new carb heat box

M

Mark Goldberg

Bearhawk Aircraft
Today Bob received the latest carb heat box from the kit factory. He is 100% happy with it. However, it is not too smart to just make these without someone actually trying it on an engine AND seeing how the carb heat box fits the cowling. Bob THINKS it will be fine. But we need someone to try it on. Someone who already has their cowling made. Maybe even someone who is flying.

If you are interested in trying this and can do the trial fit soon - please give me a call to discuss. Mark 512/626-7886
 
An update on the new carb heat boxes for those of you waiting. We now are confident that it is working well itself and also fitting well inside the sheet aluminum "surround" we have been sending with the 4 place, Companion, and Model 5 kits. Also we have sent that aluminum part on the most recent Patrols.

We have made the decision to make two versions of the carb heat box. One version for the 6 cylinder engines like the pics shown above. And a slightly different version with a smaller filter for the 4 cylinder engine installations that do not need the big filter. The factory is starting to make them now - the ones for 540's. I will send down to the factory the smaller filter to make sure the ones they make for the 360's has the filter fitting well also. So good progress and hopefully have them available in a few weeks. Thanks for your patience to those of you waiting. Mark
 
Yes. All four cylinder engines can use the carb heat box with the smaller filter. But you could use the one with the bigger filter as well. No real need though. The air flow requirements for the 360 installations is more than adequate with the smaller filter.
 
Bottom LIne: Does this Box fit a Bendix FI Fuel Servo?

I just read the Beartracks article on this Carb Heat Box. It seems like a great solution for both Bendix FI and a Carb. It will fit my Vetterman Cross Over Exhaust too. I have Bendix FI. So I wonder if the mount for the box to the Bendix Fuel Servo has the same footprint as a MS Carb? Does anyone know?
 
Brooks, I can't answer your question. But things did change somewhat since my update on 3/24. I was told by a tech rep at K & N that they did have a smaller filter the same width of the larger one we made the box for. When Bob received it he saw that it was not the same width and was not compatible with the carb heat box we made. So there will just be one size fits all.

There are a couple of carb heat that didn't work but would serve the purpose of checking for clearance etc as the dimensions are good. We could send these around so a builder could check fit. Mark
 
Hi Mark, do I understand correctly, the latest plan is to use the same heat box with the big filter also for the Patrol?

Do we already have photos of one fitted to an airplane?
Curious how it looks.

-Stefan
 
Yes Stefan - just one size carb heat box & one size filter. The bottom of the carb heat box (where it sticks out below the cowling) is covered nicely by the bent up aluminum piece we have always sent out the with 4 place & now Companion. In the last couple years we have sent that out with Patrols as well. Not sure if you got one. I do have some coming from the factory soon.

There is another piece of aluminum required to go from the nose bowl to the top of the filter. I have not seen the finished look of the new carb heat box with both those pieces of aluminum fitted.

However, 8 or 9 of the carb heat boxes just got sent out to builders. Hopefully we will see some pics soon. Mark
 
What is the latest on the heat boxes?
Anybody has already installed them on a Patrol?
Super curious to see a picture.
 
I have one. I have fit it up, but not installed it yet. It fits with a Vetterman Cross Over Exhaust without modification but its close. Bob said he thought it would be fine even without a heat shield using Bendix Fuel Injection.
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if you read Kent Paisley’s Speed with Economy, want to get creative, and look a bit foolish it fits backwards too. so unfiltered ram air could be fed straight into the box maybe getting a bit more power improve volumetric efficiency up high. I’ve wondered….if the engine consumed filtered air from the lower plenum (instead of fresh air from the open atmosphere) would certainly lower the amount of air exiting the lower plenum, might it improve cylinder head cooling a bit too at the cost of some power?

But no one does it so I assume there more to it then my creative mechanical thoughts might be able to understand.
 

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Since it is so close when using a Vetterman exhaust, I tried to get K&N to provide some info on the temperature rating for the flexible/rubber stuff used in their filters. I was hoping for a "good to x degrees". All I got was the lawyerly answer that it is "adequate for the intended application".
 
Thanks for the pic. I like that it is lower profile than the MA4. What I don't quite understand is how the top part cuts into the cowl, sort of undercutting the nose bowl. Doesn't that create a strange scoop? I guess the filter is big enough for an O-360 that the top part could be ignored (not exposed to the airstream)??


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(If I recall my conversation correctly) Bob's view was that as long as it did not touch the exhaust I am fine because AL is so good at dissipating heat.
 
Does anyone have pictures how they finished this new heat box? There is a fair amount that sticks inside the cowl. Thanks Scott Patrol 0360




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I have yet to do the heat box detail. Mark also sent me this shaped sheet metal part. How should I say this, it does not jump at you how these parts go together. Kind of hoping somebody gets to it before me.
 

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Wondering about the zero clearance on the carb heat box. Vetterman exhaust says 3/4” is the absolute minimum clearance to their exhaust, 1/2” if in a very high velocity airflow such as an exhaust area.
 
In my case (Companion/angle valve O-360/carburetor) there was barely 1/16" clearance. While it probably would have been OK, I decided to use a different heat box. The thought of possibly having to re-work the lower cowl after paint etc. didn´t appeal to me at all. Also, K&N wouldn´t help with any info on the melt/burn point of the filter and I was worried about a melting chunk getting ingested. So in the end I took the conservative approach.
 
My final decision was…I did not install as shown. The risk is very high using the airbox with Vetterman crossover exhaust and Bendix FI combination as it is shown on this post.
 
While working on the baffles I finally made the big hole into the bottom cowl and put it on. First observation is the heat box sticks out less than anticipated, which is good. The cover sheet (which supposedly the same as for the Four Place) is way too big and it's not immediately clear how to make it fit.

The second observation is that about 1/3 of the intake filter is inside the cowl. What would be a good way of dealing with this? Option A) cover the top part and seal it against the cowl skin. Option B) build a steep ramp from the nose bowl to the top of the filter.

On a side note, I have pretty good clearance between the heat box and the exhaust (Patrol, Lycoming O-360, Vertterman cross-over). I could easily fit a heatshield in between if the filter gets too hot.
 

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Click image for larger version Name: IMG_3355.jpg Views: 0 Size: 2.42 MB ID: 89990 Here is what I did. Now keep in mind I'm a first timer with all this, so I'm not the expert to look to. Anyway...mine came oversized as well, so I cut a bunch off of it and bent new flanges to fit my cowl. Originally it would extend from the edge of the nosebowl to the aft edge of the cowl, so I shortened it to be flush with the air box and to terminate at my cowl exit. But in doing that I ended up with a narrower aft edge. My ideal would have been to have this thing flare out to match the width of the tunnel at its aft edge. At this point I was ready to fly so I tested it as is. I figured if I needed better cooling, my first step would be to make a new one of these that had a larger aft edge dimension. But my cooling is great so I'm running it like this.
 

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I dig through my photos and found this photo of the exhaust end. Sorry, it is a pretty crappy photo. Let me know if you need something better and I can take some next time I’m at the hangar.
 

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I recently go my heat box enclosure done, at least the important part of it. One thing that got me puzzled is how big the part was I got from Mark. In the end I decided to use only about half of it and it came out quite nicely. I actually like it as feature of the overall shape of the airframe.

heat box cover 1600.jpg
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