FNQFLYER

The size of the prop used on these diesels (or any for that matter) depends on the purpose to which it is put.  I currently run a 14 x 8 on a diesel converted ASP 32 for the Texaco event in old timers / SAM  I have run as big as 16 x 8 on 40's at around 4 to 5,000 RPM.  The size of the prop is determined by the use.  Eg ED 2.46 racer (rear induction in a control linr team racer  had a 9 x6 needle prop but a 12 x 6 for Nostalgia

fiery

My Feedback: (2)

I ran an 11 x 7 on my PAW .40 R/C and found it suited the engine perfectly. Good thrust - right in its band for efficient power production (torque).

RDJeff

My Feedback: (11)

What type of props work best with these? I'm thinking the K series from Master Airscrew, made for 4-strokes would be the ticket, but I'd like to hear from the experts.

The Senior Telemaster is all done now, just need to mount the engine and the exhaust system. The engine still needs a couple more break-in runs, but that is always fun!

RDJeff

My Feedback: (11)

I've got several runs on the .40 now, maybe 30 minutes run time altogether, and I've noticed that it doesn't throttle well. It runs fine with the throttle wide open, and will idle way down, but stumbles a lot when the throttle is opened back up. It always comes back, but some of the stumbles are several seconds long. This is with both a 12x7 and a 13x6 prop. Could the props be too big to allow smooth throttle operation? Perhaps I have a different problem? Thanks for any help!

Mr Cox

I don't have any of the large PAWs, but it sounds like a low end tuning problem to me. Try leaning the low end, if they have an adjustment...

Diesel Die-hard

Actually, it's the standard diesel cooling-off syndrome - many R/C diesels do it, and the PAW's seem particularly prone. The best compression setting for high-speed running takes piston/cylinder temeperature into account - the hotter the cylinder, the lower the optimum compression setting. When you throttleback for any length of time, the cylinder cools down. When you throttle back up, the cylinder is below its optimum wide-open temperature and hence the compression is too low for best running. It takes a few seconds for the temperatiure to re-establish itself, after whch the engine will run smoothly again. That's just the way it is with many R/C diesels! You can get around it to some extent by running slightly over-compressed at full throttle, but that's not good for the engine in the long term. Better to accept the few second-long "stumbles"!

RDJeff

My Feedback: (11)

Die-Hard, I wondered if that was maybe the problem. I guess as long as it doesn't die, then everything should be okay. Will it get better as the break-in proceeds?

Recycled Flyer

The Senior Telemaster has the engine open to the breeze and I am just wondering if some sort of cowl would keep the heat in better?

A cheap and dirty fix that you could try is to simply roll some large O rings down over the cooling jacket to reduce the wind chill factor - I have seen that done with large control line diesels that are open to the breeze and the grooves that is cut between the fins holds the rings in place nicely, and it is ultimatley 'tunable' by removing or adding rings as you see fit.

Cheers.

fiery

My Feedback: (2)

That is a great idea!

I have also seen black heat-shrink rubber tubing used for the same purpose. Another one for the quick and dirty file!

Mr Cox

Sure, there is a cooling down effect in diesels and the ideal compression setting is slightly different between low and full throttle. But there shouldn't be much hesitation once you get the tuning right. On the smaller PAWs it helps to put in another carb that has a low end adjustment, while on the stock carb it is always a compromise.

On some engines it helps to limit the full throttle opening (on the transmitter), the last portion of throttle opening does little for the top revs but alters the carb setting.

If you want to see good, instant, throttling diesel engines then have a look at some of the movies of Norvel conversions from AndyW.

RDJeff

My Feedback: (11)

I got in a few more bench runs last night, and with about an hour of break-in time on it, I was able to lean the mixture down, and now it throttles very well! I ran a 13X6 K-series Master Airscrew on it, and got 6,000 rpm out of it, and a smooth 2,200 rpm idle. Then I switched to a 12X6 version of the same prop, and got 8,200 rpm, and the same idle speed. Throttle response is pretty much right now. I think it's ready to fly tomorrow!

