Long story short, I built a Dash 5 pattern ship and have 4 flights on it now. The 61RF is mounted inverted with a pipe and runs like a scalded dog on the ground.

First flight went great. Second and third flight the engine started to surge a little and dead sticked. I had a kwik fueler rather than a fuel dot and figured it was sucking air causing the surge so I changed it out and put a plain old fuel dot onboard.

Ran the thing on the ground with a different prop and tuned it up. Strong as all get out and no surge with the fuel dot so we took it up to see how it would do. Flew great for about 2 minutes and it just died. No surge, just quit on me.

Now I'm trying to figure out why it runs great on the ground but each time it's been in the air, it quits after a few minutes. Anyone have any suggestions? I'm open to just about anything at this point.

Thanks. Paul

Paul,
Did you have your tank leveled with your carb centerline? Is your engine pumped?
What size prop are you using?
How much nitro and oil?

Would you mind sharing some photos of your plane? I have a Dash 5 OS .61 powered also and love it....

Well, let's see here..........tank is pretty much inline. Might be a tad higher than the carb but not by much. It is pumped yes. That's probably the biggest reason I took the kwik fill out. With the pump I just figured it was sucking air. Putting the dot in did seem to help that as I ran quite a bit of fuel through it on the ground and it just ran great.

Tried a ton of different props but this last flight we were running an 11 x 7 just because I couldn't shorten the pipe any more out at the field since I'll have to take some length off the header and the 11 x 7 hit the pipe just like it should.

I've always used Cool Power 10% unless the LHS was out and then I'd use 15%. Haven't had any issues there and like I said, she runs fantastic on the ground.

I've got a shot of it in the photo gallery but to save you having to go looking, here she is............

Usually with a tuned pipe, you have the problem of the engine unloading in the air and rev'ing up more than it does static on the ground.
So it may be leaning out in the air on you.
My old method was to tune the engine on the ground with a prop with 1 pitch less than the in the air prop I use. For example if I used a 11x7 prop in the air, I would tune it with a 11x6 prop on the ground. That would get me closer to the needle setting needed for in air flying.
Later some engines had a second servo operated in flight mixture control that one could use to tweak the engine in the air too.

But in any case you may be a just little too lean when the engine unloads more in the air on you than it does on the ground.

Yup, that might be part of it. When it first started, we found that it was good with a 13 x 6.5 on the ground but couldn't get a good read since it started with it's surge.

This past weekend, we changed a couple props looking for a good match to the pipe and the 11 x 7 was best out of what I had. We did lean the low end just a tad and it hit better so perhaps we went just a little too far.

I'll have to do a little wing repair from this past flight. The thing just will NOT slow down and it sailed right past us when it did dead stick. Ended up in some rough turf and tweaked the left wing. I've got to unsheet some of the wing and fix up the wing tube socket / box before I fly it again but I'll give your suggestion a go.

Oh yeah, did have the adjustable carb on it to begin with but replaced it with one without the adjustment. It's got a plain 86 on it now. Running a 6 channel rx and just didn't have the servo space.

Thanks.

A 61RF needs more prop than an 11x6. It's a long stroke pattern motor. The hanno's we're running 12x11's if I recall correctly. I think you're under propped and may be putting the plug out to boot.

The best prop for that engine/application is the 11/8 Zinger. That is not a Hanno, and it will not pull the high pitch props.
You better be running 20% castor bean oil in that engine, or it will spit the cylinder liner out the exhaust.

Ask me how I know.

FBD.

What's the RPM reading with the 11X7 prop?
I think, based on personal experience with my Dash 5/O.S. .61 RF, that the RF Long Stroke motors like bigger props, like 12X8, even 12X9.

Even with pumps, it is my experience that with the OS engines, you want to find peak RPMs and back out about 400 to 600 rpms
I was flying mine with Byron 15% Nitro 18% oil fuel and my engine was spinning an APC 12X8 at well over 11,000 rpms on the ground.
I put over 150 flights with that set up with great performance.

Here is mine built from scratch with a friend's set of plans. This picture is after the upgrade to the O.S. Hanno.

Dave, I didn't say it was a hanno, I just said that the hanno's were swinging big props.

I'd be aiming for a 12x8 on an RF, and possibly a bit bigger on an RF-P. That's making the assumption that some pinhead hasn't cut the header down to 5" to make it rev it's box off. If that's the case, then all bets are off.

Oh and I hear you on the 20% oil, my 61SF looks pretty nasty inside these days.

Yeah, I knew the prop we ran was too small. It had a 12 x 8 on it when we first cranked it up but it wouldn't come up on the pipe and I couldn't change the header length at the field. That's when we played with the prop and found the 11 x 7 hit good. I plan on reworking the header a little bit and going back to the 12 x 8 or so.

The header and the pipe haven't been touched or cut to this point. It's set so the baffle is right at 18.5" (if I remember correctly) without cutting anything. I'll have to play with it once I get it on it's feet again and settle on a prop.

