rcuser002

My Feedback: (12)

Friends,

I have a Diamond Dust that will be powered by a OS.32SX (½ gallon broken in? according to diredctions) and a Macs #1120 tuned pipe.

Macs Product’s website recommends running an engine “at full speed, open-face with nothing attached to the exhaust" to get the highest rpm reading then cutting the header in ¼ inch increments until the final cut causes it to decrease in RPM.

“This is the best tuning length for static and vertical performance (fun flying, aerobatics and hanging it on the prop).”

The average cut should equal about 3.5 inches when all is said and done according to their chart.

Without the header attached, I’m getting 16,000 rpm with a 9x6 APC prop on 15% cool power.

The needle is set at 2 turns out in order to accomplish this reading. Any more lean and the transition sort of stutters.

Does this sound about right?

If so, then why does the little OS booklet that comes with the engine say to start the engine at 1&1/2 turns out?

What rpms should I be expecting after this and should I stick with the 9x6 or go to a 8x8 or 8x7?

root aka Bob G

bob27s

My Feedback: (19)

"turns" on the mixture needle means absolutely nothing......

What is noted in the manual is a reference only, at best. It is not a setpoint.

You use a high speed mixture needle setting that provides the proper fuel flow and mixture for your engine/prop/exhaust/aircraft/fuel system in combination.

On a piped setup..... if you are at 16K with the 9x6, thats pretty good. I'd stay there.
Lean the engine, find peak rpm, ....... note that rpm...... then back out the needle so the engine drops 400-600 rpm for flight. Note the sound of the engine at peak, and backed down... and you probably will not need to use the tach very much from then on.

As for prop choice... you will be best off sticking with the 9x6 for the time being. The engine is happy, and you will have decent launch thrust for the Diamond Dust.... and resulting level flight speed will be pretty good.

Idle and throttle transition - and resulting smoothness, is adjusted by making small adjustments on the low speed mixture screw.

vasek

My Feedback: (4)

sounds interesting running an engine open-face (your next-door must love you)

just thinking out loud here; would't it hurt the engine to run it without any back-pressure ? (Bob?)

thanks,
V.

Lomcevak Duck

My Feedback: (14)

Before you tune your pipe, make sure you are tuning it for the prop you want to use on the plane. I had an OS .32SX on my Diamond Dust, and it was a great combo, but I dont think you'll be happy with that prop. I Was using a 7x7 (APC 9x7 cut down to 7" diameter) and getting 17,500-18,000 RPM on the stock muffler. If you're only getting 16k the engine isn't unloading to its potential. I forget what Combat Pigg was turning, but it was more prop than me with a little more RPM. I think he was running a Macs tuned muffler.

rcuser002

My Feedback: (12)

I'm at 16K without the header attached - when I put it on, there should be a noticeable increase in that 16K reading ....perhaps up to 18K...maybe even more (from what I have read in these forums) especially if I go to a smaller diameter.

Should I go to the 8x8 without the header and see what that gives as a starting point before I put the Macs tuned pipe on and start to cut the header down to 3.5 recommended length???

vertical grimmace

My Feedback: (1)

Running an engine open exhaust hurts nothing other than your hearing! Look at all of the C\L engines running open exhaust. None of my C\L combat engines run with exhaust. Including my Nelson .36 which turns 24,200 rpm.

Lomcevak Duck

My Feedback: (14)

Yes. Put on the prop you are going to fly with, then tune the pipe for that prop.

combatpigg

My Feedback: (3)

I think the best prop [by far] for this combo is the 8x8. My OS puts out 18,000 on 15% nitro and the engine has many runs on it. I would tune the pipe to suit the 8x8 prop.

I agree about open exhaust being a good alternative. I'm building a little Mustang that will be run just like a C/L combat plane, bladder tank and open exhaust.

rcuser002

My Feedback: (12)

Combatpigg,

Thanks for your time.

I'll be running 15% Nitro and going with the recommendation of the 8x8 APC

Do you think I should run the 8x8 APC open-faced to get a base reading to pass.....

or just start with the header & pipe attached and strive for 18k or more than 18k?

root

p.s. How close should the pipe be to the header inside the silicon sleeve?

