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HomeScale✈️AircraftScale HeliScale Helicopter Main Discussion › gear ratio and 3 blade head
07-19-2006 06:16 AM  14 years ago
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The_Dave

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gear ratio and 3 blade head
OK Vario experts I have a question!

I got the 3 blade installed on the Benzin Trainer. Set up as per suggestion. I was able to fly it and had good control. However, I think I have the wrong gear ratio. The smoking clutch was my first clue! I suspect that the ratio used for a two blade head is different than what you would use for a multi-blade head.

Can someone dial me in?

Thanks!
Mark McAlpine - 2005 - We will never forget.
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07-19-2006 08:50 AM  14 years ago
Peter Wales

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You need nearly 50% more power to run a 3 blade head over a 2 blade head with a flybar.

If the clutch is slipping, then the motor isn't running fast enough or the clutch is worn. If the motor is too slow then yes, you need to change the gear ratio to get the motor speed up and keep the headspeed constant.

I would look at the clutch anyway and if it has blued, it should be changed as its temper has gone and it will eventually break. While its down, check the liner for wear and burnt surface. If its not too worn then a scuffing will clean up any burnt areas.
Peter Wales
http://scalehelicopters.org
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07-19-2006 05:40 PM  14 years ago
The_Dave

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~
Peter Old Friend, thanks for the reply.

I have two additional gear sets that I can use, would you have a recomended ratio?

I did a quick inspection of the clutch this morning, and although it got hot I don't think I damaged it. Clutch to liner clearance is not out of line so I think I am ok.

As a side note, I set up the 3 blade so when I have a blade directly over the boom and move for-aft cyclic I get no movement of that blade. I was able to get it light on the skids and even slightly airborn and control movments seemed to be correct....once I can get the power to the blades I will know for sure.
Mark McAlpine - 2005 - We will never forget.
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07-19-2006 05:44 PM  14 years ago
The_Dave

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Another question...anyone know the stock ratio on a Benzin Trainer?

I have additional ratios that I can install that are:

87/21 = 4.14 to 1
85/23 = 3.69 to 1
Mark McAlpine - 2005 - We will never forget.
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07-19-2006 08:34 PM  14 years ago
Notar (RIP)

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The stock benzin with 800mm mains is 9.09:1 That is the 90 tooth main, and 18 tooth pinion, or 90:18
The 85:23 gear ratio is 6.71:1
The 87:21 gear ratio is 7.53:1
Joe
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07-19-2006 08:35 PM  14 years ago
The_Dave

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Thanks for the reply Joe...which do you recomend?
Mark McAlpine - 2005 - We will never forget.
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07-19-2006 10:52 PM  14 years ago
Peter Wales

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the 90:18 is the lowest ratio you can get and will give you a headspeed in the 1100rpm range. If thats slipping then you have a clutch problem. Using any of the other gears will increase the headspeed and make the problem worse.Peter Wales
http://scalehelicopters.org
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07-19-2006 10:57 PM  14 years ago
The_Dave

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Talked with Joe, he says the book calls for the 87/21 gears. I am almost positive I have the 90/18's installed. I did not get a super good look at the clutch this morning so I will have to check that.

Also, I just flew this machine last weekend with a 2 blade head, not so much as a whimper from the clutch system. I only ran the 3 blade head for two minutes or less, I don't think I could have done that much damage....I hope not anyway....
Mark McAlpine - 2005 - We will never forget.
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07-20-2006 07:21 AM  14 years ago
The_Dave

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Update....

I did not have 90/18 gearing installed but the 85/23's.

I now have the 87/21's installed and will test fly tomorrow.

I also checked the clutch, I don't see any bluing of the clutch shoes and I checked the clearance on the clutch and it is 5 thousandths (10 total) so i thin I am good there as well....

Thanks for everyone's help....
Mark McAlpine - 2005 - We will never forget.
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07-20-2006 03:20 PM  14 years ago
Christopher J

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Let us know how it turns out.

BTW, Your signature line....it's great. Mark was a great guy.
Christopher J
same as I ever was
"Still all set & Flying the original"
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07-25-2006 08:12 PM  14 years ago
The_Dave

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OK, made a test flight this weekend and things are much better. The proper gearing is the trick!

I have to set up pitch curves as I just have it eyeballed currently. The phasing was balls-on and I was able to fly it around no problem at all. I did not do any super fast forward flight as I am still tuning the engine but I did shoot an auto and it was amazing how much lift the blades carry....

Some have suggested a mixer for the head to manage it but at this time I don't see a need, perhaps FFF will show some uglyness that would warrent the mixer.
Mark McAlpine - 2005 - We will never forget.
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07-25-2006 08:30 PM  14 years ago
modtron

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Oxford. UK

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The Dave,

The mixer (Helitronix) is very good, but not essential. It is required if you want to put gyro's on to stabilise the head.

Modtron
Oxford UK
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07-25-2006 09:21 PM  14 years ago
The_Dave

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Thanks for the info. At this point the head is fairly stable...time will tell I guess.
Mark McAlpine - 2005 - We will never forget.
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08-07-2006 09:34 PM  14 years ago
The_Dave

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UPDATE
OK, I have about an hour on this head now. It is flying and the machine is working well.

I have noticed that it is a ton of work to fly and I am hoping to get used to it. My biggest complaint is that it likes to park itself in the turns. Kinda rears its nose up and makes a fuss. I assume this is normal and I hae been "forcing" it through the turns.

Any ideas on how to make it more manageable? Can I do something with the phasing to lessen these tendices?

Please Advise.
Mark McAlpine - 2005 - We will never forget.
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08-08-2006 02:55 AM  14 years ago
Joel Rosenzweig

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The gyros on the elevator will eliminate the difficulty that you describe, among other things and specifically what you mentioned, the tendency to pull back when transitioning from forward flight.

As you found, the multi-bladed head can sometimes be a handful to operate. And yes, you can certainly get used to it. If you decide that you don't really want to spend your time getting used to it, then you can mount the gyros.

I flew my Lama with 3-bladed head for an entire flying season and learned how to fly it comfortably <enough>. However, it wasn't the most enjoyable experience. It was work. If you are more naturally inclined, it might come easier to you. Since I'm not the world's best pilot, I was looking for a little assistance to tame the rotor head. And that's why I developed the mixer in the first place. With gyros, it's a completely different flying machine and I don't have to learn to fly it any differently than a flybarred machine.

Joel-
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08-08-2006 12:59 PM  14 years ago
Jack Martin

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Yeppers, Joel's mixer will almost completely resolve that after testing and adjustments.
Jack
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08-08-2006 10:49 PM  14 years ago
brokenheli

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three blades
It's not just the gear ratio( if the gear ratio at all ) it is also the cord and length of the blade. the blades must be a narrow cord.
because you are creating more lift hence more drag: narrow cord, shorter length makes it even out at the same head speed
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