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  #41  
Old 08-20-2007, 01:00 PM
rv969wf's Avatar
rv969wf rv969wf is offline
 
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Location: Beaver, OK
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Default Yep

Quote:
Quote:
Originally Posted by RV8RIVETER
I am thinking along the same lines as what you have done, but mine will be rounder and extend a bit farther back to incorporate exhaust pumping.

Have you tried anything like that?

This is a mock up of one extension that I tried and inside of the extension is a venturi shaped like the inside of the throat of a carb. I kept the exhaust shortened up and let the exhaust exit at the critical point prior to the venturi several inches forward of the outlet to help pull a vacuum/augment the lower cowl. Results were good as far as helping with lowering CHT?s as the manometer test showed it was working, but I could not stand the vibration, noise and the extreme heat on the floorboard. The exhaust was so hot that I couldn?t even put my feet on the floor and I was afraid of melting the bottom of the plane. I could?ve put a stainless barrier with a heat insulator sandwiched on the bottom of the plane, but like I said I could not put up with the noise so I went back to a shorter extension and put a turndown on the exhaust. I did see some improvement with cooling, but not as much as I thought. I?ll leave this mod to the RENO guys or the racers that don?t mind hot feet and a lot of noise.

The last pic is my final outlet shape and size, approximately 8" aft of the firewall with the exhaust right at the edge. Not the best design in the world but it's quiet and very pleasant with no heat on the floor.

The exhaust diameter is 3" to give anyone an idea of the outlet size.





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RV-6 IO360A1B6 C/S Hartz 200HP ?
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Race car engine builder/Machinist/Fabricator 1982--present.

Last edited by rv969wf : 08-20-2007 at 01:15 PM. Reason: added pic
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  #42  
Old 08-20-2007, 01:12 PM
Yukon Yukon is offline
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Quote:
Originally Posted by dan
I was under the impression that most EFISs integrate IAS/OAT/Groundspeed/GPS track to calculate TAS & winds aloft. Some of those calculators that don't have GPS track available used to have you plug in winds aloft. Guess not? Do they just use IAS+OAT? Either way it's not as reliable (imho) as a 3-way GPS groundspeed vector calc. Especially for this "top speed" stuff.
TAS=IAS corrected for installation error, temp and pressure. Accurate TAS is a necessity before GPS groundspeed and track info can be incorporated to derive winds, not the other way around.

If David has confirmed the accuracy of his computed TAS with a 4 way ground speed check, then it is what it is. I just hope I live long enough to hear the alternative community come to grips with the reality of the speed and effciency penalty these engines are displaying. I think David gets it.
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  #43  
Old 08-20-2007, 02:35 PM
Tom Martin Tom Martin is offline
 
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On my blue HRII I had made a number of cowling exit changes to smooth the airflow and when incorporated with smooth inlets I did get a minor increase in speed but more importantly a cooler running engine.
I then tried an exhaust augumentation tube on the plane. It was about 12" long with the same outlet area and shape as the cowling air exit. The exhaust pipes were cut so that they went straight into this tube, as did all the cooling air. The size and length of the tube corresponded with some of the work done 50 years ago by the US military.
Results
1. The sound was really cool on the outside of the airplane and deafening on the inside.
2. The engine ran hotter
3. There was no increase in speed.
4. I melted the plastic grommet off my centre mounted com antennae!

The tube is in my cupboard with some of the other failed experiments.
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  #44  
Old 08-20-2007, 03:09 PM
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rv6ejguy rv6ejguy is offline
 
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Quote:
Originally Posted by Yukon
I just hope I live long enough to hear the alternative community come to grips with the reality of the speed and effciency penalty these engines are displaying. I think David gets it.
Air cooled engines have few options to converge cooling airflow efficiently unlike a properly ducted coolant radiator. My experiments with a cowl flap showed a solid 5 knot gain and this is with a crude setup. With a separate duct and proper exit and flap, theory suggests we might see as much as 11 knots. Clearly reducing unneeded cooling air mass flow in cruise via cowl flaps must add some speed- how much depends on the efficiency of the design.

Archival research and modern day flight reports on the ME109 and Spitfire shown a speed difference of between 18 and 29 mph with radiator flaps open vs closed in WOT speeds. Much of the speed increases found on the Reno racing P51s like Voodoo, Strega and Dago Red have involved revised duct shapes, exit designs and internal diffusers so there are large drag reductions possible with optimized setups.

Eggenfellner is releasing a new cowling design with separate rad plenums to address the real or perceived cooling problems experienced by some of his clients. A step in the right direction for cooling but exit control probably can still be improved considerably.
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  #45  
Old 08-20-2007, 03:50 PM
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gmcjetpilot gmcjetpilot is offline
 
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Default Failed experiments are knowledge & Carb Jets...

