Big Wheels Keep on Turnin'

[VictorBravo]

The ongoing saga of my little BC-65 cylinder head temperature chase continues.

Last week I invoked the emergency provisions of Dr. Seuss' theory of Calculatus Eliminatus. I have tried everything else, which left only one thing untried.

I made a template of the lower cowling and firewall, specifically tracing the actual size and shape of the air exit under the firewall onto paper. This drawing was then held up to the front of the cowling, and I was immediately hit with 'the mighty sledgehammer of the obvious'.

The combined size of the air intakes at the front of the cowl were approximately one and one half or more as large as the area of the exit under the firewall. It's commonly known that this is just about exactly backwards. The one thing that I had ASSUMED was correct was the original factory design of the air inlet and outlet. So I spent darn near a year now, chasing everything else.

Two or three things have been considered to solve this airflow bottleneck at the exit. Louvering or shark gills in the cowling, an enormous cowl flap, or reshaping the cowl to hang lower under the firewall making a bigger exit.

The last option was chosen as the best method because it would change the look of the airplane the least. The plan was decided to stretch the cowling down an inch or two, and make a spacer or standoff part for the gap between the lower cowl (and Dzus fastener) and the welded center firewall mount.

Despite my desire to use a jackhammer after all these trials and tribulations, it was admitted that the best tool for the job was an English Wheel.

Today was my second trip to go see an old guy at another local EAA Chapter who owns and operates one of these mystic magic marvels. The first trip didn't stretch the metal much because the metal was hard. So I took it to a heat treat place and had it annealed back to half-soft. I don't want to talk about the burned paint and carbonized felt strips... it looks like the back side of the moon!

Today we rolled it again between the big steel wheels and stretched on it again, and it moved a bunch. Put it back on the airplane and noted where it still needed some more squishing.

But the center of the cowl now sits another inch and a half below the center firewall mount. Should let out a lot more air!

Tomorrow I'll try to go back and have the guy whack at it some more.

I could have built an entire Zenair 701 or a Hummel Bird or a nice cabin in the woods in the same time I've spent on this one little problem !

[flyguy]

Re: Big Wheels Keep on Turnin'

Doesn't sound like you are having much fun, but the results should be interesting.
Is there actually anywhere left out here to build a cabin that isn't prohibited in some way, environmental or otherwise?
DC

[crispy critter]

Re: Big Wheels Keep on Turnin'

Doesn't sound like you are having much fun, but the results should be interesting.
Is there actually anywhere left out here to build a cabin that isn't prohibited in some way, environmental or otherwise?
DC

Bill,
It's great to see you taking one for the team on this one but just so you know...you don't have any problems that the rest of us don't. The only difference is that you have installed the cylinder head temp gauge and most of us have not.

[mulwyk]

Re: Big Wheels Keep on Turnin'

Yes, DC, it certainly is possible to build a cabin. (Well, maybe not in California) I built a 600 sq.ft. "hunting cabin" in Hand County, South Dakota several years ago. The were no building permits required or prohibitions at all. None.

The owner there is even allowed to do his own electrical and plumbing work. (I did hire an electrican to do the rough-in and then the inspector walked me through the finish work.) We also hired a backhoe guy to do the excavations and put in a septic tank and we hired a cement geezer to do the concrete work. All the contractors worked on a handshake-and-a-six-pack basis...no written contracts at all. (Foundation, drainage, electrical = $2000)

The rural electric cooperative charged $100 to hook us into their system and the rural water system charged $500 to bury a 2 mile long pipe to our place. (Thank you, federal earmarks, for both of those.)

We paid $4800 for 20 acres of pasture and woodlot (in 1992) and after buying a big pile of lumber (and lots of our own labor!) we ended up with a nice little cabin for under $18,000.

It IS still possible... you just hafta move out to the midwest and be willing to work your tail off.

[VictorBravo]

Re: Big Wheels Keep on Turnin'

Don't know zippo about building cabins or houses... but... don't it make more sense to build most all of the cabin in your backyard and then have the pieces trucked in to wherever your property is? You can run all your wiring and what not, put all the hardware and stuff in, leaving quick-connects for water, power and whatever else.

Again I don't know much about this stuff, but it sure sounds a lot easier than figuring it all out standing on a mountaintop somewhere with coyotes howling in the background.

Heck, couldn't you buy a used mobile home, rehab the interior and set it up just the way you want it at home... and just have the thing taken out to your property in one trip?

