Can not get a good flight with my PAW 35. I have about 20 flights in my 47oz. re-kitted arf cardinal have tried 12x6, 12x6w, 12x7, 13x6 cut down to 12.5 props. Starts out ok but sages by the vertical 8s.

     Rob

Dunno about being an expert, but I've been running a PAW 35TBR in a semi-scale Supermarine Spiteful with good results. I use an 11x6, 11x7 or 12x6 prop (all work well) with a uniflow tank.  Fuel is 25% castor, 33% ether, 42% kero, plus 1.5% ignition improver, although I've tried a few different blends and the engine doesn't seem to care much.

My guess is that your engine is either overheating or going overcompressed. Why this would be is hard to say. Some of the props you're using, while well within the recommended range, are bigger than I'd go for in this application (and FWIW I believe the guys flying stunt with the 40TBR still only tend to use an 11x6 or 11x7). Perhaps your engine doesn't like the additional load when manoeuvring.   Have you tried something like an 11x6?

Overcompression is an obvious possibility. These things need to be given a decent warmup before launch, and the compression adjusted if necessary. Both my 35 and a friend's need the comp wound in half a turn for starting; it then has to be backed off immediately once the engine's going.  I prefer not to mess with the compression of a running engine, but in this case it's unavoidable.

You didn't mention what fuel you're using. Too much ignition improver can cause an engine to overheat.

Hopefully there's something useful in all that and it hasn't just insulted your intelligence.    

Cheers,
Steve

If a propeller change doesn't help, then you might try a more aggressive warm-up.  I do this on my OS 20-FP, which is a cold-blooded beast that doesn't seem to really warm up until it's been run a good long time.  I start it, then run half a tank through it on the ground, lean, then I top it off and fly.  I cheat; because it's a profile I can lean it out just by squeezing the muffler pressure tube, so I hold the tube until it starts sagging lean, then let go, the hold again while it goes through peak, etc.

I get much more consistent flights out of it that way.

If you're buying his fuel anyway, you might want to have a conversation with Mr. Clutton about your problem.  He'd be an expert, by all means!

                     I hope you get it corrected Rob, that engine is just too nice to sit on a shelf. ken

Hi Rob,
    I have two PAW 40's and although they are yet to see a model I can relate to you about what I have been told about them for Tony Eifflaenders Gold Cup team mate and several good club fliers here in Oz.

Believe it or not the recommended prop for a PAW 40 is an 11x7 and aim for about 9 500 rpm in flight. I have seen incredulous looks when quoting such high revs for a cast iron pistoned large diesel but the original was flown at quite a rate of knots.

This was borne out the previous owner of my 2nd (2nd hand PAW 40), he actually made a smaller venturi than the asthmatically small original trying to keep the revs down to about 8 500 and failed to get a good run also quoting IPN% as problems.

Anyway, if the 35 is much like the 40 then I would be tempted to let it run free with less of a load and forget the hype of diesels being able lug along happily.

That, and as mentioned before let it warm up before backing off the comp to a run setting. It has after all a steel liner and cast iron piston with cast iron contra piston all waiting to come up to temperature before the compression and heat related ignition point can be set properly.

If you get a bad vibration when the engine gets its head then I would investigate prop balance (of course) and how your big diesel is mounted - firmly I hope!
Is by any chance your Cardinal  - a profile model?

Good luck!

P.S Oh, I nearly forgot, PAW does offer a piston lightening service as part of its tuning services and maybe the 35 needs help in this area?

Rob, if you're using sensible fuel and not running overcompressed, there's one other suggestion I can offer.  While I've never had any overheating issues with the 35, I can't say the same for the 19.  Between us, a friend and I have 3 plain bearing 19s, a 19BR, and two 19TBRs.  Of those, the 19BR and one of the plain bearing engines have been very prone to overheating, regardless of settings and fuel.  I've been at my wits' end trying to solve this, and couldn't.  My final throw of the dice was based on the fact that PAWs tend to have a very sloppy fit between the cylinder and the fin assembly.  Some people are of the belief that oil is designed to fill the gap and thus transfer heat; I reckon that for proper heat transfer, it should just fit better in the first place.  (The other thing to bear in mind is that the 19 and 35 are bored-out versions of the 15 and 29 respectively, and actually have less fin area despite having more capacity.  Perhaps they are inherently more marginal for cooling?)  What I did was pull off the fins off the 19BR and wrap a couple of layers of Alfoil round the cylinder, so that the fin assembly fit nice and snugly when I replaced it - the idea being to have a good proper metal-to-metal fit.

I flew this for the first time this morning.  One flight was very slightly overcompressed (evidenced by slight slowing in manoeuvres); despite this, the setting never actually changed, and the engine didn't overheat.  The second flight was fast and slightly lean. Once again, it held the setting perfectly and showed no signs of overheating.  I'm not yet ready to believe that I've cracked the problem - it'll take quite a bit more flying yet, plus trying the same thing with the misbehaving 19DS - but it's looking promising.

The overheating symptoms I was experiencing were that the engine would initially have a good setting (even slightly undercompressed), but would load up after a few manoeuvres.  Vertical and overhead 8s were particularly prone to causing this.  The engine would sag and slow, and not pick up regardless of what the model was doing; generally I would land it and stop the engine to try and avoid damaging it.  The cylinder head would be sizzling hot.  Does any of that sound familiar?

Very interesting Steve and I have heard of the foil trick before and the Eifflaenders stating that oil 'will' fill the gap but stopping short of saying that is what is actually intended.

The PAW 19 that I have never seemed to overheat but as you know, I used one of those underwhelming 9x4 props so again, perhaps letting it spin out a bit is an answer.
(Wonder if the vintage combat boys ever faced the heat issue with their smaller props too?)

