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Bergen R/C Helicopters > Of Gassers and centrifugal clutches...
 
 
gigi
Veteran
Location: Port-au-Prince, Haiti

I am a bit concerned about the number of posts I see about people burning up Intrepid and Observer clutches. Evidently, if the heli is getting off the ground, it must have at the very least 1,200 rpm of head-speed, which would typically equate to over 7,500 rpm on the engine. It seems to me if that clutch isn't engaged solidly by that point, something is off somewhere, either the clearance to the lining has become too large, or the holes in the male part of the clutch are not big enough (spring too strong) or they are not located at the optimum point, or who knows what else.

The only two gassers I've ever seen are the Predator and the Intrepid. I've seen two examples of each, and it seems to me the Century clutch engages at a much lower rpm than the Bergen unit, and I would venture to guess it doesn't slip at low head-speeds, be they inadvertent or intentional. It seems the Intrepid clutch would be perfectly suited to a glow engine, which runs up to 14,000 or 15,000 rpm, but it seems, to me, to be marginal at the lower rpm of the gassers I know it works fine at headspeeds greater than 1,650, but I think it should begin to lock at 3,000 to 4,000 rpm, and not slip at all when past 6,000 or so engine rpm. Are these unrealisic parameters, given the torque the clutch must transfer to the main gear?

I, for one, would *love* to run a 1,400 rpm "hover speed" on my Bergen, but I fear burning up the clutch! I know the motor has more than enough grunt for the work. Anybody else agree, or should I take a chill pill, and spin my 710's to 1,800 rpm, and be done with it?

Gigi

My heli spending has gone way down since I got a Honda 919 :-)
06-15-2005 Over year old.
 
 
Malorie
Elite Veteran
Location: Paw squared, MI

If you want to run a lower headspeed, then get yourself a suitable gear ratio, like 7.5 (12 tooth pinion). That way your motor is at a proper RPM at the low headspeed and your clutch will be securely engadged.

Or do you prefer your clutch to be engadged at an idle so the head never stops?

Malorie

Life's a journey, NOT a destination.
06-15-2005 Over year old.
 
 
Chris Bergen
Key Veteran
Location: location

As Mal said, we do offer different gear ratios.

If you're only spinning the engine at 7500, you are nowhere near the power band of the engine. Try this as an experiment, in your car, go up a steep hill, in 4th gear, at 5 miles an hour. This is what you'll be doing to the engine in your heli at that speed. Conversley, go 60 MPH in 1st gear. How long does the engine last then?

A helicopter is a whole lot of moving parts that have to be working at proper RPM's, in the proper fashion to be able to fly. Start changing some of these parameters and they stop flying.

Chris Bergen
06-15-2005 Over year old.
 
 
RV-4Mike
Senior Heliman
Location: San Diego, Ca.

Gigi,

My experience is just the opposite of yours. Unlike the glow machines I've flown (and I admit my experience is limited) I find that the clutch on my EB starts to engage just off idle and appears to be fully engaged at a relatively low rpm. After flight I've never detected any excessive heat from the clutch bell so dont believe I've ever experienced any clutch slippage.

Mike
06-15-2005 Over year old.
 
 
gigi
Veteran
Location: Port-au-Prince, Haiti

Touché, Mal, I don't want to replace my clutch with a solid coupling. Although it could make for a novel way to "rotor-start" the heli, kind of like bump-starting a car with a standard transmission. Haha! (I picture the heli on a stand, and I swing the blades from underneath) Of course, you'd need a shear pin in the drivetrain, in case of crashes, or Bergen would have to produce lots of main gears.

Chris, I agree entirely with you about the gearing, and the car example you've used is a good one. I drive manual-transmission cars, and ride motorcycles, and am a certified gear-head. I promise you I know enough about power-bands, and how to use the transmission to get the maximum performance out of a vehicle. However, if I'm not in a hurry, I can elect to short-shift at 2,500 rpm in my car instead of at 3,500 or 4,000 if I'm climbing a hill, or if I'm racing a buddy, I'll bring it up to its 7,000 rpm redline. Do you see how I tailor the performance according to my needs?

