Author Topic: Wierd Brodak-40 problem (Read 4722 times)

Andrew Borgogna · « **on:** July 30, 2007, 01:47:58 PM »

After seeing my B-40 run so well for the last year, my friend Larry Renger got one for his Brodak Smootie. Well this engine has a problem. It runs fine for the first half of the flight and then for whatever reason it goes blubbery fat. It is as if someone opened the needle a couple of full turns. We plan to put his motor in my Cardinal and my motor in his Smoothie to isolate the problem to either the motor or the fuel supply. I am betting on something wrong in the tank/fuel feed area. Larry is running a Brodak uni-flow tank no pressure, and I am running a stock clunk with muffler pressure. Larry is also running the stock Brodak muffler and I am using a tongue muffler. I don't recall his prop size, I am running a 11x4 Master Airscrew. We both use Excalliber 11x11x10 fuel. It really is a wierd problem, I am use to seeing engines go lean not fat during flight.

Any ideas.
Andy

Busby · « **Reply #1 on:** July 30, 2007, 02:06:33 PM »

I have had the same problem with one of my planes, going rich as the run progressed.
A very quick way to check prior to doing surgery or swapping engines etc is to plug the uniflow as opposed to the overflow and try a flight.
If the uniflow has a split in the tank it will gradually lean out as the flight progresses.
This will identify your problem and then you can repair the tank.

Andrew Borgogna · « **Reply #2 on:** August 12, 2007, 02:03:53 PM »

Well finally got Larry's B-40 in my Cardinal and the results are in.

Here is the results of our testing. Larry put his motor in my Cardinal he use my prop, spinner, muffler and fuel to reduce the variables. Well the results are the motor behave very well. The problem with Larry"s Smothie is in the tank/fuel delivery system. His motor on my plane behaved just like my motor in my plan. I still belive the B-40 dollar for dollar is the best value on the control line market. I will be very interested to hear the results of your engine problem. Please let me and Larry know how things work out.

Here is an interesting fact, from this forum and the SSW forum has I have never seen a posting regarding a person who has figured out how to make the B-40 run better than it does right out of the box. I think that says a lot about the Brodak 40. Nobody is making money by modifying B-40's, at least nobody I know of.
Andy

Bob Hudak · « **Reply #3 on:** August 12, 2007, 07:06:35 PM »

I would like to know what the problem boils down to on the fuel delivery issue.I have a freind who is having the same problem with his Brodak mounted to a Oriental.

Andrew Borgogna · « **Reply #4 on:** August 13, 2007, 10:25:30 AM »

Bob
As soon as Larry figures out the problem I will post it here. Some differances between my setup and Larry's are I use a tongue muffler he used the stock muffler. I used a stock (non uniflow) clunk tank, Larry used a metal uniflow tank. I used muffler pressure and Larry does not. Finally I use a heavier Master Airscrew 11x4 prop. Not sure what Larry is using.

Other things to consider my tank is mounted against a foam pad and held inplace with rubber bands, where Larry's is snuggly mounted within the plane. This is a strange problem and has been reported by two other flyers, it would be nice to compare planes and setups and look for common things that might be the root cause.
Andy

john e. holliday · « **Reply #5 on:** August 13, 2007, 10:45:27 AM »

Try a couple of drops of Armor All in the fuel. It could be the fuel foaming in the tank that is solidly mounted. But, then again I use metal uni-flo tanks with no problem. Have fun, DOC Holliday

Larry Renger · « **Reply #6 on:** August 13, 2007, 12:26:27 PM »

Last time I ran the engine in the Smoothie, I looked at the fuel hose and saw no bubbles. Plus the problem is that the engine goes RICH in the middle of the flight. Fuel foaming should get worse as the tank empties, and the engine should run-away or die lean.

I'll pull the tank out, then yank the back off to see what there is to see. Then put a RSM tank in instead of the Brodak.