R/C Phile

My PAW .60 i just as described on the earlier posts. It does not have much power but I did get it to throttle and run as well is it could by picking an "In between" carb setting and running the compression a bit on the high side. Eric Clutton says to reduce the compression to the point where the exhaust is light and "straw" colored, mine had just a bit of chocolate color to it. It's far from knocking but not quite as "Loose" as what is preferred by Eric. I ran it a bunch that way and have not seen any signs of distress.

That way, I could let it idle for a minute or 2 and still have clean acceleration. That's more than enough for my flying as I only "truly" Idle for a few seconds after rounding the final turn before landing and while going downhill after vertical maneuvers.

I do have to clarify "Clean Acceleration": It's not an instant zoom-up like a glow, more like a steady and progressive acceleration, as if there was a heavy flywheel attached to the engine. Not quite the response for 3D flying but good enough for touch and goes and last minute landing aborts.

It's a nice engine but If I bought another diesel .60, it would be an MVVS .61

RDJeff

My Feedback: (11)

Well, that was a fun experiment! I had the local expert take it up on it's maiden flight, and it is indeed underpowered. The first flight was with a 13X4 prop, and the plane did a long takeoff roll, followed by a rather sedate climb. He flew the pattern a couple of times, then brought it in. We swapped props to a 12X6, and took it up again. This time it took off a bit quicker, and actually climbed, this time a bit less sedate. After a few times around the pattern, the plane had enough altitude to do a loop. After that, he did a slow pass, and the radar gun read 22 mph, followed by a "high-speed pass" at 33 mph. Upon landing, the instructor declared that the plane was always too close to the edge for a beginner pilot like me, although he enjoyed flying it because of the need to stay alert and really fly the plane.

I haveto wonder if a smaller prop turning at a higher rpm would do enough better to make it practical to fly...

ddd

To Fiery, That's one of ours.

buzzard bait

33 mph flat out...love it! Really, it does sound like great fun. I bet it teaches you to do coordinated turns.

I'm trying to picture it doing a loop.

RDJeff

My Feedback: (11)

I already took the PAW out, and put in the O.S. .61 FX. I took it to the field, but it was too windy to fly. Next week...

Now I need to find another plane to fly with the PAW.

R/C Phile

I had mine on a smaller plane that needed some speed to fly and the 12 X 10 Zinger was the best prop for it. I was getting 8200 rpms which would translate to 77 mph theoretical speed.

The 12 inch diameter was large enough to produce decent thrust while not overloading the engine and allow it to rev while the 10 inch pitch gave enough speed to gather some momentum (Enough for decent climbs and medium size loops).

For a little more thrust and still a theoretical 59 or so MPH, I got 7900 rpms out of a 13 X 8 APC.

The high pitches allowed to turn the torque into (some) speed.

You might want to try that when you get more experienced with the plane. I tried about 6 props ranging from 15 X 6 to 12 X 10 and the plane went from practically un-flyable (15 X 6) to a becoming a decent performer (12 X 10).

Trfourtune

I believe that some of the performance deficiencies on the large PAW engines is due to the fuel used when testing. if you are using a break in level of fuel (30 castor,35 kero,33 ether,2 ipn) to judge the engine, you are missing the potential.
Once fully broken in and you have a few hours on it, start changing your mix. i would go to the fully run in mix (PAW-25,40,33,2) for a while.
If you have a TBR/BR, fully broken in you should be using (per PAW) roughly 20,48,30,2. or you can push it to 15,50,32,3 but i wouldn't for longevity reasons.
Only then can you see the full worth of the engine. We are generally impatient and push it too soon thinking that's all we got.
Old thread but this is one of the few discussing this topic. My 40tbr is strong. my 60tbr not so, but it's planned for a WW1- 1/6 scale biplane-point being to fly slow scale. The 15's and 19's are sweet! I don't have smaller ones.