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Century Hawk - 50NX - Raven - Predator > Truth on Hawk Gearing??
 
 
CompyMike
Senior Heliman
Location: sacramento, ca

My Posts This: Topic  Forum		TT39 gearing

I was running my Hawk with the stock 9.76 gearing and a TT39 w/ a OS carb. Ran way better than with the TT carb. Fan came loose and I believe it broke the conrod. Was using an alloy fan. Getting another TT39 and was wondering if I should try a different gearing? I had it gov at like 1850 but I would like to run a higher headspeed. Maybe like 1950.

So with the stock gearing of 9.76 and running the motor at 16000 (Best HP for TT39) my headspeed should be about 1650. But I was running 1850. Which means my engine was running over 18,000 rpms

So if I ran the 8.735 gearing I could run a 1830 headspeed with the motor running at 16,000 rpms.
OR if I was to run 1950 with this gearing my engine would run at 17,000 rpm's. Would this be ok? Or would 30 to 40 size engines only be able to handle the 9.76 ratios?

Am I going down the wrong path here?
10-16-2009 10:15 AM
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the Wasp
rrProfessor
Location: Vt

My Posts This: Topic  Forum		""but I would like to run a higher headspeed. Maybe like 1950""
""Am I going down the wrong path here?""

Mike, I realy can't say much about Gearing Ratios with the TT Engine, never had a TT Engine, BUT you do have that OS Carb and it could have changed the Power Band rating of that Engine a bit,

you are buying a new Engine so I would tell you to buy the OS 37, people say it's a real monster, and the OS is probably a Higher Revving engine than the TT,

as for the Rotor Head at Higher Head Speeds you should have the larger 6mm Feathering Shaft with Thrust Bearings, and you realy should have Glass or Carbon Blades, wood blades are just not that reliable at those higher speeds..

here are Century's 30/50s Gear Ratio/HS/ES

53T Counter Gear 13T Pinion 9.408 1701HS @ 16,000, 1807HS @ 17,000
55T Counter Gear 13T Pinion 9.763 1639HS @ 16,000, 1741HS @ 17,000

55T Counter Gear 14T Pinion 9.065 1765HS @ 16,000, 1875HS @ 17,000
53T Counter Gear 14T Pinion 8.736 1831HS @ 16,000, 1946HS @ 17,000

Jim
Buzz Buzz Buzz
10-16-2009 10:37 PM
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CompyMike
Senior Heliman
Location: sacramento, ca

My Posts This: Topic  Forum		Yes thanks Wasp. I am very similar with your gear ratios.
I'm just wondering if I do a taller gear ratio so I can run a faster headspeed... will my motor be more likely to bog.

I didn't think about the OS carb from a OS46 changing the power characteristics of the TT39. It might. Made it easier to tune and boy it idled a lot better. And it revved a lot smoother.

Maybe I should just try and run the 14T pinion. That would be the 9.065
10-16-2009 11:33 PM
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Hate_To_Crash
Senior Heliman
Location: Near Lake Tahoe

My Posts This: Topic  Forum		Mike:

Look at the specs for the TT .39

Specification Displacement(c.c. / cu.in.) 6.45 c.c. / .394 cu.in.
Bore(mm / in.) 21.6 mm / 0.850 in.
Stroke(mm / in.) 17.6 mm / 0.693 in.
Practical R.P.M.(R.P.M.) 2,000 ~ 17,000 rpm
Output(BHP/RPM) 1.35 BHP / 16,000 RPM
Weight(g/oz) 290 g / 10.23 oz

It just doesn't have the RPM range to get where you want to be
If you want the higher Head Speeds and you want to run the TT .39 you have no choice but to use the below combo

53T Counter Gear 14T Pinion 8.736 1831HS @ 16,000, 1946HS @ 17,000

About 1850 is about all you are going to get with that motor and that's pushng the motor pretty hard

If you want to run higher Head Speeds you will need to get something like the OS 37 See Specs

SPECIFICATIONS
Stock Number: OSMG1945
Displacement: 0.37 cu in (6.07 cc)
Bore: 0.806 in (20.5 mm)
Stroke: 0.725 in (18.4 mm)
Practical rpm: 2,000-21,000
Output: 1.4 hp @ 18,000 rpm

The TT 39 max HP at 16,000 max RPM 17,000
The OS 37 max HP at 18,000 max RPM 21,000

How I calculate the right combo to get head speed without bogging the motor is

Motor Choice OS .37
Using the black primary and the 14T pinion you get a 9.065/1

Peak HP is at 18,000 so 18,000 / 9.065 = 1985

Now set the Gov for 1950 and the motor will run at 17,675 just below peak as not so stress the motor

Now with the 37 you can run Head Speeds right at your target
10-17-2009 01:10 AM
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CompyMike
Senior Heliman
Location: sacramento, ca

My Posts This: Topic  Forum		All great info guys and Mike G.
Here is a thought....

I have heard with electric helicopters you want to gear the helicopter so the rpm of the motor is running
just pass the peak of the torque curve of the motor. So... if the head starts to bog and the motor rpm drops,
the motor torque will peak and help get the rpm back up.

For instance
Generic Brushless motor max torque is at 13,000 rpm.
So you gear your motor to run at 13,200 rpm.
Now when you do a energy demanding stunt and the motor
goes from 13,200 rpm to 13,000 it finds itself at max torque.

Could this possible be true for nitro engines and gearing too?

So I have My TT PRO 39H specs

TT Pro 39H
Low RPM: 2000
High RPM: 17,000
Output: 1.35 hp @ 16,000 rpm

With the 9.74 gearing and a 16000 engine rpm I should have a HS of 1642.
That would be where my max HP of 1.35 HP.

