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HomeAircraftHelicopterMain Discussion › why do people not use 4 strokes on helis?
03-07-2008 02:39 AM  10 years agoPost 21
rob10000

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Western Massachusettes

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Kyosho used to market a 4-stroke helicopter. If my memory serves me correctly, I believe it was called the "Virago."
Legato.

It was a 4 stroke Nexus. 'nuff said.

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03-07-2008 03:19 AM  10 years agoPost 22
captb

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Arizona Desert

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I don't know why OS and others are still in the stone age with pushrod four strokes, if you got Honda, Suzuki or any of the big four japanese motorcycle builders to design a small hi rpm performance 4 stroke it would be in the running with 2 strokes and still have torque.

If it's gonna happen it'll happen up there!

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03-07-2008 03:48 AM  10 years agoPost 23
David Blain

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Mt. Dora, Florida (USA)

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I was told because the Four strokers (Looking at the power curve) tend to make a steady flatter type curve and the two strokes even though the power (final output) may be less tend to have a HP/Torque band in the middle ranges where the helicopter needs it...
So if you compared the "mid-range" torque of the four to the two the two would have more power in the mid range area....

NOW this is what "I was told", so IF I am wrong, I apologize to the four stroke guys... Any input or correction, I can only learn from!

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03-07-2008 03:56 AM  10 years agoPost 24
joeycoates

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Dallas, Texas

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Pull-n-pitch, I think that you have the details right, only backwards. 2-strokes "tend" to be peakier then 4 strokes. A 4 stroke makes flat linear power whereas a 2 stroke make high peak power, but over a narrow range. Hense why my old CR-80 had terrible acceleration until it hit its sweet spot at which time it would take off like a rapped ape.

Now a good peak spot is not neccisarily bad for the helicopters as they tend to run in a fairly narrow RPM band, while the throttle may be opening and closing by and large it is doing the opening and closing based off of load while the RPM's themselves remain fairly constant as opposed to an airplane where the throttle opening and closing actually results in a wide variance of operating RPM's. This may be why the 2 stroke works better in our particular application.

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03-07-2008 04:02 AM  10 years agoPost 25
David Blain

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Mt. Dora, Florida (USA)

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Joeycoates--
Thanks for the information, I am glad I had it "close" to being right.. It never hurts to keep learning in this field.....

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03-07-2008 01:35 PM  10 years agoPost 26
kcordell

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O Fallon, MO

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It was called the Legato and used the OS 52 four stroke, more of a 30 size model.

Team Futaba, Team Synergy/Rail, Team Scorpion, Team Castle Creations, YS Engines, VelTye

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03-07-2008 01:50 PM  10 years agoPost 27
SSN Pru

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Taxachusetts

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have people not tried the new 4 strokes? maybe you do get better power out of a os 50 hyper or somthing but it seems a saito would hold its own.
A 4 stroke of the same displacement as a high output 2 stroke OS .50 Hyper can never compete for HP and weight.

Stupidity can be cured. Ignorance is for life!

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03-07-2008 03:13 PM  10 years agoPost 28
Four Stroker

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Atlanta

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The Kyosho Legato and the Vario Skyfox/OS90 have about the same performance.

The YS 110S in an XCell 4 stroke should do quite well.

I think everyone fully understands that a 2 stroke makes more power per weight/displacement than a 4 stroke. That was never the point. Putting a scale fuselage on a 3D heli would really hurt it's performance on 10% fuel.

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03-07-2008 03:34 PM  10 years agoPost 29
w8qz

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Grand Rapids, MI - USA

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Ultimately, it's the power-to-weight ratio. A 4-stroke, using conventional 'poppet' valves, is RPM limited by the valve train (i.e. valve float at high RPM / valve(s) hitting the piston). A 2-stroke is not limited in that fashion. The higher you can push the engine RPM, the more power you get out (never mind efficiency, of course.)
Now, if someone can come up with a 4-stroke that doesn't use poppet valves (maybe something like the RCV engines), tweak it for high RPM operation, and turbocharge it - then the power-to-weight ratio can approach what the 2-stokes can do.

Personally, I'd rather have a quieter machine, and put up with less power - but then, I don't know how to do any fancy heli tricks, either

"The helicopter is much easier to design than the aeroplane, but is worthless when done."

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03-07-2008 04:28 PM  10 years agoPost 30
Hughes500Pilot

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Anaheim, CA

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Kyosho had the Legato, Kalt had the 4 stroke Baron, Century had the 4 stroke Phoenix, Heim has the 4 stroke Ultra Star, X-Cell's 4 stroke uses YS 91 4 stroke and Vario has the 4 stroke Boxer. Vario's Boxer has a 27cc twin cylinder 4 stroke boxer motor.

Click link below...

http://www.runryder.net/t54280p1/?p=387510#RR

-Steve

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03-07-2008 05:19 PM  10 years agoPost 31
nivlek

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Norfolk England

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I think that the RCV CD series of fourstrokes might work . No pushrods , no valves to bounce etc , should allow them to rev harder than your usual aero fourstrokes .

http://www.rcvengines.com/rcv_modelhome.htm

At the end of the day , it gets dark .

