Backplate pressurized OS 25 fp progress!

I was able to do some engine testing yesterday with the OS 25 fp I am using in my Noblarf. As y'all may recollect, I am attempting to get consistent runs with the tank pressurized from the crankcase.

Initial flight testing had shown that the engine would only run dead lean and beyond, to the point where the exhaust was coming out a very dark brown.

After doing some reading, and getting various input both in person and from this fourm, I decided that the engine was overcompressed and had too hot a plug. Bill Netzband's plug article, as recently posted, confirmed my direction.

On pulling the head, I found that I was running a 4-stroke plug (OS-H) that actually protruded down into the cylinder, almost touching the piston at TDC. Increased compression, lousy combustion chamber shape, and too hot, all rolled up into one!

Coke cans turn out to be very nice, soft .005" thick Aluminum, so three head gaskets were produced (eat your heart out K&S). Also, at the Ontario show I purchased a variety of plugs to try. Enya #3 and #4 (Which turn out to be Hot and Hotter, thanks a lot!) OS #8, Fox Standard and Cold. I will be on the search for even colder plugs, as these have become popular with the RC car racing guys.

I tried 2 then all 3 gaskets and 3 different plugs. Finally settling on a combination that seemed to work the best. I didn't take any rpm figures, as all I was interested in was achieving a docile engine. The runs were all on 15% Nitro 9%synthetic, 11%castor fuel, swinging a 10x4 stock Zinger. Weather was cool and dry - perfect.

Bottom line is that with all 3 gaskets and the coldest plug Fox makes (#4302) the engine is perfectly tractable, at least on the bench. I can now get stable runs anywhere in the usual running range I want. Even got a 2/4 break when I tilted the test stand! The needle is very sensitive, and I may yet switch to the ST needle just to get finer adjustability. Needle response time is remarkably slow, I still don't know what that is about.

Next week we'll see if that holds up in the air where it counts. And, naturally, over the course of the year when the weather is hot and humid, the altitude different, etc., etc., etc.

The needle is very sensitive, and I
>may yet switch to the ST needle just to get finer
>adjustability. Needle response time is remarkably slow, I
>still don't know what that is about.

That is due to the incoming pressure into the needle. The volume increases reapidly as the needle is pulled away from the seat.

First, get ahold of an OS 1a RC NVA. This is the smallest they made, with a .35 mm. pitch thread. It should tame the needle setting down. If you need more, make a pressure restrictor. simplest is to put a piece of .018 line in a short brass tube. Glob some solder into the end, and then pull the line out. Its stainless and shouldn't get soldered in. this gives you a short, .018 restrictor to put between the bladder and the needle valve to reduce the pressure and fuel flow so the needle can be set.

I think the 10 LA backplate needle valve will also work. It isn't as easy to mount as the 1a.

where do get these needle valves does towers have them?

I tried 2 then all 3 gaskets and 3 different plugs. Finally settling on a combination that seemed to work the best. I didn't take any rpm figures, as all I was interested in was achieving a docile engine. The runs were all on 15% Nitro 9%synthetic, 11%castor fuel, swinging a 10x4 stock Zinger. Weather was cool and dry - perfect

Have you tryed 10% nitro and 20% all castor?
Thunderbolt plug?
Are you stock NVA on the backplate?

Scot(iz got to know)Riese

Hello Designman,
Sounds like your headed in the right direction, and I have a question. What wre you usin' to cut your head gaskets, and where did you get it?? Thanks, Gil:D

Tower has the LA 10 backplate #####. about 8$ This is for remote mount tho < like a bladder or case pressure.Suction/ Stunt seems to work better closer/or in the venturi.
MM PN # 21007000 Cover Plate 10LA

In the distant past, I just used an X-acto knife (#11 blade).

I use a compass with a blade in it run in reverse. Instead of cutting through the aluminum, you scribe out the circle. More like a lathe cutting tool than a knife. I scribe the outside diameter and leave it. Then I cut all the way through on the insde. Scissors then finish the outside cut. Crude, but it is effective. Use an Xacto to scrape off the burrs.

