4-4 run from a Stalker .61..

[Joe Yau]

Just wondering what are the tricks to get the straight 4-4-4  run from the Stalker .61 RE ?   (instead of the typical 4-2-4 runs.)  and still keep the 5.2 lap time.  

Thanks in advance.

[John Miller]

In the cases where I've seen this style of run, it often made use of higher pitch props, and 20 to 30% nitro.

If you want to try this, be sure to add additional head gaskets to lower the compression. The Stalkers come set up to run on FAI no nitro fuel so the compression is pretty high.

[Lauri Malila]

 Hi.

 I have no experience of Stalker, but a little with .60 Retro Discovery. I have found out that:

 -Modifying the muffler to be less restrictive (smoothing all possible sharp corners and enlarging the gas passages inside muffler about 50% bigger in area) gives more power thus you can run richer. This also cools down the exh. gas temperature and the muffler does not get blocked from carbon so fast.

 -Some time ago I got faulty series of pistons from Yuriy. When lapped to correct nominal size, they seemed ok, but there was some residual stress left from raw machining, maybe from lathe vibration, that made the pistons unround. When hand-fitted in cylinder, they seemed perfectly round but more accurate measuring showed some undulations in the surface, instead of round, the pistons usually had 16 or 20 "angles".
 As new, engines with these pistons had a beautifull, strong run in 4-stroke mode only. They run well only with castor oil and usually lasted only about 300 flights. After that the engines just seized. I found signs of very high friction especially in front part of piston and also in conrod bushings.
 My theory is that because of good nominal fitting, the surface pressure gets too high because a smaller area of pistons surface is in contact with cylinder wall. Also the thermal transfer from piston to cylinder was poorer. All this caused a too hot piston and thus detonation. I tried to cool the engine down by lowering compression but it led to other problems, especially in colder weather.
 Of course I cannot recommend you to screw up your piston, but maybe it's worth trying to increase the engines running temperature. Try blocking the air vents in your plane´s cowling.
 I know some F2D people have been using more loose cylinder/case -fitting when flying in winter. It is to keep the cylinder hotter.

 -One thing that helps for sure, is to minimize the crankcase bottom end volume. The Retro Discovery´s construction is quite robust, and with small efford (and a small lathe ) it is possible to make a new backplate that fills the case better. I have also reduced the hole in crankshaft with dural sleeve. The reason why this helps is that the engine behaviour is allways more stable when crankcase pumping efficiency is higher, there is a minimum amount of fuel/air mixture in the engine to be thrown around by G-forces.
 The higher pumping efficiency also increases the velocity of fuel/air -mix inside the engine and it is possible to use a bigger venturi - More power.

 Sorry for slight off topic.

 Lauri

[Brian Hampton]

It seems there are rather more versions of the 61RE than I was originally aware of but my gold head 2-2 version (as it's called) runs in a rock steady 4 stroke using true FAI fuel and no mods. In my experience, running a stunt engine hotter leads to a runaway 2 stroke so I try to keep them as cool as possible.

[Joe Yau]

In the cases where I've seen this style of run, it often made use of higher pitch props, and 20 to 30% nitro.

If you want to try this, be sure to add additional head gaskets to lower the compression. The Stalkers come set up to run on FAI no nitro fuel so the compression is pretty high.

Thanks John.  I'm currently running a 12"x5.75 3-blade,  I guess could repitch it up a bit and see how it response.

I have no experience of Stalker, but a little with .60 Retro Discovery. I have found out that:

 -Modifying the muffler to be less restrictive (smoothing all possible sharp corners and enlarging the gas passages inside muffler about 50% bigger in area) gives more power thus you can run richer. This also cools down the exh. gas temperature and the muffler does not get blocked from carbon so fast.

I will have a look at the muffler..  Thanks 

It seems there are rather more versions of the 61RE than I was originally aware of but my gold head 2-2 version (as it's called) runs in a rock steady 4 stroke using true FAI fuel and no mods. In my experience, running a stunt engine hotter leads to a runaway 2 stroke so I try to keep them as cool as possible.

I have the Pro RE 4-2 (2002-3) version.  I'm a bit curious what prop you're running on your Stalker?

[Randy Powell]

Joe,

You're in Vancouver. Talk with Alan Resinger. He is THE Stalker guy.