issues). Rear Bear has its cowl flaps across the top of the fuselage, as does a Corsair; this is not the best placement if you like to look thru your windshield (just where is that leaking oil gonna go?), so there are practical limits to our quest to achieve lower cooling drag.

Carry on!
Mark
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  #72  
Old 08-23-2007, 02:17 PM
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RV8RIVETER RV8RIVETER is offline
 
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So, Mark when are you going to switch the Rocket to updraft cooling?
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  #73  
Old 08-23-2007, 02:31 PM
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Quote:
Originally Posted by RV8RIVETER
So, Mark when are you going to switch the Rocket to updraft cooling?
As soon as I get your deposit check!

Seriously, the side panel idea has been kicked around here for quite a while. The exhaust would be dirt simple (3 short pipes), but would sound really weird, as you would hear only 3 cyls at a time from the ground -- kinda like a T28 or Wildcat...

I think it's too easy to ignore, as the cowl mod would take minutes, the outlet panel would be easy (some of it would have to be stainless of course), and the exhaust could be mocked up out of steel for testing purposes.

Maybe John Huft will try this idea before I can get my plane in the air??

Cheers
Mark
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  #74  
Old 08-23-2007, 03:17 PM
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You might be interested to know that CFD plots on a 6A show the area just aft of the lower exit and the sides of the cowling just forward of the firewall have about the same pressure distribution (around ambient). One foot aft of the wing leading edge on the belly is actually very low pressure. One foot ahead of the windshield is also low pressure so this might give the highest Delta P for cooling outlets.
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  #75  
Old 08-23-2007, 04:30 PM
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Default Has anyone ever thought of this??????

Has anyone studied how an air blow nozzle works?

I?m talking about the air blow nozzles that you use to blow parts dry with. There are many designs out there and the OSHA ones that have holes placed in the side are the ones I?m talking about. Most of them are designed so if you block the tip where the air comes out, the air can be relieved out the other side holes. Now some of the more expensive ones have somewhere around a 45 degree hole that angles towards the outlet to produce more air pressure at the nozzle exit point. The way they are designed, it allows extra air to be pulled into the mainstream to provide more output per given about of air pressure. I play around with an air nozzle that I have and it was interesting playing with it because if I blew air into one of the holes that is drilled on the side, it pulled a vacuum/suction through the inlet. Next time you?re at a store that has air nozzles, look at them and you?ll see what I?m talking about. Don?t look at the ones that have a hole 90 degrees to the air stream, as they are junk.

OK, enough about air blow nozzles. I?m not sure if it would work, but why can?t a person provide an external air source with a scoop to your cowl outlet and feed high-pressure air on each side of the cowl outlet at somewhere a 45-60 degree angle to speed up the air at the cowl outlet ? One would probably need an extended cowl aft of the firewall to do this. This could probably help with mixing the hot and cowl air and provide a little bit of thrust and it should help pull air through the cowling if it was designed right. That?s the big question, if it was built properly and tested.

I sketched a couple of pictures just as ideas to help understand. The first picture is a top view. The second picture is a sketch of an air blow nozzle that has two 45degree holes on each. 3rd picture is the actual air nozzle tip.

Anyway, I?ve been thinking about this for a long time but just don?t have the time to tinker around like I used to, so I?ll leave this up to someone else. Who knows, it might work and it may not, there?s only one way to find out. Any takers out there???????


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  #76  
Old 08-23-2007, 06:36 PM
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Default Ross, was that from the EAA Mag article?

Quote:
Originally Posted by rv6ejguy
You might be interested to know that CFD plots on a 6A show the area just aft of the lower exit and the sides of the cowling just forward of the firewall have about the same pressure distribution (around ambient). One foot aft of the wing leading edge on the belly is actually very low pressure. One foot ahead of the windshield is also low pressure so this might give the highest Delta P for cooling outlets.
Ross is that the April 1997 article with the RV-6A CFD plots?

I remember the above article when it came out. I have been looking for a copy for awhile and Gent was nice enough to send me a scanned copy a few months ago. I enjoyed it, but was a little disappointed with the lack of belly plots.

Can't argue with your analysis of where pressure is ambient / low from the info avaiable. However I'd point out two big draw backs of the computer model/analysis, no cowl exhaust / cooling flow or prop wash affect. One good pressure plot of the belly would have been nice.

Dispite the area under the plane not being well represented with a pressure plot, I think you're right, you have to go aft of the wing leading edge to get lower pressure. Not so sure how low it really is.

