Brodak 40 run

LAST EDITED ON Aug-16-04 AT 09:25 AM (CDT)
 
Having trouble with my Brodak 40. ( had it in another plane, mounted inverted, no muffler pressure, it ran perfect ). Now it is in a profile, can not get it to run worth a flip! It runs fair ( a little unsteady ) on the ground, but goes sour in the air. Uncertain whether it leans out, or goes rich, but it looses all power, barely keeping plane flying. Tried two differnt metal tanks, and a clunk tank, runs the same with all three. Cleaned spraybar, new fuel line, plug, etc. Will muffler pressure help?
ALSO, what other engine will mount in its place?

My guess is that it is running lean (a complete guess). The main problem with going from a full fuse engine configuration (where the uniflow pickup is relatively close to the spraybar hole) to a sidemount configuration (where sometimes the uniflow pickup is pretty far outside of the spraybar hole--depending on the specific tank), is that the engine tends to lean out quite a bit after takeoff.

The solution (if this is the problem) is to launch pretty rich and/or use a narrow tank.

LAST EDITED ON Aug-16-04 AT 10:34 AM (CDT)
 
Use muffler preasure on the tank and see if that smooths it out for you.

LAST EDITED ON Aug-16-04 AT 10:59 AM (CDT)
 

Is the center of the tank slightly above the center of the venturi?

Prop size? is it the same as prior?

How are you setting the needle on the ground? What speed or sound are you setting to?

Are you certain your tank doesnt leak air? and are you plugging the vent with NO leaks prior to flight?

Based upon the information provided so far, I wouldnt necesarily recommend going to pressure. It could mask a more fundamental problem.

JMHO

1) three different tanks, all set slightly higher than center
2) 11/4 cut dowm to 10.5/4
3) 9400 rpm at launch, rich needle
4) 10/22 fuel ( half syn/castor)

Jim Morway is running a similar set up with respect to prop manufacture and fuel. He has left the 11x4 APC prop in stock length and launches at 9000 rpm. So I would have to agree with Alan on launching a little richer. The downside of the comparison is that Jim's is in an upright mount position. Give the richer launch a try and see what happens.

Does it seem to needle OK on the ground? Is adjusting the needle giving the expected result or does it tend to jump from too lean to too rich?

If adjusting the needle doesn't give a smooth rpm change I would say you have a vibration problem.

I have to agree with Bob here - it's the excessive nose vibration. No tank or needle setting can help if that's the case.
How is the nose section of your profile constructed?
I had a profile once with a 3/8" balsa nose, laminated with 1/16" 3-ply bich plywood on both sides and 3/8" square motor mount inserts. Unsteady runs, little power, high fuel consumption. Laminated an additional 3/32" 5-ply birch doubler - all problems went away.

most likely it is a vibration problem. Have a similar problem with a profile after a crash. Despite reinforcing the nose, the motor still runs erratically. something has loosened up and is allowing bad vibrations. In my plane I can't see any bubbles in the line or anything.

You might check the mounting bolts. My B40 would start to run erratically when the left rear bolt was the teeniest bit loose- even an 1/8 turn.

I've had mine in a profile Oriental and now mounted upright, always ran perfect 4-2-4. Centerline tank slightly above NV. I agree with the others that I would look at vibration. Try holding the model around the tank and see if you notice any difference, taking care not to squeeze the tank.

OS mounting.....

Ronnie

I had considered vibration. I just built the plane from scratch, 1/2" balsa with 1/16 ply. doublers, and a 3/4 " "fake cowl" on inboard side. Thought that would be strong enough, guess not. I have checked everything else, so I think I will figure a way to beef the nose up.
Thanks, DRM

I would replace the dual hole spraybar.

My only experience with a B-40 is with an ARF Nobler (in helping out the eventual winner of the Beginner ARF event at Brodak, Henry Werner).

Eratic as heck, until NVA was finally replaced with an ST unit. It now runs with 11/5 Rev Up and hasn't been adjusted in several flying sessions. A nice combo, if I say so myself.

We tried all sorts of things - it could just be the way he holds his mouth or something. But, that's what I'd do - change the NVA.

And of course, I'd do it with grace and style, while wearing my wife's underwear.

I recall PW using the 2Star NVA/Saito venturi/manifold & had problems with the NVA...burrs inside the spraybar. I work as a machinist, and had no idea how to deburr the inside of a spraybar. I asked Paul what he did, "threw it out". Hmmmmmm. 2Star makes Brodak .40's, ya know. Steve

>I recall PW using the 2Star NVA/Saito venturi/manifold & had
>problems with the NVA...burrs inside the spraybar. I work as
>a machinist, and had no idea how to deburr the inside of a
>spraybar. I asked Paul what he did, "threw it out". Hmmmmmm.
>2Star makes Brodak .40's, ya know. Steve
>
>http://www.nwskyraiders.com/index.html

Got rid of MY piece of SHI% NVA on my Brodak 40

FYI: I did notice when I was adjusting n/v, setting would be close, then with a very slight turn, rpm changed a bunch, then had to back it out a lot to get it back to where it was. I have put an OS nva in the engine, will try it later today.

Note: handy tool to keep in flight box, torch tip cleaner. Basically a large assortment of tiny round files, great for cleaning spraybar holes. Compact, so it does not take up much space.

I would agree with the vibration theory. I don't see how the NV would suddenly start causing the problem. If there were machining burrs present, they would have been there from the start. If they have the potential to cause this sort of problem, it would have been a problem from the start.

Can someone explain to me how internal burrs would cause a problem? The burrs are internal in the spraybar and are more than likely firmly attached. As the tapered needle is turned out, the annular opening increases in area in proportion to the taper of the needle regardless of the "irregularity" of the shape of the bore of the spraybar. It doesn't have to be perfectly circular to work.

I have a Double Star 40 that ran poorly. I gave the engine to Duane Cowan to look at. He cleaned up burrs in the needle valve. Runs good now.
Also try a differant prop, size etc. Harmonic balance might be a problem.

Burrs inside the spraybar are not necessarally firmly attached. They can break off at any time and cause intermittent problems. Remember, this is a metal fragment that was not supposed to be there in the first place.

FYI: Different nva did not solve problem. Engine ran a little better, but still performed basically the same way. Going back to the vibration idea, will rebuild nose. Thanks for all the ideas.
DRM

I would think that vibration is your problem. You have already said the engine worked fine upright, you cleaned the needle, changed tanks, etc. I don't know if you defoamed your fuel. Vibration plus fuel foaming add up to lots of foaming. But it may just be the nose section. Been there. Done that.

If it is vibration, you should see bubbles in the fuel line. I thought he said that it was also pretty erratic on the ground too (unless it has been set so rich on the ground to make up for the leaning in flight).