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Author Topic: starting a Brodak 40 or 25 AAC  (Read 1573 times)

Offline Fred Quedenfeld jr

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starting a Brodak 40 or 25 AAC
« on: December 16, 2018, 08:52:59 AM »
When I first got the brodak 40 it was a bear
It would want to break my finger on every flip
I run 22% oil
now I can never tell when it is ready to start
on the OS la 46  or FP 25 I can prime and choke til you get a bump than a coupe flips and they run
I never seem to get the "bump" with the brodak AAc any suggestions
Fred Q
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Online Dan McEntee

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Re: starting a Brodak 40 or 25 AAC
« Reply #1 on: December 16, 2018, 09:22:39 AM »
   Each engine, even sometimes the same size and brand, has it's own recipe for starting. You nay be over choking it. I remember my Brodak .40 experiences not requiring too much of a choke for cold starting and less when warmed up. I usually use the back flip method on most ABC or high compression engines. If you get a bump, ( and sometimes you won't due to conditions) bring it up to the normal compression point, then sharply whack the prop the other direction. You can use your finger, a chicken stick or anything similar like a piece of heavy hose. Large bore engines and carbon props are usually best started this way to keep you fingers out of the prop. Practice makes perfect and a note book helps you remember what each engine in your fleet requires.
    Type at you later and
     HAPPY HOLIDAYS!!
     Dan McEntee
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Online Dave Moritz

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Re: starting a Brodak 40 or 25 AAC
« Reply #2 on: December 16, 2018, 01:09:33 PM »
Dan:

I'll give the backwards flip a try on my two larger engines. A question:  When you bring the prop up to the compression point, I take it that that prop motion is in the forward rotation rather than in the backward rotation? If so, then when I strike the prop backward, it will initially be loose and not up against any compression (true of false?).

Thanks for the pointers.

Dave mo...
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Offline Tim Wescott

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Re: starting a Brodak 40 or 25 AAC
« Reply #3 on: December 16, 2018, 02:05:21 PM »
What Dan Mac said about variation.

What I do on a lot of my profile models is to learn how much of a prime I need to give, and then just count turns of the prop.  It's easier on a profile because you can see when you have the fuel pulled up to the needle (or spraybar).  Most of my engines need four to six turns of prime.  Then I flip the prop through a dozen times (I count), then I put on the glow power, flip, and fly.  I usually get a one-flip start.

You need to learn the needs of your engine.  My OS LA and FP engines are timed conservatively enough that I can just pull the engine through with the venturi choked.  My Magnum 36 has earlier intake timing, so there's enough pressure left in the crankcase to push the fuel away from the needle if I hold it choked -- that one I have to hold my finger off the venturi through compression, then put it on and pull it through, etc., for the right number of turns to get prime (I think it's six -- I haven't flown that engine much recently).  The 46LA in my Atlantis is my only inverted engine; it almost always just wants a few flips without choke to distribute the fuel that's dribbled into the venturi, then check for bump, then flip & fly.  Of all my engines, it's the one that I'm most likely to need to check for a bump -- I haven't gotten it fully figured out yet.

I don't have personal experience with the Brodak engines, but I can believe what Motorman says -- getting them primed right before you flip may help a lot with the problem of not getting a bump.  But if they really settle out that much over the first 50 flights, be ready for their priming needs to change, too.
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Online Brett Buck

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Re: starting a Brodak 40 or 25 AAC
« Reply #4 on: December 16, 2018, 02:53:03 PM »
Quote from: Fred Quedenfeld jr on December 16, 2018, 08:52:59 AM
When I first got the brodak 40 it was a bear
It would want to break my finger on every flip
I run 22% oil
now I can never tell when it is ready to start
on the OS la 46  or FP 25 I can prime and choke til you get a bump than a coupe flips and they run
I never seem to get the "bump" with the brodak AAc any suggestions
Fred Q

    Is this with the engine upright (like on a test stand) or on its side? If so, the problem is probably because you are over-choking it, filling up the crankcase, so when it does pop, it sucks up too much fuel, and then quits. It also tends to get "fierce" as it says in British model magazines.

