chorner

.... and if you really care about your engine, add a small amount of RedLine Break-in Additive to your mix. It contains zinc, and phosphates that greatly enhance wear charcateristics and works like having castor oil in that it thoroughly coats and 'sticks' to the mating components and creates a very good boundary layer between the two parts - much more so than straight 2 stroke sythentic can & will alone. Use it at least until you use up the first bottle of it, then maybe once in a while thereafter. Kind of like when you buy a new car - and you would traditionally run it on a castor based oil, then switch to synthetic after a certain mileage.

Pretendpilot

.
wouldn't this be bad for break-in? I always heard it is better to have an oil that is less effective to beak-in, so the parts WOULD wear together?
.
btw, what RPM does the 777 like to run at? is it better to load it to 4k or to 5k or?

TimD.

My Feedback: (207)

I like 4000-4500 on the ground. It will unload another +/- 1000 in the air. I use a 20x14-3blade and 22x12-3blade

chorner

No, the oil actually helps seat the rings properly! Has a dual purpose with the additive.

The 7-77 will be bogged down IMO if you run it under 5,500 on the ground. After break in you can run a 24x10 around that rpm or a 22x12 at a little over 6,000 and hit the power band nicely. Just my experience. If you run it in CDI it'll do 6,400 rpm on a 24x10 with methanol which I run it at... and handles it just fine (though I certainly don't pin it full on a dive). I guess depending on the plane and for a more "scale" flight you'd want less RPM but on my 32lbs Corsair, I bring the RPM up.

Straightleg

Pete,
I have an older 7-250, but maybe these things can help you on your way. Here are my experiences:
Fuel system
The pulses from the air intake that the Walbro needs to draw fuel, can be weak. If you have long fuel lines and the engine stops under accelration or in top of loops, it is caused by G forces on the fuel, and preventing the fuel to reach the carb. Use a pump.
Prop
As written above, 34x12 is way to small(pitch) I use a Biela 32x22, which pulls 20% more than a Menz 32x18. To high rpm will give you less pull and a selfdestructing engine. 4000 rpm on ground is a good start. Remember that equal specs on props, is not always the same prop from different brands.
Fuel
I use environmental fuel(which is actually alcohol) Gives less carbon buildup inside engine.

/terje

Pete S-RCU

OK, it's a 34x14 prop, my mistake.
More questions, the nipple on the exhaust ring is for fuel tank pressure or also I'm thinking smoke oil?
My carb has a primer bulb on it, do I need a tee fitting and connect fuel lines to both fittings?
I will never be able to reach it in the plane, so it would be nice to just plug it and not hook it up?
Although they sent an ignition sensor module and wire, it's been run at the factory and so I'm thinking it's not needed.
I think the ignition sensor is inside the rear of the engine where the ignition unit is mounted.
How would I hookup a telemetry tach to this engine, I have a Spectrum TM1000 unit?
I'm using one on my Saito FG57T twin and it just hooks to the ignition module, works good.

Straightleg

OK, it's a 34x14 prop, my mistake.

More pitch


More questions, the nipple on the exhaust ring is for fuel tank pressure or also I'm thinking smoke oil?

Only for smoke

My carb has a primer bulb on it, do I need a tee fitting and connect fuel lines to both fittings?
I will never be able to reach it in the plane, so it would be nice to just plug it and not hook it up?

I do not have this type of carb. I use a brass tube to inject a small amount of fuel into the crankcase. Works very well.

Although they sent an ignition sensor module and wire, it's been run at the factory and so I'm thinking it's not needed.
I think the ignition sensor is inside the rear of the engine where the ignition unit is mounted.

On my engine, the ignition sensor is mounted on the engine front housing, which have a cord that goes to a double connector from the ignition module. The other is for battery.

How would I hookup a telemetry tach to this engine, I have a Spectrum TMknow
I'm using one on my Saito FG57T twin and it just hooks to the ignition module, works good.

I do not know

/terje

Pretendpilot

thx chorner. wow, that's a lot more rpm than I thought would be good for this engine. the manual says the rpm range is 1000-6000 with 6300 being max. I figured they are probably over-rating it, since the 4.8hp appears to be over rated (maybe for 6300 rpm?) sure would be nice to see a torque curve, but I couldn't find one.

jspauld2

Pete,
I don't believe there are any extra wires included with the engine.

As for the telemetry, unfortunately there is no 'plug and play' option out there. The built-in telemetry feedback is unique to RCExl style ignitions like what's on the smaller gas engines by Evolution (Saito, Zenoah, and others as well). You would need to use a universal sensor and find a way to measure the RPM from the crank

Hope this helps.
Jimmy

Pete S-RCU

You're right, I found where the sensor goes.
Yes, the tach thing will be a problem.
Maybe a coil wrapped around the plug wire would generate enough volta to trigger the tach in the TM1000 rpm module, couldn' hurt to try?

Next, is the prop thing.
I didn't realize the pitch is different on a large prop.
Seems like a 12" pitch would still give about the same speed as a smaller 12" pitch prop,
just a lighter load on the engine.
I think I'll break it in with the prop I have, just watch the rpm to keep it low enough.

chorner

Don't think it's the voltage that has anything to do with the TM1000 not reading the RPM. It's an incompatibility with the output of the RCEXL tach and the RPM input adaptor. Some have tried tapping straight into the hal sensor with luck.

