Pat Johnston Strikes Again

I spent a great day at Stately Johnston Manor last Thursday while on vacation. Pat and I flew his P-40 (man, that plane flies good) and his QED profile. The QED is a 40 sized profile modeled after the cross country racer of the same name. Pat has a Saito 40 on the plane and it was a blast to fly. We discussed designing a full bodied version. If you're looking for a plane to compete in Profile 40, the QED with the Saito 40 is a great choice. It's a lot of fun to fly.

On another note, Pat's been using the P-40 semi-scale plane to do the last bit of break in on a new Saito 56. Encountered a strange problem. We would get to just after the outside loops and the engine would quit, just like it ran out of fuel. Still had half a tank. We took the tank out, checked for leaks and bad tubing (it's a clunk tank with standard venting that's always run great before). Everything looked fine. We changed out the tubing anyway. We tried changing fuels and managed to get it to fly an entire pattern, but right after the outside loops it would still suddenly loose about 500 rpm. 5 or 8 laps seemed to cure it and the rest of the pattern was flown. Pat was using some RC fuel with lube added. 10% nitro, 23% oil. We switched to Powermaster 10/22 and the engine ran the whole flight with the lose of RPM noted. Both fuels have been used previously in Pat's other 56 and ran great.

Never seen this happen before. The engine had about a half hour or 45 minutes on the test stand before going in the plane. We finally decided it just wasn't broken in yet, but it seemed awefully weird.

Any thoughts?

Randy,

I am having similar problems with the fox 35 on the twister. clunk tank with fixed uniflow. It will die on a hard outside corner of the square loop going inverted. If I ease through the corner it will be ok.

Last year at Woodland the motor quit on the third outside loop on the twister with a 4.5 oz square wedge uniflow in very strong wind. It wound up and either flooded out or starved out. Pulled like a horse.

Bob Smiley

Randy,

I had identical runs a couple of years ago, with the engine going suddenly slow after the outside round loops. I was completely mystified until, after one flight, I happened to rotate the prop and the engine squeaked. I was running a 10%nitro, 20% oil fuel but had been fooling around with extra nitro. When I added extra nitro, I increased the volume of the fuel and effectively reduced the Percentage of oil (and alcohol). With this figured out, I simply added oil as well as nitro in appropriate percentages and the engine run problem was solved. I think the engine was getting hot due to insufficient lubrication. At the point of the outside rounds the hot engine was dragging internally. A little later, I think, the AAC sleeve grew enough to accommodate the hot piston and relatively normal running characteristics returned. It seems you had enough oil, so I'd suspect the new engine was running a little hot from lack of break in. More time on the bench, a smaller prop, or a little extra oil in the fuel should eliminate the problem until you have more time on the engine.

More time on the bench, a smaller
>prop, or a little extra oil in the fuel should eliminate the
>problem until you have more time on the engine.
>
>Al

More nitro with the more oil ALSO is the best combination, I think. That would be YS 20/20. The nitro keeps the engine much cooler and richer, and the synthtic blend oil combination makes it the best CLPA fuel for Saitos (at least) I have ever tried, and I tried a bunch.

>Randy,
>
>I am having similar problems with the fox 35 on the
>twister. clunk tank with fixed uniflow. It will die on a
>hard outside corner of the square loop going inverted. If I
>ease through the corner it will be ok.
>

Completely different problem. I can tell you how to fix it, but be prepared for the slings and arrows. By the way, it has nothing at all to do with the tank.

>
> Completely different problem. I can tell you how to fix
>it, but be prepared for the slings and arrows. By the way,
>it has nothing at all to do with the tank.
>
> Brett

While I am sure Mr. Smiley does in fact want an answer to his problem, I would like all concerned to acknowledge the fact that prior to Brett giving his answer I am the first to step up and say he is wrong, wrong, WRONG!!! Sling and arrows indeed...

