Taylorcraft Closed Cowling Cooling Success (2019)

I posted some of this a couple of years ago but based on some discussions and observations at OSH this year,  I thought it might be worthwhile to flesh it out a little.

Assuming no significant problems with the engine, I think the single most important factor in BC12D cooling is the crankcase baffle… the one that’s usually all bashed up or missing altogether!   But before we get into that, let’s explore the basics…. 

The key to successful cooling of our air cooled aircraft engines is to get air to flow through the cooling fins!  Sounds simple enough right?  For air to flow, there must be a pressure differential (delta).    In the case of the Taylorcraft “Closed, Pressure Engine Cowl”  as the Factory called it, the engine cowlings were designed to create higher pressure above/forward of  the engine and lower pressure below and aft of the engine.  The division created by the baffles and seals.

How air flows around the engine is more important than how much air flows, but it’s not enough to have flow, we need to force or at least encourage air to flow in contact with cooling fins and other key parts.

A common problem on older aircraft is the loss of some or all of the pressure differential within the cowling.  No delta=no flow=low cooling effectiveness.  Changes to the baffles, seals, upper and lower cowlings and of course the pesky crankcase baffle can create problems.  Our cooling air will take the path of least resistance which may not be the path we want, or may flow very little or not at all.

The original felt seals on the Taylorcraft are not adequate (at least not for very long) in my view and there are far superior materials available now.  This is an area I chose early on not to be authentic.

The most common causes of losses in the differential (other than the crankcase baffle) are poor baffle seals (both condition and fit), holes in the baffles including gaps around accessories, crankcase shapes etc., and holes in the forward part of  the lower cowling.

Our BC12D's have a couple of specific weaknesses worthy of special attention:

The nose cowl has an intake (chin scoop) that can send air below the engine.  This is actually what we want to avoid as it has the tendency of reducing the delta.  

The crankcase baffle, if it’s in good condition, channels air along the lower case to cool oil returning from the cylinders etc., more importantly it chokes the airflow going under the engine such that the majority of air coming in the "scoop" is forced up past the crankshaft behind the propeller hub and into the upper cowling area.  This is good.  

Trouble is the crankcase baffles are often in poor shape or, as in the case of CF-CLR, missing altogether.  I used to tape over the lower intake for winter operations but I now suspect this actually made the engine run cooler!

As far as I’m aware, there is no source to purchase this baffle. I was not able to come up with a drawing either.  I suspect it may have been a Continental part.  I asked the Forum for photos and from the photos I fabricated one that works:

I didn’t keep good records of the fabrication process and my blog is otherwise short on information on how I made the baffle so here are some more photos and step by step.

 I began with craft card and the portion of the baffle that goes between the case and the intake manifold.

No, I don't have the pattern as the attempt made from this card had to be scrapped.  The second attempt was made referencing the scrap piece.

 It is necessary to make a big dimple to accommodate the intake mount boss.  I used a big socket, washers and nut and bolt to pull the dimple.

The material I chose is 6061-T4 .025" because I felt it was soft enough to do the required forming, but durable enough to last a while  (I also had some on hand).  If it had been a little softer it would have been perfect but it worked fine.

 As always, a little determination and patience is needed for multiple R&I for trimming and fitting.

 Form the flanges where the front portion will attach.

And it's also nessesary to form reliefs for the intake connectors (rubber hoses and breeze clamps).

 This shot shows how the airflow is both routed along the lower crankcase area, and choked to force most of the air from the chin scoop up.

I also shows that some stretching of the flange is required to achieve the curved profile.

 Craft card again for the forward half (I did keep this pattern).

leave enough material for trimming to fit the nose bowl later.

 6061 T4 .025' again.

 clamped in place to drill some rivet holes (3/32")

 Ready to rivet.

I etched and alodined my baffles (but that's my problem).