   You may just have to choke it a priori (3 pulls through, aerate, attach battery, back-bump (see other thread)). If it ends up too much, then try 2 next time. Generally it will want much more fuel when it is cold than hot.

   Not getting a bump on a pull-through means you are not forming a near-ideal mixture in the cylinder. Some engines just don't do that, having never started a Brodak engine, I wouldn't know.

     Brett
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Online Dan McEntee

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Re: starting a Brodak 40 or 25 AAC
« Reply #5 on: December 16, 2018, 02:58:09 PM »
    Just to add about choking, I ALWAYS take my thumb off the venturi after the piston goes over top dead center. If you leave it there, it will push the fuel back towards the tank, on any engine I own.  Depends also if upright, inverted or sidewinder. Inverted can flood easier.  Most of my Super Tigre engines like a lot of fuel, even if inverted and especially if cold. Some engines like to be flipped through smartly a few times after choking just to swirl things up a bit, but be aware that am engine can start like this with no battery if conditions are right and the compression is high enough.. And yes, bring the prop around to the compression point in the normal rotation direction, then back flip. A variation of this is to just grab the spinner and spin it backwards in the same manor. That way you don't even get your fingers in the prop arc. And I'll say again, practice makes perfect.
   Type at you later,
  Dan McEntee

  PS to add: You will see some days where you just don't get a bump on engines you normally would. Went flying today, and while it was in the high 50 degree range, a chilly breeze was blowing and it was fairly high humidity. I did not get any bumps, but got several one flip starts today. You just have to follow the routine you work out for each engine.
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Offline Chuck_Smith

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Re: starting a Brodak 40 or 25 AAC
« Reply #6 on: December 16, 2018, 03:42:49 PM »
Great advice here and I'll just add that when faced with an unfamiliar engine I usually do this:

Choke until I see fuel  ( if you can see the fuel line ) in the line reach the NVA and then 1 more choke. Flip the engine over 5 or six times without the battery connected. The engine should feel nice and "loose" at this point. Connect the battery and flip. If it has a half hearted attempt to run remove the battery, choke once more, flip 5 or six times and repeat. If however, the motor kicks and snorts like you describe, I'll backflip it. If backflipping doesn't work I'll remove the battery and flip it about 10 times, reconnect and then flip and see what happens. Also, a spinner makes backflipping a "snap".

IMHO it's better to err on the side of not enough choke than vice versa.

Sometimes a new engine just needs a few runs on it to start easily.

I'll add that with a new engine there's no shame in using the electric starter on the test stand. On a test stand I use a different method:

(IMPORTANT NOTE, THIS DOESN'T APPLY TO TUNED PIPES OR "TONGUE-STYLE MUFFLERS!)


Set up a clunk tank with muffler pressure (two line tank).
Don't choke the motor
Connect the battery
Have a helper place a finger over the exhaust hole on the muffler ( being keenly aware of where the prop is!!!)
Engage electric starter
When she lights remove finger from the exhaust.

The spinner flick method is the most desirable for me. Some engines that like to flick start have a nasty habit of running backwards if you try to flip them. Then, when they cough and start to stop - BANG!- they change rotation. It's cute with a .28 or .35, but with a .75, not-so-much.

Chuck



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Offline Target

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Re: starting a Brodak 40 or 25 AAC
« Reply #7 on: December 17, 2018, 03:57:45 PM »
One relatively well known combat pilot told me that he couldn't get his Brodak .40 to break in, and it would run erratically.
He ran it on combat 30% nitro a few flights, and presto, it became a great stunt run on the regular 5-10% nitro we use for stunt.
Believe it or not.

R,
Target
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Regards,
Chris
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Offline Geoff Goodworth

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Re: starting a Brodak 40 or 25 AAC
« Reply #8 on: December 19, 2018, 07:57:33 AM »
My starting procedure for a Brodak 40 installed in a profile model.

Choke one or two turns until there is fuel in the line. With a profile, if I overdo it, the fuel runs out of the venturi.

Flip five times. Connect the battery. Flick once and fly.

Sometimes it requires a second flick; any more than that and there is something wrong.
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