Dave,


A 13x8 may be a bit easier to find.

It offers a similar load. You may even find that a 13x9 serves the purpose better.

Yep,</p>

I gotta agree, in general, (I don't deal in the HP calcs) with Dar on this one. Some folks are leery, for some reason, to get these 'long strokes' down into their torgue band of rpm. These engines are designed/timed to run there and the pipe/setting plays a significant role inachieving it.

Don't forget about the engine/prop unloading some in the air.</p>

Terry in LP</p>

Well, there's absolutely no way a 13" prop will fit on my UFO. On top of that, a 13x8 probably won't provide the speed I'm after. This model should exceed 100mph.

David

You'll just have to get a 12" high-pitch prop, then...

Joe Bridi was probably thinking about 14-15K and an 11" prop, when he designed the newer UFO.
Sort of like his earlier Dirty Birdy...

Yes, exactly, something like this:

http://www.rcuniverse.com/forum/fb.asp?m=8797318

I ordered a 12x10 and a 12x11N from Tower. It will be a while. Ken Enya ships from Japan faster than Tower does from Illinois.

David

Either that or...</p>

Put a SuperTigre, FSR, Rossi, Webra Speed, etc. on it and run 11" porps at 14,000. </p>

Terry in LP </p>

Yeah, I weighed several options before I even cut out the first wing rib for the UFO. The SF below 12,000 is extremely quiet; it's really not too much different than a 4-stroke. Personally, I love loud, screaming engines, but a lot of other people don't and my field does have noise restrictions, though not terribly strict. Nevertheless, I will still build a model for the Webra 1030. Maybe by the time I get it built I'll have a quiet pipe for it, too.

David

A bit more testing today...

I added 1/2" back to the header for a length of 6 1/4" and got this:

84°
Powermaster GMA 5/22
new OS #8
APC 12x10
10,838
1.62hp
9.33lbs. static thrust

It is extremely quiet. I would definitely have difficulty hearing it running in flight with another engine running.

David

HI been running my OS 61 SF on a 12/6APC must say i am very pleased with its performance-but more than one reply i have received said to go to a 12/10 APCto be running in my- power band- see just when you think you know it all-POP-the bubble breaks- trust me i do a lot of research- but thanks guys -that is what all this discusion stuff is aboutto learn and improve what you are doing- i will give the 12/10 APCa trymy SIGSUPER KAHOSis going to be a bearto handle if this works- it is now

let us know how you like it

HEY METALLICA JUNKIE- i like that band alot tooway COOLwill let you know the next time the SUPERCHAOSis outhave 20 planes flying so might be a while - but i am EXCITEDabout trying the 12/10 and running in the 10-11,000 RPM range and making an improvementthe CHAOSwill be a beast - (it was before ) less fuel use- less engine wear- all good stuff- nothing like running an engine in its power band- its always power to weight- for maximum performance-have to say what i have learned here has come as a complete surprise-the reason is i have some old 60 engines that will only run on 11 inch props some 61's75's running on 12/6 -and now my 61 SF running on a high pitch 12 inch propmost all the time RPMS= horse power-my basic rule does not apply to this great OS 61 SFPOWERHOUSE-WOW live and lean-from the boys on RCU

Well.

I got tired of wondering about whether I could turn my SF into a Hanno Special type big prop swingin' powerhouse by copying the port timing and decided to try it out on a used SF ringed engine. Figured I could use the rest of the engine for parts if I dorked it up. I measured (multiple times) the ports on my stock Hanno MkII liner (SF too) and re-read the C. Lee review of the Hanno Special. The liner from the SF was a match for the Hanno liner except for the boost port width and the exhaust port height/timing with that extra width at the top. I had done some 'porting' to model engines in the long dark past and had used small files. This time I broke out the trusty Dremel tool and chose a fine, tapered stone bit to use. I carefully marked the .025" I wanted to raise the ports and the side cuts, put my magnifying visor on and went to work.

