tomfiorentino

Hi everyone,

I'm looking for feedback in a few areas:

Tuned Pipe: I have a Hatori pipe that has a screw plugging a hole that I am assuming is for a pressurized tank setup. Would this be utilized in non-pumped engines only? Also, the consensus I have gathered from other reading is to start the pipe length out at around 15 inches...plug to widest cross-section of the pipe. Can anyone confirm that as a good starting point? As far as tuning is concerned, can anyone recommend an authoritative website discussing the protocol for dialing in the pipe? I'm not clueless here...I understand the theory pretty well but I just want to collect my thoughts on target RPM and which way to move the pipe etc. before I'm out in the barn with an engine screaming at me...ha ha!

Tank set-up: The engine is going into a Dash Five which is an old pattern kit that is fairly small. I would like to have the tank closer to the wing tube and CG than up front behind the firewall. I realize everything has a limit, but how long can the fuel lines be from the tank to the pump before I start running into a problem? What is the conservative and "safe" range in this regard?

Reliablility: I didn't get much play on this question in another forum so I thought I would add it here...probably a better place. Kind of open-ended, but how reliable and trouble free are these pumped and piped engines. It's new...and I am pretty neurotic about after run oil, in-line filters etc. But at the end of the day and in the long run are these engines more of a set-it-and-forget-it proposition or am I buying into a fair amount of tinkering. I understand that parts for the pump are not readily available, if at all, so I can make the engine a nice piece of art on my office credenza. Heck, these days I'm only flying because I am teaching my 9 year old so I have enough monkeying around to do at the field. Another thought is to buy a Saito 125, which will fit nicely, and fly with no scewing around. Comments?

Appreciate the help!

Tom

Bax

My Feedback: (11)

The screw on the tuned pipe blocks a hole where a fitting can be installed to provide pressure to the fuel tank. Use it in non-pumped installations. With a pumped engine, you don't use pressure to the tank. The tank just gets vented to the atmosphere.

To set up a tuned pipe, you need to have it too long to start with. You then install the desired propeller and fill the tank with the type of fuel you wish to use. These cannot change once you've tuned the pipe to the engine. If you change prop size (in pitch, diameter, or both) or fuel, you'll have to re-tune the pipe.

Start the engine, lean it to maximum RPM, and then tach it. Shorten the pipe system by 1/4". Repeat the process: start, lean, and tach. If the RPM increases each time you shorten the pipe, keep going. When the RPM remains the same or decreases, leave it there and then start flying the model. Listen to it very carefully. There is a very distinct sound when the engine is "on the pipe".

Don't use the silicon joiner to "trombone" the pipe system shorter while the engine's running. You'll find that you won't be able to keep a setting that way. You have to lean the engine at a given pipe length and see how it runs.

Some other things: A too-short pipe system will cause the engine to trend lean as it's run. A too-long system will cause the engine to trend rich. Pipes have to have time to warm up before they work well, so you can't just "start and go". You'll need time to get everything warmed-up. More RPM needs a shorter pipe, so if you have a slow-turning engine, you'll go with a longer pipe.

As far as a non-pumped installation is concerned, you need to keep the fuel tank as close as possible to the engine. Much farther aft than behind the firewall will result in fuel-draw proplems. If you want the tank at the CG of the model, you'll need a pump.

tomfiorentino

Great Bill, thanks for the feedback.

Regarding your trombone comment, do you mean don't use the silicon and use something else or are you just indicating not to try and adjust the pipe while it is running. Rather, I need to run it, warm it up, tack it then shut it down to change pipe length then start all over again.

Just to be clear I have the pumped version of this engine. So would having the tank back from the engine say 7 to 10 inches create a problem or is that too far? What is a safe range?

How about the reliability factor Bill. Am I setting myself up for some constant tinkering or are they pretty steady once you have them set-up?

I'm glad you responded...I have seen many of your other posts and I figured you would be the guy to talk to.

Tom

Bax

My Feedback: (11)

When we said "trombone", we meant that you don't run the engine and then slide the pipe inside the silicon connector to shorten it. You must stop the engine, adjust the pipe, richen the engine a bit, restart, then lean to peak, and use the tach.

Use of a pump won't affect how the engine reacts to the pipe. The pump just makes sure that fuel gets to the carb.

Once set up, the engine will run very consistently because the pipe does have a "window" where the RPM can vary a bit and you'll still be getting the full effect. This allows for most changes in weather. However, drastic changes in conditions may require that the pipe be retuned for maximum effect.

tomfiorentino

Bill,

I think I did pretty good with a benchrun and the pipe on my OS. I am using a Pattern 12 X 11 APC, Powermaster 15% with 18% synthetic/castor blend and it was about 54 degrees out.

I started with 15 inches from plug to where the pipe flares to its largest diameter. I let it get good and warm and tacked 10,300. After shortening by 1/4 two times, I ended up at 14 1/2 inches and tacking at 10,800. It ran strong, but I believe the needle became a little more sensitive and the transition to full throttle was a little more "peaky". I seemed to be losing a little range, but the exhaust had a little more crackle to it which I think is the distinct sound you told me I would hear.

I'm going to work with it a little more, but please tell me what happens when I go too far? How will I know when I am done? Is there a optimum RPM to look for with that engine/prop/fuel combination?

I was getting a fair amount of spitting out of the carb (don't know if that is normal) and some exhaust blow-by at the header pipe. Can I use some high temperature silicon to make a gasket at the header pipe?

By the way, the exhaust blow-by was fairly black but nothing metalic to it. Is that caused by the hot header pipe kind of burning the oil just due to the hot temperature or is this a sign of a problem.

Thanks for contiuing to check in on the thread for me. Your feedback is great...

Tom

Bax

My Feedback: (11)

If, when you tach the engine, the RPM levels-out after you shorten the pipe system, you've reached the limit for that propeller. You can go back one increment and then fly the engine to see how it goes. Fine-tuning must be done as a result of flight testing.

A tuned pipe will make the high-speed needle more sensitive. That's just a result of using a pipe. You may lose a little engine RPM range at the lower-end, so your idle may be a bit higher.

Fuel spitting out of the carburetor is a result of a very long intake duration. The only real way to stop it is to add an air filter or a longer intake tube on top of the carburetor. Usually, though, this would happen at lower throttle settings, and is not usually important, though it will cause the engine to become quite dirty with burned fuel residue. If you have exhaust leakage between the engine's exhaust stack and the pipe header, it's best to file them so that they have a very good fit. A gasket will allow flexing, which will loosen or break the bolts that hold on the header. Using silicone as a gasket material will work for a time, but you must make sure absolutely none gets into the engine. It will "kill" the glow plug.