More SuperrHots Fun! Throws, more engines, radios, angst...

Update: Did some refresher studying. I see that a blown plug is a sign of an excessively lean run. Well that plug is blown alright -- to smithereens. I just examined it under magnification and almost the entire element is missing. Only an 1/8" remains at the top, attached to the plug casing at the spot weld.

That means A) I had a mortally lean run, and B) The engine ingested the missing element section. Damage incurred by ingestion depends on the element failure mode--whether it fragments of vaporizes, I assume.

I assume I will minimally need a new sleeve and piston, 1/3 the cost of the engine. Dave

or, C: the plug simply wasn't up to the standards required by the application

possibly, or maybe not, elements have been known to drop out and blow right out the exhaust port without damaging the piston or liner.

on another front, you indicated that the engine ran ok, then ran out of fuel and quit, and then wouldn't restart.

Normally, IF the engine was running lean for very long, it would either sag badly or even get the piston hot enough to stop the engine (ABC type engines)

Also, I have seen engines in the past that reached a certain point in the "break-in" process where they got exceedingly fussy, and requires some tender loving brutality to get them running up to snuff. I have a FP-40 that went through that whole process back in 1996, and once past that point, it has flown hundreds of flights since.

Having said (typed) all that, Cool Power has NEVER been my fuel of choice for ABC or ABN engines, even with added Castor Oil. I always used Omega (back when I could get it) and had better luck with that. Now with the nearest hobby store 60+ miles away, I have switched to Red-Max and have them blend mine special and ship it to me. Ain't cheap, but it beats spending $20 on gas to go buy a gallon somewhere.

In short, It may not be as bad as it seems,

"Don't cut your throat yet Calhoun."

It looks C is the case. I tried a brand new OS 8 today and it fired right up. The other OS 8 and Fox plug I tried were used but thought to be ok. Apparently not. I should have tried a new plug straight away but it simply didn't occur to me. I've truly lost much of the knowledge and feel of running these engines, modest though it once was.

Yes--exactly, it ran fine until the last drops. That fragment of element remaining on the blown (first) plug must have been enough to ignite the fuel/air charge through some final fraction of that last tank.

Interesting. The engine is running now as it did before the blown plug, but I wouldn't call it user friendly yet. It tends to spit and run backwards occasionally. The high speed NV setting seems to affect this quite a bit, but I wonder if 5% nitro would be much better than

Frankly, I ran a lot of CP through my 40fp without problems, but that fuel is broadly condemned, I assume not without reason. What is CP's primary weakness? The question is academic, I won't be buying more.

Care to share your Red Max recipe? I remember those folks as being very good to work with.

I will have to find a Muffler alternative. The included one's end piece and barrel rotate mindlessly at high revs, regardless of tension on the through-bolt. The cake is iced with glorious leakage. It is comical. The Tower 75's Muffler is notorious for this according to the RCU guys, but I demurred, thinking it simply couldn't be that bad. Well, it is -- and worse.

The Bisson Pitts seems to be a mixed bag on that engine. Perhaps an MCP, major surgery on the 75's retched stock Muff, or a Mac Muffled pipe. But then weight and CG again become an issue.

I had forgotten the agony and ecstasy of this hobby. Dave

Do yourself the biggest favor you have ever done, and get a #%$&*# electric starter. A chicken stick on that large of a new motor is a plain and simple headache! You can then play with the settings to get them right, without having to worry about getting it started again.

Can you drill it so that at least a portion of each hole is in each half of the case? Do that, and put a small sheet metal screw in it.

Put a little gasket maker from an auto parts store on the joint, then tighten it down and let it set up.

The old screw in the "seam" trick has worked for me many times in the past. Looks kind of a kludge, but it works.

Sometimes with a muffler that won't tighten(or when you break the screw through it) you can replace the screw iwth a 6-32 threaded rod and double nut each end. mk (there's more than one way to skin a cat)

Yes they are very easy to work with,

Going from memory here, I don't have the formula in front of me,,

MY preferred mix is

They DO NOT recommend using that much Castor, but they will happily blend it that way if you order it like that.

I use the same mix in all my engines from the FP-40 up to the Webra 1.20 and all my 4 strokes (OS Surpass,(1) OS Surpass pumped,(1) and Saitos(4) ) all .91 size even though it is NOT recommended to use Castor, or at least THAT much Castor in the 4 strokes. But then, it's not recommended to use that much nitro in the Webra either.

FWIW, the Red Max (FHS) fuels seem to have a higher viscosity than any other fuels I have tried. In other words, you usually have to open the main needle a few clicks if you change from another fuel.

Hobby Services is sending me a new Muffler (no charge, they are merciful) which I will modify as you described. I'll either use self tapping screws or tap the holes for machine screws.

