---------------------------------------------------------- TeamGrumman-List Digest Archive --- Total Messages Posted Wed 08/13/03: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 12:01 PM - Cowling Update 6.0 (Aucountry@aol.com) 2. 01:02 PM - Re: Cowling Update 6.0 (bob milligan) 3. 09:50 PM - Re: Cowling Update 6.0 (Aucountry@aol.com) ________________________________ Message 1 _____________________________________ Time: 12:01:58 PM PST US From: Aucountry@aol.com Subject: TeamGrumman-List: Cowling Update 6.0 --> TeamGrumman-List message posted by: Aucountry@aol.com Finally. It seemed like years, well, it has been 3 yrs., just to get to the first flight. First impression. The cowling looks so dramatically different from the pilots seat. I can't believe I've never sat in the pilot seat and looked at the cowling from that perspective. After engine start, I let the oil temp come up about 130, which didn't take long since the ambient temp was 108, and then did a quick mag check at 1500 just to see if everything was ok. It's been a while since this engine was run. I watched the EGTs and CHTs pretty closely. All pretty even and not bad. Taxi to the departure end of runway 24. Engine run up, watch EGTs during mag check, 30 degree rise for each one, Checked for which cylinder was going to lean-peak first, #3 as if you didn't guess already, mixture to full rich, request high speed taxi to the other end, cleared, go. The wind was 15-19 at 210, so I had a pretty decent cross wind. I got airborne to about 5 feet without much effort. #3 CHT went to 400, all others around 375, EGTs were pretty constant. I love that JPI. Taxi back to the hanger and check for any heat damage or chaffing that might be a problem. None. Engine start, back to 24, runup, takeoff for one run around the pattern. I climbed at a pretty shallow rate to keep the airflow high through the cowling. CHTs on #1, #2, and #4 were pretty constant at about 390-410. CHT on #3 went to 450 so I pulled the power back and let it cool on down wind. #3 actually cooled faster than the rest on down wind and on final all were pretty even. Back to the hanger for a look. What I found was #3 has a missing cooling fin on #3 next to the plug (going down the space between the valves). #3 also shows some evidence of being run hot in the past. I filled the 1/2 diameter gap where the fin is missing with a small piece of foam to direct more air through the remaining fins, spaced out the rear baffle about 1/16 inch with washers to try and move more air through the back side of the head. Then flew again. The result, temps on #3 still went to 450 but took longer and I was able to level off at 4500 feet and run flat out and lean some. When #3 got to 450, I pulled the power back, went full rich (interestingly, CHTs are not affected that much by mixture setting. That amount of mass takes a long time to cool when hot). The high temps on #3 are a problem with all Tigers I've looked at. This isn't necessarily a bad thing. What I mean is, I have something I can work with. The other cylinder head temps never went above 408. AND, they were all within a few degrees of each other. (403, Plus or minus 5 degrees.) This tells me that I need to look at just #3. On the way back, I pushed the nose over, increased indicated airspeed to 160 kts, and watched the reflection in the cowling to look for any bulging or deflection in the fiberglass. NONE. That's a good thing. Dave is making up a (bagged) carbon fiber upper cowling and we are going to weigh the two and see what the difference is. Stay tuned. Gary www.AuCountry.com Home of "Team Grumman" TeamGrumman-List@matronics.com http://www.matronics.com/subscribe ________________________________ Message 2 _____________________________________ Time: 01:02:10 PM PST US Subject: Re: TeamGrumman-List: Cowling Update 6.0 From: bob milligan --> TeamGrumman-List message posted by: bob milligan on 8/13/03 12:01 PM, Aucountry@aol.com at Aucountry@aol.com wrote: > --> TeamGrumman-List message posted by: Aucountry@aol.com > > Finally. It seemed like years, well, it has been 3 yrs., just to get to the > first flight. > > First impression. The cowling looks so dramatically different from the > pilots seat. I can't believe I've never sat in the pilot seat and looked at > the > cowling from that perspective. > > After engine start, I let the oil temp come up about 130, which didn't take > long since the ambient temp was 108, and then did a quick mag check at 1500 > just to see if everything was ok. It's been a while since this engine was > run. > > > I watched the EGTs and CHTs pretty closely. All pretty even and not bad. > Taxi to the departure end of runway 24. Engine run up, watch EGTs during mag > check, 30 degree rise for each one, Checked for which cylinder was going to > lean-peak first, #3 as if you didn't guess already, mixture to full rich, > request high speed taxi to the other end, cleared, go. The wind was 15-19 at > 210, > so I had a pretty decent cross wind. I got airborne