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03-07-2008 05:29 PM  10 years agoPost 32
GimbalFan (RIP)

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Big Coppitt Key, FL

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Just when you think you've seen everything. Those RCV engines are quite remarkable!

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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03-07-2008 05:35 PM  10 years agoPost 33
nivlek

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Norfolk England

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I purchase a brand new in box / second hand RCV 58CD at a RC bring and buy sale for £55 last Novemeber . It's only had four tanks of fuel through it , but it's a really sweet runner . It's turning a 12.25 x 3.75 APC prop at just over 10,500 on the ground . I expected it to have some gear noise , but I can't hear any , it sounds somewhere between a conventional fourstroke and a two stroke .

At the end of the day , it gets dark .

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03-07-2008 05:38 PM  10 years agoPost 34
SSN Pru

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Taxachusetts

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The manner in which the RCV engine converts the horizontal motion of the piston into rotary involves gearing which gears it down too.

Stupidity can be cured. Ignorance is for life!

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03-07-2008 05:40 PM  10 years agoPost 35
nivlek

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Norfolk England

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The manner in which the RCV engine converts the horizontal motion of the piston into rotary involves gearing which gears it down too.
Only on the SP series , not the CD series .

At the end of the day , it gets dark .

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03-07-2008 05:46 PM  10 years agoPost 36
GimbalFan (RIP)

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Big Coppitt Key, FL

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From their site:
Their 'CD' engine:

Their 'SP' engine:

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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03-07-2008 05:50 PM  10 years agoPost 37
nivlek

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Norfolk England

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On the SP series , the crank shaft is geared down at 2:1 , so the crankshaft turns at half speed . On the CD series , the gearing is 1:1 , so it is not geared down , and the crankshaft turns at normal speed .

At the end of the day , it gets dark .

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03-07-2008 05:51 PM  10 years agoPost 38
joeycoates

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Dallas, Texas

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Actually I do not know that they would really work all that well, I have an RCV 60sp (the funny looking one that has a pistion parallel to the crankshaft, the sleeve is actually part of the crankshaft) and while it is super reliable and it has a very high "coolness" factor, it really does not make a lot of power and it is further geared down 2-1. Now the regular series of engines like the 91 and 58 may be usable, but I do not think that higher rpm's are the answer but rather gearing the drive system to work with a 4 strokes usable range would be not only more productive but much cheaper.

An 8.5 ratio gives you 2000 rpm headspeed @ 17,000 engine rpms, perfect for a YS50 or OS Hyper.

A 5.0 ratio would equate to 10,000 engine rpm's @ 2000 rpm headspeed and 10,500 @ 2100 headspeed.
A 5.3 ratio would be 10,600 rpm's @ 2000 rpm headspeed and 11,130 rpm's at 2100 rpm headspeed.

Personally I would go with the the 5.0 as the 82 is rated to a r-max of 12,000, but that is really starting to get out of its "happy place" operating range. And it definatly has the tq to pull the 5.0.
Heck, maybe even a 5.1-5.15 would be better, someone would have to do a little bit of experamenting to find out.

But what might be even more interesting would be the new Saito 115 that is supposed to come in at 20.5 ounces and make well over 2hp with the 4 stroke tq to boot! Now we're talkin'... If I had access (and knew how to use) a cnc lathe then I might be willing to to a little bit of experamenting myself. The darn thing would be hard as hell to bog and I think that it would have some wicked performance.

Oh well..

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03-07-2008 06:05 PM  10 years agoPost 39
GimbalFan (RIP)

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Big Coppitt Key, FL

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I've driven a friend's rotory-powered Mazda RX-7 and was impressed with the performance. Some engine manufacturers are making rotary engines for RC models -- how are they on hp/wt?

EDIT -- Seems OS/Graupner are still making an RC rotory, with these specs:

Stock Number: OSMG1401
Displacement: 0.30 cu in (4.97 cc)
Practical rpm: 2,500-18,000
Output: 1.27 hp @ 17,000 rpm
Weight: 11.8 oz (335 g)

That's 1.72 hp/lb. A Hyper50 outputs 2.12 hp/lb -- so the rotory looks a little better than a typical 4-stroke but still not up to a 2-stroke in raw power.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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03-07-2008 06:10 PM  10 years agoPost 40
joeycoates

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Dallas, Texas

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Not really up to snuff, and very thirsty to boot as are the Mazda Wankel engines. The RX-8 typically gets 12-13.8MPG in the city which is one of the biggest gripes that you will see on the RX-8 forums. They are also notorious for lack of tq unless turbocharged.

This is not to say that I do not think that they are cool as heck, but I do not think that they would fare well in our application. They also tend to have lobe seal issues when run hard, at least the Mazda rotaries do. One good lean/hot run on the dyno will put you in for a rebuild, there is a place here in Dallas (Mesquite I think technically) that specialises in Mazda rotaries and I have heard horror stories about people trying to get that last 3% and killing the seals. Not a cheap rebuild either if I remember correctly.

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HomeAircraftHelicopterMain Discussion › why do people not use 4 strokes on helis?
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