Lasar Cowl Closure

[Skates97]

23 hours ago, Buckeyechuck said:

Out of slot as I was starting to remove the top of cowl.  Stopped to take photos. 
 

Thanks for all the ideas. There are some large gaps at the starter. Any closure ideas?  Would this have much effect on air to #4?  

As @takair mentioned baffle seal pop-riveted in works well. We used felt as it was easier to work with and form around the starter/alternator gaps than baffle material.

https://www.aircraftspruce.com/catalog/cspages/felt.php?clickkey=5104

[47U]

On 11/12/2024 at 9:05 AM, Skates97 said:

We used felt as it was easier to work with and form around the starter/alternator gaps than baffle material.

Plus 1 for felt… it just seems right on vintage birds.  

[Andy95W]

Hi @Buckeyechuck.  Hope your annual is going well.

Since you have the cowling off, this would be a good opportunity to take off the top part of the doghouse and look down at the cylinders for holes that can be blocked off.  I found a big area behind #3 around the oil pressure adjustment.  Also check for the intercylinder baffling (and its tightness) below the cylinders.  It’s sheet metal that is between #1&3 and #2&4.

You’ve done nice work with the aluminum tape, but to put this in perspective: the tape is sealing a 1/16” gap that’s about 10” long.  That’s about 5/8” square.  In just the one picture below, you’ve got a 1/2” gap that’s about 5” long- or about 2.5 square inches!

The only way to cool CHTs is to get the air to flow through the cylinder fins.  Any air that isn’t going through the fins isn’t just detracting from the cooling, it’s actually working against you by also decreasing the pressure differential.

It’s a lot of creative work to seal up the air box.  It’s definitely worth it in the end.

Good luck, and good luck with your annual.  Please keep us posted!

[Buckeyechuck]

 

Is this opening normal or should it be sealed?  It is behind the barrel on #4 cylinder. Had to pull the battery box to get this photo. The same opening is behind #3. 

[Andy95W]

Mine isn’t like that. The orange baffle seal material could be extended down to seal in that gap nicely and then secured with a pop rivet at the bottom.

You’ll find some creative solutions to sealing all the holes. Big pain, but it’s worth it in the long run.

Good luck, keep us posted as you continue the progress!

[Buckeyechuck]

Any idea what this tube is for?  It can’t be to cool the battery box. I have the tubes that supply cooling air to the mags but can’t figure this one out.  

[takair]

Do you have air going to the fuel pump?  The E has one where your battery sits. That one might be intended for the pump.

[Andy95W]

That tube is supposed to be connected to the battery box with a rubber hose attached to a fitting.  Your battery box fitting might be missing.

The original idea was to pressurize the battery box in order to ventilate corrosive battery acid fumes out the tube at the bottom drain through another rubber tube to the cowl flap area.  Not so important nowadays with sealed batteries, but should still be connected for cooling.

[Buckeyechuck]

12 hours ago, takair said:

Do you have air going to the fuel pump?  The E has one where your battery sits. That one might be intended for the pump.

Yes, there is a small SCAT tube that comes from a small opening in the front of the lower cowl up to the area between the accessory case and the firewall. 

[Buckeyechuck]

9 hours ago, Andy95W said:

That tube is supposed to be connected to the battery box with a rubber hose attached to a fitting.  Your battery box fitting might be missing.

That makes sense. There is a tube in the side of the box that I’ve assumed was just a vent. Since I am using a sealed battery, should I still connect it, or should I seal off the tube to force that air across the #4 cylinder. 
 

I’ve closed off the gaps at the rear of the doghouse, lower cylinder barrel area, on both sides, and tightened up the front baffling as well. Still finishing up the annual so haven’t determined any benefit yet. 

[Andy95W]

49 minutes ago, Buckeyechuck said:

That makes sense. There is a tube in the side of the box that I’ve assumed was just a vent. Since I am using a sealed battery, should I still connect it, or should I seal off the tube to force that air across the #4 cylinder. 
 

I’ve closed off the gaps at the rear of the doghouse, lower cylinder barrel area, on both sides, and tightened up the front baffling as well. Still finishing up the annual so haven’t determined any benefit yet. 

That’s a lot of not easy work.

Yes, I would connect the hose to the box, and then make sure the bottom hose to the cowl flap area is also connected.  That will keep the air flowing like it should (plus add to battery cooling).

Looking forward to more updates!

[TaildraggerPilot]

On the doghouse: try laying a bead of high temp RTV (orange) between parts, rather than lay tape all over them. If your screws stay put, the RTV will make a great gap seal, and yes, you can pull parts apart with little fanfare. The RTV creates an abstract gasket of sorts, and you should be able to just screw doghouse panels back together using the same RTV “gasket” previously applied. 
 

