Nose Cowl Inlet Discoveries

 I'm still trying to solve my high cylinder head temperature problem.  Cylinder cooling depends on the size of the inlet openings, to get good inlet pressure.  Then the baffles have to assure the air coming in goes through the cooling fins, with no leaks.  The rate of airflow across the cylinders depends on the outlet size to create a pressure drop from above the cylinders to below them.

I started with the assumption that the Taylorcraft nose cowl openings were obviously larger than the old cowl so it should work fine.  I've worn myself out looking for leaks and playing with the outlet opening and skirt.  I've made some improvements but never solved the problem.

The other day I had the bright idea that maybe the grills on the Taylorcraft cowl were blocking the airflow.  After all the Taylorcraft used a 65 HP motor and mine's 85 HP.  I decided to remove them and see if it improves the flow, when the airport reopens in November.  This required removing the nose cowl to get them out.

While I was removing the nose cowl I decided to position the old nose cowl so I could visually compare them (I don't throw things away until I'm sure I won't ever want them).  I think the current term is OMG.  Houston, we have a problem.  The useful area of the Taylorcraft openings is clearly smaller than the old cowl inlets.

Time to lay this out in CAD to learn some truth.

I used the prop opening to align the 2 cowls in TurboCAD.

The Yellow line is the old Inlet.  The one thing you see is that it is positioned to focus air on the cylinder head.

The Magenta line is the top of the front baffle.  The best airflow is above that line.  Most of the Taylorcraft inlet is below that line.

Yes the grill is blocking airflow to my cylinders.

Here are the numbers:

Old  Inlet                                  T'craft Inlet

33.9 sq in                                  58.6 sq in without Grill  (much bigger)

                                                  39.2 sq in with Grill       ( not much bigger)

Above Line

26.1 sq in                                   23.6 sq in without Grill (10% smaller)

                                                   15.5 sq in with Grill      (41% smaller) OUCH!!!

I've removed the grills and redone the skirt without the lip.

They're ahead of schedule on the runway so I may wait to recover the fuselage until after the runway is done so I can see if this is the answer.

They have the base gravel down and this runway really looks good.

The first picture is looking SW and the second looking NE.

Very flat, slightly downhill to the NE

July 19 Added Lip to Cowl Skirt - July 22 Last Flight From Gordonsville's Old Runway

 

My last experiment, for now, was to add a small curved lip to the bottom of the shallow cowl skirt and reinstall it in place of the steep one.  By the time I got done, on a very hot, humid evening, it was too late to go flying.  I hammered the curve using a plastic hammer and dolly while holding the skirt so it was curved, like when it is installed.  I only did about 20" in the middle where the skirt is perpendicular to the airflow under the cowl.

It came out nice but made the temps hotter so I was back on the ground in 15 minutes.

They're rebuilding our runway, last paved around 1955, to get rid of the cracks, widen it from 40 feet to 50 feet, get rid of the hump near the north end and the dip near the south end.

Looking southwest from the displaced threshold for runway 23.  There's a low spot near the south end.  From here the runway goes downhill, behind me to the northeast

This view is from the north end looking back uphill to the displaced threshold

Another nice warm evening flying.  This was the first change I made which made the temperatures worse, so I learned something from it.

This view is from the end of runway 5 looking back to the northeast.  You can see the dip near this end.  The runway will be flat but still run downhill when they are done.  This end can't be lowered because it's at the property line and the adjoining land owner won't give permission to cut into their property.  The crack will be gone and you'll be able to see if someone or something is on the runway when you start your roll to the south.  Their plan is to reopen it in November, about Thanksgiving (120 days).

While it's closed I plane to recover the fuselage and tail which I covered with cotton it 1994, 28 years ago.  Time goes by quick

July 13 - Reinstalled Steeper Cowl Outlet Baffle

I removed the shallow outlet skirt and reinstalled the steeper one.

It made on change but I had a nice warm evening flight for about 1/2 hour. 

The setting sun was lighting up the clouds east of us nicely.

It was pretty when the sun finally hid behind the clouds over the Blue Ridge, to the west.

I have one more experiment to try before they close the runway.

