4-2-4 engine break for a nats winning engine

An open forum for questions on any control line glow engines

Moderators: Frank Klenk, SteveM

4-2-4 engine break for a nats winning engine

Postby stringjobs » Mon Dec 01, 2014 2:28 am

I am wondering about the timing and hemi head required to produce a 4-2engine brake it's required for a decent start engine run you can't just put a venturi on an RC engine the timing is completely different 14000 RPM is not an engine run that you want for a start ship you need to launch at 88 hundredrpm and then when it breaks you want to bug 10 thousand the difference between putting venturi on RC engine is it will just run away after the three consecutive loops and never come back to a rich engine runwho did you consult for the engine timing frank bowman built me a can be 61 and he machined one ounce off the engine lightness is imperativetom lay worked exclusively with super Tigers sixties however he can get a can be 61 to run like announce winning enginethere are different can be 61 they varied drastically the early pewter thrust washer with the sin pewter Dr washer the timing was almost perfect so they can be 60 ones with the turned knurled Dr washer the timing was completely different and was not rightit required a lot more rework the TECO with the pewter sin Dr washer worked much better it was almost perfect now frank bowman he meant machined a1 ounce off the engine that big web coming down from the exhaust. Lightneds. Must be concidered. Tom lay did internal mods as well as a frank boman ring. His rings are seperior to os and rivil moki. There are many engine grues out there . The common fix. Is to lower the sleve and raise the ports. This works much better than decompressing the engine and opening the intake bore. For example ; droo the sleave .008-.012 andraise the intake ports .020. With a hemi head. Also blend the crank bore to bypass bump out of the casting.. you cant just put a venturi on a rc timming crank and get the same results. Tom mugglton has the numbers foe the 4011 ans frank boman has thenumbers for the 61. There is also lew wollard and bob hunt. Please get this right. If the .40 and .61 ran right out og the box you coukd sell a ton of them. If it just haulls ass its no use for stunt . You cant fly mock one one stunt. It needs to run rich untill you load the engine in a manuver.please consult the expert engine. Turners for advice befor you get to far into production. I can send you guys engines to copy if you will consider this. Launch at 8800 and peak at 10500. Not 14k
stringjobs
 
Posts: 3
Joined: Mon Dec 01, 2014 1:15 am
Location: lax

Re: 4-2-4 engine break for a nats winning engine

Postby stringjobs » Mon Dec 01, 2014 3:18 am

You need to have 18 degrees of blow down or timming over lap. Bob hunt had a tape explaining this by a guy named dick papis if memorie servies me right. Point. Id if you get this right you could sell them like hot cakes. Conversly if it not done right you will get a bad rap. You do it right your engines will be at the nats like they use to be back in the day the 6.5 rulled the roust. There are not many engines that could compeat. I see a line of lee customs. Tom lay customs tom muggltons and maybe bob hunt speicals. Lew wollard len numan has a .35 that will haul a sig magnum. The stalion .35 is one under rated engine, it has tontons of torque. Rear roter torp .40 rocks as well as the s bump. The veco .50 on and on you have a great legacey if done right. Please consult the experts if only to comferm what your doi ng is correct. Pick up some gma engines to backwards engines from the pros. Stunt engines are different than rc engines. You can not fly stunt at max rpm.it needs to slow down and not fly 85 mph strait down. Randy smith has maybe the best stunt engine on the market. Bob, randy ,frank are all great guys and easy to talk to . Dont forget lenard newman his site is called the stuka stunt site. Frank's rings are second to none. Please consult the experts while there around. Lew wollard. They will all tell you this and i am sure to help a usa engine company all they know to help you make an engine second to none. Tom mugglton is. Amachinest glad to spend the time. Please make a real stunt engine that runs 4-2-4 right out of the box. Its vitial you get this right. Dont be shy pole the experts.
stringjobs
 
Posts: 3
Joined: Mon Dec 01, 2014 1:15 am
Location: lax

Re: 4-2-4 engine break for a nats winning engine

Postby loucrane » Fri May 22, 2015 2:26 pm

Hi, Stringjobs,
It’s been a while since your post. Since then the "need" for a 4-2-4 run in Stunt has lost a lot of favor.

The new-metal engines do run happily at higher RPM than the older iron-piston-in-steel-sleeve types. Winning stunt fliers are less concerned how it sounds than how it works in flight. If it works better, it is better. So we launch at around 11.5 KRPM on a 4" pitch prop, or something like that... It lopes along smoothly. lightly loaded until we pull a maneuver. Then, prop load increase is easily met by the somewhat richer needle setting - with no dramatic change in exhaust sound. And when the loads are released the engine had not gone to a very different heat and mixture condition.

The simplest answer for the Schneurle, ABC engines, first designed for RC, has been to accept a rich 2-cycle run at higher RPM, on a combination of prop, plug, fuel and needle setting that works, with a uniflo tank or pipe or muffler pressure fuel feed. The right steady, rich 2-cycle combination is harder to upset than an over-rich 4-cycle that changes firing mode, torque output and heat, then drops back to the previous conditions.

The RC-based engines have a long RPM range in 2-cycle operation. They do gain power when loaded to near the max they can put out with the successful prop/fuel/plug/load combination. They even can actually gain RPM under load, but it is harder to hear that change in 2-cycle. In 4-2-4, the engine might not actually gain RPM instantly, when it shifts from firing every other to firing every rev. We hear about twice as many exhaust noise pulses as soon as load drives the engine into firing every rev. That DOES NOT mean RPM has doubled.

Yes, the Bob Hunt/Dean Pappas articles were great! I'll miss Flying Models magazine...

Best timing for a 4-2-4 run means less these days because we've tamed the beast of the hi-RPM RC engine.

My favorite timing for 4-2-4 engines like the old Fox 35 was 130°exhaust/120° bypass; 10° total blowdown. That allowed longer use of combustion pressure before venting AND the longest practical bypass flow duration. The 4-2 break could be moved to higher RPM - think higher power - in 4-stroke before break. The RPM after the break was still only slightly above the highest 4-cycling RPM when the setting was right. Prop power applied relates to RPM when the load conditions are the same.

I believe Lew Woolard's Silver Fox 35s and Fox schneurle 40s use the same time and blowdown. He recuts certain pieces a certain amount to get that. Given Fox's old reputation for dimensional variances, I measure each one and adjust what and how much I cut to get "my" numbers in that specific example. Not much difference, usually, but I feel better about it.
loucrane
 
Posts: 95
Joined: Mon Jul 26, 2004 2:39 pm
Location: Sierra Vista, AZ, USA


Return to Control Line Glow Engines

Who is online

Users browsing this forum: Google [Bot] and 1 guest

cron