Fastsky

I have started building a Super Sportster twin and from what I have been reading it looks like the most reliable engine brand for this plane would be the OS and I want decent power so that means the OS 25FX. Are there any other suggestions to consider??[8D]

evan-RCU

The older versions were FSR and FS and SX, all were excellent motors and if you get a good deal should be considered. The .32 SX is one of the best motors ever made.

Fastsky

I just happen to have a 32 SX on my sons LT25 and it has has always run top notch. It spins a MAS 10-6 prop at the same rpm as my 40FX but is noticably quieter and uses less fuel doing it. I don't think I need the extra power on a 25 sized twin and it would run me an extra $106.00 for the 2 engines. That would pay for about 5 gallons of flying fuel!! [X(]

Ed_Moorman

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I have a pair of .25FXs on a little twin delta and they are fast, easy to tune and extremely reliable. On other planes I have tried TT, GMS & Magnum. I fly those on other planes, but stick to OS for my twins.

Forget the GMS .32s. I bought 4 of them for twins and 2 have been back for warranty repair and I still can't keep a pair running reliably. Two are sitting and the other 2 are on an old TwinStar I have on floats. Look closely at the picture. The left engine is out.

Fastsky

Re: "I have a pair of .25FXs on a little twin delta and they are fast, easy to tune and extremely reliable." < thats pretty much what I expected! Nice pic of the Twinstar. What props work the best on the 25FX?

WMB

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How about a build thread. Sounds like a great idea!
MikeB

JohnBuckner

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I recently have started converting some of my non scale bashed multi's to the 25FX and found this engine to be far superior to anything in that size I have used in the past and the big improvement has been in throttling characteristics which makes everything so much more enjoyable.

Bought eight of them as an experiment with two being for my little twin seniorita and six for my Six Pack project ( telemaster) still not finished yet but getting closer. The Seniorita has been flying for three years now with Magnum 30FS and I have never been totally happy with them. The FX's have been a hugh improvement on that airplane and all eight engines have been flown on that airplane now.

I was so happy with the engines I went one step further and equiped them all with Ultra Thrust pipes, not for the power although is its considerably more but for the throttle response and the sound. Can,t wait to fly the Six pack.

So happy I have been with the FX's that I plan to get four more for my older multi bash the five year old Quad Kaydet. The original engines were Magnum 28's.

John[8D]

Fastsky

Re: " I plan to get four more for my older multi bash the five year old Quad Kaydet."< sounds like I better buy some myself before they run out !! Whats the "ultra thrust mufflers" that you are talking about?

JohnBuckner

My Feedback: (1)

Ultra Thrusts are quarter wave tuned pipes. They are not just empty can mufflers and they provide the proper full length internal tract to perform the resonnent magic. Most of the sport engines I have used them on will typically see a 10 to 15 hundred gain in static RPM and unloaded, Who knows? Throttle response is also a major advantage and the real reason I went to these pipes for the multi's.

The pipes are not cheap at almost the price of the engine but nothing else comes even close. Sold by Dave Shadell here at Performance Specialities:

http://www.pspec.com/results.asp?category=8

It was interesting when I ordered the pipes and Dave realized that six were for one airplane, It took 10 minutes to get him calmed down from laughing so hard. Never having sold so many for one airplane before Good guy and knows his product.

John

Fastsky

Thankx for the feedback John. I'll consider them when I get closer to finishing the twin. [8D]

Ed_Moorman

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I have used both Ultra Thrust and Jett tuned mufflers. I find them to be equivalent. I have Jetts on my OS .25FXs. Run great. If I was buying another, I would get the Jett since bob27s, the Jett representative, hangs out here on RCU answering questions.

For speed, I run APC 8-7 or 8-6, but if I plan to land on the concrete runway (no gear on my twin delta) I usually run 9-6 Master Airscrews.

In one photo, you can see the GMS .25 rear needle assembly I use.

