Hey Guys,

I was lucky to snag a Summit III with an O.S. .61 RF motor. The motor looks new but the bearings were rusted and pitted, so I replaced them with some Boca Bearings. It is not a pumped motor, but it does have a pressure nipple on the backplate of the motor. It has a nice tuned pipe but they have no pressure tap on the header. So the question is, do I just use the pressure tap on the back of the motor? The tank is mounted on the CG and has some pretty long fuel and vent lines. Will the crankcase pressure be sufficient to pressurize the tank. I always ran the Hanno pump motors back in the day.


Thanks,

Maddogg

You could install a pressure nipple on the pipe or header. Case pressure might be too high without some kind of regulator.

Terry in LP

Most likely if a motor has been tapped for crankcase pressure a pump was used or a fuel regulator.(Perry pump/Cline regulator) Since the tank is placed on CG and the lines are long you might have fuel delivery issues, so a pump or regulator will be needed. You can also move the tank forward to the original position as drawn on the plans and then tap the pipe for pressure for a conventional setup. Is the plane a tail dragger or trike gear?

Hey Paul,

It is set up as a taildragger. I am not going to compete with it, I just like the way the the old pattern planes fly. I forgot to mention that the motor is a .61 RF Longstroke motor. The pressure nipple was not added on the backplate it was done by the factory. If I did move the tank forward where should I put the pressure nipple, on the header or on the pipe?

Thanks,,

Maddogg

Hi Maddogg

Take a look at the picture of the back plate of the .61 RF it does have a boss for a nipple but it came blocked by a screw. If yours has a nipple installed, remove it and plug the hole. Pressure fitting placement on tuned systems (As per Macs Products)

The most consistent pressure is found where the pipe first reaches its apex in width. However, this may be inconvenient. Many modelers choose to place it in the header plate. The problem here is a possible pressure spike which can develop when the aircraft is in a power dive, out running the system tuning. The spike may flood the engine causing it to lean or die. (This occurs seldomly, though.)
Note: Never place the pressure fitting on the header tube or the muffler part of a tuned pipe.


Even though Macs recommends not to tap the header for pressure, I’ve never had a problem. Different installations sometimes require this.

tapping the actual header plate is the safest way to install a pressure tap, i use 8-32 pressure taps, never a problem, but saw many headers returned to mac's for repair because of stripped out header tubes and cracked header tubes from pressure taps, if one looks at both he nelson and jett tuned mufflers they are using pressure from the equivalent of a header plate tap, and i own a few of those and zero problems, plus rigging pressure lines that are much shorter always makes things easier for refueling as well.

I dont know about changing the tap possition on your set up. I kind of like the idea of the tank resting on the CG. For that though you will need the pressure of the crankcase, just needs to be regulated. A Perry regulated pump would be really nice once properly adjusted. IMHO.


DM

You are either going to have to run a pump or close it off. The pressure in the crankcase has to be high enough to not only push the fuel through the ports of the engine; it is now having to make up the volume in the tank as the fuel goes down to push the fuel forward. You want a pump.

Ok guys here is an update. Thanks for all the help I really appreciate it. I went ahead and tapped the pipe at the apex and installed the nipple. I blocked off the case pressure. I left the tank on the CG and ran the motor last night. It fired right up ran pretty good. Sure enough though, at 45 degrees nose up it would die if you punched the throttle. I went ahead and flew it and just left the power up. It sure did bring back some memories. Two clicks up and that was it. I think I am going to move the tank up front to shorten all the lines and give that a try. I will give an update tomorrow. Again, thanks for all the help!

Maddogg

I have a new never started O.S. .61 RF (w/o box)with a 10 cc Macs muffled pipe and header to sell. I'm flying SPA andcan't use it. Anybody interested?

Ok guys, I am done!!!! I can't get this thing to run right no matter what I do. Who wants to buy a Summit III with a barely running O.S. .61 RF with new bearings? Geez!!!


Maddogg

I have an Atlanta that was a pain in the.. butt. Rossi FIRE mounteed inverted with pipe, tank behind firewall. Ran great on the ground in the air it would surge and die. I moved the tap around, same thing. I ended up adding a Perry oscillating pump, problem solved. Later the original owner said that set up needs a pump.

DM

I agree with Aurora 60, A Perry pump or a Cline regulator will fix your fuel delivery issues.

If you are lucky. Not all Cline/Perry setups are successful. Good Luck

i have an os pump and carb from an rf. well i actually have the engine minus piston and sleeve. but if you would like to buy the pump and carb my e-mail is [email protected] say 60 including shipping. but a presure nipple in the header will work just fine.