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Jun 21, 2004, 05:42 PM
Decrash's Avatar
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O.S 49-PI rotary wankel

Does any have one of the (overly expensive) engines? How do they compare? Are they easy to start?
I am most likey gonna buy one, I heard they have the power of a .45 but have the gas consumption of a .60 size.
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Jun 22, 2004, 02:22 PM
Decrash's Avatar
Thread OP
Doesn’t anyone have one of these?
Jun 23, 2004, 06:14 PM
The only Wankel I have seen is the OS 30.
I have a new one never flown.
I was told it has closer to a 40 power but uses the fuel of a 30.
Mine has been carefully bench run and it has a very cool sound.
Sorry but this is all I can tell you.
Jun 24, 2004, 05:29 AM
It flies? I like it!
Drinks fuel, sounds neat, a bit low on the power to weight ratio (heavy for the output). Definitely a cool toy but not a better mousetrap.
Jun 24, 2004, 04:57 PM
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Tony Oliver's Avatar

OS Wankel

If you get one, don't dismantle it without being very careful to keep a record of where the gearing was before you took it apart.

I was given the parts of one a few years ago to clean and assemble. It's a fiddly job and a time consuming one at that.

Lousy photograph from an early digital camera but here it is. Motor ran well for its previous owner but it seems they need good cooling.

An early one owned by a club member caught fire in the air and destroyed a VK Cherokee - 'is that some film come loose?' reply 'It's not film, it's flames! The ********** things on fire'

Do you remember the old cream plastic cased servos? The ones in the Cherokee looked like well chewed mints after the heat got to them. The engine lived to fly another day.
Jun 25, 2004, 12:26 AM
Suspended Account
The Peripheral Intake of the OS Wankel Motor 4.9cc is a very nice piece of work. The weak point is that the apex seals have to run over an interrupted surface and if over spun may catch in the port. This is very rare. The other concern is that there is a great deal of temperature differential across the end plates. In larger engines this can be addressed with side seals on the rotor. On these small engines OS has used a plasma spray coating that has been machined out of flat so that when hot it is flat (built in warp). Many engines are destroyed during “rebuild” as the builder (destroyer) try’s to lap the side plats flat. The fasteners need to be torque very slowly and in a cross over pattern so as not to upset the side plates.
As for the operation they are hard to start relative to a ringed Veco engines. Power is the same as most 2 cycle high performance sport engines of the same displacement. The rub is that the displacement of a Wankel is hard to measure when compared to a round peg in a round hole type engine. They are a lot easier to muffle that a 2 cycle engine. They do NOT respond to a tuned pipe. The carb is out of date as it is an air bleed type. Converting to one of the twin needle carb found on some of the higher-powered 2 cc car engine would be a wise upgrade. Fuel burn is the same as an open faced (no muffler) 2-cycle engine of the same power output. The OS likes small props and high RPMs 16K to 18K. I like mine as a novelty item (it is only one of two OS engines I’d own). It does run well just needs a starter to start; this in my opinion is a flaw for a “sport engine”. If you want power in this class range (price) look a the YS 45 (7.5cc), Rossi 45 (7.5), the Jett or Nelson sport class engines .40 cid (6.5cc) to .50 cid (8cc). To place on your mantlepiece or in your collection the OS is a great engine!

P.S. The photo above is of the OS 30 Wankel. It is not the PI 49 as witnessed by the side induction. This motor is a classic circa 1979.
Last edited by Konrad; Jun 25, 2004 at 12:39 AM.
Jun 25, 2004, 02:18 AM
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Tony Oliver's Avatar
Sorry about that Konrad.

I omitted to make it clear that the motor I was commenting on was the .30

Jun 25, 2004, 11:27 PM
Suspended Account
No apologies needed, you were factual in saying that this (photo) was of an old OS Wankel. I just wanted to point out that not all OS Wankels are the same. Side induction vs. peripheral induction on a Wankel is about as different as loop scavenging vs. schnurle scavenging on a 2 cycle engine.
Jul 14, 2004, 03:43 PM
Registered User
I believe the .49PI and the .30 are the same motor, perhaps after OS took over the motor and removed the cooling fin.

Jul 14, 2004, 05:39 PM
Suspended Account
Both the .30 cid and the 4.9 PI are the same size engine. They have both always been made by OS. OS bought the license from Graupner who holds the licensse from NSU for all engines that are 10cc or smaller. Graupner never made the motors that OS makes. Graupner did make a Wankel but do to a mathimatical error it was bigger than the OS. The Graupner and the .30 OS Wankel are side induction type engines. The newer OS 4.9 PI Wankel is a Peripheral Intake (PI) design. Side induction verses peripheral induction on a Wankel is about as different as loop scavenging vs. schnurle scavenging in 2 cycle engines.

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