Tank Size for Brodak 40

[Steve Scott]

My boy and I have a Sig Primary Force ARF with a Brodak .40 and are using the stock Kavan tank which came with the ARF.  Kavan lists this as a 4oz tank but it holds only 3½ oz (100cc) which gives us barely 4 minutes of flight time.  That was plenty when he was flying the beginner pattern but he's starting to practice the full pattern now.

We also changed from an APC 10-4 prop to the APC 10.5-4.5.  Sig Champion 10% fuel with a bit of added castor/Klotz to bump up total oil to 22%.  Didn't have my tach with us today but we launch and the engine runs pretty much at a fast 4 stroke setting.  Lap times were 4.7 seconds on 60' lines.

I'm guessing we'll need a 6 oz tank and fill it with 5 oz of fuel but that seems a lot for a .40.  The engine only has about 20 flights on it after doing the factory recommended procedure.  Engine runs great - steady setting until the last lap when it leans out then a clean cutoff.  There is barely a drop or two of fuel left in the tank.  Plumbing is uniflow with forward facing vent - the stock Brodak muffler has no pressure nipple.

He loves the way the PF flies - just wants a longer engine run.

[Larry Renger]

I dunno, but my previously troublesome Brodak 40 has become a real pussycat and I can do the full pattern with my Smoothie on 59' lines and 5.05 second laps on 3.75 ounces with time to spare!  I added one head shim and am running GMA 5/22 fuel with an APC 10.5x4.5 prop.  Plenty of line tension everywhere.

Andy needs over 5 ounces to complete a pattern with the same engine, so I haven't a clue what the magic is.

[Ralph Wenzel (d)]

4 oz. ought to be about right for a well-broken-in Brodak .40. This level of break-in requires far more heat cycles than suggested in the instructions. It's flyable after about 15 - 20 2-minute runs, but this engine won't be fully broken-in for at least 3x that many runs!

I had been flying a Cardinal/B.40 for about 4 months, maybe 60 flights, and suddenly the engine went dead rich, and the needle hadn't moved a bit. I cranked the needle in over 2 turns during the next 5 flights, and economy increased noticeably with each adjustment. At that point, I didn't have to touch the needle for over 5 months!

Stick with it. It's a wonderful engine if you give it time to run-in properly.

[Bob Zambelli]

Go with what Ralph and Larry said - the Brodak .40 is a fine engine that requires substantial break-in time, the amount of time depending on how tight the engine was manufactured (tolerances).

As pointed out, the run time will increase dramatically once it is properly run in. Sounds like you're doing everything right - just be patient.

Here's something I would suggest - don't get locked in to a particular range of prop sizes and pitch - experiment a bit - try some 6 pitch, 10 to 11 inch diameter. Remember, no matter what others use, the prop that pulls your plane the way that pleases you is the best.

Virtually every Brodak .40 I've seen requires 4 ounces or less for a proper pattern.

Bob Z.

[Jim Oliver]

Just to add one more data point to the graph:

B40, Powermaster 10/22, Zinger Pro 11x5, 4 oz. metal uniflow, stock muffler/no pressure,take off at 8800 rpm or so,  elevation about 250 ft. msl, run time of 6 min. plus a little depending on conditions.

Cheers,
Jim

[Alan Hahn]

One comment, my B40's also use less than 4 oz. However don't make the mistake of finding out your's needs a little more during the upperward leg of the clover!
Whenever I am flying a new setup and am a little uncertain on how much fuel I need, I'll cut down on some of the level laps after takeoff and the inverted flight, just to be able to get to the last couple of maneuvers. Then I count how many leftover laps I have at the end. Anyway I gradually sneak up on the correct amount of fuel.
It does sound like you need a little more time on the engine.

[Norm Faith Jr.]

Steve, my four year old+ Brodak, stock muffler, no pressure, runs on a 4oz. Sullivan clunk tank with a forward facing vent, 10/22 fuel, 11X5 APC, launched at 8900. I have no idea of how many flights it's completed, (hundreds) but it always "starts on Que" and runs right at 7 minutes. It just growls away. Best engine I've ever owned. BTW it has been on the same airframe all of that time. 38oz. Modified Twister.
Norm

[Steve Helmick]

A lot of the B.40 venturii measure up around .302/.305", which is quite a bit bigger than required in most cases. You might try a Bruline Fine air filter on it, which should bring the effective venturi diameter down to around .285", which is a good size for the B.40 in most cases. Your P-Force should not make it work up much of a sweat. Several layers of nylon stocking material can do the same thing, and may be available cheap if you ask nice.  Steve