Also the pitch isn't "different" on a large prop. It's just whatever gives the engine the proper load, and you can adust slightly with pitch and diameter to better suit the specific application.

Pete S-RCU

The issue is getting a signal to the tach, the coil 'might' provide it?
It may also have to be amplified to a usable level?
If so, I could possibly build a little amp with a few op-amps.
Something to think about.

jspauld2

That's not a bad idea. I do not know the specifics needed for the input on the TM1000, and you may fry one or two along the way, but I think the theory might work. As long as you are careful with what you are feeding the TM1000 this might work. I'm definitely not an electronics expert, but it seems well thought out.

Maxam

My Feedback: (62)

A word about prop pitch and diameter. Lets say we have an 18x12 prop. The pitch to diameter ratio is .67 . Now another prop is a 24x 12 so now the ratio is .5 and finally a 32x12 is .38 ratio. If all props are spinning at 5000 rpm the airplane should fly the same speed. The issue is aerodynamic efficiency. The first prop has an efficiency of 77%, second 64% and the third is 53%. Yes super low ratio's have great STATIC thrust but as the airspeed increases the efficiency goes down dramatically. I hear people say a slow plane should have really low pitch. The Pietenpol air Camper recommended prop is a 76x 48 with a ratio of .63! That is a long way from the very low pitch's some modelers use. As Bob Boucher says "low ratio props are good for stirring paint" . He is an aerodynamics pHD who owns Astroflight. Now 3D was not popular in those days but please think about this when a prop is selected. Yes I am building a Pietenpol Sky Scout and it will have a Seidel ST-540 40cc radial. Prop will be an 18x12. -Tom

Pete S-RCU

I have a Eurcoupe with a Saito 57cc twin in it.
It has the CH igniotion system with a rpm output that works with a digital tach, or the TM1000 telemtry module.
Won't work with both at the same time however, probably the input impedance is too low and the signal gets dragged down too low.
Will have to get my scope out and measure the signal to see what I need.
Will have to wait till the weather warms up a bit before I can run the Saito and do my research.
S/B fun.

Pete S-RCU

That's interesting, I should probably consider a 34x18 or so.
Would like to know more before I buy one, they're not cheap.

Straightleg

Amen !

j lauria

Maxam As I have always followed your advice in the past, including buying the UMS 9-99 for my87inch Ziroli Stearman, I have decided to put in the OS carb using the CH adapter. I have several questions regarding the installation. I don't believe the stock choke assembly will work with it. I see that Chorner uses an Os choke valve. I find that Tower lists a choke valve as number LXCF23. Is that the correct one to use? No matter how I look at the set up it looks like getting to the LS mixture control will be difficult. I am thinking about setting it a little rich and relying on my on board ignition to keep thinks going at low RPM. Any tips on installing the OS carb and tuning this engine with it would be appreciated.

MY Stearman has flown quite well with the stock 9-99 with a 24X12 prop but could use more at the high end. I have to admit though that after 40 plus years of modeling my engine knowledge benefits greatly from this thread. The introduction of the radial has enhanced my modeling pleasure, but I would be lost without this thread.

Maxam

My Feedback: (62)

Hi J. After owning a new 7-77 I would say a 24x12 is a bit small on that engine! Maybe your 999 would like a 25x12 or... You can use the throttle linkage with a bit of modification but do replace the pivot point rivets. They are way too sloppy. I am not sure of the choke catalogue number, but it must be the one for the Gemini 160. If your Stearman is not cowled, you can get to the idle adjustment. Make a long thin screwdriver from a push rod by filing the blank end and screw the threaded end into a drilled dow rod for a handle. You can only adjust at high throttle position with the engine off of course. At least you can get to it without removing the engine. Your comments make this thread rewarding. Thank you. -Tom

j lauria

Hello Maxam,
Many thanks for your reply. The whole set up makes sense to me now. The carb must be installed with the HS control coming out of the left side of the aircraft. This requires that the throttle control linkage be moved to the right. I now understand Chorner's comment that he countersunk a hole in the mounting plate to flip the carb around. I made a long thin screw driver as you suggested and sure enough the LS adjustment can be reached from the top of the engine. I wouldn't think of hiding this beautiful radial under a cowl, it looks perfect in my Stearman and always draws compliments at the field.
I shale stay tuned as you folks continue to to make comments and give advice enhancing the radial engine experience.
Regards-John

j lauria

Maxam,

Can the portion of the replacement carb which houses the LS mixture control be rotated a few degrees clockwise so that the adjusting screw is facing more straight up toward the front of the engine and therefore easier to engage with a screw driver? It looks to me that one would have to readjust the throttle stop screw to do this. I am reluctant to change the settings of the throttle stop. On my setup in the Stearman I have to approach the LS screw from behind the firewall for a good straight shot at the screw from above. This is certainly doable but requires removing the hood panel which extends over the firewall. Since I will probably be tuning the engine with this panel off it won"t prove too inconvenient.

John

chorner

I think the only "saving grace" if there were to be one, is that you generally don't need to fiddle with the LSN at all once the engine has been broken in and properly set. So it's overall a very minor annoyance.

j lauria

chorner,
Thank you for your input. Your previous posts on this subject have been very helpful as well.
John

Maxam

My Feedback: (62)

Do NOT move that device!!!!! It is precisely set!!! Changing its position will change the spray bar orientation.

j lauria

Maxam,
Many,many thanks !!! I knew I could count on you to keep me out of trouble.
John