Well, what I'm saying about the clutch on the Intrepid is that I feel it should let me run my rotor rpm in the range of 1,400 to 1,800. Using the stock ratio of 6.43, that translates to a motor rpm of 9,000 to 11,500, give or take a few. My very point is that this stock ratio is well-chosen for the engine, but since the clutch has been known to slip if the head-speed is below the minimum recommended 1,650 rpm, I'm saying that in my opinion, the clutch should be re-optimized to be fully engaged by the time the engine is at 7,500 rpm maximum, and it should be able to handle the maximum torque of the engine from that point forward.

I never said I wanted to run the engine at 7,500 rpm. What I want to be able to do, without changing ratios, is to have the freedom to run a lower head-speed without worrying about my clutch slipping, and I don't think I'm out of line with the bracket I desire, namely 1,400-1,800 rotor rpm.

Of course, we could argue all day about this, and we don't need that. Maybe I'm the only guy on this planet who would enjoy seeing his Intrepid hovering at 1,400 rpm. Anyway, I do it all the time with my Raptor, I bring the governor down, and it's like another facet of the heli's flight envelope to explore, which I personally find fascinating. To go back to your car analogy, it would be to see how many rpm are required to achieve a smooth, proper take-off on a given hill, in a given car. For example, where a 4-cylinder Mazda 626 might require about 1,250 rpm, a Toyota Land-Cruiser with a 4.2 liter Turbo diesel 6 cylinder can manage with just 800 rpm to do the same job.

I wouldn't fly the heli at 1,400 rpm, I'd *HOVER* it. Just like you don't need to redline a car to get it moving from a stop, you don't need the engine to be at peak torque to barely keep the heli off the tarmac in ground effect.

I'm just saying the clutch could possibly be optimized so people don't need to worry about smoking it, if they experiment with lower head-speeds. The engagement point should be right off idle (2,500 to 3,000 rpm) and it should be able to tranfer full engine torque past 6,000 to 7,000 rpm. If it did, it would be a better unit than the one currently on my machine, which seems to engage at around 5,000 rpm, and which holds fine at the two speed I currently run, 1,650 and 1,800 rpm, but which makes me afraid to "play" with my helicopter's lower rotor rpm characteristics.

Rav4Mike, my own clutch has never slipped. But I don't experiment and play with my heli like I would, if I trusted that the clutch wouldn't slip.

Haha.

Gigi

My heli spending has gone way down since I got a Honda 919 :-)
06-15-2005 Over year old.
 
 
Chris Bergen
Key Veteran
Location: location

The difficulty here is that you want to run something other than what we specify the heli is designed to do, and then say we need to design it differently.

The next guy wants to do something else entirely, so he wants us to design it differently for him.

How many different ways do we make it? We already have ways of changing the gearing, so if you want a 1400 headspeed, put in a 12 tooth pinion. Much easier than designing different clutches for different engine RPM's, don't you think?

Chris Bergen
06-15-2005 Over year old.
 
 
FLAP
Key Veteran
Location: Michigan

automatic transmission
06-15-2005 Over year old.
 
 
Malorie
Elite Veteran
Location: Paw squared, MI

Quote 
automatic transmission


My thoughts almost exactly. I was thinking more along the lines of a manual transmission though.

Chris,
Sell him one of the pre-skim cut linings, then it'll be just like those other birds where you have to hold the head back at an idle.


Life's a journey, NOT a destination.
06-16-2005 Over year old.
 
 
gigi
Veteran
Location: Port-au-Prince, Haiti

I'll take my lumps...

You're a bunch of funny guys, Flap and Mal The problem is, what you guys don't understand is that I want to MOMENTARILY fly with a low head-speed, and the engine can do it, but the clutch (needlessly!) won't let me do it because I fear burning it up! So, I want low engine AND rotor rpm, not fast engine rpm and low rotor rpm. Does that make sense? 'Probably not, but no worries, I know what I mean.

I do see your point, Chris. Maybe I'm mistaken, but it just seems to me that if the clutch engaged earlier, and held on for dear life sooner in the rev range, that there would be only benefits. After all, if it can hold at a given rpm, it will hold at a higher rpm, correct? But the opposite is not necessarily true. In fact, that's the operating principle of a centrifugal clutch. Anyway, no sense in beating this dead horse... As I said, my own clutch doesn't slip, but every time I hear a Predator spool up, I think to myself that I like what I hear a bit more than when it's my Intrepid that is spooling up. Food for thought, maybe.

