Baffle Mod - Page 5

dealfair · #41 07-09-2013, 10:02 PM

Quote:

Originally Posted by Toobuilder

As I stated before, my most recent flight started out at 120 degrees on taxi, and was a still very warm 71 degrees at 8500 - yet I had two cylinders under 295 in cruise. Thats a bit too cool for best efficiency.

Michael, what numbers are you wanting to see there for best efficiency??

Toobuilder · #42 07-09-2013, 11:38 PM

Well, it's a heat difference machine, so hotter is better as long as the materials can survive. And I understand that the engine is quite happy at 350-375. So that's my target.

Of course, you don't want a "false" temp reading by choking off portions of the head - you want the right airflow at all points. So that's what is driving the quest for good overall airflow through the system, then choke down the whole thing to regulate the temps. If that makes any sense.

Brantel · #43 07-10-2013, 07:51 AM

Quote:

Originally Posted by DanH

Yep. The lower sections of my aluminum baffles are fully lined, so I don't depend on the aluminum to keep air between fins. The aluminum wraps are not much more than a backup to ensure the fiberglass/silicone wraps stay in place. Best I can tell none has shown any sign of debonding.

This is Loctite 598 (aka Permatex Ultra Black) rolled into ordinary 9 oz plain weave fiberglass between plastic sheets, then cut to size with scissors and stuck to the fins while wet.

Can we see a pic of the top side?

DanH · #44 07-10-2013, 08:53 AM

Quote:

Originally Posted by Brantel

Can we see a pic of the top side?

Not much to see. The wraps stop at the 3 and 9 positions. Wraps on top (say 3 and 9 up to 1 and 11, like the ones Don posted) are kinda low on my experiment list. Next is probably cleaned up cylinder baffle exits and the addition of exit ducts.

MarkW · #45 07-10-2013, 09:21 AM

After seeing the pictures of the Formula One and Dan's fin sealing I think to myself what a great idea and probably worth doing. I then realize that if the aluminum baffle around it doesn't seal to the fin seal then some of the air will be between the seal and the baffle. This would prove to be even less productive on the wrong side of the seal/tape. So I guess I will stick with the old plan rather than having to spend that much effort right now. I have the taper fin ECI cylinders and getting a good seal there will be an effort.

Looked at a Piper last week and could not believe how poorly the baffles were sealed. There was a 3/8" gap all the way around the rear crankcase.
I guess they make up for poor sealing with large inlets and poor speed.

DanH · #46 07-10-2013, 10:01 AM

Quote:

Originally Posted by MarkW

I then realize that if the aluminum baffle around it doesn't seal to the fin seal then some of the air will be between the seal and the baffle. This would prove to be even less productive on the wrong side of the seal/tape

Little bead of silicone eliminates that leak.

MarkW · #47 07-10-2013, 10:58 AM

I was thinking a soft dam of some kind but a bead of silicone would make a perfect and easy soft dam. Thanks.

OLDSAM · #48 07-10-2013, 03:26 PM

While thermodynamics is not my primary area of expertise, and I have yet to purchase, let alone baffle, an engine, one thing that occurs to me as I view the baffles pictured that are adhered to the outer ends of the fins is that the width of the gap between the baffles on the inlet and outlet sides of the cylinder may (or may not) be critical.

The direct contact between the baffle and the fins, keeping all the air in contact with the sides of the fins is certainly the most efficient manner to transfer heat at any given airflow. However, the total airflow is an important factor also, and the subject of this thought.

I suspect that there is an optimum gap width between the baffles, measured along the fins, that will result in the optimum airflow along the fins. As the gap is made wider, thus the length of the fins in contact with the baffle being less, the airflow will increase due to the area of the inlet and outlet being larger, and the pressure drop, or friction loss as it's sometimes called, of the air passing through the passages formed by the baffles and fins being less due to the reduced length of said passages. However, the cooling efficiency at a given airflow will be less due to the larger percentage of unbaffled fin length. At the other end of the spectrum, as the gap gets smaller, the airflow will decrease due to the smaller inlet & outlet, and the increased length of the passage between fins and baffle resulting in a larger pressure drop through the passages at a given flow rate. Somewhere between very wide and very narrow gaps, I would expect to find an optimum dimension of gap width on the inlet (top) side and the outlet or bottom side. The optimum might occur with different widths on the inlet and outlet sides, maybe slightly larger on the intake side. Or vice versa, due to the air expanding on the way through.

'Twould make an interesting development project, if it has not already been researched.

whiskeypapa · #49 07-10-2013, 06:52 PM

Oldsam,
I'll bet some F-1 driver has done the math. I was also thinking that there must be a perfect radius for the inlet and outlet portions of the cylinder wrap. There was a post by Paul Lipps, as I recall that showed how he set his cylinder wraps up.

BTW, Dan - fantastic thread!!!

dealfair · #50 07-10-2013, 08:41 PM

Quote:

Originally Posted by Toobuilder

Well, it's a heat difference machine, so hotter is better as long as the materials can survive. And I understand that the engine is quite happy at 350-375. So that's my target.

Of course, you don't want a "false" temp reading by choking off portions of the head - you want the right airflow at all points. So that's what is driving the quest for good overall airflow through the system, then choke down the whole thing to regulate the temps. If that makes any sense.

Yes, thanks Michael.