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HomeAircraftHelicopterMain Discussion › why do people not use 4 strokes on helis?
03-07-2008 06:15 PM  10 years agoPost 41
SSN Pru

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Taxachusetts

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They also tend to have lobe seal issues when run hard, at least the Mazda rotaries do.
They have problems under high boost. Thats one of the biggest reasons for eliminating the turbo on the Renesis engine (the RX-8) rotary...

I have one of those OS Wankels. I haven't run it and probably never will. It's gonna be a collectors item. Hell, right now it retails for well over $350!

Stupidity can be cured. Ignorance is for life!

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03-07-2008 06:18 PM  10 years agoPost 42
nivlek

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Norfolk England

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I've got a couple of OS Wankel engines as well !
They seem to need a good amount of castor oil to seal properly , OS recommend 25 % ! The last time I ran them I was using Superglo 16% synthetic 4% castor, but they "leaked" a little making their horrific fuel comsumption even worse !

Power wise , about the same as a 36 , fuel consumption about the same as a 90 , mess unbelievable , temperature extreme , sound priceless .
I've always wanted to fit one in a heli , but they are just too messy . They will run OK at a little over 11,000 , they don' like to be loaded any more than that , but they will really sing if you let them rev . They have fantastic throttle response .

At the end of the day , it gets dark .

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03-07-2008 06:25 PM  10 years agoPost 43
GimbalFan (RIP)

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Big Coppitt Key, FL

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I've learned a lot from this thread. I now understand why 4-strokes are popular on large planks. I'll be sticking with 2-strokes for my helis, but my next fueled plank will be a 4-stroke of some sort, maybe even one of those RCV's. Hell, they're even reasonably priced.

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

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03-07-2008 06:28 PM  10 years agoPost 44
joeycoates

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Dallas, Texas

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Yea umdpru, I am talking about the turbo'd engines as most of the high power ones that I have seen were the twin lobed versions in the third gen RX-7's although there is one guy that I know of here in Dallas that has a JDM three lobe rotary in his RX-7 . I think that in Japan they sold a sedan with the three lobe rotary, I forget the technical designation on the three lobe engine though...

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03-07-2008 06:29 PM  10 years agoPost 45
SSN Pru

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Taxachusetts

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Gimbal,

If you want a reasonably priced, powerful, well behaved, and well built 4 stroke you absolutely can not beat Saito. OS's in my opinion are just as good with one exception - slightly lower power output.

I can't believe you have never had a 4-stroke... Especially being an old fart an all

Stupidity can be cured. Ignorance is for life!

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03-07-2008 06:31 PM  10 years agoPost 46
GimbalFan (RIP)

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Big Coppitt Key, FL

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I'm an old fart, no lie -- but I'm only 3 years into RC. Seems I picked a good 'era' tech-wise to jump in, eh?

I'll have a close look at the Saito line too.

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

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03-07-2008 06:44 PM  10 years agoPost 47
nivlek

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Norfolk England

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I do like Saito engines , but I prefer Laser fourstrokes , although they do cost more !
I think why these two brands are so good is because fourstrokes is all their respective manufactures make .
I also have a OS70FL , their el cheapo and it has been very good .
However , I am looking forward to putting some more time on my RCV .
Roll on summer .

At the end of the day , it gets dark .

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03-07-2008 06:51 PM  10 years agoPost 48
joeycoates

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The new OS engines i.e. the 56a and 81a have really caught up power wise not to mention that they now recycle the crankcase vent oil back into the case to lubricate the bearings/top end, but they are $$$ compared to a comperable Saito. Great quality though. I think that they will maybe end up cutting the prices to remain competative in the sales arena as Saito 4's are just spanking them in sales.

The Saito's are very well behaved and run strong. The YS's are pretty pricey as well but they make big power. Can be a bit tempermental though on initial setup, but once you figure them out they run great, very consitant. You have to watch the lean runs though as they will spit a prop off at you in a heartbeat, I have a hole in one of my T-shirts as direct testimony to that fact.

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03-07-2008 06:56 PM  10 years agoPost 49
GimbalFan (RIP)

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Big Coppitt Key, FL

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Why does a 4-stroke running lean spit props?

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

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03-07-2008 07:02 PM  10 years agoPost 50
nivlek

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Norfolk England

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Why does a 4-stroke running lean spit props?
It backfires and loosens the prop nut . I saw an OS 48FS throw its prop in the pits , the prop wizzed passed us all , travelled the width of the runway , around 100ft , then , just like a boomerang , came all the way back and landed back in the pits .
Come to think of it , my boomerang never came back like that at all !

At the end of the day , it gets dark .

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03-07-2008 07:05 PM  10 years agoPost 51
SSN Pru

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Taxachusetts

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I also have a OS70FL , their el cheapo and it has been very good .
I have one too, what a sweet starting and running engine.

My starting procedure for my OS70:

1. Choke on, full throttle, pull the prop through twice.

2. Choke off, full throttle, pull the prop through twice

3. Idle throttle, merely bump the prop Backwards against the compression

Worked like a charm, fired up without fail every time....cold. hot it required a starter it was old!
The YS's are pretty pricey as well but they make big power. Can be a bit tempermental though on initial setup, but once you figure them out they run great, very consitant.
Yeap, all YS's are like that. I have a 1.20 4s and a .45 2s. Power house engines! and run consistently tank after tank after tank after tank after tank after tank... you get my point

Stupidity can be cured. Ignorance is for life!