I wish there was an intake ramp mod, similar to the one available from LASAR for traditional baffle F’s, to make better use of the adjusted intake airflow created by the cowl closure mod.

Edited December 10 by Taildraggerpilot

[1967 427]

12 hours ago, Andy95W said:

That tube is supposed to be connected to the battery box with a rubber hose attached to a fitting.  Your battery box fitting might be missing.

The original idea was to pressurize the battery box in order to ventilate corrosive battery acid fumes out the tube at the bottom drain through another rubber tube to the cowl flap area.  Not so important nowadays with sealed batteries, but should still be connected for cooling.

I agree with Andy about acidic gases, but I suspect the main reason they vent the air box is H2 gas.  Hydrogen gas is a byproduct of a charging battery and a sealed battery according to Google isn’t completely truly sealed.  “While called "sealed," aircraft batteries are not completely sealed in the sense that they have no vents; they are designed to contain the electrolyte and prevent leaks under normal operation, but may have small pressure relief valves that can release gas if the battery becomes overcharged or experiences extreme conditions”.

I remember as a kid the comment that you should always charge a battery in a well ventilated area due to the byproduct of hydrogen gas.  I always thought that was ridiculous, until I actually had a small explosion under the hood of my friend’s car.  I assumed there was a small arc at the battery terminal and the hydrogen under the hood ignited.

 (FYI, my friend didn’t believe me when I told him about the explosion)

[Buckeyechuck]

If you look at the photo, the battery box vent tube comes off the side and goes down about 8” to the pilot footwell part of the firewall.  You can see it just above the white battery cable.  No way it attaches to the tube off the doghouse in that configuration. Something must have been modified over the years. Battery box drain tube routes to left cowl flap opening.   

[Andy95W]

[Buckeyechuck]

2 hours ago, Andy95W said:

Amazing how much difference there is in 2 years of production. 

[Andy95W]

All that junk on the battery box was an external power plug that was added in the 1990s.  It wasn’t wired correctly and I removed it the first time I took out the battery box (ironically, to close up gaps in my doghouse behind the left upper engine mount).

[cliffy]

BIG QUESTION-  When was the last time the CHT TOTAL system was checked for accuracy? That means gage, wiring and probes?

Is it 40 years old and never recalibrated? 

You don't know how hot you really are until you know your gages are accurate. 

[MikeOH]

3 minutes ago, cliffy said:

BIG QUESTION-  When was the last time the CHT TOTAL system was checked for accuracy? That means gage, wiring and probes?

Is it 40 years old and never recalibrated? 

You don't know how hot you really are until you know your gages are accurate. 

Fair point, but it seems improbable that if they show within 1 degree before startup (I.e. room temp) that they are going to be badly off at temp. 

[cliffy]

Fair point also!

[Buckeyechuck]

1 hour ago, cliffy said:

BIG QUESTION-  When was the last time the CHT TOTAL system was checked for accuracy? That means gage, wiring and probes?

First in response to the above quote, I installed a JPI analyzer (not primary) shortly after the overhauled engine was installed. Due to the high numbers, one of the first thing I did was check the TC readings in a cup of boiling water. They checked ok.  
 

I’ve had one flight to check for improvements after the annual. I did a lot of work to close up the doghouse in the back and across the front of the #2 cylinder. After takeoff, climbing out at WOT, #3 was hottest at about 430 with #4 about 10 degrees cooler. This is opposite of how they ran before and much cooler. I’m not sure how much is due to climb at WOT, how much is due to doghouse improvements, and how much was due to the 30 degree outside temperature. I’m back in Florida now for the holidays and will update again once I get a few more flights. Here is a photo in cruise from the first post annual flight. 

[blakeforslund]

On 11/3/2024 at 11:15 AM, N201MKTurbo said:

My old M20F always ran cold. When I added the cowl closure, my CHTs went up and my oil temps went down. And the plane went a couple of knots faster.

If this is true, it would be great for me!

[N201MKTurbo]

13 minutes ago, blakeforslund said:

If this is true, it would be great for me!

It is a cheap and easy mod. If you have sheet metal skills, it is an afternoon project. The hardest part is removing the lower cowl. Just remember measure twice and cut once.

[Buckeyechuck]

1 hour ago, N201MKTurbo said:

It is a cheap and easy mod.

If this is done as a DIY, how is it logged?  337?

[N201MKTurbo]

1 hour ago, Buckeyechuck said:

If this is done as a DIY, how is it logged?  337?

If it has an STC, you will need to file a 337 and an IA will need to approve it for return to service. 
 

You need to make friends with an IA.