Don't think I'm just criticising, it's more like giving you some feed-back. Of course, you don't have to take it as gospel, but at least, keep an open mind. Your goal should be to make the best Bergen helicopters you can, and this is some information that may (or may not) be helpful for the future. 'Fact is, there have been problems with people smoking clutches, and maybe, just maybe, the existing clutch design can be further refined and tweaked. If you ever do, let me know, I wouldn't mind one. The amazing thing is, it would work just as well for me as for the guy who doesn't mind spinning his rotor all the time at 1,800+ rpm.

Anyway, it's nice at least to get some feed-back. Keep up the good work, and good luck at Model Expo 2005. 'Wish I were going too!

Regards,

Gigi

My heli spending has gone way down since I got a Honda 919 :-)
06-16-2005 Over year old.
 
 
FLAP
Key Veteran
Location: Michigan

Gigi,
all kidding aside, I have some of the same sentiments as you. I burned up my first clutch ever, in 20 years of flying, due to running too low a head speed with the load of a camera mount. I had never been a big fan of high head speed (actually engine speed). I don't think there is any getting around the recommendation to get the engine (and therefore clutch engagement) to the correct RPM. I believe that is about 10,000?? on the engine...and then you customize the gearing based on desired rotorhead speed.
My only issue is that I suspect that more high freq vibration would come from the engine than the rotor head.
06-16-2005 Over year old.
 
 
Malorie
Elite Veteran
Location: Paw squared, MI

Quote 
I want to MOMENTARILY fly with a low head-speed, and the engine can do it, but the clutch (needlessly!) won't let me do it because I fear burning it up!

Quote 
I feel it should let me run my rotor rpm in the range of 1,400 to 1,800. Using the stock ratio of 6.43, that translates to a motor rpm of 9,000 to 11,500

Quote 
seems to engage at around 5,000 rpm


So have you ever tried it to see if the clutch is even slipping at 1400RPM (9000RPM Motor speed)? It sounds to me that if the clutch is starting to engage at 5000RPM then it would be fully engaged with an additional 4000RPM.

As is typical with ALL manufacturers, they need to over-estimate the minimum RPM for CYA purposes. That doesn't mean that it won't hold there, just that they won't say that it will.

My point is that you want a redesign of a part and you haven't even tested to see if it is capable of doing what you want in it's current form.
Quote 
I want to MOMENTARILY fly with a low head-speed

Quote 
I wouldn't fly the heli at 1,400 rpm, I'd *HOVER* it.


So before redesigning a good working design, why don't you test it to confirm that your concern is not unfounded?

BTW, making the clutch sprung more lightly will increase the number of broken shoes, which you currently NEVER hear about with a Bergen clutch. It is a fine line to walk, make the clutch too stiff and it doesn't have a usable PRM (not a problem with the Bergen clutch). Make it too weak and you start breaking shoes (not a problem with the Bergen clutch). I think Bergen walks that line nicely.

Life's a journey, NOT a destination.
06-16-2005 Over year old.
 
 
daveye
Senior Heliman
Location: North Carolina

I would have to agree with Mal on this one. The Bergen clutch shoe is practically indestructible. I have installed new liners then pinched the clutch so that it fits looser and have done these 2 times now on one of them and not a broken shoe yet!

David
06-16-2005 Over year old.
 
 
gigi
Veteran
Location: Port-au-Prince, Haiti

Good feed-back

Now we're getting somewhere, Mal

I understand very well what you've explained about the relationship between the clutch stiffness and the possible failure modes. So maybe it is that the current design is a good compromise from a reliability stand-point (as long as the engine is turning 10,000+ rpm, at any rate).

Do you know if Predator clutches are braking shoes? I've never heard of any yet, and I've seen them spool up enough times to get a feel for the difference between the Predator clutch and the Intrepid unit.

