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Old Jul 29, 2014, 02:37 PM
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Quarter Scale Luscombe - 4 stroke Twin advise needed.

I have an old JMD quarter scale Luscombe kit that I plan to get around to someday, and I want to use a 4 stroke twin on it. No other engine type will do!

I expect the Luscombe to finish up weight-wise close to that of a typical 1/4 scale Cub, but it does have about 80% of the wing area of a Cub due to its narrower chord.

I am looking for an engine that will give it appropriate scale-like performance, not a hot rod. I initially thought a Saito Fa-90TS would be about right, but I now suspect that would be somewhat under powered. I am now thinking of an O.S. Gemini II FT-120.

Any thoughts out there as to what 4-stroke twins give good scale-like performance on 1/4 scale Cubs - and thus would likely work on my Luscombe as well?
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Old Jul 29, 2014, 06:59 PM
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I have an O.S. FT 160 4 stroke twin in a 1/4 scale cub... its just right for a cub 16- 20 lbs... if you want to go GAS, the NEW O.S. GF30 single four stroke... a 30cc 4 stroke GAS is about the same as a 20-23cc 2 stroke... then a little bigger GAS is the O.S. GF40 single 4 stroke, equivalent to a 33cc 2 stroke.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXBY68

http://www.towerhobbies.com/products.../osmg0798.html

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCZLF



John M,
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Old Jul 29, 2014, 08:16 PM
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Thanks for your thoughts John M. I think that an O.S. FT 160 twin is likely one of the best possible engine choices for my project.

After my original post, I found a build thread on a lightly built 1/4 scale Cub with an O.S. FT120. Based on his experience and that a Cub has somewhat lower wing loading, I think I will be keeping my eye out for a deal on a good used O.S. FT 160.

As I said, for this model it's GOT to be a 4 stroke twin! I don't want to overpower it, but it seems that the extra power of an FT 160 vs. an FT 120 will be beneficial in this application.

Someone please correct me if I'm wrong, but it is my understanding that the FT120 II and FT160 have the same external dimensions and nearly the same weight?


Edit:
I hear a tiny little voice screaming No, No! - but would a Magnum or ASP 160 twin for the right price be worth considering?
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Old Jul 29, 2014, 10:18 PM
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Yeah, I'm the same way about 4 strokes... I'm putting a O.S. GF40 on a H9 1/4 super cub... I want a bit more power reserve than the FT 160 can provide... the FT160 is based on the FT 120, with bigger / bored out cylinders and pistons... the 160 may have a slightly longer stroke though; produces 2hp and is a perfect choice for scale flying... it will swing an 18-6 prop with no problem and should give you a little extra if needed, all depends on the flying weight.

Both the Magnum and the ASP 160's are basically O.S. knockoff's... I haven't heard anything negative about either... my inlaw picked up a used O.S. FT 160 off of ebay that was in very good shape for $435... all we had to do was change the bearings, the back bearing was a little pitted (not enough after run oil was used)... other than that, it has great compression and runs very strong.


John M,
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Old Jul 31, 2014, 04:26 AM
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I've been pleased with my Magnum 1.60 twin. I put an OS needle and seat in it, though.

I'm envious of your JMD Silvaire.

To ease the envy, I have plans, kit, and glass for the Hostetler version. http://www.hostetlersplans.com/luscombe.html
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Old Jul 31, 2014, 11:45 AM
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Originally Posted by TomCrump View Post
I've been pleased with my Magnum 1.60 twin. I put an OS needle and seat in it, though.

I'm envious of your JMD Silvaire.

To ease the envy, I have plans, kit, and glass for the Hostetler version. http://www.hostetlersplans.com/luscombe.html
Tom, thanks for your thoughts on your Magnum twin. With any of the Chinese copy engines, it seems typical for the finer points of the carburetor to get short changed the most in the replicating process.