Since these replies are dropping in at random, this one is to Scott Ries. I am using an OS 25 fp, not LA, and a standard venturi and NV system.

The whole point to the exercise is to use 15% or more nitro and actually run a modern engine in stunt the way the engine was designed to run. HIGH POWER, BIG PROPS, LOW FUEL CONSUMPTION.

OK, I'll turn myself in to the "Un-Stunt Activities Commitee" for lifetime blackballing. I'll never score over 250 points in competiton again.

Even if I get it running so the plane goes through the maneuvers right, the judges won't like how it "sounds" and I am DOOMED! (Except if Trostle is judging, he actually watches the maneuvers).

But that is another thread entirely, and if you want to "go there", start another post, please.

I drilled the pressure tap to .013, and am not using a bladder.

Whoah! Why would the tank pressure be, in any way, dependant on the venturi needle setting. Think that one over again please.

Did you measure crankcase pressure vs. RPM before and after? Would you, please?

This is interesting. With a similar setup, the OS .15 ran more reliably with a Thunderbolt RC plug than with a standard Thunderbolt, more reliably with an APC 9-5 than with an APC 9-4, and more reliably with 10% nitro fuel than with 5%. Coincidentally, each change that made the engine run more reliably made the plane go faster.

I remember the needle-valve lag from using crankcase pressure in combat long ago. Switching to bladder pressure eliminated the lag. I also remember that fuel system leaks were the bane of crankcase pressure systems. Fuel system leaks are much more easily diagnosed (and can be corrected more quickly) with bladder systems. I offer these bad memories for your information; I'm not encouraging you to switch to a bladder.

Larry stated above that he was using the OS "H" glowplug, and I am pretty certain, there is no such animal. The 4S plug is the "F". Maybe it would be good to re-state the fuel used, venturi size, NVA setup, and whether the engine is new or thoroughly broken-in. While I agree that the "F" glowplug was not appropriate, I would be very surprised if any Fox glowplug would work better than the correct Thunderbolt, Zinger, McCoy or K&B (all made by Ohlsson). In the original thread, I also suggested fuel system leaks. I don't trust silicon fuel tubing that much...neoprene is still good stuff. Steve

These replies aren't falling into the places I want them to go, so please bear with me.

I can't say anything about the "H" plug, except it looks like an OS and it has "H" clearly stamped on it. It definitely has the extended nose of a 4-stroke plug, and I can confidently state that it DID NOT WORK WELL in this particular application. Other than that, I know nothing!

>These replies aren't falling into the places I want them to
>go, so please bear with me.
>
>I can't say anything about the "H" plug, except it looks
>like an OS and it has "H" clearly stamped on it. It
>definitely has the extended nose of a 4-stroke plug, and I
>can confidently state that it DID NOT WORK WELL in this
>particular application. Other than that, I know nothing!

by any act, error, or omission, I have, intentionally or
unintentionally, displayed any breedist, disciplinist, sexist, racist,
culturalist, nationalist, regionalist, localist, ageist, lookist, ableist,
sizeist, speciesist, intellectualist, socioeconomicist, ethnocentrist,
phallocentrist, heteropatriarchalist, or other violation of the rules of
political correctness, known or unknown, I am not sorry and I encourage you
to get over it.

I'm posting this without checking my motor but the OS Wankel has a propriatery plug and that might be the one that Larry is using This plug extends a little farther then the standard OS so you just might be really advancing the timing more then you want Dennis

Reply to Howard (Hi there!)

I would love to measure that, but am really strapped for time and don't have any convenient way to do that study. I agree that it would be tremendously useful. Sorry.

>Did you measure crankcase pressure vs. RPM before and after?
> Would you, please?
>
Ron B.
F4Fguy

Howard:Check my Ans.(#1)to "Ron"-Topic#7587 Avg Crancase Pressure vs BMEP.Incidentally,I can't understand the fascination with running inappropriately tuned engines requiring inefficient prop diameter/pitch ratios.It's analogous to trying to use a Formula I engine at a tractor pull.Retuning for increased torque at lower RPM is not that difficult.
Sorry,that was an aside not directed at you,but at the POWER(whatever that is)freaks out there.