I'm not saying Bergen must redesign their clutch. Nobody is putting a gun to anyone's head here. But the very reason I wrote this post is because I am afraid to do something I would love to do with my Bergen (namely, lower my ENGINE rpm, and simultaneously, my rotor rpm if I'm just putt-putting around the landing area) due to what I feel is a clutch which can potentially ruin itself if the heli is operated in this condition. So I am saying, hey, guys, this is what think. You guys can take this as free, honest, unbiased, and I add, technically correct feed-back from a customer who otherwise likes your product. It just may be valuable information, that you may not see yourselves, because you don't run your helis this way. Let me tell you that I now know through PM's that I am not the only nut on this planet who thinks the low-rpm requirement of the Bergen clutch is too high. Do with that information what you will, I provided it with the best of intentions.

Gigi

My heli spending has gone way down since I got a Honda 919 :-)
06-16-2005 Over year old.
 
 
gigi
Veteran
Location: Port-au-Prince, Haiti

Quote 

The Bergen clutch shoe is practically indestructible.


Yes, it seems when the clutch shoe slips, it's the lining that takes the heat.

I add that no, I did not try running a lower head-speed than the recommended 1,650, because where I am, it would be a major bother to receive another lining, in case it did slip, and I did not realize it.

'See, I'm assuming someone intelligent enough to fly a model heli should be able to recognize a slipping clutch, and land immediately. It's BECAUSE I've heard of all the cases of fried, slipping clutches at low rotor rpm, and given the assumption above, that I don't want to risk mine. What if the slip is very subtle, and quietly destroys the clutch, while I think to myself all is fine and dandy? I don't think it slips "big-time", in a recognizable way, I think it all looks nice and peachy until you've over-heated the clutch, and there you are, up a creek without a paddle. So I'll stick to my 1,650 rpm, having voiced my opinion.

Gigi

My heli spending has gone way down since I got a Honda 919 :-)
06-16-2005 Over year old.
 
 
Malorie
Elite Veteran
Location: Paw squared, MI

Quote 
I did not try running a lower head-speed than the recommended 1,650, because where I am, it would be a major bother to receive another lining, in case it did slip, and I did not realize it.

Quote 
What if the slip is very subtle, and quietly destroys the clutch, while I think to myself all is fine and dandy?

Quote 
I'm assuming someone intelligent enough to fly a model heli should be able to recognize a slipping clutch, and land immediately.


I'm sure your opinion has been heard and noted.

Life's a journey, NOT a destination.
06-16-2005 Over year old.
 
 
tapeworm
Heliman
Location: Atlanta, Ga

Quote 
But the very reason I wrote this post is because I am afraid to do something I would love to do with my Bergen (namely, lower my ENGINE rpm, and simultaneously, my rotor rpm if I'm just putt-putting around the landing area) due to what I feel is a clutch which can potentially ruin itself if the heli is operated in this condition.




If you want to do new things you can't be afraid.

Eric
06-16-2005 Over year old.
 
 
Chris Bergen
Key Veteran
Location: location

I tried to post earlier and something fubar'd here.

I certainly welcome feedback, as long as there is an understanding that we have to take a lot of other things into consideration before making any changes, as Mal mentioned for instance, reliability, useability in other applications.

We produce varied helicopters for different purposes, and try to keep a commonality of parts as much as possible to keep costs such that you guys will want to buy them.

Experimentation is good, matter of fact, that's why we're where we are today. Some experiments turn up things that can be applied to all of the goods, others are only good for a certain application.

Chris Bergen
06-17-2005 Over year old.
 
 
gigi
Veteran
Location: Port-au-Prince, Haiti

'Good enough

Mal and Chris, You guys all make good points. I'm glad we can have these informative exchanges. After all, it's true I know nothing of the rigors of producing and selling such a complex product as a range of model helicopters, and you guys have been doing it well for a while. And you can't be all things to all people, it just isn't that easy. So keep up the good work, and I'll keep learning. Thanks for your patience.

Thanks for the advice, Tapeworm, it applies to more than helis as well, and is quite timely, as I'm looking at something different these days, and can use that kind of wisdom.

Regards,

Gigi

My heli spending has gone way down since I got a Honda 919 :-)
06-17-2005 Over year old.
 
 
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Bergen R/C Helicopters > Of Gassers and centrifugal clutches...
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