The JMD Luscombe is indeed a nice kit - on account of its beautifully made fiberglass fuselage, wheel fairings and cowl.
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Old Aug 01, 2014, 06:31 PM
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silvaire, if you manage to pickup a good used O.S. FT-160; most likely it will have the older carb with the air bleed screw and just the one high speed needle... O.S. updated the carb on the FT-160 to the same carb that is used on the FF-320 which has the 2 needles, low speed, and high speed... you can buy the new carb separately for like 70 bucks (maybe even cheaper on ebay or amazon)... its definitely worth getting the upgraded carb; its more reliable at idle and mid-range settings

New Style Carb with Low & High Speed Needles
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCA62


This is what the old style carb looks like... the small screw with the spring to the right of the main needle is the "air bleed screw"... wasn't their best designed carb.

http://www.osengines.com/parts/images/46181000.jpg




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Old Aug 03, 2014, 02:00 PM
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John M, the updated carburetor design info is good information to know.

Do you know about when OS changed the FT-160 production over to the newer style carb? This would be helpful to know in my used engine searching.
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Old Aug 03, 2014, 05:44 PM
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Yes, all new FT-160's produced come with the new carb... $940 bucks; a bit steep, thats why we went looking for a good used one... the new style carb fits the older engines, nothing was changed with any of the castings, i.e. crankcase, or with the way the carburetor body mounts, so its just as simple as swapping out the old carb with the new.

***EDIT***

The carb design change on the FT-160 was done some years ago; at least ten years, but I'm still seeing the older FT-160s on ebay... there's was one not too long ago, for $450... it had the old style carb... not sure if its still there or not.


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Old Aug 05, 2014, 02:25 PM
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I researching the O.S. FT-160 , I was astounded to find that it was first introduced nearly 30 years ago - waaaay back in 1985!
I wouldn't be surprised if this isn't some sort of a record for the longest time in production of any 4-stroke model airplane engine.

From what I have found so far, the carburetor seems to be the only change ( or only major change) made in all these years?

My 1/4 scale Luscombe is something of a "back burner" project at this time, and I'm in no major hurry to find an engine.
I appreciate all the the helpful comments. I think I now have my "ducks in a row" to purchase a used FT-160 when the right deal comes along.
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Old Aug 05, 2014, 09:43 PM
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I knew it was in production a long time, but wow 30 years...that's something to be said about the design... that must be including the FT-120I, FT-120II, throu to the FT-160... I wouldn't mind having one of its "big brother", the FT-300, that's another nice engine.

I'm looking into converting the FT-160 into spark ignition... but instead of having the magnet / hals sensor on the prop washer... taking a look at the back timing cover... it wouldn't take much to take a drive dog off of the cam / drive... something on the lines of a 2 position distributor... one magnet and two hals sensors.... that way there's no wasted spark issues... I'm thinking out loud of course, but with the right machinist, it could be done, would be interesting.


Anyways you can't go wrong with the FT-160 as is... we have a couple members that fly them at our field, std glow (as designed)... I don't think I've ever seen a dead stick landing with either... very reliable engine.

John M,
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Old Aug 06, 2014, 12:26 AM
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Quote:
Originally Posted by John_M_ View Post
I knew it was in production a long time, but wow 30 years...that's something to be said about the design... that must be including the FT-120I, FT-120II, throu to the FT-160... I wouldn't mind having one of its "big brother", the FT-300, that's another nice engine.
......

John M,
Actually John, the original FT-120 was first produced in 1979.
(This is also the same year that OS introduced their FS-60M (marine) and was still building the FS-75 - both OPEN ROCKER style engines!)

The FT-160 and FT-240 engines date from 1984.

The FT-120II came along in 1985.

The FF-240 (flat four), FR5-300 (Cirrus 5 cylinder radial) and FT-300 designs all date from 1986.

This is all according to the official OS website Engine Timeline pages:
http://www.osengines.com/history/ostimeline10.html

Hard to believe how REALLY OLD these time proven designs have gotten to be!
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Old Aug 06, 2014, 12:09 PM
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I'll bookmark that OS time line url... Interesting the FT-120II came after the FT-160... my old brain had me thinking in the terms of progress, i.e FT-120, FT-120II, and finally the FT-160.

I've been in RC since they discovered dirt, and don't think I ever saw a FT-120 or a FT-120II at our field, and I've been flying at the same field ever since I was 9-10 years old and free flight before the field was built back in the early sixties... I can remember seeing a lot of O.S. engines, it was the engine to have even back then, they have certainly built a good reputation over the years.

If I ever see another good buy on a 160, I'll let you know.


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