Quote:
Originally Posted by Tom Martin
Results
1. The sound was really cool on the outside of the airplane and deafening on the inside.
2. The engine ran hotter
3. There was no increase in speed.
4. I melted the plastic grommet off my centre mounted com antennae!

The tube is in my cupboard with some of the other failed experiments.
Boy is this a great thread thanks to all of the above. Thanks for the info. I was thinking of doing something like this. My old 1958 piper Apache had augmentor tubes and they do sound awesome to people on the ground.

Quote:
Originally Posted by Bob Axsom
I installed the rich mod kit to the carburetor also back when I was fighting a timing problem in the initial test phase. The customer support fellow told me they tried to get van to go with that version initially. He said that Van later changed and the rich carb version is now their O-360-A1A configuration. That no doubt effects a lower temp in my plane as well. Bob Axsom
Quote:
Originally Posted by Bob Martin
My setup is very typical RV-6 C/S 0-360 A1A from Vans circa 1994-95 with the M4-5 10-3878 as it came from Vans. I bought the enrichment kit A666-660 from precision and installed it. The kit lowered the chts about 25 degrees. but still too hot at 425. I then drilled the main jet out just last nite and lowered the chts another 25 degrees to 400. needless to say, I'm very happy.
Don't bother getting the 666-660* main jet; save your money ($292.91) and just drill the original jet, usually 3 drill sizes up from stock size. (As you saw the A666-660* still needed to be drilled. Just drill the one you have. You can go one or two drill #'s at a time if you want. I have the O-360-A1A and went thru this and need three drill #'s larger jet. Precision Airmotive customer support are the ones that told me not to bother with the A666 because it would still be lean. The A666* kit was for Mooney's that ran lean, offered as an optional service bulletin. RV's have better free flowing air box, filter, exhaust and fast speed means more pressure behind the induction, so RV's run lean (O320 or O360). There's no stock jet that really works perfect.

Bob Martin, I am glad your CHT's are down, but do you know the "acid test" for main jet sizing? Go to 8000 ft, WOT, Full rich, stabilize, note EGT's, lean slowly until first cyl peaks and note that EGT. The delta rich to peak (ROP) should be about +150F. Less means you are lean. You don't want to be over rich either. If CHT's are high it can be something else, often baffle gap on jug #2 and #3.

Some RV's are so lean, EGT drops almost immediately when leaning, with almost no EGT rise, meaning they are running near peak EGT all the time. It's really bad on takeoff at full power. Of course the lean test is done at 75% pwr or less. I would not use CHT as the only measure of main jet correctness. (What CHT is high, it could be baffle gap?) A second test is on the ground. Run up to say 1,200rpm and lean slowly till the engine dies. You should see 50-100 rpm rise before the engine rpm starts to drop off and shut down. Also PEAK power is made at about 160-170 ROP, so not only will a proper main jet help temps it makes more power.

Drilling the jet (a little) will not increase overall fuel burn, since you usually are not at 100% power; as long as you pull the throttle back and lean as you normally do, fuel burn is not really affected by the main jet, unless you fly WOT & full rich at sea level all the time.

BACK TO COWL EXITS.............

*Service bulletin M20-98 for Carburetor, Marvel-Schebler, done at discretion, issued 7/24/62 for M20,M20A, M20C/F (62-67)
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Last edited by gmcjetpilot : 08-20-2007 at 04:54 PM.
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  #46  
Old 08-20-2007, 04:07 PM
David-aviator David-aviator is offline
 
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Default Bell shaped exhaust plenum

Alan Judy, I am mesmorized by your bell shaped exhaust plenum.

At present I have the cowl upside down on the work bench ready to carve/shape some urethanen foam for a new exhaust outlet and incorporate a couple cowl flaps. That bell shaped figure you have - is it designed to speed up air flow exiting the cowl? Is there a science to it, or did you just make it look pretty? Would you do it again?
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  #47  
Old 08-20-2007, 04:53 PM
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Bob Martin Bob Martin is offline
 
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Default

Quote:
Originally Posted by gmcjetpilot
Don't bother getting the A666-660 main jet; save your money and just drill the original jet, usually 3 drill sizes up from stock size. (As you saw the A666 still needed to be drilled.) You can go one or two drill #'s at a time if you want. I have the O-360-A1A and went thru this. Precision Airmotive customer support are the ones that told me not to bother with the A666 because it would still be lean. The A666 kit was for Mooneys that run lean, offered as a service letter. RV's have better free flowing air box, filter, exhaust and fast speed means more pressure behind the induction, so RV's run lean (O320 or O360). There's no stock jet that really works perfect.