Bob Reeves · « **Reply #7 on:** August 13, 2007, 01:03:18 PM »

Quote from: Larry Renger on August 13, 2007, 12:26:27 PM

Last time I ran the engine in the Smoothie, I looked at the fuel hose and saw no bubbles. Plus the problem is that the engine goes RICH in the middle of the flight. Fuel foaming should get worse as the tank empties, and the engine should run-away or die lean.

I'll pull the tank out, then yank the back off to see what there is to see. Then put a RSM tank in instead of the Brodak.

Not necessarily, typically fuel foaming is caused by the airplanes nose being resonate with the engine at a certain RPM. Changing the fuel volume (or almost anything) will change the resonate frequency of the nose. You take off with a needle setting to compensate for the bubbles. 1/2 way through the flight the nose is no longer resonate, the bubbles stop and it goes rich. You need to do something to change the resonate frequency of the nose.. Plastic clunk tank, heavier/lighter muffler etc. If the engine can deal with it going to a lower or higher pitch prop to change the engine RPM will sometimes work.

I have found on Profiles that sometimes making the nose too stiff can come back and bite you.

Randy Cuberly · « **Reply #8 on:** August 13, 2007, 02:19:32 PM »

This "richening" problem sounds suspiciously like a small leak in the tank.
In a uniflo system the fuel can only be drawn from the tank as air is drawn into the tank through the fuel head. This creates a "restriction" in fuel draw that lessens as the fuel is depleted from the tank. This is the "compensation" that creates a more consistent run from beginning to end of tank.
The rub comes in when a leak or hole in the tank is in an area that is covered by fuel during the early stages of flight and the system functions normally (air being drawn through the fuel head), becomes uncovered by fuel and thereby opens another passage of air into the tank. The previous "restriction" mentioned disappears and the engine will richen.
Pretty much the same thing can happen if there is a split in the uniflo line inside the tank (not uncommon with brass tubing and vibration.
Solution: Check the tank for leaks under water or simply replace it with another.

Randy Cuberly

Larry Renger · « **Reply #9 on:** August 13, 2007, 07:11:49 PM »

As far as resonance is concerned, there is no visible vibration in the nose of the plane, and no visible bubbles in the line. Also, I have tried various props and rpms.

I will definitely give the current tank a thorough inspection to find its problem. Then replace it.

As far as an air leak is concerned, on a uniflo tank, the wedge is at atmospheric + ram or muffler pressure, the rest of the tank to the inboard side is at a slight vacuum (we are talking about roughly 3 g's acceleration, so the pressure head should be noticeable, equivalent to a 6" drop!). If there is an air leak, it should leak air at all times, fuel or no.

The point to uniflo is that there is NO change in the slight restriction of fuel flow as the tank level changes. The uniflo vent causes the pressure at the outside of the tank to be constant. The pressure inboard changes by the above mentioned 6" head, but that isn't where the fuel pickup is. The engine sees a constant pressure head, thus constant run.

Now, assume there is a leak in the uniflo line half way down the tank. That acts as the new uniflo outlet, and we have constant pressure head there, and outboard of it, until the leak point is uncovered. At that point, the tank acts as if it were normally vented and the pressure at the bottom of the tank will slowly decrease as the fuel level drops more, making the engine run LEANER, not richer.

Randy Cuberly · « **Reply #10 on:** August 14, 2007, 10:48:48 AM »

Larry,
While there is some logic to what you say, it isn't a true description of what happens in either case of leaks.
A small leak towards the outer section of the tank that is covered by fuel will certainly leak all the time however the air that enters through that leak also is drawn through the fuel head and still provides approximately the same "resistance" to fuel exiting the tank as does the uniflo line. when, however the hole is uncovered and air is allowed to enter into the tank without the fuel head resistance the pressure differential between the inside of the tank and the fuel head increases. Result it is easier for fuel to be drawn from the pickup tube and the engine richens.
I would mention that in some cases if the leak is large enough fuel draw will become eratic as the hole is covered and uncovered. The engine run will also become eratic, not just richer or leaner.
In the case of a split in the uniflo line inside the tank it has roughly the same effect as uncovering the end of the uniflo line. The air is no longer drawn through the fuel head and the resistance (pressure differential) inside the tank decreases and the fuel is easier to draw from the tank. Voila richer engine run at that point.