I always had the daydream of having a mobile home trailer helicoptered in to the flat top of one of those vertical wall spires in Arizona and Utah, and clear about 500 feet of brush for a STOL strip

[tawadc95]

Re: Big Wheels Keep on Turnin'

Bill,is that a recently installed cylinder?just wondering as chrome cylinder wall with chrome rings makes alot of heat.
likewise a steel cylinder with steel rings.

[tawadc95]

Re: Big Wheels Keep on Turnin'

I clicked send to soon...with steel cylinder and steel(cast)rings the rings wear fast but not all that hot.
both examples dirty fresh oil pretty quick any of that going on?

[VictorBravo]

Re: Big Wheels Keep on Turnin'

Question for Forrest, Mike R., Kevin M. , and any of the other many-time restorers:

Are any of you aware of a difference between the pre-war B model closed cowling and the post-war BC-12D cowlings? Specifically, did they make the lower cowls hang down under the firewall a little lower (larger cooling exit area) on the post-war airplanes?

Looking at photos of post-war BC-12D's, it APPEARS to my eyes that the cowls are a little more rounded and have a deeper "belly" than the cowl on my pre-war airplane.

This would mean that the welded firewall Dzus bracket would have been longer (further below the firewall) on the later airplanes too.

I'm NOT talking about the awful flat-wrap wheelbarrow-looking thing they put on the F-21's. I'm talking about an inch or two difference between an earlier BC and a BC-12D.

Also was there any change with the Model 19 or F-19 in this area?

This info will help me unravel this mystery, and possibly provide some useful ideas for anyone with heating problems.

tawadc95, my oil is clean and the damn thing just plain runs too good for there to be any big cylinder problems. Also I have two hot cylinders (1 and 4) catty corner from the cool cylinders (2 and 3), and my airflow experiments have changed which one is the hot and second hottest ones. I am fairly confident there is no internal engine problem.

[crispy critter]

Re: Big Wheels Keep on Turnin'

Bill,
I am almost certain they are the same.Let me ask you another question...what rpm are you cruising the engine at and what is your cruise speed at that rpm? Also,are you running your carb a little lean,are you using auto or 100LL,and do you ever have to clean your plugs between 25 hour oil changes?

[Forrest Barber]

Re: Big Wheels Keep on Turnin'

They are a bit different, We found that the louvered one with the longer lip (late 1946) did do better, the under crankcase baffle is very important too! You cannot push air , it has to be "drawn" ....

[tawadc95]

Re: Big Wheels Keep on Turnin'

Bill, I was thinking about adding a cht gauge to mine but I think I might not now.....if you don't know about something does that mean it doesn't exist?

[VictorBravo]

Re: Big Wheels Keep on Turnin'

Thanks for the reply guys. This evening I fabricated an alum. spacer to take up the newly increased depth of the lower cowl. It bolted to the original Dzus fastener fitting on top, and I riveted the Dzus wire spring into the bottom. Net result is that the bottom cowl is about 1.25 to 1.5 inches lower at the firewall mount. Will post photos soon if anyone is interested.

Tomorrow, weather permitting, will be the acid test. If it runs hot, you all will hear me screaming all the way form Los Angeles.

Kevin it's not running lean, the climb RPM is about 2000 or 2100 max, and my baffles are sealed up tighter than 90% of all the T-crafts in the world. Running 100LL, and plugs were fairly normal.

Wish me luck...

[flyguy]

Re: Big Wheels Keep on Turnin'

Good luck, let us know. As said before, my right rear cylinder runs hot the same.
DC

[VictorBravo]

Re: Big Wheels Keep on Turnin'

OK, here's a sketch of the spacer and where it goes, in case somebody needs a visual.

Remember this can only work after the lower cowl is stretched out using an English Wheel, Planishing Hammer, Tin-Basher's Hammers and shot bag, etc.

My cowling needed to be annealed before it was English Wheeled.

Not to scale...

[crispy critter]

Re: Big Wheels Keep on Turnin'

Bill/Forrest,
I had forgot about the louvers in the post war. Also,I was looking at your under engine baffle and it has a sharp edge where it narrows under the engine between the case and the spider. This could cause an airflow disturbance because of the sharp corner. However this should affect the oil temp and not so much the CHT unless your oil temp is running hat also.

They are a bit different, We found that the louvered one with the longer lip (late 1946) did do better, the under crankcase baffle is very important too! You cannot push air , it has to be "drawn" ....