to about 5 feet without > much effort. #3 CHT went to 400, all others around 375, EGTs were pretty > constant. I love that JPI. > > Taxi back to the hanger and check for any heat damage or chaffing that might > be a problem. None. > > Engine start, back to 24, runup, takeoff for one run around the pattern. I > climbed at a pretty shallow rate to keep the airflow high through the cowling. > CHTs on #1, #2, and #4 were pretty constant at about 390-410. CHT on #3 > went to 450 so I pulled the power back and let it cool on down wind. #3 > actually cooled faster than the rest on down wind and on final all were pretty > even. > > Back to the hanger for a look. What I found was #3 has a missing cooling > fin on #3 next to the plug (going down the space between the valves). #3 > also > shows some evidence of being run hot in the past. > > I filled the 1/2 diameter gap where the fin is missing with a small piece of > foam to direct more air through the remaining fins, spaced out the rear baffle > about 1/16 inch with washers to try and move more air through the back side > of the head. Then flew again. > > The result, temps on #3 still went to 450 but took longer and I was able to > level off at 4500 feet and run flat out and lean some. When #3 got to 450, I > pulled the power back, went full rich (interestingly, CHTs are not affected > that much by mixture setting. That amount of mass takes a long time to cool > when hot). > > The high temps on #3 are a problem with all Tigers I've looked at. This > isn't necessarily a bad thing. What I mean is, I have something I can work > with. The other cylinder head temps never went above 408. AND, they were > all > within a few degrees of each other. (403, Plus or minus 5 degrees.) This > tells me that I need to look at just #3. > > On the way back, I pushed the nose over, increased indicated airspeed to 160 > kts, and watched the reflection in the cowling to look for any bulging or > deflection in the fiberglass. NONE. That's a good thing. > > Dave is making up a (bagged) carbon fiber upper cowling and we are going to > weigh the two and see what the difference is. > > Stay tuned. > > > Gary > www.AuCountry.com > > Home of "Team Grumman" > TeamGrumman-List@matronics.com > > > > > > Nice work, Gary. You obviously have R&D experience. Have you considered a plenum on top of the cylinders to side-step the baffling problem? (no pun) Bob Milligan ________________________________ Message 3 _____________________________________ Time: 09:50:01 PM PST US From: Aucountry@aol.com Subject: Re: TeamGrumman-List: Cowling Update 6.0 --> TeamGrumman-List message posted by: Aucountry@aol.com In a message dated 08/13/03 01:06:05 PM, flyer.bob@verizon.net writes: > Have you considered a plenum on top of the cylinders to side-step the > baffling problem? (no pun) > Every time I hear about plenums I wonder why in the hell people think dedicated plenums work better than letting the top cowling act as the top of a plenum. All they do is add weight and complexity and prevent you from seeing bird nests on top of the engine. I could put a 10 Million cubic foot a minute blower (pumping 100+ degree air) on top of the engine and it would, more than likely, have no effect on the ability of the air to cool #3. Since all the other cylinders remained below 410 and oil temp was under 210 (with an outside air temp of 108 on the ground and 97 in the air at 4500 feet), I am confident there is sufficient air available to cool the cylinders. The problem is not the sealing of the incoming air to capture whatever air comes in and use it for cooling. The problem is the basic shape of the metal baffle where it wraps around the bottom of the cylinder head and how it directs the available flow. On a Tiger (could be the same for a Cheetah, it's just been a long time since I investigated a cooling problem on a Cheetah), take a good close look at the #3 rear baffle. You'll find, under the intake for the carb, there is a roughly 2 inch by 2 inch by 1/2 inch area that allows for airflow aound a portion of the cylinder head where the fin depth is about 1/16 inch. This area is also on the front face of #2. However, #2 gets a direct shot of incoming air. This is not a great design here. I'm using RV-6/8 baffles (they fit a million times better by-the-way) and this small manifold, to channel air around this narrow spot, does not exist. I changed the #2 baffle to channel a bit of air around to the bottom of the cylinder. I thought that the shape of the rear baffle from the RV-6/8, which is entirely different from the Grumman might allow enough air around the back that it wouldn't need to be modified. I was wrong. The change is almost done. I hope to have this done by tomorrow. I've got pressure rakes and static and total pressure probes coming on Friday. Does anyone know if pressure measurements have ever been done on a stock Tiger? Stay tuned. Gary www.AuCountry.com Home of "Team Grumman" TeamGrumman-List@matronics.com http://www.matronics.com/subscribe