Brett
>
>While I am sure Mr. Smiley does in fact want an answer to
>his problem, I would like all concerned to acknowledge the
>fact that prior to Brett giving his answer I am the first to
>step up and say he is wrong, wrong, WRONG!!! Sling and
>arrows indeed...
>

Hey, I've gotten almost as much hate mail on the topic of the "Fox On Profile Burp/quit" as I have about you. And it has been about equally rational.

>Randy,
>
>I am having similar problems with the fox 35 on the
>twister. clunk tank with fixed uniflow. It will die on a
>hard outside corner of the square loop going inverted. If I
>ease through the corner it will be ok.
>

Let me first preface this with the fact that I am fully aware that many readers believe that this is all being made up, and doesn't really happen in real life, and that everybody who thinks so is ignorant, delusional, anti-American, a Fox-basher, etc. Given that I already know this, please refrain from reminding me of my many shortcomings in this area.

To fix this problem, you need to reduce the volume of the bypass. One quick way is to cut a piece of 1/4x1/8 spruce long enough to be wedged between the liner and the bypass and not be able to work itself loose. A slightly classier way is to fill up the bypass with J-B Weld, and only leave a passage about 1/4-5/16 wide and bypass depth open. The result of either of these is to increase the velocity of the fuel/air charge as it passes through the bypass. It will NOT reduce the power at stunt revs, in fact, mine seem to run more strongly afterwards, although it's pretty minor. And it does nothing at all for the shaking that will destroy your profile engine mount in very short order.

Thanks to Frank Williams for finally figuring out the root cause of this extremely frustrating problem and addressing it. You can do all sorts of things to the tank, fuel, plug, fuel line, etc, that will affect the "burp", but none of these address the root cause.

Thanks to Frank Williams for finally figuring out the
>root cause of this extremely frustrating problem and
>addressing it. You can do all sorts of things to the tank,
>fuel, plug, fuel line, etc, that will affect the "burp", but
>none of these address the root cause.
>
> Brett

Brett,

You are really beginning to annoy me. First you supply, or simply repeat, the one correct answer (the one I did not give to Mr. Smiley when he called last night--just leaving my options open, don'cha know). Then you claim to have received hate mail about me. Well, actually that bothers me not at all. But you already knew that.

LAST EDITED ON Aug-11-03 AT 03:20 PM (CDT)
 
>Never seen this happen before. The engine had about a half
>hour or 45 minutes on the test stand before going in the
>plane. We finally decided it just wasn't broken in yet, but
>it seemed awfully weird.
>
>Any thoughts?

I am a little apprehensive to say that this isn't enough, but my math says 45 minutes only equates to about 21 oz of fuel. That is not much. I typically put a gallon through a new Saito engine on the bench. That takes about 4 hours, and that is a Saito 72, which burns 25% more fuel than the Saito 56.

I expect to be putting out full power by two flights, and that has always been the case using this amount of break in. I used to refill the 12 oz fuel tank on my bench several times through the day (10-11 times). This last engine I took a clue from Al and dropped a clunk into what was left of the gallon after completing the initial sloppy rich idle runs, started it up, set the needle where it was smoking real healthy (about 4-5 clicks rich), and went and did my yard work. A few hours later I shut it off, let it cool, and started it back up and took it in a few turns it in until nearly peak and ran it there for the rest of the gallon.

After that gallon of Sig stunt fuel, I ran about 20 oz of YS 20/20 through it to clean out all of the castor while it was still hot. Then I cleaned it up and bolted it into the airplane. No further break in appeared to be required. I do however, recommend checking the valves at this point.

But, hey that's just me. I hate to mess with engines when I am trying to fly. Bobby G. is a huge proponent of lots of break in on the bench. His new engines put out top power the very first day. No kidding, he made a believer out of me. On my own, I have found that babying an engine too much during break in serves absolutely no purpose either. At some point of the the break in the engine must be set to heat up a bit like it would in a stunt run. Either that or expect to break it in while turning in cicles (which is no fun).