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03-07-2008 07:06 PM  10 years agoPost 52
nivlek

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Norfolk England

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My Fl doesnt even have a choke . It has a very simple airbleed carb , but it works like a charm .

At the end of the day , it gets dark .

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03-07-2008 07:07 PM  10 years agoPost 53
SSN Pru

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Taxachusetts

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Mine isn't an FL. Its an FS 70 II Surpass.

I hate that new 4s's don't have chokes. The chokes make them much easier to start by hand...

Stupidity can be cured. Ignorance is for life!

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03-07-2008 07:16 PM  10 years agoPost 54
SSN Pru

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Taxachusetts

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ENYA VT-240
Coolest 4s engine I have right now. It currently is pulling a 1/4 scale Sopwith Baby around.

Sounds like a miniature harley davidson. I left the exhaust stacks straight and I make it a point to purposefully do a fly by and point the stacks at the pits.

Always brings a big grin to my face!

Stupidity can be cured. Ignorance is for life!

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03-07-2008 07:44 PM  10 years agoPost 55
joeycoates

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Now that is pretty cool, I would be pround to have one. Good choice on aircraft as well.

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03-07-2008 08:42 PM  10 years agoPost 56
KC

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WA

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thats a cool looking motor

4 strokes are awesome in 3d planes. theres no contest between a YS or Saito 80-90 and a 2c 60 for clean 3d with a plank.... the 2c throttle feels behind in comparison and usually results in overcorrection and a bobbing plane in a harrier or need to rock the AOA to maintain level travel...it looks like a porpoise at sea world.

a 2c in 3d planes is like a 4c in 3d helis, they work, but theres better!

its all fun, I think someone should try this engine in a heli next! (its only 200grams)

http://uk.youtube.com/watch?v=TiPl0...feature=related

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03-07-2008 09:15 PM  10 years agoPost 57
SSN Pru

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I never experienced a single problem in any aspect of 3D flight with my Morris Hobbies Knife and YS 45 combo...

Never a flame out and instant throttle response. Used to hover that thing up and down the runway...

The neatest was doing an inverted flat spin and not loosing altitude!

Stupidity can be cured. Ignorance is for life!

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03-07-2008 09:28 PM  10 years agoPost 58
pchristy

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Devon, England

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One other thing to bear in mind: 4-strokes tend to run hotter than 2-strokes.

Not so much of a problem in a plank, where the head is sticking out in the breeze, but it can be a problem in a heli!

Also, its hell getting at the valve gear to adjust the tappets!

--
Pete

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03-07-2008 09:57 PM  10 years agoPost 59
Way2slow

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Jeffersonville Ga

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Four strokes are much better suited for fixed wing than heli. Most of the four strokes you see in planes are in the scale models where they want the look and sound more realistic to the real thing. Have you ever looked at some pictures of P-51's with two strokes and see how stupid they look with that little bitty prop on the front. They are also the engine of choice in 3D planes where speed is not important but torque and air over the wing is. The four stroke makes much more torque at a much lower rpm than the two strokes, therefore they can spin a much larger diameter prop and hold a the plane vertical much easier. The larger diameter prop is able to push air over a larger amount of wing surface for greater control at slow speeds.

Along the same note, you will probably never see a four stroke in a pylon racer.

If you want speed and HP you use a two stroke. If you want the look and sound of the real thing, or want the torque, you use a four stroke.

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03-07-2008 10:24 PM  10 years agoPost 60
RonHill

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FLL, FL

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Furious Predator
not really twice the power. i remember reading a book on 2 stroke and four stroke engines when i was starting out the hobby. they said that 4 strokes generally produce about 70% of the power of an equivelant 2 stroke.
A quick trek to the OS site shows:

OS .50 Hyper 1.9 HP
OSFSH .52 0.9 HP

So it less than half the power.
To get 1.9HP you need the OS120SE

joeycoates
Oh, a 4 stoke has much quicker throttle responce then a 2 stroke, this is why htey are so common on 3D style airplanes, you need the instant and very linear power that a 4 produces.
I am going to disagree. The nature of a 4 stroke is that it takes twice as long to react. I put a 4s in my 3D planes because I need torque to spin a bigger prop more than I need speed.
I am sure that many on here may argue with what I have said, but I fly both the 2's and 4's, have for 22+ years.
I have flown both for 22+ years as well.

On planes I prefer 4s. They are easier to tune and hold a tune much better. They are more fuel efficient and burn the fuel better so you get less goo on the model. And they produce less noise which makes the neighbors happy.

If I need speed or weight is an issue, I put on a 2 stroke. Right now I only have one plane with a 2s.

For 4s it is hard to beat OS or Saito. I find the OS to be a little less trouble to run, but the Saito has a bit more power.

Wankel's: Had one in my 83 RX7. Not much for torque (1st gear was almost worthless...15mph), but once you got into the power band it really moved, AND you could turn so much more RPM that you could run it up longer in each gear.

For RC they seem to be more for the cool factor than actually better than either a 2s or 4s. When people bring them to the field everyone wants to listen and watch it.

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