ralphp

My Feedback: (6)

I have an O.S. Gemini FT-120 II twin cylinder . Does the fuel tank need to be pressurized? If so how?

aerowoof

no but it does not hurt to use muffler pressure

ralphp

My Feedback: (6)

It only has the exhaust header pipes. Do I tap into one of them?

Sandmann_AU

I picked up an FT-160 Gemini twin - as yet not run while I wait for the right sized prop to come in however I've asked the same question. I'm told the OS twins have small carbs on them for their size which allows them to draw from the tank well without tank pressure. You could pressurise the tank by replacing the standard exhaust pipes with with a pair of pipes & mufflers from an appropriately sized single cylinder 4 stroke OS engine but from everything I hear it's not a problem, and doing so might create problems with flooding, needing a regulator on the fuel line. I'm also told that these engines don't need mufflers, as they're a lot quieter than the faster spinning single cylinder engines.

Something else to look at - the carbs on the FT-120's and the early FT-160's didn't use separate low and high speed needles, rather they had a high speed needle and an air bleed screw for idle mixture. A lot of them have been replaced by the later twin needle design carbs, and I've heard mixed reviews on the air bleed types - everything from "problematic, poor idle, and lacking in power" to "nothing wrong with it if it's adjusted right". I'm sitting in the "wait and see how it goes when the prop comes in" camp before I spend bucks on a newer carb. If you do decide to get the new carb, Tower Hobbies have them in stock.

ralphp

My Feedback: (6)

Thanks. I am going to give it it's maiden flight today

Sandmann_AU

What have you got it in? And what prop? From what I'm told the twins aren't actually as powerful as their single cylinder counterparts, due to the added friction of the extra cylinder, but will turn a chunkier prop (who knows how or if that logic works, surely a bigger pitch/diameter would mean more power?)

Will be very interested in hearing how it goes, please keep us informed. Good luck on the maiden.

ralphp

My Feedback: (6)

I have it in a GP Super Skybolt. Balanced out perfectly and I am using an APC 14x6 prop

Sandmann_AU

Heh... that's exactly what I'm threatening to put my FT-160 into, much to the disgust of (and against the advice of) several people on here.

Is yours an ARF or a kit? The ARF's are apparently a lot lighter than the kits at around 7lb... my kit's had a major repair from a high speed nose-dive into the ground and has snapped two horizontal stabs while pulling out of dives. I eventually replaced the stab with a solid slab of balsa with two rectangular carbon fibre tubes embedded in it and a couple of holes to shed a little weight. As you can probably guess it now needs a fair whack of lead up front to balance the heavier tail and it currently comes in at around 12lb, so I'm hoping the heavier FT-160 will bring it back into balance with the nose lead removed, which will give me more power for no added weight. I'm currently running an ASP 120 4 stroke in my 'bolt with a 15x8 master airscrew prop. It chugs about the sky ok and has lots of vertical but I really want to get more speed out of it without sacrificing the climb. I'm waiting on the LHS to get a 16x10 master airscrew prop in for me.

ralphp

My Feedback: (6)

I had an OS 91 FX and had more speed and verticle than needed, but was a blast to fly. Although this motor weighs several ounces more than the 91 it sets much closer to the firewall so it equaled itself out. You will probably still need the extra weight. And yeah, mine is an ARF

Sandmann_AU

If you're mounting the engine directly to the firewall, how are you handling the distance to the front of the cowl? My 160's 14mm shorter than my 120 (plus the gap between the carb and the firewall) so I'd planned on making a spacer from some sort of hardwood to move the engine further forward.

ralphp

My Feedback: (6)

I just moved the cowl back on the fuse and it seemed to work out ok. If it servives the maiden I will send pictures. For now I took the cowl off in case of adjustments needed.

Sandmann_AU

The nose of the fuse on the ARF must have a slightly different shape to the kit's... my fuse tapers in over the first inch or so, so much so that I had to sand like crazy to get the cowl to fit on at all, and of course the cowl's tapered too. Cutting it down and moving it back's not an option for me so I'm left with either not using a cowl or moving the engine forward to get the prop to the right point.

I guess that answers a question left unanswered from when my 'bolt nose dived and I was looking for a replacement cowl - no I can't use the ARF cowl, and I made the right choice in getting an aftermarket fibreglass one instead of the chintzy 2 piece ABS one that GP supply.

Stickbuilder

If you are going to run a prop that small in both diameter and pitch, be careful that you don't over rev the engine. The 160 twin will take a little 14 X 6 up into never never land. I spin an 18 X 6 with mine, and it will pull everything it should.

Bill, Waco Brother #1

Roby

I have several of the OS1.60 4S.
Fuel draw without pressure is not a problem.
I typically use a 16x6 prop .


Regards,
Roby

ralphp

My Feedback: (6)

Thought that I would let you know that the maiden flight with the 120 went picture perfect. Tons of power and the sweetest sound you have ever heard. By far the best combo of all the planes I have and I have several. Your 160 should go to the extremes!!!

Sandmann_AU

Glad it worked out so well for you - did you get some pics? I managed to get mine running today for the first time (the prop for it finally came in yesterday). You're right, the twin sounds great, and it's not going to need mufflers at all. Had to fiddle a bit with the carb to get it running nice - never used an air-bleed type before. Got it running sweet with only a slight lag on transition so I doubt I'll need to splash out on a newer carb for it. Couldn't get one cylinder to run without power on the glow at all so put a used F glow plug in and it came good, but the other cylinder stops on a slow idle without power on the glow so I figure I'm up for a new pair of plugs - no biggie.

I'm taking my 'bolt out for a last fly on the 120 single cyl tomorrow... hopefully Murphy's Law won't catch me and it'll come home in one piece so I can put the twin in it. Can't start the engine fit (well, could but not going to) till I get the choke assembly and new prop nut set from tower in the mail... "any day now". Then I just have to figure out how to seal up the hole for the 120 single in the cowl so I can re-cut it to suit the twin.

ralphp

My Feedback: (6)

I'll get some pictures this weekend and send them. I also installed a McDaniel onboard glow system . Works great- have them on all my 4 strokes

Stickbuilder

On my 160's I use the on board glow system, and it's set to come on at less than 1/4 throttle. These engines will lose tons of power if you lose a cylinder on your approach, so it's best to invest in a good on board system. One other thing, I don't know what fuel you are trying to run, but none of my OS 160 twins like anything above 10%. They are stone dependable, but you really should look at the glow systems.

Bill, Waco Brother #1

ralphp

My Feedback: (6)

I run 15% on everything.

Stickbuilder

The 160's do not like this much Nitro. Believe me, it will run better and you will lose your transition problem on 10%. I have several of these engines, and they do better on less Nitro.

Bill, Waco Brother #1

ralphp

My Feedback: (6)

Thanks I'll try it

ralphp

My Feedback: (6)

skybolt