I say two hours of "cold" break in and two hours of "hot" break in makes for good pattern practice. That's FOUR HOURS. That is why I say use 5% Sig or Powermaster GMA for break in. It's cheaper than YS 20/20 (which all that nitro and oil just gets blown out of the muffler anyway), and the extra castor oil seems to work very well for breaking in engines. Spend the $12 and burn the whole gallon, you will save money in the end if your TIME is worth anything to you.

Randy,
I fly Radio Control also using 4 strokes. I have a OS 52, OS 70, Enya 53, Enya 120 and a Enya 155 all 4 strokes. All my motors get a gallon of fuel minimum through them before they will even idle reliably and not until they have 2 gallons of fuel through them do they start to make the power they were designed to put out. You are asking to much of these motors. They are not like breaking in a 2 stroke, you or your plane is at high risk flying the pattern until you have more time on them, believe me I have learned the hard way. Run your 4 stokes longer before you do the pattern. Your motor will be happier and so will you.

Well, you were all wrong. Pat wrote me tonight and said that he changed to an all synthetic oil fuel. 10% nitro, 24% oil and the problem went away. Engine runs great. I should note that several of you were at least partially right. The consensus is, it doesn't have enough break-in time. Pat is switching between the all synthetic fuel and some half castor, half synthetic fuel now and it runs fine. Figures.

I should note that the Saito 40 powered QED had virtually no break-in on the the bench and has run consistently and strong from day one. Hmmm...maybe there some sort of inverse relationship between engine size in the 4 strokes and needed break-in time. The Saito 40 needed virtually no bench time while Godzilla's 72 needs 5 gallons of fuel for initial break-in... :p

Anyway, the problem seems resolved.

The Saito 40 needed virtually no bench time
>while Godzilla's 72 needs 5 gallons of fuel for initial
>break-in... :p

Steve Moon's new Saito 40 completely lost compression never to return. Maybe you got lucky...

The only Saitos I know to fail had short break in times. I would much rather have an engine blow up on the bench. Call me crazy.

Hey Theo,

It was a joke. I agree with you. Pat has never been one to spend a lot of time on the bench. And his stuff always seems to run pretty well. He was well aware that the primary problem was just not enough time on the engine. We just wanted to rule out other contributing problems. Since Pat has a flying field just outside his door that is available 7 days a week, he flies a lot. I mean really a lot. This time of year, it's every day for several flights. So it just doesn't make sense to him (I guess) to waste time running an engine on the bence when he can put it in a plane, run it rich or whatever and get to fly.

I should be so lucky.

>Hey Theo,
>
>It was a joke.

I know. I can dish I just can't take it, right?

Not bench running an engine is simply not smart and a complete waste of one's time. I too used to short the break in time, and it was really not smart. Airplane are to valuable to subject to shaking, sputtering, coughing, potentially FAILING engines. IMHO. A flameout could be a disaster for example.

Maybe I should charge a "break in fee" and advertise in PAMPA.

"5 gallons or its free"

'zilla,

Hey, you're preaching to the choir. I run mine on the bench. Have a setup much like you describe. Test stand and big, honking tank. I ran my last Saito 56 at idle (well, about. 4000 rpm or so) for an hour before touching the throttle. It had 2 hours on it before I installed a venturi and has about a half hour on it with the BAV (about a .320). I think it's almost ready for a plane.

But that's just me.

LAST EDITED ON Aug-13-03 AT 01:10 PM (CDT)
 
>'zilla,
>
>Hey, you're preaching to the choir. I run mine on the bench.
>Have a setup much like you describe. Test stand and big,
>honking tank. I ran my last Saito 56 at idle (well, about.
>4000 rpm or so) for an hour before touching the throttle. It
>had 2 hours on it before I installed a venturi and has about
>a half hour on it with the BAV (about a .320). I think it's
>almost ready for a plane.
>
>But that's just me.

Isn't that just insurance for more fun flying? I think so.

Glad we agree. 4 strokes have a lot of moving parts, best to get them all juiced up and real slippery before subjecting them to a square eight.