Larry, with all due respect, because I know you have a lot more experience in these matters than I do, why are you going to all the bother of crankcase pressure when that engine, right out of the box with the stock muffler will swing a 9-4 or 10-3 APC at around 11,000 rpm and haul butt all day long that way? Just curious....

Best, Hoovie

Larry is having fun pushing his envelop.

Thanks, Eric, I am indeed. Including shaking up some of the preconceptions of the assembled multitude.

The replies are falling into strange places, but here goes.

Basically, I believe that one should run an engine where it is "happy". The modern OS engine are designed to run at a steady 2-cycle at relatively high rpm. We keep trying to re-do the Fox .35 run with it's dependence on a high pitch prop and 4-2-4 break to control the speed of stunt models. As shown by the tuned pipe guys, that ain't the only way. There is a third way, in my opinion. Use the modern engines as they were designed to be run, and set the propeller diameter and pitch appropriate to the speed regime we want to use.

Now, with the hyper "G" loadings that we hit in Aerobatics, I felt that backplate pressure would give me the most reliable run and, with a fully open venturi, the most power. (I am running a .25 in a model that most use a .40 or .46 in).

When I set up the model to use that system, I suddenly found that the engine was acting like an overcompressed diesel. I was cramming in more fuel/air mix, than the engine was able to handle. The rest is history.... (see the rest of the thread)

The bottom line, is that I hope to be able to do the pattern with 2.5 or so ounces of fuel, and have a totally controllable engine independent of weather, altitude, etc.

LARRY I'm running mine OS-25FP on a pipe in the Morning. I've been testing differant venturis, head gaskets and spray bars. I have some 15% nitro that i'm going to try. Case pressure ...I have an interst.

Scott(keep up the good work)riese

>Coke cans turn out to be very nice, soft .005" thick
>Aluminum, so three head gaskets were produced (eat your
>heart out K&S).

Ron B.
F4Fguy

Larry:
I was just browsing and came across this in your post.
Coke cans are actually pretty much harder than K&S Al sheet(except the 6061 T6 .032"&.062").Aluminum cans are produced from 5000 series AL by a process involving extrusion,drawing and "ironing"which works the metal to a fully work-hardened state.They are deliberately left in this condition to get the highest properties possible,allowing thinner walls and/or higher carbonation pressure.Also the thickness isn't always constant,walls usually thicken with distance from the top.Getting back to hardness,you can(no pun intended)soften them to almost the same as the 1100 alloy K&S by annealing for about 4-6 [email protected] allowing to cool in the oven. Additionally,never re-use AL gaskets as they do work harden under the clamping force of the head(you have to deform them slightly to get a seal).

At the risk of your thinking that I am trying to get you to do yet another experiment to satisfy my own curiosity, how about leaving the coke in the can when you anneal it in the oven? You could use another, empty can as a control.

>At the risk of your thinking that I am trying to get you to
>do yet another experiment to satisfy my own curiosity, how
>about leaving the coke in the can when you anneal it in the
>oven? You could use another, empty can as a control.

Ron B.
F4Fguy

Howard;

Yeah!Yeah!That's the ticket!

Larry, I fly the Thunder tiger 15 and 25gp engines. the 15 we use for combat and training.
When i use a tank and a slow setting for the trainer, 2oz last for 6min on the 15. When run faster ,on pressure with a small prop , same wing, 2oz last 3min-4min.
My combat setup is TT25, 15/22 fuel,9x4 prop for 75mph.3.25oz last 5min.
For 55mph your prop might be near 10x4, (add one gasket)


I suggest that power is fuel burnt and that to run the engine near 14k you will burn the same fuel as a 10k . 40 at the same airspeed, (same thrust= similar fuel burn)
Also observed; bladder has a very slight difference in mixture because of offset to the venturi. The outside s might be a touch leaner.. If the bladder was back further, with a longer fuel line, I am pretty sure that you could get a slower level run and a slightly faster run at nose up attitude, as ;long as gravity works.MM