The article is very cool (no pun) but lacking on belly plots and some critical detail for cooling. Prop wash and cowl exit air flow is probably not trivial for fuselage air flow, but it's a good starting place.

The impression I got from the article was the main interest was overall characteristics and wing aerodynamics. The wing of course is mostly unaffected by prop wash. His wing body fairing idea was interesting.



Upper or Side cowl flaps?

This seems to be a reoccurring theme. The oil cooler door does bulge as was mentioned. WWII fast movers had exhaust exits on side of fuselage. Hummm, I say no to full updraft cooling, as some where kidding about, but what about an upper auxiliary cowl flap?

Ross mentioned ambient pressure fwd of windscreen by a foot? It seemed like a lot was going on in the CFD plots, but some where on the top of the cowl I'm sure a reasonable pressure gradient can be found to locate the cowl flap. It's changing very fast, so flight test would be in order, to get the ideal location. Will that location be practical?

If you use a sealed plenum you could locate the flap where you like in the upper cowl. Room for a door mechanism would be limited and a challenge may be. If the ideal location is near and fwd of the firewall or over the accessory area of the engine, behind the upper plenum in the low pressure area, all the better.

The late Tony Bingelis showed some variations on the upper cowl flaps in his book's. If you introduce air out the cowl top into to slip-stream, it will add drag. This idea may be more for the hot climate folks, than a speed secret? The lower louvers idea Yukon mentioned is easier than an upper cowl flap, but the nice thing about an upper flap, on the ground after shut down, you can open the chimney during cool down. The cowl (and engine) cook after shut down.

May be the side air exits are best? The Thorp T-18 had side cowl out lets? Hummm noting new under the sun?
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Last edited by gmcjetpilot : 08-23-2007 at 07:24 PM.
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  #77  
Old 08-23-2007, 09:20 PM
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I sprung many years back and purchased LOFTSMAN/ CMARC/ POSTMARC to run my own CFD plots. Not cheap but fascinating. Not sure if Peter Garrison still sells this. There is probably something better/ cheaper these days.

I have side exits with entry ramps feeding them. These were highly effective to solve initial cooling problems with the Subie. I noticed no speed degradation with these.

I've tuft tested the stock 6A exit and videoed it in flight. It is a big mess.
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  #78  
Old 08-24-2007, 05:00 AM
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Kahuna Kahuna is offline
 
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Quote:
Originally Posted by gmcjetpilot
There's no doubt "Van The Man" has thought about almost everything under the sun, coming up with his combo (the total package), efficient, light, easy to build & maintain, in stock per plans config.
Boy do I disagree with this. There are MANY things he has not spent the time to consider and there are thousands of these flying with incredible mods that Vans has neither contemplated, nor implemented to improve his design. Van brought a basic design to the table which is a tremendous platform to improve upon. He is spending little time doing that. Good on all you guys who are making it better.
Best,
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  #79  
Old 08-24-2007, 06:38 AM
David-aviator David-aviator is offline
 
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Quote:
Originally Posted by Kahuna
Boy do I disagree with this. There are MANY things he has not spent the time to consider and there are thousands of these flying with incredible mods that Vans has neither contemplated, nor implemented to improve his design. Van brought a basic design to the table which is a tremendous platform to improve upon. He is spending little time doing that. Good on all you guys who are making it better.
Best,
Making it better must mean improved cooling and more speed.

Better cooling is good. More speed may not be. These machines have definite structural limitations and to push the speed envelope beyond what has been flight tested certainly advances the risk meter.

For sure these airplanes will come apart in smooth air long before Mach one. In turbulence or under load, sooner yet. Just how far that break up point is from the design limits is totally unknown. Cruising at 220 knots may not be a good idea at all. We know a quick stick movement can break a wing as is. If one needs to go that much faster, there are plenty of airplanes designed to do it.

...just disagreeing a little in the other direction.
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  #80  
Old 08-24-2007, 12:36 PM
doneil doneil is offline
 
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Default CFD Plots on 6A

Ross

You mentioned "CFD plots on a 6A at 0 alpha".

Can you tell me if this information is available in the internet and where?

Several years ago I think I remember a picture or a drawing of the high and low pressure areas on the 6A in Kit Planes or Sport Aviation or maybe the RVator. I have spent quiet a bit of time looking for it and have not been able to find it again.

Do you or anyone else know about this? Or maybe I just dreamed it up?

Thanks

David Roberts
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