I'll jack up the oil to 18 to 20% as suggested and go with that.

First build for me, and first piped engine so the learning curve is taking control right now.

Great information guys. I will change a couple things up while it's on the bench and see what we get. Thanks for all the good advise.

Paul

If your header length works well with the 11X7, you are certainly going to have to lengten it more to work with the higher load of the 12X8.

Notice the Mac's specs on the .61 RF (near the bottom of the page)

http://www.macspro.com/tuning.asp

It calls for a 6" header (long) and a 11,300 rpm with the 11-8 Zinger.
Notice the header length on my RF. Mine turned 11,400 with 15%
PowerMaster with some added castor. I left it alone.

BTW, that engine is not likely to "come on the pipe" no matter what you
do to it. It is a long stroke engine.

If you have never tried the Zinger props, give 'em a try. If all you use
is APC's, you're in for a suprise.

FBD.

Dave, on the Macs spec sheet it's calling for a 6" header length with a 12 x 8. Did I read it wrong somehow?

Right now the header is about 6.5" so going by the specs on the Macs sheet, I can shorten it about .5", change the prop back to where I was and tweak from there. I'll probably have to richen up the low end since we did lean it a little too.

I'll give a Zinger a go. I think I have one back there but I'm not sure what size it is.

Maybe I'm not hearing the engine right but I'd swear when we ran it on the ground, you could hear it "hit" on the pipe. Not sure what rpm is was at but man, you could hear it jump at a certain throttle level.

I have my reservations about that pipe length. In the 90's we were running longer pipes on these long strokers to gain better throttleability, and a wider power band (oh god i hate using that phrase). If you're having the RF go all peaky on you, then Methinks the pipe's been clipped for peak revs, not for a broad power range.

What has the length of the stroke got to do with a pipe resonating in tune with the engine?

Just curious. Thanks.

....could you clarify the terms...."a pipe resonating in tune with the engine".
I cannot answer your question, because I cannot understand it.

FBD.

Hi Dave,
the quote was "BTW, that engine is not likely to "come on the pipe" no matter what you
do to it. It is a long stroke engine."

Sooo ....... since all the above was in the same papargraph it represents a particular point or line of thought according to the use of common English.

There are two statements in that line of thought, one is that the 'engine is not likely to come on pipe,' and the other is that 'it is a long stroke engine.'

And taken at face value you could reasonably assume that you meant that the cause of the engine not coming onto the pipe is that has a long stroke.
So Iasked why this is so. Or 'What has the length of the stroke got to do with a pipe resonating in tune with the engine?'

But I take things very literally and that may not have been your intention.

Cheers.

.....this is a low RPM "torque" engine. It does not have the port timing
necessary to turn high revs. When an engine comes on the pipe, the
RPM jump about 3 thousand. Normally an engine has to unload in the
air to get on the pipe.

Watch how control line speed planes are whipped by the pilot to get the
engine on the pipe.

FBD.

FBD, partially true but not entirely true. IF you're talking an over square speed motor, they'll certainly JUMP on pipe, but all 2 strokes will respond to the pipe. Some gently, some aggressively. The shorter the pipe, the peakier they get.

My 140 RX has a pipe as long as my arm, and it's a long stroke motor, are you going to tell me it doesn't come on pipe because it doesn't jump onto it?

....yo, Bro....I don't want to argue. I've been running these OS .61RF engines
for over 10 years. I wore out 3 engines in this same Super Kaos, including an
RF engine. (also a K&B .61 and an OS .60 FSR)

Goodbye.

FBD.

hmm, that's weird, I haven't worn a single motor out yet, and I have motors that have been running longer than 30 years.

Maybe I'm doing something wrong.

It's not about years it's about air hours or flights. At 1 flight per year, an engine will last... forever??.
The OS 140RX is NOT a longstroke engine. OS went back to the 'square' configuration (bore = stroke). Vibration levels went up in the longstroke engines. Read the review in RCM magazine.

As for the original OS 61RF-P in question: what plug are you using and what does it look like after these short flights? That engine will turn a 12x10 APC very happily with a pipe length of about 16.5" measured from the glo-plug to the 'high point' or first baffle of the pipe.
How hot was the engine when you landed? Overheating will kill the liner in the 'ABC' (really ABN) OS engines by causing it to peel [:'(] .
Avoid castor oil. Set the engine up to run slightlly rich. I use K&B 1L glo-plugs and get 60+ flight per plug with no element distortion. If the glo-plug element is not a nice smooth spiral (or missing altogether) after flying then the engine is running too hot due to a lean run or the pipe set too short.
As for castor oil... I have more than 7000 recorded flights with Hanno specials: Castor oil just builds up on the piston and sleeve making the engine run hotter. I know guys swear by it, but the quality of current synthetic oils eliminated the need for it decades ago.

You're correct about the 1.40, ratio of .894:1