Why aren't there any gearboxes for glow engines?  
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All Forums >> RC Airplanes >> Beginners >> Why aren't there any gearboxes for glow engines?
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Why aren't there any gearboxes for glow engines? - 7/25/2003 2:57:05 AM   
Nik



Posts: 287
Joined: 1/12/2003
From: Painted Post, NY, USA
Status: offline 		This maybe a dumb question, but I can't find an answer to it.
Why aren't there any gearboxes for glow engines?
Shouldn't that give way more thrust and efficancy?
I don't see a problem, it should be easy to acomplish!

-Nik
       Post #: 1

Why aren't there any gearboxes for glow engines? - 7/25/2003 3:00:43 AM   
brschmid



Posts: 274
Joined: 7/19/2003
From: Moorhead, MN, USA
Status: offline 		the most power is in the upper end of the power curve, so i don't know why you would want the engine going full speed, but the prop only a fraction of that.

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Why aren't there any gearboxes for glow engines? - 7/25/2003 3:04:30 AM   
Nik



Posts: 287
Joined: 1/12/2003
From: Painted Post, NY, USA
Status: offline 		Got ya!
Dumb question! Sorry!

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       Post #: 3

Why aren't there any gearboxes for glow engines? - 7/25/2003 3:08:53 AM   
Montague



Posts: 4653
Joined: 4/19/2002
From: Laurel, MD,
Status: offline 		Not a dumb question at all.

Actually, the reason is more of reliability and cost than anything. There actually used to be a few geared .61 engines available. But the power to weight ratios of our engines is such that it's just not needed.

Turning a larger prop at a lower RPM is generally more efficient. And as it was pointed out, many of our engines produce peak power at higher rpms. So it makes a lot of sense to wind up the engine and then gear down the prop. It's just too much hassle. Just think of trying to keep them oiled. And we are talking about an input rpm that could exced 20krpm in the air, so you're going need some quality gears and bearings in there. That's $$$$.


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There have been - 7/25/2003 3:09:10 AM   
JohnBuckner



Posts: 3999
Joined: 12/23/2001
From: Kingman, AZ, USA
Status: offline 		Dubro, Sullivan, byrons and possibly others in the past have made belt reduction units just for sixty size and larger glow engines.

I doubt that any are in current production because the proliferation of large gas engines pretty well killed the market. These units were popular during the early days of the popularzation of giant scale flying before the gas engines were available and worked well for the reasons you outlined and were reliable. I would love to get my hands on an old Dubro unit.

John

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       Post #: 5

Why aren't there any gearboxes for glow engines? - 7/25/2003 3:19:12 AM   
vtol_guy


 

Posts: 897
Joined: 1/13/2003
From: Driffield, UNITED KINGDOM
Status: offline 		i wish gearboxes were standard, common item, i need some quite badly


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Why aren't there any gearboxes for glow engines? - 7/25/2003 4:14:11 AM   
Woodsy



Posts: 1745
Joined: 9/24/2002
From: DrouinVictoria, AUSTRALIA
Status: offline 		In Aus i'm pretty sure we can still get them, generaly for the 60-90size engines, there used a little bit buy the WW1 scale type guys to swing a bigger slower prop


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Why aren't there any gearboxes for glow engines? - 7/25/2003 5:21:27 AM   
ykol20



Posts: 129
Joined: 6/12/2003
From: wilmington, NC,
Status: offline 		I think it would be worth it, to get a .60 size warbird to turn a nice scale looking prop, instead of having a little 2 blade on it. Depends on the application.

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       Post #: 8

Why aren't there any gearboxes for glow engines? - 7/25/2003 6:14:11 AM   
Spaceclam



Posts: 4640
Joined: 4/13/2003
From: chatsworth, CA, USA
Status: offline 		electric motors don't replace gas engines, and probably never will. to turn that same prop, an electric motor typically has to have a reduction of something like at least 4:1. a gas motor will turn the same prop at about 4-6 times the rpm. If you get a big enough electric motor t oswing that prop at the same rpm without reduction, it would draw so much current you would need something like a car battery to power it. now, car batteries weigh so much that it would be completely useless.

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Why aren't there any gearboxes for glow engines? - 7/25/2003 8:06:12 AM   
Woodsy



Posts: 1745
Joined: 9/24/2002
From: DrouinVictoria, AUSTRALIA
Status: offline 		Where did the electrics come in to the conversation????


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Why aren't there any gearboxes for glow engines? - 7/25/2003 8:29:57 AM   
JohnBuckner



Posts: 3999
Joined: 12/23/2001
From: Kingman, AZ, USA
Status: offline 		Beats me, Woodsy?

John

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Why aren't there any gearboxes for glow engines? - 7/25/2003 8:36:00 AM   
Tweet



Posts: 481
Joined: 6/11/2003
From: Windsor, CO, USA
Status: offline 		Brschmid,

The most efficient setup would be the engine running at peak power (higher RPM) and the prop running at peak efficiency (larger diameter and lower RPM).

This is true for full scale as well (turbo props are a great example as they are geared). Recip engine full scales match engine RPM and propeller RPM fairly well (and add adjustable pitch props in many cases).

I'm guessing the reason it isn't done often for models is, as everyone has said, for reasons of cost and reliability. I'd also add that the need for efficiency in models isn't as great. Thrust to weight ratio is typically much higher than for full scale airplanes and also no one really cares (too much) about fuel economy, which is a big factor in full scale (sometimes).

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Why aren't there any gearboxes for glow engines? - 7/25/2003 9:28:48 AM   
Spaceclam



Posts: 4640
Joined: 4/13/2003
From: chatsworth, CA, USA
Status: offline 		it would weigh more to get an electric motor to spin a 14x6 prop at 9500 rpm giving you 10 mins of flight time (battery weight included) than it would to have a gas engine that would swing the same prop at the same rpm for 10 mins.

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Why aren't there any gearboxes for glow engines? - 7/25/2003 2:01:09 PM   
njl


 

Posts: 54
Joined: 5/8/2003
From: Twyning, UNITED KINGDOM
Status: offline 		Some of the RCV engines use gearing. The output shaft is attached to the cylinder valve which turns at a slower rate (half I think) than the crank shaft. Never used one but the design looks interesting however I've heard mixed reviews.

Nick

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       Post #: 14

Why aren't there any gearboxes for glow engines? - 7/25/2003 5:07:35 PM   
DBCherry


 

Posts: 5554
Joined: 1/25/2002
From: Hubbardston, MA, USA
Status: offline 		Okay Spaceclam,
Once again. WHY are you talking about electrics?? No one else has mentioned them, this is a thread about geared glow engines.
Dennis-

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