Fastsky

If I am just looking for more speed/power wouldn't I be better off just going to OS 32SX,s??

JohnBuckner

My Feedback: (1)

I think you may have missed my point as to why I went to the Nelson pipe (Ultra Thrust). First the FX is just about an ideal two stroke in the 25 size even with the stock muffler and I beleve user friendliness for a multi is superior to some others in that displacement.

Indeed with a quarter wave pipe there is a substancial boost (and of course that includes Dub Jett's pipes) in power however that obviously with my bash multi's is not needed and those airplanes are never going to be fast with anything hung on.

The Reason I went to resonent pipes is the superior throttle response that is easily achevable with them. This has proven out to make the the Seniorita far more enjoyable to fly.

John

Montague

What changes with the throttle response for you with those pipes? I ask because I run a lot of mousse cans on my combat ships, and usually the result on most engines, including the OS FX, is to cause the engine to get a little "peaky", you get a noticeable and abrupt power increase as the engine gets on the pipe at the pipe's designed RPM. The Ultrathrust's I've seen (and I have one around here somewhere) seem to do the same. I'd think you would want as linear a response as possible, and a tuned exhaust would be the opposite of that based on what I've seen in the past.

Yet it's working for you, so there's something else going on. Maybe the pipe has less backpressure (or maybe more? for better fuel draw?) at lower rpm, and you're using props that are keeping the engine from actually getting on the pipe?

I really wish there were more interstiong .25 size twin designs out there in kit and ARF (I'm kind of time-limited right now). I have a pile of "broken in" ex-combat engines and using them several to an airplane sounds like a good idea.

CanDo

I'm also running OS .25FX engines and APC 9x6 props (~13K RPM) on my Rich Uravitch OV-10 Bronco. It has roughly 30 flights and no flameouts!

JohnBuckner

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Just completed the re engine of the Quad Kaydet with the 25FX/ultra thrust and this is how the old girl looks now. Flew it last saturday and sunday for a total of six flights and the new combo was not a disappointment. Ground handling and taxi is far better now, in fact its a joy. Power of course is a substancial improvement over the Magnum 28's/muffler it will stand on its tail stage center and continue vertical untill I can,t see it. It was good before but with this combo its superb. Best part is the engines will ideal very low without hassle and the throttle response is much improved just as with the Oxy Moron. Best of all they all quit when the throttles are cut. Prop's were reduced from APC 9x5's to 9 x4's.

She's on the table now to get her floats replaced for the London Bridge float fly, nine ten and eleventh this month.

CanDo

A year or so back a local bought an Ov-10 from someone and I did the first flights on it which were fine with Magnum .25's. Its been a while but I think the span is somewhere around fifty inchs. I told him it may be a Uravitch plan built airplane but don,t really know. Did not appear to be an ARF. Please take a look at the photo, perhaps you can help with the ID.

Just acquired a perfect bash project. Its a wreaked ARF 46 sized decathalon of some sort. and been looking for a good starting point for a while. After completeing the Six Pack project which should occur in december this one will go on the boards to bash into a Champion Lancer in the last photo and won,t be a particularly difficult one either. It will get 25FX's/Ultra's

Spent a wonderful summer in sixty five training folks add on ratings in the back seat of one, a very memorable airplane so looking forward to this kit bash.

John

CanDo

Hi John,
Rich's OV-10 is 52" span (I extended mine to 56"), so I would say you probably have one of his models. This is what mine looks like just after I recovered it.
-Les-

jaka

Hi!
To me that sounds strange! A pipe usually makes the engine throttle less good!
OS engines are tops but using Nelson pipes on them, in a twin or more... seems totally wrong to me.
Much better throtteling action using ordinary silencers

JohnBuckner

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Jaka

Fact
Two airplanes a twin and a quad totalling six engines both with many flights. One with Magnum .30FS's and one with Magnum .28's with baffled stock mufflers

