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HomeAircraftHelicopterHelicopter Main Discussion › CNC alu main bearing blocks VS plastic?
04-25-2009 10:42 PM  9 years agoPost 1
LaurenceGough

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UK

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Hi guys,

Just wondering what people's thoughts are on this.

CNC alu main bearing blocks VS plastic for a 450 sized heli.

Difference of around approx 3 grams.

Lightweight like a Mikado Logo (it all adds up) or would the alu blocks give better frame stiffness?

Any input is great, thanks!

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04-25-2009 11:24 PM  9 years agoPost 2
Heli 770

rrProfessor

USA.

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It will add stiffness to the frame and act as a heat sink.

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04-25-2009 11:24 PM  9 years agoPost 3
Dale M

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Lakewood Ca USA

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The aluminum will survive a crash better than plastic but i'm happy with the weight savings as well. Spent lots of time making my rex as light as I could get it. 748 gr. with a 2170 flightpower.

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04-26-2009 12:03 AM  9 years agoPost 4
Yug

rrMaster

UK. Herts

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Different materials have different properties and it's using the appropriate materials which is the art of good heli design. Plastic is good at absorbing vibes but is hydroscopic so it's properties can vary a little over time, while metal is constant. Both can break in a crash. The use of plastic in larger helis is often beneficial in prolonging bearing life but with small helis, do to their low inetria, it makes little difference. However, the bearing blocks in a small heli are not particularly meaty so metal is a good choice simply because it's stronger. I got there in the end

Vegetable rights and Peace

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04-26-2009 12:19 AM  9 years agoPost 5
LaurenceGough

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UK

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The bearing block is so far down the line it is highly unlikely to break in a crash (that and the fact that it's pretty beefy and unlikely to break). Anyway, I do not really mind about crash performance .

Dale M, that's pretty light, how does it fly lighter much improvement? I'm trying to keep it as light as possible while retaining as much precision as I can for 3D flight.

Heli 770, that's interesting, do the main bearings really get that hot on a 450? Or am I reading that wrong?

Thanks everyone.

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04-26-2009 01:26 AM  9 years agoPost 6
Heli 770

rrProfessor

USA.

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Technex
The main shaft bearings in a 450 is half the size of a 50 bearing and it's spinning about 1000 rpm faster. The bearings seems to last longer with the alum. blocks, 450XL vs. 450SE with alum. blocks. Another good example is I have a Shogun C/F frame with alum. blocks and the bearings last longer than my other two without them.

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04-26-2009 02:24 AM  9 years agoPost 7
Sillyness

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Little Rock AR

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I like the plastic simply because it's easier to change the bearnings. Don't think anyone could actually tell the difference otherwise.

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04-26-2009 03:03 AM  9 years agoPost 8
LaurenceGough

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UK

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Well another reason why I asked is the fact that the bearings inside my CNC main bearing blocks have actually gone notchy and need changing. I can get them out fine but whenever I go to replace the bearings they end up notchy when they are seated fully, way to tight. Tried the oven, a vice, hammer, everything (not touching the inner race). Ran out of bearings and patience now. All the bearings I tried were silky smooth before, talk about annoying...

I can order some more CNC ones (complete with bearings) but I have some plastic ones which are dead easy to change bearings (as you say Silleyness).

Only problem with the plastic ones (other than possible chance of flex) is that the bearings are only protected against rotation by friction inside the block. I guess I can just use a few drops of CA? (Still removable then)

To be honest you don't see many people using plastic blocks on a 450 (doing 3D) so this is why I asked, just to make sure... Maybe it's the heat issue?

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04-26-2009 07:53 AM  9 years agoPost 9
Dale M

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Lakewood Ca USA

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The one comment that I always heard right from day one was "oh man, the trex is soo overweight". After a couple years I took one and went through it to make it as light as I could. It flew really, really well. Not the greatest in the wind (naturally) but it had no difficulties doing any maneuvers. Slightly longer flight times as well. I used the micro heli frame, leaving the floor out. Plastic boom block. Mainly plastic in the head and tail. No horizontal fin. Made the vertical fin thinner. No skid nuts. Extra lightening holes in the frames, skids, etc. Even the canopy. Started at something like 37 grams and ended up at 12 grams... No extra wire length. Everything cut to length. Like you said.. It all adds up!

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04-26-2009 06:40 PM  9 years agoPost 10
LaurenceGough

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UK

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Thanks Dale, I always try to keep my heli's as light as possible (within reason) but this time I'm going to make even more of a effort without compromising anything (hopefully!).

Saving 3.2grams with both of them installed compared to the alu ones, doesn't sound much but can feel it for sure when holding them and the heli frame in your hands.

The other nice thing with the alu ones though is that you can tighten the screws as much as you want, they aren't stripping. Plastic ones you have to be real careful with.

I'll see how the test flights go and if I can feel anything different (worse) then I'll get some more CNC ones with bearings pre-installed.

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