There is some tricky forming to get the chin scoop to nestle nicely, bearing in mind that there is motion between the crankcase baffle and nose bowl (provided by the rubber engine mounts)

The baffle (scoop) riveted to the back of the nose bowl should fit reasonably snugly into the crankcase baffle like this (viewed from aft and below) and hopefully there's enough flexibility in the installation to accommodate engine movement.  Ultimately  there will be chafe here however and my plan is to add teflon tape or similar once the locations are revealed!

The rest of the baffles should end up looking something like this for the A65:

(Note the front baffles – the seals extend forward and up from the lower flange so the air pressure seals them against the nose bowl.

In this photo you can also see the “channel” created by the crankcase and front baffles that ducts the air from the chin scoop to the top of the engine.





If an air filter assembly has been installed, another potential problem is introduced.  The filter housing needs to be sealed to the cowling in some fashion otherwise your cooling delta is reduced again.

 .032" doublers were made for each of the sides and top and bottom seals and I riveted them to the airfilter housing (AD 3/32" rivets).

Taylorcraft designed a relatively complex cowling system as part of the effort to outperform the competition all using the same 65HP engine.  

The lower cowling has four vents, each with a flange, and there is a flange along the bottom edge.  These flanges are not just for show.  

By protruding into the airflow,they cause a drop in pressure, drawing air from the cowling below the engine.

CF-CLR had Aeronca exhausts on it when I got it and the holes through the lower cowling most likely acted as an unintentional but detrimental air intake.  Air being forced into the cowling in this area will increase the pressure under/aft of the engine, reducing the delta and therefore the airflow through the cooling fins.  To ensure against this probability, a small flange can be added like the ones commonly seen on some piper aircraft and "Power Flow" upgrades.

Something like this or smaller should do the trick:

So in terms of a Cooling Checklist:

1. Have a look at the chin scoop and how well your crankcase baffle seals around the scoop and the engine case. (when standing in front of the prop, you shouldn't be able to see your engine or lower cowl area through the chin scoop!)

2. Check to see if your air filter housing is sealed against the cowling,

3. Check the location and size of tailpipe opening(s) and how the cowling is formed around them,

4. Look for any openings in the top cowlings, baffles and lower cowling that may upset the delta, the "plenum" created by the upper cowlings, nose bowl, engine and engine baffles should be as air tight as possible (except of course where we want airflow.  Through cooling fins etc.)

5. Check your baffle seals to ensure they are installed correctly and that they actually seal against the cowl, and finally

6. plug any holes where air can by-pass the cylinder cooling fins.

Also, the A65 has what Continental called a "summerization kit." 

It consists of two tabs that are attached to the inboard end of the inter-cylinder baffles. I actually didn't know anything about this when I was fabricating new inter-cylinder baffles for CF-CLR but noticed the gap between the baffles and the crankcase at the inboard end and, as a matter of course (based on what I've shared above), unknowingly incorporated the summerization kit into the baffles.

I figure it's better to have them there full-time and deal with any "over cooling" if and when I ever fly at -25C again!

One more tidbit...  Depending on how you do your baffles and baffle seals the area where the top cowling hinge point meets the baffles leaves a hole the size of a quarter on each side.

While we don't usually pay much attention to this sort of thing, the solution was simple so I incorporated this "plug."

Simply three pieces of baffle seal stuck together with superglue and then superglued  to the upper cowling.  Every little helps!




The Final note is about the exhaust shroud and ducting;

In normal operation, air travels in from the front baffles, through the shroud(s) and out, either via the carb air box, exhaust tail pipe shroud, and the cabin heat valve.  This takes considerable heat, from the exhaust, directly out of the cowling area.  Important to note that this happens regardless of whether you using the carb or cabin heat.  So well configured and maintained carb and cabin heat systems are good for overall cooling success.

That's all I have.  I'm happy to report that CF-CLR runs at a constant 150 F (on my guauge) which I think is in the ballpark of where we want it to be.