Something here puzzles me though mate, if the engine was overheating due to poor heat transference to the cooling jacket, how could the head of it be sizzling hot?
Perhaps it IS working as intended and the issue is before that?

That's interesting - I'd never heard of anyone trying the foil thing before.  Damn, thought I'd actually come up with an original idea..

Prop-wise, I've had overheating even with a narrow-blade 9x6, which is not much of a load for the 19. Blaming it on the prop doesn't explain why all the other 19s run quite happily.

As to how the head gets sizzling hot if there's poor heat transfer: I don't know.  Perhaps once the cylinder's hot enough, it expands sufficiently to transfer more heat to the fins, but by then it's too late.  Or the fins only get really hot when the model's on the ground and there's no airflow over them any more.  Who knows - we could fill the forums with this but it'd still be largely guesswork.  What matters more to me is that what we saw today was more encouraging than anything else we've tried in the last couple of years.  Still early days though - I'll keep at it and report back.

Hello again,
I must admit that I do not run diesels with a muffler. So the problems with oil residue colour being different with a muffler is a new one to me. I run diesels for stunt and sport so I never get into the realms of high revs that the combat and team race guys regularly use. I find that an unmuffled diesel at moderate revs is quieter than a silenced glow.
  I have heard of the problems with heat transfer and using aluminium foil etc. I rather doubt that they are applicable here. We are talking of a moderately reving engine, not one of the stressed screamers that you find in combat or team race. I have never had the problem of severe overheating in normal sport / stunt usage. I am not saying that the people that advocate foil  to help with this are wrong, just that we are talking of a different application.
  I have some experience of the bigger PAW diesels, but I prefer to use MVVS diesels when you get to the 35 and above. The main reason being lighter weight and less vibration. If you are using a PAW35 in a profile model. Then I suspect that this might be the problem, if everything else has been sorted. The bigger PAWs do have a reputation for more than the usual vibration problems.
  Why not contact PAW directly if you are still having trouble, they are a very friendly and helpful group of people! paul@paw.ac should get you to Paul Eifflaender. He would pass on your query to Tony, who has flown his Freebird with a PAW 35 with great success.
  Thinking about the Freebird, this has a very sturdy bearer arrangement, deliberately designed to strengthen the front end. Rigidity could be your problem, if you have mastered the diesel art and eliminated the usual problems.

Regards,

Andrew.  

I concur Andrew, fuel foaming caused by vibration could well lean out an engine and especially so when you reach the overheads with a partially empty tank.

I would be keen to hear if the 'sagging' is evident if the overhead stuff is done firstly instead of lastly.

Now the original Freebird/PAW 40 combination featured a chicken hopper tank with a very tight and small 'hopper' container that probably contained that possible foaming aspect quite well.

Yes, but we're talking about diesels here, not glows.  Any diesel I've ever used will misfire when lean, not sag.

And Steve, perhaps easier to get our friendly machinist mate to machine up a set of heat shrunk on fins or simply skim coat solder onto the outside of the steel liner for a real tight push fit.

What, easier than wrapping a bit of foil round the cylinder?!  (In any case, the machinist in question is busy making conrods for T2.5s, and I'd hate to disturb such important work!)

It's been a while since I had the back off the 19BR, so I can't remember if the crank's balanced or not.  I'd be very surprised if it was.  My 35 on the other hand, does have a balanced crank - just as well, as the piston is a heavy little lump of metal. 

Made 6 flights today with my PAW 35, did not have any 11" props so I cut down a Xoar 12x6 to 11.25 Flights were very consistant with no change from the 1st lap until 2 or 3 laps from the end. Power was lacking but it was a step in the right direction. I will experiment with more 11" props.

Thanks for all the help
  Rob

Parallel thoughts -
http://controlline.org.uk/phpBB2/viewtopic.php?t=2126

Rob,
One thing you could check with the PAW's is the motor mount. They really like a wood mount not one with hard aluminum pad that we use with motors with machined flat mounts. If you have it on AL pads and tighten it down it can stress the case and cause all kinds of run problems as it warms up. Also make sure the fuel has enough oil in it. The Davis fuel is really formulated for ABC or AAC engines not iron/steel. The Dr Diesel old English blend should be OK or something with 29% oil, 30% either, 30% kero and 1% ignition improver. The PAW's are like the Fox 35's they like lots of oil. Also don't over load them, they are a shorter stroke motor and like their "r" s. I ran mine with and 11x6 Zinger with no problem. When setting the motor first back off the compression until it starts to miss then adjust the needle to smooth as best you can then trim the compression and do a final needle a little on the rich side. Once the setting are found you can start a cold engine by going 1/2 turn down on compression and 1/4 turn open on the needle, once started back off the compression first then trim the needle and go fly. If is was sagging you had to much prop.

Best,           DennisT

Dennis, I am not sure about the metal mounting pad problem being a real issue mate.
Many Team Race PAW's mounted on alloy crutches do just fine!

Another 'piece of the puzzle' could well be the venturi size as supplied.
Just recently I was informed that my PAW 40's should be running a slightly smaller size than the factory standard when used for control line stunt and this news from Tony Eifflaender himself, so its not hard to believe that the 35 should be similarly treated.

The control line PAW's seem to be delivered for general CL use and being optimized for stunt use may well need a slightly smaller venturi.

One of my 40's is second hand and the previous owner said that it constantly suffered from heat problems that were incorrectly diagnosed as DII problems and eventually needed a new piston/liner set due to damage. So it was sent back to the factory to be 'set up' for stunt and this is where the news came from concerning the venturi size.
It would seem that PAW's (the 40 at the very least) need to be held back a bit to get the best out of them for stunt use, and doesn't this hold true for stunt engines in general?