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HomeAircraftHelicopterHelicopter Main Discussion › Does a Nitro/Gas heli really need a One way Bearing?
05-15-2011 05:14 AM  7 years agoPost 1
RM3

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Killeen, Texas - USA

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Guys, just want your opinion on this.
I was flying my Radikal G20 the other day (it flies really good BTW) and noticed that when I landed and after I shut off the engine, the blades and main gear as well as tail drive gear were all free wheeling just as it would if doing and auto. So I began to think, what then is the point of a one way bearing if the drive system uses a clutch that disengages from the engine and the whole thing spins freely then? Now the one way bearing and the drive system are working perfectly with no binding and are very smooth. I can see that there could be a situation when doing an auto and during the flare (or even during zero pitch in Idle up) that the rotor would actually spin faster than what the idling engine would but the iding engine would not be spinning the clutch fast enough to cause it to grab the clutch bell and slow the main gear. So how do you think a heli with a smooth clutch system work with a main gear that is hooked up to the main shaft directly? what would be the potential Problems? Given the additional idea that a Throttle curve is used to set head speed at a given pitch, maybe I don't see what others do, so give me some ideas.

showing a preference will only get you into trouble, 90% of everything is crap...

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05-15-2011 05:35 AM  7 years agoPost 2
jgunpilot

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Pollock, LA

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Without a one way bearing, the drag of the engine would make if impossible to maintain rotor RPM in an autorotation.

That's it, in a nutshell.

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05-15-2011 05:42 AM  7 years agoPost 3
CX1

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Canada

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it will auto just fine with out a 1 way bearing

My Raven is direct drive only the clutch acts as a oneway
the intermediate gear causes a lil drag but not enough to prevent doing auto's

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05-15-2011 05:42 AM  7 years agoPost 4
thenewguy

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Corvallis, Oregon Where there is liquid sunshine!

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Basically,

If there was a mechanical failure that locked the motor or clutch you need a system in place that would still allow the main rotor to spin freely.

Thanks,
Chris

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05-15-2011 05:47 AM  7 years agoPost 5
Fdykes

rrNovice

Laurel, MS usa

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Yes you have to have the one way bearing in the main gear. Reason if the engine was to quit the main rotor blades would continue to turn the engine until it slow down enough for engine clutch released. Also the tail rotor put unnessary drag on the main rotor, when the engine quits the torque is gone.

Ole FD AMA4500 Team JR & Team Cool Power

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05-15-2011 05:55 AM  7 years agoPost 6
jschenck

rrProfessor

La Vista, NE.

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Reason if the engine was to quit the main rotor blades would continue to turn the engine until it slow down enough for engine clutch released.
exactly it - engine clutch wont disengage if the one-way isn't there. Try shooting an auto with a heli that has a locked up one-way. I've done that many times and there is a lot more drag even after the engine clutch lets go of the bell.

BTW - it's not a one-way bearing. This device doesn't "bear a load" so to speak. It's a clutch because it grabs and releases something (it clutches to the main shaft)

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05-15-2011 02:09 PM  7 years agoPost 7
BarracudaHockey

rrMaster

Jacksonville FL

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It's a sprag clutch.

JS has flown Raptors which have a habit of locking up the one way.

Andy
AMA 77227
http://www.jaxrc.com

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05-15-2011 02:15 PM  7 years agoPost 8
CX1

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Canada

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exactly it - engine clutch wont disengage if the one-way isn't there
and yet I can auto with out it, it is common for the oneway to lock up or slip so I removed and put on a Hawk intermediate gear and a raven crown gear. the auto's do suffer a bit but is very manageable.
Even when I burned up my last engine and it seized in flight and just before coming in for a hard landing I was able to save the heli, but that engine will never run again.
wish I had captured it on camera
I guess only Century 50's can do it
Reason if the engine was to quit the main rotor blades would continue to turn the engine until it slow down enough for engine clutch released.
the clutch engages because the clutch shoes are spinning from the engine, if the engine stops or slows enough the shoes release.

you can not engage the clutch by spinning the clutch bell
go ahead and try to start it by spinning the head

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05-15-2011 03:14 PM  7 years agoPost 9
GMPheli

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W. Bridgewater, MA USA

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As Fdykes said, the engine clutch will not release until it slows to a certain rpm. Let's say you have your machine set up for a 2000 head speed. With an 8.4 to 1 ratio your engine is spinning at 16,800 rpm. Now the engine clutch engages and dissengages significantly below that rpm. Each clutch is different, but I am going to assume around 5000 rpm. This means that as your motor dies, it will drag the head speed down to 595 rpm before the clutch dissengages. If you have enough altitude, you can get the headspeed back, but if you don't...

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05-15-2011 03:47 PM  7 years agoPost 10
jschenck

rrProfessor

La Vista, NE.

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you can not engage the clutch by spinning the clutch bell
go ahead and try to start it by spinning the head
true, you can't engage the clutch by spinning the bell, only makes sense. But if the clutch is already engaged then spinning the bell will keep the clutch ears in place because it'll keep the clutch and engine spinning.

Don't know about the Hawk/Raven. I havn't owned one. I have locked one-way's on a few Raptors and the Vision's. You can shoot the auto but it's about like shooting an auto with a 450, not a lot left a the bottom of the auto.

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05-15-2011 03:50 PM  7 years agoPost 11
CX1

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Canada

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if the engine suddenly stopped
yes the centrifical force of the clutch assembly will keep the shoes engaged but only briefly as soon as the shoes start to slip it will disengage. any back pressure from the main gear will also cause it to slip/release.

a larger clutch might hold on longer but will have same results

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05-15-2011 05:25 PM  7 years agoPost 12
rudyy

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E. Amherst, NY

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Without the one way clutch, you will have a hard time doing an auto.. too much drag on the complete drive train wasting a lot of useful potential energy.