Electric starter---LOL. I actually have one, but it has no torque. I'll have to get a better one. You're right, a chicken ^&*%$^& stick is a nighmare. Dave

My planes are strictly utilitarian affairs. The Kludge motif blends in well. Dave

Well--I dug out my no-torque "Hobby Shack" starter, and it works like a champ on the Tower 75! Starts it up every time, no running backwards.

I seem to remember it having trouble on my OS46SF occasionally, but then I was using a lead acid battery. Now I'm using a sealed Gel type. More current available? I'm doubting this and thinking the 46 has better compression than the Tower 75. The 75 is now turning a MAS 13x6 at about 10.4 k -- seems like it's struggling, but that's after 6 or so tanks, and not peaked.

I don't know, it turns a Zingali 11x7 at 14.5 k, but at least the 75 is working. I'm wondering if I sucked some of the 'nads out of it during my ham-handed break-in. Oh well, a new piston and sleeve is only 30 clams.

Anyway--I was never much of an Electric starter fan, but I am now. Thanks... Dave

So, when is the SH going to fly? mk

I'm guessing about 2 weeks. It's taken much longer to achieve flight status than I anticipated. Thanks for the help and interest. Dave

Bob, I'm curious about how you arrived at these percentages, but it does strike me as a reasoned compromise.

I do have another SH question, hopefully the last. I do not have plans or manual and Midwest no longer supports this model.

Engine mounting: If your SH is accessible, can you tell me were the engine prop shaft is located relative to the plane's datum? I make the assumption that the datum is a line passing through the center of horizontal stab and wing center. I'm thinking that the shaft (thrustline) and datum should be collinear.

I'm stunned by the amount of time it's taking to get this thing flight ready. By this time I could have built a new kit, which will probably be a CG Ultimate. Thanks for sticking with me. Dave

I'm not Bob but I'll chime in again :) When I got my SH it had a cowl, the engine was mounted so that the spinner lined up with the cowl. I May be able to get pics later. mk

Thanks for chiming MK. I did not build a cowl when I built my SH years ago. I did have an engine on at it back then but I think the mount was lower on the firewall than it possibly should be. It was placed so that the shaft was 1/2 - 3/4" below what I assume is the planes datum.

I don't recall any obvious bad habits due to this--ballooning at full throttle, for example. But the real problem is tank placement, which is dependent of course on carb location. I'm having a devil of a time with this. The tank compartment is barely over 5" long and even a Hayes 11 oz barely fits length wise.

I want to avoid siphoning and/or excessive richness with the tank to high, or excessive leaning with the tank to low. I'm trying to nail it so that the tank centerline is 1/4 - 3/8" below the carb. Engine mounting upright puts the carb too high, mounting sideways possibly to low. Sideways is the preferred method in this case--easier throttle linkage, Muffler under fuse for less splattering, etc.

I'm using a Hayes square mount which limits placement options. A round version may have been better. I really don't want to get into making a custom hardwood mount--that will take me a month to engineer and build.

I'm obviously slow and am always amazed at guys who claim to get a kit into the air over a weekend.

Anyway.....blah, blah, blah. Too many variables. A fixed spec on the prop shaft/datum relationship will eliminate a variable and firmly dictate other parameters: tank local/type, engine mount, mounting orientation, etc. I'm being a bit of a perfectionist and as a result will NEVER get this thing in the air! lol Dave

A very wise feller down in Cajun Country did some primitive testing of the corrosion prevention properties of various oil / fuel mixtures. Based on his results, I chose the mix I use as being a good compromise of the good and bad of the various mixtures he tried.

Ok, I FINALLY got a chance last evening to hit the archives and dig out the plans for the SH.

According to the plans, CG is right AT the center of the wing main spar.

Thrust line is 0 in the vertical, and 0 to 2 right thrust. (mine flew nicely at 0)

thrust line passes directly through the center of the wing (Yes, it IS the datum line as you recalled)

In my OPINION, whether the centerline of the crankshaft is directly ON the published thrust line,, or a bit above or below that line should have relatively little effect on how the plane operates. the firewall on this plane is relatively tiny, so to get more than around 1/2 inch away from the published number is going to be a bit difficult.

If my OPINION is wrong, perhaps some of the folks who understand it better could jump in and tell me where my reasoning is at fault.

I saw far too many new or recently setup planes come to the field looking pretty, and going home in pieces to ever put a timetable on getting one of mine in the air. Better to take whatever time it takes to get it all right before it goes to the field.

bob

Thanks for the info Bob and well considered analysis. It turns out the shaft will be 1/2" below the datum. We'll see what happens, probably won't be dramatic. Maybe I'll have to add some down thrust.

Now I can just get the throttle servo to stop groaning... Dave