PS: (Edited to add this)...The uniflo line usually enters the tank on the inboard and crosses inside the tank to the outside near the fuel pick up. A split in this line invariably means that the uniflo line is uncovered somewhere around mid-tank or so...

Randy C.

Larry Renger · « **Reply #11 on:** August 14, 2007, 04:38:25 PM »

Your second comment is: "when, however the hole is uncovered and air is allowed to enter into the tank without the fuel head resistance the pressure differential between the inside of the tank and the fuel head increases. Result it is easier for fuel to be drawn from the pickup tube and the engine richens."

I see no reason for this to be true, and stand by my comments.

Anyway, it is moot in this case as I removed the tank from the plane, and it had no leaks, either in the tank shell or the uniflo line once I pulled the back off. The uniflo outlet is about 1/2" in front of the fuel pickup, which is about 1/8" from the rear of the tank. I prefer a bit more spacing, but it should be functional as is.

Very curious.

Randy Cuberly · « **Reply #12 on:** August 14, 2007, 04:46:42 PM »

I see no reason for this to be true, and stand by my comments.

Anyway, it is moot in this case as I removed the tank from the plane, and it had no leaks, either in the tank shell or the uniflo line once I pulled the back off. The uniflo outlet is about 1/2" in front of the fuel pickup, which is about 1/8" from the rear of the tank. I prefer a bit more spacing, but it should be functional as is.

Very curious.
[/quote]

It is indeed very curious....
As for the "leak" thing you can prove it imperically very easily by poking a tiny hole about halfway out on the bottom of the tank and fly it...I did, several years ago.

I'd be very interested in what you come up with for a solution to your problem.

Randy Cuberly.

L0U CRANE · « **Reply #13 on:** August 14, 2007, 04:47:22 PM »

I think we're saying about the same thing in words JUST different enough to confuse...

If I understand the uniflow venting principle, it works this way:

The accelerated gravity head of the fuel's mass is nearly identical at the internal end of the uniflow tube and at the pickup tube end. We do open the needle slightly more than for open vented operation. We usually offset the uniflow tube end inboard by about the diameter of the pickup tube to get some cut-off warning.

As Randy points out, any crack or hole in the uniflow vent tube "above" its outlet end immediately becomes an open-vented tank condition when that uncovers into 'dry' space, not a uniflow condition. ('Above' in the sense of the force resultant direction.) Randy probably has the numbers to refute this, but I feel that the 'dry' volume pressure inside a uniflow tank is a bit lower than atmospheric, due to the need for the engine to draw vent air against the standing fuel in the vent tube that would be at the level of the fuel outside that tube, otherwise. Seems to explain the richening observed when the vent does uncover. ...before the fuel level allows bubbles to cause the final lean-and-quit that we do get.

Also seems to suit Larry's problem: Air has less viscosity than fuel, which seems to suggest that air will vent through a split or crack more easily than while said flaw is still submerged in fuel.

Interested to hear the diagnosis, prognosis and course of treatment, too...

Randy Cuberly · « **Reply #14 on:** August 14, 2007, 05:01:03 PM »

Quote from: L0U CRANE on August 14, 2007, 04:47:22 PM

I think we're saying about the same thing in words JUST different enough to confuse...

As Randy points out, any crack or hole in the uniflow vent tube "above" its outlet end immediately becomes an open-vented tank condition when that uncovers into 'dry' space, not a uniflow condition. ('Above' in the sense of the force resultant direction.) Randy probably has the numbers to refute this, but I feel that the 'dry' volume pressure inside a uniflow tank is a bit lower than atmospheric, due to the need for the engine to draw vent air against the standing fuel in the vent tube that would be at the level of the fuel outside that tube, otherwise. Seems to explain the richening observed when the vent does uncover. ...before the fuel level allows bubbles to cause the final lean-and-quit that we do get.