Bob Martin, do you know the "acid test" for full rich mixture (main jet sizing)? Go to 8000 ft, WOT, Full rich, note EGT's, lean until first cyl peaks and note that EGT. The delta rich to peak (ROP) should be about +150F. Less means you are lean. Some RV's are so bad EGT drops almost immediately when leaning, with almost no EGT rise, meaning they are running near peak EGT all the time. It's worse on takeoff at full power. Of course the lean test is done at 75% pwr or less. I would not use CHT as a measure of main jet correctness. A second test is on the ground. Run up to say 1,200rpm and lean slowly till the engine dies. You should see 50-100 rpm rise before the engine shuts down.
George,
Thanks for the info.
I did pass the LEAN test with flying colors. and Precision said if I passed the test, then look at baffling! I had to ask about the kit, then they said it would help. They didn't say anything further.
There is a lot of info out there on this subject, but not in one place, or not written either.
The Mooney Kit, actually has almost the same size main jet as the 10-3878.
there is restriction bushing that installs in the nozzle vent channel that enrichens the mixture, so I got the first cooling effect with very little nozzle change, maybe .0001. So I think the kit was worthwhile as it did supply me with a second main jet if the drilling was to get weird for some reason.

I'm actually kinda following AVWeb's John Deakin's articles Pelican's Perch #63, Where should I run my engine.
Under The Takeoff:
"Normal climb CHT in a well baffled normally aspirated engine is around 330F at full power and sea level, at any decent climb airspeed. CHT might be higher if you insist on low climb airspeeds. If you see higher CHT's on your engine monitor, YOUR FUEL FLOW IS TOO LOW."

Also I spoke with Bart Labonde at Oskhosh and he told me he use to drill all the 10-3878 carbs on the 0-360's until he started using the richer 10-4164-1.
He suggested drilling about .0003 at a time until it was rich enough.

This thread started as a cooling issue and I thought this information was important to the topic, but probably better suited to a new thread.
I agree with your comment that there is no stock jet that works perfect!
Why did I have to figure this out?? I have never seem this in print before you said it. This is VERY important as I believe many RV guys are running hot and don't know this information. I'm just trying to get it out there.
George, thanks again for your input, I always learn something from your posts.
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  #48  
Old 08-20-2007, 05:23 PM
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rv969wf rv969wf is offline
 
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Default Hmmm, good question

Quote:
Quote:
Originally Posted by David-aviator
Alan Judy, I am mesmorized by your bell shaped exhaust plenum.

That bell shaped figure you have - is it designed to speed up air flow exiting the cowl? Is there a science to it, or did you just make it look pretty? Would you do it again?
First off I'm not an engineer, just a tinkerer, kinda trial and error and see if something works or not.
About the Bell shape outlet or whatever we want to call it. I played around with different shapes, made out of aluminum and taped it to the cowl/plane with tape, then I'd go fly and take notes. In another thread I mentioned about using oil to see where it went to see if it turned back into the cowl outlet or stayed aft. What I found with my -6 is the slight bell shape seemed to help divert the air downward and to the sides at the lip/edge. I know this doesn't sound good at keeping the exit air attached to the bottom of the plane or getting the cowl outlet air mixed smoothly with the air stream. What I found was a slightly stronger pull on the lower cowl pressure but not much and it seemed to break the air from trying to reverse at the edges and not allow the air to travel back inside the cowl.
Think of it as your flaps, when you drop them down, they divert air. I did the same thing with the outlet and probably created some drag. I could not measure any speed loss or gain, but I?m guessing for maximum speed a straight outlet is probably best. I finally got tired of trying this and that and just left it the way it is. I also don't know if the lower plenum that I made that wraps around the entire engine had anything to do with this or not. I personally like the looks of John Hufts RV-8 cowl outlet the best. It is very short in height, with an extension and it's straight as a 2x4. John was trying to keep the air up against the streamline/belly of the plane and he did a much better job then I did and his airplane if way fast, he won the Oshkosh Air Venture race this year. I've got an area about 1 1/2ft aft of the cowl that is clean, meaning no exhaust stain, then from 1 1/2ft and back the exhaust stain is attached with a very smooth pattern looking slightly different than a rectangle cowl outlet. That 1 1/2ft area is right under your feet and if the exhaust is facing straight back, it?ll drive you nuts and yes I flew like that for awhile and got tired of it. If you ever get a chance to look at Dave Anders cowl outlet do so, the last time I saw it, it was half moon shaped also, but was straight if I remember. I stayed with the half round design to match the round inlets at the front of the cowl. I could have probably seen better gains with a different design, but it seems to be working very well and I'm running cool (330F range CHT's) this time of year in Oklahoma in 105F air. I wasn?t looking for a huge speed gain, but mostly was working with balancing temps year round. Hope this helps.
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Also Fly North American NAVIONs
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Last edited by rv969wf : 08-20-2007 at 10:52 PM. Reason: oops error, ok I'm a blonde....LOL
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  #49  
Old 08-20-2007, 06:18 PM
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kevinh kevinh is offline
 
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Gerry was kind enough to send me some photos of this mod. I too will try this out on my airplane (looks like and easy thing to do a quick proof of concept on).

