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HelicopterGasser Model RC HelicoptersOther › My Minair gassers and their gear ratios
06-01-2010 06:31 AM  7 years agoPost 1
rbort

rrProfessor

Franklin, MA - USA

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When I first purchased my 1005 gasser back in 1997, it came with a 6.43 gear ratio. Though it flew OK, I was not experienced at the time and I called someone in California (sorry forgot their name) and they recommended that for best performance I change to 6.92 gear ratio which I did back in the 1998 timeframe.

That heli has flown really well since then with a slew of motors, from the original G23, to a Hanson G23, to a Hanson G26 and then the varieties of that with Al.

I got my Spectra back in 2005 and that machine came with a 7.15 gear ratio. I flew it with both a stock 231 as well as a Hanson 3D max and when I went to the 3D max I changed the GR down to 7.08 to step in the direction of the GR my 1005 had. Its been flying great all this time.

Well lately with the introduction of the big bore kits and the Wally long stroke motors, many people were talking about having to change the GR back down towards the 6.4 area for those larger motors.

Like everyone else, I decided to try this out with the 29cc motor that I have and I bought myself a 14 tooth pinion from Minair and switched the gear ratio from 7.08 to 6.57. After a few test flights I noticed the motor was not as happy as it used to be and the machine seemed to bog more easily. I tried this with the 29cc motor as well as a G26 Pro motor. I even decided to step further towards the 6.92 that I'm happily running with the 1005 and changed out the main gear to make the ratio 6.64. Several more flights, and I was still not happy with the performance. I turned up the head speed up to 1900, the model became much faster in cyclics, but continued to bog or have a more variable rpm speed during maneuvering which I dislike. Calculations said the motor is running in very similar rpm ranges, but performance was lacking for me.

Well finally last night I decided to switch the 14 tooth back out of my Spectra for the original 13 tooth pinion. Went out today and flew it again with the 7.15 GR and man what a difference the 29cc was much happier in my opinion rotor speeds were practically consistant. I did turn them down to compensate for the GR and remain in my same target rpms so the cyclics slowed up a bit but today I felt it was a happy good performing machine once again.

The moral of this story is that in my opinion, even for the 29cc motor that I'm running, I feel that a higher number gear ratio, 7.15, is better than the 6.64 I was running. You do end up running a lower head speed, but man what a difference the machine feels when you maintain rpms throughout the maneuvers. Minair was absolutely right about the higher gear ratio when they designed the Spectra.

Also, I was able to put in more top end pitch which makes sense, as the slower you run the rotor, the easier it is to turn, and hence the more pitch you can put back in to compensate.

Everything is running perfectly now, and I'm good to be on my way to MHA on Thursday. Hope to see some of you guys there

-=>Raja.

MA 1005 Hanson 280, 4129 flts
Spectra 27 3DMax, 3187 flts
Whiplash V1 Hanson 300, 1425 flts
Whiplash V2 Hanson 300, 185 flts

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06-01-2010 12:45 PM  7 years agoPost 2
jschenck

rrProfessor

La Vista, NE.

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What is your headspeed? My Predator is running 6.76 which is better than the stock 6.28 (14T pinion vs. stock 13T, 88T main gear) and I'm looking for 1850-1900 headspeed.

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06-01-2010 05:08 PM  7 years agoPost 3
rbort

rrProfessor

Franklin, MA - USA

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Head speeds

Last night I reset the head speeds to 1580 in normal, 1700 in idle up 1 and 1820 in idle up 2. Before this with the 6.64 gear ratio I was running 1640 in normal, 1780 in idle up 1, and 1920 in idle up 2.

Basically what I found is that the 90 size engine class does alot better running faster with the slower head speeds.

If you want to run higher head speeds, you may need a lower number gear ratio to stay within a certain max rpm for the motor.

Don't think that the engine performance will be the same if you run it at the same speed with a higher head speed. In other words, if you have a lower gear ratio, running the head faster to bring the motor to the same rpm does not make it easier for the motor and while it can spin the blades faster because of the lower gear ratio, it cannot maintain the blades faster and you'll have a more variable head speed.