Also seems to suit Larry's problem: Air has less viscosity than fuel, which seems to suggest that air will vent through a split or crack more easily than while said flaw is still submerged in fuel.

Lou,
Quite right old Chap!!! Thanks.

Randy Cuberly.

Dennis Adamisin · « **Reply #15 on:** August 15, 2007, 07:22:59 PM »

Larry:
The only time I had a similar problem to this was flying an OS35 in hot weather without adequate cool down between flights. It would show up on the SECOND run and subsequent. Eventually traced it to residual heat in the engine. When starting th eengine hot it would sound lean on the ground. So richen it and it sounded OK for about half a flight then would go way rich. I think in my case the engine was coming off the ground warm and actually cooling in the air - would take about half a tank to restabilize then go rich.

If I let it cool for roughly 1/2 hr between flights the problem disappeared.

Its probably a stretch for this to be the problem in your case but thougt I'd offer it up anyway...

BTW, did you get the elevator trim situation sorted out on the Smoothie?

Larry Renger · « **Reply #16 on:** August 16, 2007, 09:10:09 AM »

The Smoothie has the engine pretty much completely exposed, and the problem shows up on every flight. I don't think overheating is the source of my woes.

Due to the unreliable power, I haven't gotten back to fixing trim problems. One thing at a time!

Larry

Dennis Adamisin · « **Reply #17 on:** August 16, 2007, 10:24:43 PM »

OK here's another (admittedly strange) idea: Is there any angle in the fuel tank relative to the fuselage? I seem to recall you had som trouble stuffing the tank in, were you able to tip it towards the outside of the circle?

SUPPOSITION: Start of flight, full tank, max nose weight & max nose-outward yaw. Setting sounds good, but as fuel burns off yaw decreases, tank aligns with circle and more centrifugal force to full feed at back of tank = richer.

SUPPORTING DATA: Frank Carlisle's recent experience fixing flame outs on his LA Heat

EXPERIMENT 1: test flight with just over 1/2 tank of fuel - BE CAREFUL! & check for steady run.
EXPERIMENT 2: do you think you can reduce the line rake?

THE FIX - If this works, then FIND A WAY to angle the tank, possibly even substitue a medium wedge in place of wide (requires more length though...)

Larry Renger · « **Reply #18 on:** August 21, 2007, 10:25:19 AM »

Dennis, I think it goes the other way. Consider this. (Uniflo tank, a standard tank would be somewhat different)

Needle set with zero centripetal (or is it centrifugal, I can never remember, and too lazy to look it up) force. Plane goes up, the fuel pickup is now outboard of the needle, and the fuel head leans the engine out. However, as mentioned, the extral fuel weight yaws the plane out. Thus the fuel head is a bit less than it would be, and the leaning action is less. As the fuel burns and the yaw reduces, the engine moves inboard relative to the fuel pickup point and the fuel head thus increases leaning of the mix.

In the case of the errant Smoothie, the change is not at all gradual, it is very sudden. The run before and after the change are very steady, but very different. Poltergeists? Gremlins?, yup, definitely Gremlins.

Actually, there are several experiments suggested elsewhere and above that I will try if my new tank installation is still "haunted".

1. Try using the vent instead of uniflo.
2. See what happens with a short tank run.
3. Add a flow limiter orofice to the uniflo vent to reduce the allowable rate of pressure change in the tank. (big enough hole to allow full fuel flow, but not enough to allow rapid fluctuations) (This one really is best for planes that have serious engine changes in the wind as they go up and down wind, but what the heck, it's easy enough to try!)
4. I am being sent a supernatural message to go back to 1/2A engines. (3rd place in P-40, and middle of the pack in OT at the Goyet with .049 power this weekend)

Dennis Adamisin · « **Reply #19 on:** August 21, 2007, 01:14:43 PM »

I'd vote #4!