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05-15-2011 07:32 PM  7 years agoPost 13
Fdykes

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Laurel, MS usa

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I started flying heli's 34 years ago. I had Slutter Heli Boy it had no one way/autorotation bearing at all, the main gear bolted directly to the gear. Then they introduced the auto sprag clutch as an option, that made all the difference in the way it flew. You don't realize how many times on a landing approach that you are in a auto even if the engine is running. If you had a direct drive main gear and you went out and flew all of the discussion about the one way bearing would be answered after one flight. Just think on a electric heli and didn't have one and you had speed controler failure!! "YARD DART" splat!!!

Ole FD AMA4500 Team JR & Team Cool Power

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05-16-2011 12:26 AM  7 years agoPost 14
CX1

rrKey Veteran

Canada

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Without the one way clutch, you will have a hard time doing an auto.. too much drag on the complete drive train wasting a lot of useful potential energy.
Agree there is wasted energy on drivetrain
Just think on a electric heli and didn't have one and you had speed controler failure!! "YARD DART" splat!!!
another draw back for the e-guys
certainly is needed unless you are doing blade stop auto's

depending on the heli and the way it is geared and driven is what matters

a gasser /nitro could do it more easily with an align drivetrain compared to a century that has an intermediate gear

oneways are an upgrade to make auto rotations easier
like driven tails
tail gyros
fbl units

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05-16-2011 05:34 AM  7 years agoPost 15
RM3

rrElite Veteran

Killeen, Texas - USA

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Thanks for the input guys,
by what I gather from everyone It seems that it does have alot to do with how smooth the drive system is and the RPM the clutch shoes disengage from the bell. The one way just makes it more effcient, keeps it from jerking with the varing engine RPM and serves as a backup to main gear failure/lockup, and that makes good sense now. too bad it is a nessessary item, it seems to me that it is a weak point to high torque systems. I have had it fail twice on my Radikal G20, until when I replaced it with a more robustly designed unit from a bearing supplier. Again thank you all for a great debate and insider knowledge.

RM3

showing a preference will only get you into trouble, 90% of everything is crap...

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05-16-2011 04:07 PM  7 years agoPost 16
jbdww

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Round Rock, Texas

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You need it also to keep the motor from over reeving when you do 3D maneuvers as the blades will spin up faster than the motor can handle.

Skids Up
http://www.jbdww.com
http://twitter.com/jbdww/

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05-17-2011 01:17 PM  7 years agoPost 17
red_z06

rrProfessor

Dumont, NJ

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BTW - it's not a one-way bearing. This device doesn't "bear a load" so to speak. It's a clutch because it grabs and releases something (it clutches to the main shaft)
Actually, one-way bearing bears all the torque load from the engine.
Much of the one-way failure is due to over loaded bearing.

Torque from the motor shaft is converted to force at the tooth (torque/distance to tooth) The same force is transferred to main gear and that very same force is also seen in the main shaft (radial load). If you had planetary pinions, then the one way would only see torque load with zero radial load.

As for the functionality, it has to do with efficiency.

Spur/pinion gear train has losses. This loss is typically materialized as heat. You can touch the motor pinion (electric) and find that sometimes the pinion is hotter than the motor itself.

In nitro/gas, while inertia of the clutch and main gear is relatively small, it still is not zero and requires power to turn them. Same goes for ball bearing that turn them.

So, yes it can be done, but one-way/sprag makes it more efficient. This translates to better/longer auto.

By the way, our Trex600e has a locked up one-way. It has been this way for for past couple of years. Too lazy to change... Same goes for our Raptor 90SE sprag clutch. You just have to remember to do autos faster to maintain rpm.

www.JustinJee.com

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05-17-2011 02:06 PM  7 years agoPost 18
jschenck

rrProfessor

La Vista, NE.

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ok - make sense that it does bear and translate the rotational load. What I was 'speaking' of is this device does not hold any of the load that bearings manage - thrust and radial. With the rotational load it clutches and releases the loadbut doesn't provide a place to push a mechnaical load against like the radial and thrust bearinigs on a main or spindle shaft. Anyway my point is a spraq clutch is not a bearing even though the spraq does look like a needle bearing assembly.

can't wait to get back and do some flying - been out of town for a few weeks.

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05-17-2011 02:18 PM  7 years agoPost 19
Crashr30

rrApprentice

DFW

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Bottom Line
Bottom line you do not "need" it but it is a more efficient method of allowing the main gear to free wheel form the engine. If your clutch drags a little then you loose the effect of freewheeling since the clutch is dragging.

Team Synergy RC, Team Bobby Jacks, PowerMaster Fuels, Team Scorpion, YS Engines

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05-20-2011 07:37 AM  7 years agoPost 20
Fdykes

rrNovice

Laurel, MS usa

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You want the "Real Botton Line" on the one way bearing/Auto rotation clutch!!! On an electric heli if you were to have a speed controller fail and you lost the motor with out autorotation clutch!! You crash!! Reason the rotor head can not turn the motor but for a split second. Example take your heli set it on the ground take take one hand and spin the head, the head will turn 5 + turn! Ok now do the same thing but this time turn the head BACKWARDS! How many turns did it turn after you spun it? NONE correct? The reason to spin it backward's that is the same as NO AUTOROTATION clutch in the system! Now on a nitro/gasser heli rotor head would would slow dramatically until engine clutch released.
Don't believe me go take a old main gear and glue,pin, bolt the auto clutch were it is rigid locked! Go fly you heli go up high and chop the throttle!! There won't be any more discussion if it is need or not!! The only heli's that does not need one is a fixed pitch.

Ole FD AMA4500 Team JR & Team Cool Power

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