Fact
The twin was re engined with OS 25FX/stock baffled mufflers. Fact dramatically improved performance in all parameters including throttling/low idle/idle cutoff. This for five flights. Subsiquient 25 flights exchanging the stock OS mufflers for Dave's 25 sized Nelson Ultra Thrusts and changing to 9x4's to enable the engine to climb onto the pipes. Fact, 1300 improvement in static RPM along with much improved inflight unloaded thrust which you will just have to call me a liar or live with it since there is no way to prove that.
Fact the piped set up also provided slightly better throttling (agine subjective deal with it)

Fact
The four engine airplane now with the OS .25FX's/ Ultra thrust (not bothering with the stock mufflers this time) after 6 flights with this combo. A reduction in props from the prior 9x5's to 9x4's because now i know this is what is needed to get on the pipes. Fact about 1500 gain in static over the Magnum and a substancial overall increase in performance in flight unloaded. Along with a major increase in throttling/low idle/idle cutoff compared with the prior stock muffled Magnum 28. Agine last two items are subjective, deal with it.

These are my real world results in my climate and Wx/density altitude and in my airplanes as well as the way I fly my airplanes and if you take exception to that then you are just going to have to deal with it. I don,t care and I don,t care to waste my time in defending my choices. Especially since the whole point of this thread was a good choice for twenty five sized twins and my opinion as well as what I was stating is the FX 25 is an excellent choice.


CanDo

Indeed thank you very much and I will relay that to the owner of the airplane. They certainly do appear to be the same airplane. I might add the dark color of yours is georgous.

John

Montague

John,

Out of curiosity, did you ever try the 9x4 on the Mags?

I'm not surprised that you get better throttle action from the OS over the Mag, that's mostly in the carb, the older Mag carbs aren't very good. The newer carbs on the XLS line are better, but still not as good as an OS carb.

I'm not at all surprised at what you've experienced in terms of performance. I've seen planes actually go faster when switching from a 9x5 to a 9x4 prop when the engine had a mousse can or ultrathrust pipe. The extra rpm more than made up for the drop in pitch.

In general, I'd say your experience matches mine with the Magnum .28 and OS .25FX.

I'm also not surprised that you get a better idle with the 9x4 props, that also mirrors what I've seen. And I'm not surprised that you get a great idle out of the OS's with the pipe, mine also idle and transition well.

I'm just surprised that you don't get a noticeable jump in RPM as the engine gets on the pipe, and that you don't have issues with the engines coming on the pipe at the same time. Though thinking about it, in the air, a little RPM variance doesn't matter. I can hear my Mossie's engines going in and out of synch all the time in the air, and other than the sound, it's a non-issue.

Do you hear the engines hit the pipe in the air? Can you hear them come on the pipe at different moments? I think that would be a pretty cool sound, actually.

A guy at my field did have a pair of Mag .28's in a Bronco on mousse cans, but he pretty much flew that thing wide open all the time, so transition wasn't an issue . I've been phasing out my Mags from my combat planes and replaceing them with OS and Webras (though now the Webra seems to not be supported anymore), so I have some old Mags I've been thinking of putting in a small multi-engine plane, which is why I'm curious about your experiences. Personally, I don't expect the Mags to idle as well as the OSes do.

(oh, and my Mag .28s shake like crazy as well. It's the same crankshaft as on the .25, but with a bigger piston....)

Fastsky

Well its a bit late for me. The 32SX's have arrived at my door and looking too good to ignore. They are going into my twin!![8D]

moodier

My Feedback: (1)

HI;Very interesting post.Did switch drom 25FPs to the Mag 28s not real happy seems to be harder tokeep them running.Maybe should try the FXs.John see you Sat.Missed last year as was laid up but willget there this year!Are the Fxs that much better ythan the Fps?Have been happy with them and think they are easier to use than the Mags?One of the fellows here in Yuma now has a boat so we fly one day a week on water getting to be quite a few float planes here now.