July 11 - More Baffle Changes and A Nice Evening Flight

 I keep looking for some reason that I'm getting high Cylinder Head and Oil Temperatures. My belief is that there are 3 most likely causes.  The first is that I have a leak somewhere from the high pressure above the cylinders to the lower pressure below.  The second is a poorly designed outlet. The last is that somehow changing to the Taylorcraft nose bowl is causing low inlet pressure.  The last doesn't seem very likely since there were a lot of Taylorcrafts made using this nose bowl.  I decided to remove the nose bowl and reinstall a baffle I had made to force more flow below the crank case for better oil cooling.

When I removed the nose bowl it looked like my front seals weren't rubbing as tightly against the nose bowl as well as I would like, especially on the left cylinders, there was a gap between the 2 pieces of felt.

I remade these to cover the gap and to allow more felt to lay against the nose bowl for a better seal.

On the right side I moved the felt away from the baffle a little so there would be more of it lying against the nose bowl on this side as well.

The main plan was to reinstall the baffle below the crank shaft so more air would flow under the crank case to cool the oil better.

I had originally made this baffle so the felt sealed against the case, forcing all the air down. I decided to remove some of the felt to allow a little air to go over the nose of the crankcase.

The baffle is back under the crankshaft.

There is now a small gap to allow some air to move by it on the right (arrow) and left sides of the case.

Another beautiful warm evening for flying.

An algae clogged lake south of the airport.

Looking north the airport is to the right of the water tower and left of the left brace wire.

Looking south the airport is in front of the wing strut.

It was a nice flight but my efforts had no affect on the temperatures.  I haven't given up but I'm running out of time before they tear up the runway to rebuild it.

Celebrating Independence Day Flying

We finally had some more nice weather July 3rd.  I decided to reinstall the oil sump cooling baffle I had removed, before I went flying.

I annealed the area along the 2 sides, so I could form some more curve for a tighter fit to the sump.

It was a beautiful clear, calm evening. By the time I took off it had cooled down to about 80° F.  I only flew about 1/2 hour because the oil temp slowly creeped up close to the Red Line, 210° F.

The lake is Lake Louisa where we live, one street back from the lake.

The Race track is at James Madison's home, Montpelier.

This year's corn maze is in the field ringed with trees.  The corn wasn't tall enough to get good shadows, so it's a little hard to make out.  By the time the corn is tall the runway will be closed for a complete remake.

The next morning, Independence Day, was still calm and clear, and about 10° cooler.  You can see the ripples in our lake from a gentile NE breeze.

It was a perfect morning except right around Gordonsville Airport.  The wind must have been coming slightly across the mountains on the NW side of the airport, because it was turbulent in the pattern.  On the ground the wind was almost straight down runway 5.

Mike in the hangar next to me took some more pictures of my landing.

What you can't see in these pictures is that the approach from the SW is almost clear of any trees.  It's actually a very easy approach and that water tower is a good way from the airport.

Nice 3 point attitude for touchdown on 23.

July 4th evening I got to fly again, ending a short stretch of nice dry weather.

There's a resort, Shenandoah Crossing, a few miles south of the airport.  Looked like they had a good crowd for the holiday.

In the downwind for runway 5, ending 3 flights in 2 days.  A nice way to celebrate Independence Day.  Flying's about as independent as it gets.

I have an idea to try improving the oil cooling for my next flight, more later.

Removed The Oil Sump Baffle

 When I repaired all the old engine baffles I added one in front of the oil sump to help direct cool air around it and to deflect hot air from the cylinders.  The idea came from this baffle one on my Cessna 140.  It also has a Continental C-85.  I assumed they knew what they were doing when they went to all the trouble to make this baffle for the Cessna.

The baffle has a hole in it for the throttle cable but covers the sump.

The big difference in mine and theirs is the nice curved shape of their baffle.  Mine is much flatter and as a result a little wider because I quit working the metal once I had this shape.

My concern was that this flatter baffle was blocking airflow so I removed it and went flying.

A nice evening in the upper 70s, with high clouds, meant a smooth fun flight.  Unfortunately no change in cylinder head temps.  The oil temperature seamed to come up a little quicker so I think I'll finish shaping this baffle to fit the buck I made from the C-140 baffle and reinstall it.

Now that the winds have died down I have some more things to try.