Started slow, checking progress often and before long had a pretty good looking cut done to one side. Feeling good about what I had accomplished so far, I proceeded. The second cut was less of a white knuckle experience but turned out a little less 'precise' than the first. Measured and matched the cuts to within about .001" using an old dial caliper and checked the results after washing, rinsing, oiling the liner. I was a bit surprised at the lack of burrs on the cuts and used a few passes of 400 grit paper to polish them up. Checked the timing of the 'twin' exhaust ports by observing their opening while stroking the piston/rod by hand while shining a light (back lit) down the bore. They looked pretty close to me so I reassembled the engine. Had to use two 'parts' engines to get one workable due to a very slightly bent crank I hadn't noticed before and some bad bearings. Was more work cleaning the case, crank and bearings than doing the porting.

Took the engine out this afternoon to give it a try. Set it up on the bench, connected a stock header cut by the previous owner at about 5" long to a MACS 1062 Quiet Pipe and put in a Fox Miracle plug. Took the 13~8 APC off of the Hanno II and put it on the ported SF. Filled the tank with some Omega 10% w/ added Benol to make it approx. 21% oil, opened the throttle and flipped the prop a few times to prime it, hooked up the plug heater and it started the first flip of the chicken stick. Man! I'm liking these OS pumper engines! How come I didn't get some back in the '80s? It ran for about thirty seconds 'cause it was way too blubbering rich. Wouldn't start again.

Took it off the bench, turned it upside down, drained some fuel out and put it back on the bench. Turned the n/v in some and it started after a few flips. After adjusting the mix some it was topping out at 11,200! That's right in the neighborhood of what I got with the Hanno II on this same prop! It was more steady at around 10,800 or so though. The carb is gonna need some more adjusting for idle/transition and it needs some new O rings too. The header length will need to be experimented with to find a nice broad range of boost. Gonna try some different props and a different pipe or two before it's over as well.

Don't know about y'all but I'm happy about these results. Gonna do an old used RF next, I think.

Took some pics of the session.

Terry in LP

interesting results bubba!!

Ran the ported SF-P again today.

Wanted to do a more even comparison with the Hanno II so used the same Hatori 650 pipe and added 1.5" to the SF header to match the length on the Hanno II header. Ran the same APC 13~8 prop used on the Hanno II run. The SF made 11,000 max today (102F, just rained) vs the Hanno II's ~11,500 a couple weeks ago. Gonna try again on a better day.

Terry in LP

That sounds good. I still want to know what prop constant to use for those newer APC's. Try a 13x9 (older style) next time. I'm predicting around 10,000 to 10,200.

Man, 94° is too hot for me to stand outside and run engines, much less 102!

David

I wasn't out there long.

Had to wring out my T shirt when I came back inside. I'm gonna see if I can order some old style APCs in the sizes I want to try. Have 11~10/11/12, 12~11/12, 13~9/10 and a few steep old Zingers and MK f/g 12.5~8+2 etc. to try someday maybe.

Terry in LP

How does the Hanno conrod compare to the SF rod? Are they the same part? Whipping a 13x9 around using a sixty-size rod sounds like a stressful ordeal to me.

David

Same rod. Saw a pic of an MVVS 60 or 77 rod that was MASSIVE.

They ran these engines with these same rods for years turning 13 and 14 inch props as well as 12/12.5 x 11/12 props. Ask flywilly. He flew a few of them for over 1000 flights with 13" props. Besides, I have several RF/SF engines and a couple spare NIP rods and can always have a rod re-bushed if needed. I ain't skeerd! Guess a guy could even get a heavy duty one made if he had the tools/skills or knew a machinist.

Terry in LP

Doubting my memeory, I checked again.

The MVVS 77 rod is big but it is the Sport Jett 76/90 rod that is massive.

Terry in LP

11400pk 15% nitro 12x8 mas evo 61 muffler

12x7apc 11700 rtf