VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #31  
Old 09-08-2009, 01:56 PM
Andy_RR Andy_RR is offline
 
Join Date: Oct 2006
Location: Melbourne, Australia
Posts: 427
Default

Thanks Don - it was indeed the Melmoth that I had in mind.
Reply With Quote
  #32  
Old 09-08-2009, 03:07 PM
rbibb's Avatar
rbibb rbibb is offline
 
Join Date: Jun 2006
Location: Freericksburg, VA
Posts: 624
Default

I believe the factory prototype RV-6 used an updraft cooling system. I did have an annular inlet around the prop (there were no openings in front of the cylinders. Old-timers will remember "old Blue" with this cowling configuration.

Not sure how it worked but it did win the "ugly ducking" award from most observers at the time.

Not sure how it worked and perhaps some of the factory guys can shed some light on this.
Reply With Quote
  #33  
Old 09-08-2009, 04:23 PM
F1Boss's Avatar
F1Boss F1Boss is online now
 
Join Date: Aug 2006
Location: Taylor Texas
Posts: 812
Default outlets

Hey Fellas:

Lancair did a bit of work figuring out where to locate the outlets -- they found the outer edges of the belly had the lowest pressure, so they located the outlets there.

In addition, they used bluff body outlets -- these create low pressure at the outlet lip by using a specific airfoil cut at its lowest pressure point.

Since my side mounted adjustable outlets on the 550 F1 didn't work (very ignorant designer, I think. I see him in the mirror when I shave...), I decided to try the above mentioned outlets in place of the cowl flap doo-hickeys.

By golly, someone out there knows their respective stuff -- it worked!

http://img443.imageshack.us/i/dcp6382.jpg/
http://img171.imageshack.us/i/dcp6385.jpg/

Engine temps are more even, and oil temp is acceptable, tho it could be better. Climb cooling is fine; cruise cooling appears to be OK too. I need to fabricate the interior ramps to smooth the flow (I think) to get better oil cooling.

I notice no speed degradation from the increased flow -- it could be the flow is directed better, both inside and out, but not increased?

The induction air for this engine comes from the upper plenum, and I see exactly ambient pressure -- I expected a bit of ram, but it's not there. The inlets are very small -- about 36 sq in. This could be the cause of the lack of upper plenum pressure? Outlet area is about 42 sq in.

Upper cowl outlets should be shunned -- any fluids or gasses escaping from the infernal combustion device will find their way onto your plexiglas, and you won't be happy. Trust me on this one -- any oil escaping from my outlets attaches itself to the sides of the fuselage, and the H stab..and V fin...in other words, it is not hidden as a bottom outlet would help with, assuming the same leak rate.

Another design fault of such an outlet location (side or upper cowl) is HEAT. It appears that the cooling air (now very hot, thanks to that infernal combustion device)) flows in a nearly laminar manner, and happily transfers its BTUs into the side skins... which are also very happy to transfer their BTUs into the cockpit. Now, this may be a bonus at 15000'MSL, or in winter, but it's no picnic in any temps over about 70F.

So, I added an additional cockpit/pilot cooling air inlet onto the boot cowl:

http://img406.imageshack.us/i/dcp6377.jpg/

Geez that's a lot of air moving thru the airframe... but she'll still give me 200KIAS at 6000' DA/2300RPM easily. My E6b sez that's about 251MPH, but only 14MPG...."speed costs money; how fast ya want to go?" Normal cruise is 175KIAS/11GPH/20MPG which is more reasonable to the wallet.

Next mods will be the ramps on the inside of the outlets, and then an induction air scoop w/filter to get the MP where it should be. The scoop will have to go on the top of the cowl as was done on the Allison powered p40s and P51s, so I'd better make that look right...

Summary? There ain't no free lunch. Cooling drag on these ships is already very low, tho some improvement can be seen with careful modifications. The augmenter idea is probably the best path, but the cockpit noise associated with such a design is a major downside. NACA was able to get a Martin B26 with multi tiered augmenter system to run full power on the ground indefinately, and it actually produced about 120HP of thrust in flight. Of course this system took up the entire aft nacelle, but it was more or less empty to start with. The system was never used on production ships.

