First of all, were you flying a wood or nylon prop? Wood compreses and therefore loosens. Also, 4 strokes can have a nasty habit of backfiring and a jam nut helps, but not stop a lose prop. I saw a Saito 1.50 throw a Master Airscrew and spinner 50 ft on a backfire.
Earl
Another question from the newbie:
>
> While trying to run a tank of fuel through my Kader Sr /Saito 65, on the
> ground, the engine stopped and the prop with spinner (plastic) flew off
> and landed 4 feet away. The nut had come off and I thought I had that
> so tight I would break the prop. I have on order a truturn spinner with
> their jam nut adapter but it hasn't come in yet. I sure am glad I was
> not in the air. What gives?
>
> Mark
>
Hi Mark, A back-firing 4-stroke is quite capable of spitting the prop/spinner off, even with a lock nut. How was the engine running? Too lean (or running the tank empty....same thing as running too lean) and you're asking for a back-fire, which can also chuck blades off props. Wise not to be standing in front of or in line with the prop on a
4-stroker.....Murphy's Law clearly states that if it's going to throw a blade, it will throw it right at you! Murphy's Law also states that if it spits the prop/spinner off, it will ensure that the lock nut gets thrown in a completely random direction, which bears absolutely no correlation with where the prop and spinner end up :-) Bring a large magnet on a string (or a metal detector) to the field......saves a load of time crawling around on hands and knees peering into the grass :-)
That is generally acceptable evidence that you cranked it down too lean.
Use a tach and go one click at a time allowing a few seconds for the last charge to burn off and the new stuff to get to the combustion chamber. Slowly go to peak and then rapidly richen it to drop 300 RPM from peak.
Make sure you are seeing puffs of smoke at idle, or you are probably too lean there too. If so, fix it and go back to retune the high end. After a full tank of fuel, go fly.
Yeah. I fly both OS and Saito 4-C. The Saito seem to be just a little more prone to lean backfire and loosening the nut. It is difficult to keep the nuts tight on wood props. In fact, part of the routine inspection and correction actions on full-scale aircraft with wood props is the re-torque of the prop bolts to compensate for the compression of the wood.
Here is a handy device to toss into the trunk of the car, when you go to the field, for nuts, bolts, and steel servo screws (not brass, aluminum, or ss) in a large area of grass. It is cheaper than a decent metal detector.
Cut a piece of 1/4" thick plywood the same size (or larger) as the replaceable sponge type mop heads on one of those replaceable head sponge mops. Use a couple of brass bolts through the piece of plywood so that it will mount to the mop handle assembly just like the actual sponge assembly. Lay out and drill a pattern of 1/4" diameter holes, with about a 1/4" hole-edge to hole-edge spacing, into one face of the plywood. Order a bunch of 1/4" diameter, surplus NdFeB (Neodymium Iron Boron) magnets. Get ones that are about 1/4" long. Epoxy the magnets into the holes you made in the plywood. Coat the whole thing with come clear poly-U finish to protect the NdFeB magnets from moisture. Mount the finished magnet assembly on the mop handle. If you loose a nut or bolt, just "mop" the grass. These magnets are a little more costly than the other types, but they are significantly "stronger". There are a number of sources on the web for surplus magnents.
Mark- The problem starts with slippage between the drive washer and the spinner backplate. The knurled face of the drive washer is supposed to dig into the prop hub and prevent this, but the spinner backplate gets in the way. A fix I've found very satisfactory is to CA a 1/32 ply disc to the spinner backplate to provide something for the drive washer ridges to dig into and grip tight. The TruTurn spinner is very nice, but the backplate is hard and smooth, so no real help here as far as preventing slippage, but the jamming prop nut may at least keep it on the shaft. This is not an uncommon problem, especially with high compression four-strokes like your Saito.
Probably running it too lean. When I first started running four-strokes they threw props all the time. Now, they never do. I think the difference is not that they make better engines now, but that I have learned to avoid lean runs. The sound is different from two-strokes, so there's another learning curve, and a tachometer helps.
Your mixture was too lean. Saitos have a wide range of apparently acceptable needle valve setting, but you should richen it up quite a bit. It will quit throwing the propeller.
Does not need to have a spinner in the way ! I had my Magnum
4-strokes spit the double nuts and prop off during the break-in while on the test stand. Every time it happened was during starting. Never had if happen when I ran the tank dry.
Once the engines had about 60 minutes run time on them, the tendency to backfire pretty much went away.
I never had any problems with my Saitos which come with a double locking nut. And yes, I do not fly with wooden props. Never a backfire. No Special stuff. Just APC props, 5% Nitro Synth. fual. Perhaps the best trick in starting: Just make sure that the engine is not flooded. (hold the engine up and turn the prop around) Then hold your thumb on the carborator at full trottle. flik the prop 4 times clockwise. let go. then trurn the prop clockwise until you feel the compression. move the prop back 120degrees (counter clockwise) The attach the glowplug battery. use a stick and thow the prop clockwise to the compression point. Watch out: do not press it beyond that. The prop the starts spinning in the right direction.
To my opinion most problem come due to the use of eletric starters.
I'm interested to see you've been using 5% nitro fuel ? I have never used a Saito but I heard they went better on high nitro fuels, like up to 30% ? It's the main thing putting me off buying a Saito 180 but if it will run OK on 5% then I'll think again.
Agreed on all of the above. I have a saito 80 and had the same problem. I think wooden props are too light, they dont have as much inertia, so they slow down a lot more during compression. I notice no1 has mentioned trying a cooler plug?? I think it helped mine, would i be right in saying that a cooler plug will retard the ignition therefore help prevent backfiring also?? especially in hot weather.
I agree.The heat range of a glo-plug definately affects the timing. The nitro content also affects it. Some engines just don't run as good on high nitro or any nitro at all. It all depends on the design of the engine , mostly the compression ratio. I always run my engines a little richer than many do and very seldom have a prop throw. I just re-built and put new bearings in my son's Enya .80 4 stroke and started it for the first time yesterday on the stand. The second time I throttled up there went my prop , nut and washer. That's the first time in probably 2 years that I have thrown a prop. When I was breaking in an OS .46 FX over 2 years ago it kicked a prop one time in the first few minutes of running. All my 4 strokes are OS or Enya.
Seems to me that Saitos are the worst for throwing props , just my observation. Could be wrong..
I have also noticed when some guys are using the glow driver on the power panel they turn it too high and sometimes kick a prop.
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