Almost touching metal to metal??

combatpigg

My Feedback: (3)

I just followed Macs' instructions 100% It is tedious to hacksaw little pieces off, ream, clean, bolt back on, then fire up for a reading, over and over......but when the system hits resonance, it is magic. Take a very fine slice and compare the last tach reading, once you see no improvement, that's it. If you go too far, just lengthen the system back to max and lock it down. I would use a bubbless tank, so you get consistent readings and avoid high rpm fuel foaming. Hopefully, you already know how to set a high rpm needle, pinch test, etc. I like to set the needle with the nose pointing straight up, this duplicates the worst case in the air. With castor based fuel, there should be a stream of smoke with the engine screaming. I run it as rich as the pipe will allow.
You can leave just a minimum gap between the header and the pipe......in theory you don't want any lumps or bumps in the system and the exhaust port and the opening in the header flange should match. I scratch built a 90% sized DD for this combo and it really cooked, was also very low maintenance. Hand launches vertical at 2.5 pounds RTF. Expect over 120 mph and nice flared landingson grass.

glowplug50

Am I missing something, is this guy running the engine without the pipe?

Install the header and the pipe, run, needle and tach.

Cut off 1/2 inch of header, reinstall pipe, run needle and tach.
Repeat untill rpm's start to fall.
adjust pipe lenth with coupler for max rpm and back off on needle as needed for semi rich run.

rcuser002

My Feedback: (12)

Yo, glowplug50, .................Read my 1st post and you'll see where I'm coming from.

Combatpigg,

FWIW, I got an open-faced 17k on the 8x8 APC and 15% Cool Power. I spent the rest of today flying my Sig Wonder w/ 15CVA to keep my speed chops up so I'm ready to fly the Dust.

IN YOUR OPINION -
Am I OK with the Cool Power 15% Nitro which only has 17% synth oil?
Can I go with Cool Power 20/20 Pro Pattern?
What would you recommend?
I respect your opinion........
my LHS doesn't carry much else that has a 20% oil content.

Bob G

ps I weighed my DD at the post office and it's coming in at 2.9lbs

rcuser002

My Feedback: (12)

Quick question,

How many minutes of a full throttle run should I expect from a 4 ounce slanted Sullivan tank running 20/20 Cool Power?

root

Mike Connor

My Feedback: (5)

I have not run this combination but my guess would be 3 to 4 minutes. Long enough at full throttle. These deltas can also fly very slow.

rcuser002

My Feedback: (12)

Do you think I should sacrifice the weight for the time?

combatpigg

My Feedback: (3)

Root, with a well padded 4 oz tank..you will be getting quality time VS having a bigger tank that is crammed in and prone to delivering engine frying air bubbles from time to time. 17,000 is excellent with open exhaust. You might find that the plane is faster this way than with a "plumbers' nightmare" [tuned pipe] hanging off the side. Running open exhaust will mean that you need a crankcase pressure tap. The jump in static rpm with a pipe might not offset the extra drag, plus an open exhaust will unload more in the air. Always anticipate the unloading and watch the vapor trail..if the engine starts sagging immediately kill it and land. Just for this reason alone, I always top off a fresh gallon of store bought fuel with 4 ozs of Sig castor. The object shouldn't be to see how low of an oil content you can get away with, it should be to see how high of an oil content you can run without hurting performance.

rcuser002

My Feedback: (12)

Thanks Combatpigg,

My 20/20 Pro Pattern would be the easiest to use but I'm a little afraid of the 20% nitro content being a little too much for 17000 plus rpm's.

So I began searching for information on fuel mixing and came across this url for a fuel mixing calculator.

http://www.misbehavin-rc.com/pit-lan...calculate1.asp

According to the calculator, I can add 1 hefty shotglass (1.2 ounces) per quart of Cool Power 15% in order to bring the mix from its present 15% nitro / 17% synthetic oil to 14% nitro / 20% synthetic oil. This addition of oil results in a normal 1% loss in nitro content.

Now the question is :

Can I use the synthetic Amsoil Saber Outboard oil instead of Castor oil for the mix?

root

p.s. It's the kind all of the gasser pilots at my field boast about and I happen to have a quart for my Zenoah G-23 engine.

glowplug50

Synthetic always.

combatpigg

My Feedback: (3)

Look at it like this, Henry Nelson builds one of the strongest .40s in the world, his piped FAI model, and he recommends 25% straight castor. The FAI engine is made out of the same basic materials as your OS.32 and the 2 engines have similar missions. If you know for sure that the fuel mix isn't getting too lean during a run, but your glow plugs are blowing every run, then the nitro is too high for where the compression is set. The engine load might need to be lowered slightly...but not likely here. I think the OS.32 runs good enough for me on 15% nitro. I would just add castor to your 20/20 fuel and see how it goes.