NASA tested louvers on a C-421 (I think) -- very draggy. Don't go there.

As for the under-spinner smiley inlet, you can see it in action on a very popular aerobatic stars' biplane - I think Sean is his name -- the cooling capacity is very good: he can hover his plane for what looks like an amazingly long period of time. It's not an updraft system -- nor was Van's -- it's simply another style of inlet.

The CAFE foundation did a lot of cooling work -- best you look at their results for a direction to proceed. Come to think of it, they use a smiley inlet on their Mooney...so I guess it does work! Might also peek at some of the Formula 1 racers at Reno -- extreme air flow control is their holy grail.

Carry on!
Mark
Reply With Quote
  #34  
Old 09-09-2009, 03:38 AM
dhammer's Avatar
dhammer dhammer is offline
 
Join Date: Nov 2007
Location: Keller, TX
Posts: 151
Default Its been done -

A very successful certified design that used updraft cooling was the piston series of the Aero Commander. The exhaust exited up top also through augmenter tubes that assisted in pulling cooling air through the cowl. Take a look at http://www.flugzeuginfo.net/acimages...r_canciani.jpg
Reply With Quote
  #35  
Old 09-09-2009, 06:53 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 9,500
Default

[quote=F1Boss;356904
The induction air for this engine comes from the upper plenum, and I see exactly ambient pressure -- I expected a bit of ram, but it's not there. The inlets are very small -- about 36 sq in. This could be the cause of the lack of upper plenum pressure? Outlet area is about 42 sq in.[/QUOTE]

Mark, got a few photos of those inlets, in particular from the engine side?
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #36  
Old 09-09-2009, 10:52 AM
F1Boss's Avatar
F1Boss F1Boss is online now
 
Join Date: Aug 2006
Location: Taylor Texas
Posts: 812
Default inlets

Hey Dan:

Here ya go -- the upper cowl has ramps molded in as would be done in any installation. I'll get you a shot of those ASAP. There is no room for a plenum -- the intake system fills the upper cowl completely.



Carry on!
Mark
Reply With Quote
  #37  
Old 09-09-2009, 01:43 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 9,500
Default

Mark,
Given the mass flow required to cool the 550 and the small inlet size, they would have to be high velocity inlets. High velocity inlets without optimum internal difusers probably don't net much pressure recovery.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #38  
Old 09-09-2009, 02:13 PM
F1Boss's Avatar
F1Boss F1Boss is online now
 
Join Date: Aug 2006
Location: Taylor Texas
Posts: 812
Default AGREED!

Quote:
Originally Posted by DanH View Post
Mark,
Given the mass flow required to cool the 550 and the small inlet size, they would have to be high velocity inlets. High velocity inlets without optimum internal difusers probably don't net much pressure recovery.
Which is exactly what I have seen on the MP gage. The inner ramps that direct the flow along the inside of the inlets are at the wrong angle (too steep) but the induction air filter is there (dictating the ramp angle), so that's what had to be done. Once I get the induction scoop in place, I can re-set the inner ramps to a shallower angle, and maybe get a bit more pressure in the upper plenum. This will allow smaller, higher velocity outlets...I hope...

It sez experimental, and I'm experimentin'! The only problem is that if I get 'er going another +6KIAS in cruise, Ol' Mel is gonna be on me to put them 12" N numbers on 'er. Ugh.

Carry on!
Mark

Last edited by Mike S : 09-09-2009 at 06:17 PM.
Reply With Quote
  #39  
Old 09-09-2009, 06:01 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 9,500
Default

Quote:
Originally Posted by F1Boss View Post
Once I get the induction scoop in place, I can re-set the inner ramps to a shallower angle, and maybe get a bit more pressure in the upper plenum. This will allow smaller, higher velocity outlets...I hope...
Ya know, there are reasons Mooney used these low velocity, external recovery inlets on the Acclaim.

__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #40  
Old 09-09-2009, 09:21 PM
Bob Axsom Bob Axsom is offline
 
Join Date: Mar 2005
Posts: 5,685
Default Yeah but

I beat the factory Acclaim in the Texoma race last year with my stock inlets on our RV-6A.

Bob Axsom
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 08:14 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.