Here's the photos: http://flickr.com/photos/funkym0nkey/tags/rvcoolingmod/

Any comments? I won't be able to try this for about four weeks (out of the country and the RV will be sitting in a hangar alone)

Quote:
Originally Posted by Gerald Clabots
On my 7A (TMX O-360 FP) I would see 425-430 on #4 during climb out, I would lower the nose and reduce power to get the CHT down, Oil temps are not a problem other than to cold using Vans standard oil cooler, Have blocked off part of the oil cooler. CHT's were not a problem in curise.
I am presently experimenting with a mod I recently made, Seems to be working as I can now climb out with full power and see 405-410 on #4 with no need to reduce power or lower the nose to increase the speed.
This is what I did.
Took the bottom plate that sandwiches the lower cowl behind the nose gear rod off and made a new one that flares out and then back about 3 inches back of the firewall. I left 1/4 to 3/8 inch gap between each exhaust pipe, them riveted on a vertical .032 piece of alumn. on each outside edge to within 1/4 inch of the bottom of the fuselage from the rear most part of the new piece to the rear lip of the lower cowl.
Not hard to do and no need to modify anything on the lower cowl. You can easily take it off and put the original piece back on.
If any of you try this please let me kown what your results are.
Only had a chance to do about 3 flights with it so far.

N742GC 7A 65 hours.
Gerry Clabots
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  #50  
Old 08-21-2007, 11:17 AM
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Nuisance Nuisance is offline
 
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Default cowl flaps

Quote:
Originally Posted by Tom Martin
This is a very timely thread. Over the last six years I have done a lot of work on engine cooling with a couple of different rockets. Both had full metal plenums. I have done a lot of work on clean up the outlet air and also the inlet area. Almost all my cooling and speed gains have come from the smoothing of the inlet air. Having said that when you get the inlets working better it is then time to close down the outlets.
On my current rocket I have closed the outlet down to a slightly smaller area than the inlets and my engine runs cool at cruise, anywhere from 330 to 360 depending on power settings and outside air temps.
Last week, as a continuation of my experiments, I installed a cowl flap. My hope was that it would increase speed and help with balancing engine temperatures this winter. The cowling is not cut, the flap is inside the cowling, hinged forward and pulls up to the firewall, between the exhaust pipes. It takes a good pull to close it.
I have had three flights with the plane and I am perplexed to say the least. The system is helping to raise the engine temps but it is not helping with speed and infact may be reducing speed. The speed changes are very small and I have yet to quatify them but here is what is definately happening and I could use some input.
In level trimmed flight when I pull the cowl flap closed, the nose goes down in a very significant and repeatable way. When I trim for level flight in the flap closed condtion and I open the flap the airplane starts to climb.
My question is; Is this a drag situation in that closing the flap in some way increases drag, or is it simply that the airflow has in some way trimmed the plane differently? It is very hard to get accurate airspeed readings in trimmed before and after closing the flaps as it takes a few minutes to retrim and get stable again. I certainly intent on getting some accurate three leg gps data and also to fly beside another aircraft but the trim issue certainly surprised me and the results, at this stage, seem to be contrary to the common believe that a cowl flap should increase speed due to lower cowling airflow. Inputs are most welcome!!


Hi Tom and all

I am just back from a trip and getting caught up.

First, as a data point, on a C-180 I worked on speeding up in the late '90s, full open to full close (there are actuall 4 positions) made a 5 knot difference in speed.

I will take some pictures this afternoon of my 185 cowl flaps to show you, but basically there is no attempt to streamline them in the open position, but in the closed position they follow the contour of the cowl.

I think your implementation failed because you simply created a dead area when the flap was closed. Where there was airflow, now there is none, and the exterior shape remained the same. This created a large area of turbulence.

I will take a couple of pictures of the 8 to illustrate also, but I am reminded most of Fred Moreno's observation, that cooling drag is the loss of momentum of the exit air compared to the intake air. So if we can take advantage of the expansion due to heating, and create a nozzle at the exit to speed up the air, we can perhaps reduce the loss.

More later, John
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