BTW, your other fine tuning tool is a couple of extra head shims. Piped engines can sometimes benefit from an extra shim. My experience with the .32 is that it didn't need any extra fiddling around to hit 18,000 and be relatively easy on plugs and very consistent.

glowplug50

Not to be argumentitive but go to a pylon contest and see what kind of fuel is being run in the Nelsons or tthe Jetts. It won't be castor base fuel. It will be synthetic. Castor will do the job but synthetic runs just as well or better under most conditions, as explained to me years ago by a major model fuel manufacturer, Castor will hold up to higher heat than synthetic before breaking down but, by the time you have reached the heat level that synthetic starts to break down, the destruction of the engine components is already well under way with either lubricant. The advantage is clear to the sythetic as it is not crapping up your engine and doing just as a good a job as the castor might be doing. Why coke up your engine when it is unneeded? This is an old argument and the older the modler the more the argument. I have only been involved for 24 years and still have a lot to learn, but it will be a cold day before I ever subject one of my engines to the nasty leftovers of Castor based fuel.
Keep in mind that a lot of synthetics still have a little castor mixed in as a rust preventitive, but I forgive that.

freakingfast

My Feedback: (3)

For a standard sized Diamond Dust (not clipped wing or reduced size) I like to keep the disc area of the prop in the 8.75 to 9" diameter range regardless of the engine size, be it a OS 32sx (9x6.5 @ 17k on 15%) or a OS 46 VX DF (8.75 X 9.75 @ 19.5k on 30%). I would start out simple with an APC 9x6 sport prop on a known fuel 15% nitro/18% oil Power master or Wild cat. For the OS 32 & apc 9x6, good baseline RPM peak ground is around 17K with the Macs #1220 muffled pipe. The following have worked well at about the same engine load: 9x6 sport (my favorite) for great acceleration after hard turns, 9x6.5 or 8.75x7 pylon prop for top speed. I don't think running more than 15% is worth it on this engine, it puts out fantastic power as it is. More nitro shortens your run time too as you need to richen it and eats plugs faster$$$.

K.I.S.S. on your first flights, you'll have your hands full Think about combinations of speed props, nito% and shortening the header even further than Macs guidelines later on.

rcuser002

My Feedback: (12)

Because these have all been excellent recommendations, I will take a little from each of them.

I will increase my lubrication to 20% and keep my nitro content at 15% with the potential for a 20/25 blend if and when I gather the courage to employ the 8x8 prop.

I will use the cleaner synthetic Amsoil over the Castor at 1 ounce to each quart of the factory 15/17 Cool Power.

I will start out with a 9x6 APC and the header at its present 4.25 inch length for starters (remembering the 9x6 open-faced reading was 16000 rpm's) cutting 1/8th at a time to achieve a good baseline RPM peak on the ground.

Thanks for reminding me to keep it simple.

I will have my hands full just because of this being an unfamiliar "new plane", with sensitive throws being hand launched.

Rome wasn't built in a day and I DO have time to experiment with "combinations of speed props, nitro% and shortening the header even further than Macs guidelines later on".

Thanks again and again for all of your help.........I'll keep you all posted.

root

freakingfast

My Feedback: (3)

Now yer talkin!
Don't be surprised if your header gets as short as these pictures. One is mounted on a "PBF" has seen a ton of abuse, high revs, lean runs(dirt), stuff-in's, ingesting dirt and used so much fuel (all kinds) that the engine was black....so I took it apart and bead blasted it LOL. All with the same bearings, this engine just won't die![>:]
The other is mounted in a LR-1. Note, this is a "long" off set style header.

Mike Connor

My Feedback: (5)

For best overall performance on a full size dust with every thing out in the breeze I aways ended up with a 9" sport prop. An 8 x 8 may give you a bit more on top end but will suffer in other areas like launch. A smaller, lighter or cleaner delta may do well with a smaller diameter.

freakingfast

My Feedback: (3)

Like a Mike Conner or Combatpigg special?