But if I run a 1700 headspeed which would be a 16558 engine rpm,
as the headspeed drops from doing a huge sky eating loop the engine
rpm will fall and the Horse Power from the motor would go up.

You would think this would be better than running a 1642 headspeed cause as the headspeed
drops from doing a stunt you are falling away from the peak Horse Power. But I might be all wrong here.

Haven't had a chance to try this out yet. Waiting on a sensor for my throttle jockey.



1642 HS * 9.74 gear = 15993.08 engine rpm
1700 HS * 9.74 gear = 16558.00 engine rpm
1750 HS * 9.74 gear = 17045.00 motor rpm
11-04-2009 05:40 PM
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FBoss
Key Veteran
Location: Aurora Indiana USA

My Posts This: Topic  Forum		Seems like a pretty low HS.......The grey counter gear w/ a 14t pinion would give you right at 1900HS running 16.5K rpm. IMO thats pretty optimal.

The good ole times are now ,Hawk, Raven, Raven NX, Logo 10
11-04-2009 06:07 PM
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CompyMike
Senior Heliman
Location: sacramento, ca

My Posts This: Topic  Forum		Yah I wondered about that. I have that gearing setup in a frame all ready to go.
But with a higher headspeed comes the need for more power and I wonder if the TT39 is even up
for that kind of task.
11-04-2009 06:10 PM
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oldfart
Elite Veteran
Location: Vancouver, Canada

My Posts This: Topic  Forum		As a basic rule, the reason we set for a higher head speed, is to get a faster cyclic response for 3D. Of course if one is not into 3D, and wants smoother response, then one is better to run a lower head speed. (e.g. I have used as low as 1300 on some of my scale birds).

The different gearing available, allows us to gear for an rpm range that will optimize our power systems (motor/muffler/fuel/plug) at the head speeds we want to use.

As an engine can just give its max power and no more, that amount will be absorbed by the loading - weight of the heli, efficiency of blades used, rotor speed and pitch range.

As in most cases, when dialing in a heli for a particular situation, one is usually looking at some constants. For example, the power system & the heli weight stays the same at any head speed we choose & ditto for the blades. So these are constants for this discussion.

That means that as we change rotor speeds we can change the pitch ranges used in order to stay within the power available from the motor etc.

So, as one sets the heli up for more rotor speed for more cyclic response, he will have to reset the pitch ranges to insure he stays within these limits, even if he has changed the gearing to stay within the power band of the motor.

Of course for that extra pop, one always has to set a bigger range then the motor can handle, just as the top pilots do. This allows them to use some of the blades inertia to help accelerate the heli into and out of hard maneuvers. But then they have to learn collective/cyclic pitch management in order to unload the rotor as soon as that kinetic inertial force is used up. They had to teach themselves to quickly release the rotor from these pitches immediately after initiating the change (after the pop) in order not to keep the engine from bogging.

So even though your TT39 or OS32 does not give the power of the OS37 or the Toki 40 that is combined with a muffler like the CN3039 for example, you can still run a 1900 head speed, but you will have to compress your pitch ranges due to the lesser power available.
11-04-2009 06:40 PM
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FBoss
Key Veteran
Location: Aurora Indiana USA

My Posts This: Topic  Forum		cant say on that motor. I run an OS37 geared, if I recall correctly, black primary w/14t (9.04) and it runs very very well. That motor is at 18K, so Im running just below 1900HS. For me and I think most would agree the air frame likes 1850-1950 HS. Unless you are running scale Id gear for at least 1800HS.

The good ole times are now ,Hawk, Raven, Raven NX, Logo 10
11-04-2009 06:44 PM
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CompyMike
Senior Heliman
Location: sacramento, ca

My Posts This: Topic  Forum		Thanks OF and FB

Not really into 3D.
upright hover in all orientations.
Inverted tail in hovering at eye level.
Doing Fast forwards and (now) backwards flight.
Some inverted flight.
Low flips (forward ,back and side flips in all orientations).
Inverted punchouts.
Working on rainbows.
Forwards and backwards loops. Forwards flight rolls.
Have not gotten the nerve to try backwards rolls.

I do all this on a Century Swift and Trex 250.
So I hope I haven't outgrown the Hawk just yet.

I think I will use the 14T and the grey gear and see how it does.
11-04-2009 08:34 PM
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FBoss
Key Veteran
Location: Aurora Indiana USA

My Posts This: Topic  Forum		Man you are not that far behind me....There is nothing on OUR list that a Hawk can not do smoothly and precisely given good collective management along with satisfying the 100000 other details that need tending to. I dont want to speak out of turn here but I bet both of us are long way from doing said list, um...smoothly and precisely. In fact its harder on our 30s, which Im hoping turns into better on my more powerful helis. Besides those 30s have a great air time to fuel ratio!

The good ole times are now ,Hawk, Raven, Raven NX, Logo 10
11-04-2009 09:07 PM
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ReadyHeli . Power Helis . CANOMOD

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Century Hawk - 50NX - Raven - Predator > Truth on Hawk Gearing??
 
 
CompyMike
Senior Heliman
Location: sacramento, ca

My Posts This: Topic  Forum		Got to try out the hawk with the tt39 and the grey gear 14T gearing. Club member clocked me at 1900 HS. Alot of fun! Had to be very careful with the collective. Need more power!
11-23-2009 04:55 AM
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Century Hawk - 50NX - Raven - Predator > Truth on Hawk Gearing??
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