Some people don't mind this, I'm just speaking from my experience and how I like to run my helicopters. So what works for me may not work for you, I just wanted to post it to let people know what I found.

Yesterday at the field we had a BBQ and lot of people, so it was quite busy with many people flying all the time so I haven't optimized the gv-1 rpms yet, but those are the ones I'm going to MHA with. Over time I may tweak them just a bit around where they are to find the best numbers.

-=>Raja.

MA 1005 Hanson 280, 4129 flts
Spectra 27 3DMax, 3187 flts
Whiplash V1 Hanson 300, 1425 flts
Whiplash V2 Hanson 300, 185 flts

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06-01-2010 05:40 PM  7 years agoPost 4
Justin Stuart (RIP)

rrMaster

Plano, Texas

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So if you run your heli at the higher head speed with the lower gear ratio, it bogs too much?

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06-01-2010 08:25 PM  7 years agoPost 5
C.A.P.

rrApprentice

custer park IL.

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I posting here because Raja mentioned my Name & engine in this post. Sorry to hear that your big bore 29 (28.5cc) needs a bigger gr not to bog, The Hype stroker engines do not. [
[
PLEASE DO NOT MENTION MY NAME or ENGINES when you POST about gr, rpm, hp, torque or anything related to engines, You SIMPLY DO NOT KNOW ENOUGH about engines, And do not understand how my engines are put together,[
[
Theses video's are being posted to counter Raja's advise for people with big bore engine to run a bigger gr. above 6.4, Of course if your 29 can not do this without the need of super high rpm, then do what Raja is saying to do. I sure it will run fine, It takes a strong engine to hold a 6.4 gr Period!,

]The video's are not new, but they were never explained before, In these two video the 27cc which is smaller bore (34mm) then the 29(36mm) Raja has, The 27cc is running engine 6.4 GR, Can you see or hear a bog,

The first, the engine is running a an engine rpm of 11,500, headspeed of 1,718[

[The second, the engine is running at 12,200 rpm, headspeed 1,909

(1) http://www.youtube.com/watch?v=eOsQ...M&feature=email
(2) http://www.youtube.com/watch?v=LHx_...player_embedded

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06-01-2010 10:05 PM  7 years agoPost 6
AceBird

rrElite Veteran

Utica, NY USA

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Basically what I found is that the 90 size engine class does alot better running faster with the slower head speeds.
Raja, if you want to do this it is your prerogative but essentially what you are doing is de-rating your engine HP to get a more constant RPM. Any engine or electric motor for that matter will decrease in RPM when heavily loaded. Bogging occurs when the engine cannot sustain the dip in RPM. If it holds but at a lower RPM it is not bogging. What it is doing is cranking out torque.

The advantage of cranking up the headspeed is quick movements because of the added potential energy you are putting into the rotor system. Now you could increase the rotor speed and decrease the throws on your stick which would give you back the feel you are more accustom to. It would also tame the dips in RPM that you object to.

As I said you can do what you want but I don't agree with your conclusion on gearing.

Ace
What could be more fun?

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06-01-2010 10:29 PM  7 years agoPost 7
Mike545

rrVeteran

gettysburg, pa

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Did I miss something? I read it a couple of times, I can't really find Rbort bad mouthing anybody in the first piece.

"always feel thankful..... never entitled"

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06-01-2010 10:32 PM  7 years agoPost 8
Justin Stuart (RIP)

rrMaster

Plano, Texas

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I embedded your videos for you.

Watch at YouTube

Watch at YouTube

Impressive videos Wally, but remember that Raja's 1005 probably weighs 3lb more than the Radical 90 in that video. Even the strongest of engines will have more trouble with bogging in a helicopter which is 30 to 40% heavier.

Can anyone figure out what headspeed that guy is running in the video?

I find it strange that 11 pound 700 electrics with 710 blades are running 2050 head speeds while gassers with the same blades are supposedly happiest at 1600-1700 head speed. I would really like to be able to run my Spectra at 2000 head speed, but I would need a motor with a heck of a lot of torque to spin those blades that fast without bogging. 700 electric motors are rated at 8HP. I don't think anyone is going to get that much horsepower out of a 30cc motor.

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