Larry Renger · « **Reply #20 on:** August 21, 2007, 03:46:25 PM »

By the way, angling the tank only helps provide a clean fuel cut-off. As far as the engine setting is concerned, the position of the uniflo vents and fuel pickup are the only thing that matter. The fuel pickup should be at the rear of the tank, and if the tank is rectangular, you need a clunk for reliable feed. The uniflo should be fixed roughly at the level of the needle, but may need to be raised or lowered slightly, depending on the engine. The rest of the tank is a "black box" and shape and size don't matter (as long as the fuel can get to the inlet).

A couple of cases where this is proved are my Hunter Stunter (Norvel .061) and Noblarf (Double Star 40). The Hunter had a clunk tank (brass, hand made), but due to the position of the needle on a Norvel, compared to the Medallion, the uniflo vent was 2/3 of the way to the bottom of the tank. Similarly, I used a Hayes 4-oz clunk tank in the Noblarf, and it was way deeper than a standard metal tank would have been. The uniflo vent was placed at the needle level with a slight ability for adjustment by rotating the tube (curved end would go up and down a bit). Both tanks provided superb, evenly balanced runs.

In both cases, the fuel pickup was at the rear of the tank, either top or bottom, depending on flight attitude. The unifo was fixed at the correct height, about 2/3 toward the rear of the tank.

Larry Renger · « **Reply #21 on:** August 27, 2007, 04:33:04 AM »

Happiness! I reinstalled the tank in the Smoothie after a thorough checkout. This time it is wedged in with a hard rubber foam instead of glued in with Silicone. In addition I switched to GMA 5/22 blend fuel. Hey, it works! Perfect engine runs at last. Now I can finish trimming the model. Currently I am flying with a 10x5 APC prop, but picked up a couple of 10.5x4.5s to try. They have been well recommended for this engine and plane.

john e. holliday · « **Reply #22 on:** August 27, 2007, 08:38:43 AM »

Larry, glad to hear you are finally getting the bottem of your engine problems. The Brodak 40 as well as his other engines are great engines when run accordingly. Have fun, DOC Holliday

Larry Renger · « **Reply #23 on:** August 29, 2007, 07:22:41 PM »

Andy Borgogna and I went flying this morning at a local schoolyard. It is sunk into a ravine, so nobody is bothered by the sound.

Andy has a Brodak 40 on a profile Nobler (yes there is a Classic legal plane like that!). The first flight, the engine was acting very wierd, ran away half way through the flight, then came back. He felt vibration in the lines, and sho'nuff, the mounting bolts were loose. Tighten them up, restart the engine, and suddenly the rear half of the muffler started rotating. Kill the engine, tighten THAT up, restart, and a perfect run! For various reasons that was the only good flight Andy got all day (except with the 2/3 ounce park flyer R/C I brought). But he went home a happy camper.

Message for the day, if your Brodak 40 ain't runnin' right, check EVERYTHING ELSE first. As someone pointed out to me, there are NO threads on how to turn the Brodak 40 into a stunt engine. Pull that puppy out of the box, do a break-in per instructions and give it a decent fuel supply, and you got a killer 2/4 break and adequate power.

I was flying the Smoothie, and switched to the APC 10.5x4.5 prop. The 10x5 was OK, but a bit fast (4.9 sec. laps on 55'lines). The new prop pulls the model through maneuvers everywhere and isn't too fast. We didn't get lap times. I put in 4 flights, and am really liking this combo.

Next up is to try it back on 59' lines.

Peter Nevai · « **Reply #24 on:** August 29, 2007, 09:43:21 PM »

Great, so what was it? the fuel or the tank mount?

Larry Renger · « **Reply #25 on:** August 30, 2007, 10:11:51 AM »

Great, so what was it? the fuel or the tank mount? (quote)

Dang if I know. I did two changes at once. I'll try a flight with my old fuel and see if I still get good performance. It will have to be the weekend after this one, though.