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» 2019 Llanfair TH Village Fete
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Saturday 7/7/18

2018-07-07, 21:07 by Gary M Jones

I was at the field today between 14:00 & 15:00 all on my own , good flying too. There is a dead sheep along the fence line towards the gate from the pits, I saw the farmer so reported this to her. I hope no one had plans for a BBQ Smile .

Farmer …

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Post by Mark Barnes on 2013-08-28, 16:26

Need one! that is all!

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Post by Neil on 2013-08-28, 19:47

4 bladed Helicopter... Very Happy 
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Post by Mark Barnes on 2013-08-29, 09:07

Neil wrote:4 bladed Helicopter... Very Happy 
its NOT a helicopter Rolling Eyes 

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Post by Allan Patrick on 2013-08-29, 10:21

I wonder if its better to have on relatively efficient large motor but with the losses of a complex drive system and collectives or four direct drives?
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Post by Andy Sayle on 2013-08-29, 12:18

I'll put a lot of money on the control response being far better with a single drive, but variable pitch props. Speeding up and slowing down direct drive props takes a lot of doing (in terms of time), which ultimately limits what you can do with the control system. Taking all that rotating mass out of the control loop equations can only be a good thing!

That said, direct drive works perfectly well, until you try to go anywhere near inverted!

In terms of efficiencies between the two systems, I reckon it is six of one, half a dozen of the other!

It looks fun though. If the skills in my thumbs ever got anywhere close to being able to fly something like this in the way it is designed to be flown, I would get one in an instant! For now, I shall stick to pootling around, taking snaps and turning leds on and off Smile

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Post by Allan Patrick on 2013-08-29, 13:59

To improve the duration and load carrying capability one could put a 100cc petrol engine in it
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Post by Allan Patrick on 2013-08-29, 14:03

In fact, scale it up as big as wanted. Since a lot of the cost would be in the control system which doesn't change much with size it would get proportionately cheaper as it was made bigger...

What size engine, props etc to lift 100 kg?

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Post by Andy Sayle on 2013-08-29, 14:38

I reckon quite large! If you think a Trex 700 can lift around 12.5kg (but not do much other than hover), then you would be looking at an multirotor with eight 700 sized rotor heads, each around 1.5m dia or so (700mm blades). I've just done a quick sketch and you would be looking at a frame with a diameter of 4.2m (to rotor shafts), overall diameter including rotors about 5.7m

Now if you say that each rotor head needs driving with a 15cc engine (91 size), then you woul dbe looking at around a 120cc engine. Obviously the specific performance from a larger engine would be much lower, so say 150cc for good measure. Then make an allowance for transmission losses, and you are up around the 200cc size as a minimum. Add in some extra weight for for structure and stuff, and I can easily see a requirement for a 250cc engine.

You would probably find then that the weight has gone up enough to warrant a move to an 800 sized rotor head, thus an increase in size of the airframe, and therefore weight, and as a result more power needed....

Andy

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