Whirley,
I've recorded the first batch of episodes (1-4). I'll be at Heliflight next week at some point so i'll drop you an e-mail and let you know when, then you can pick it up at your leisure.
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Right Then,
I watched the first four episodes of 'A Chopper is Born' last night and although I haven't had time to sit down and contemplate the content of what I saw I have the following comments to make on the helicopter.
Belts
It seems foolhardy to me for the manufacturer to allow an inexperienced builder to be cutting his or her own belts [primary drive & clutch!] It seems like a sure way to build a flaw into the primary drive system. (Oh, it’s only a nick, it'll be alright.) Furthermore, I think the statement: 'It's to ensure they are equal length' is an absolute nonsense, considering how they are made there is no reason why moulding them together would ensure they are equal lengths! IMHO the real reason is cost and transferring liability.
Triplex chain
Why they have used a triplex chain in the primary drive train is absolutely beyond me. If one pin breaks [as Mark stated] 'the whole thing drops to pieces'. Nice. Why not three simplex chains, engineering in some redundancy. Once again I would venture cost as the reason. Possibly weight also.
Casting in the Rotor control system
[The main rotor tension element was not cast]
I find the thought of cast swash-plate elements and main rotor control assembly somewhat disturbing also. Sand casting is a process that is inherently difficult to control and works to relatively poor tolerances. While the swash plates do not have to tolerate large loads, the loads they do experience are oscillatory, and hence fatigue is a serious concern for these components. So them why then are these components cast, a process subject to poor tolerances, large material quality variations, inclusions, porosity, and generally a poor crystalline structure unless additional heat treatment is carried out subsequently. Hence, it is my guess that also such components have had to be dramatically over-engineered in order to ensure safety - hence the comments from Mark on how heavy the system was and the known useful load limitations of the EXEC.
Cable attachment T-pieces
I am unconvinced that the T-pieces used to tie the two control cables to the lower swash-plate are particularly well designed. If one cable were to snap then I feel that the second cable would become slack as the other half of the tee was now unrestrained, this would then slacken all of the remaining cables as the swash plate rotates to equalise cable tension and there would be a great deal of play in the control system. Possibly so much that the machine becomes un-flyable?
* This is based on what I could see on the program, which was very limited. If anyone knows better then I stand to be corrected.
Cables for primary controls
The cabling installation was very neat on the EXEC thanks to the sleeves used to support cable tension. However, the cable arrived shrink-wrapped, and so we could assume they will never come out of those sleeves. How do you inspect them - how do you know that they are no fraying?
T-rotor pitch change System
From what was shown on the program the entire tail rotor centrifugal loads on are supported by a single circular shaft clip. This seems like madness to me! If that clip fails, the tail rotor departs!
Drilling of main frame & Boom
One of the first things that were shown on the program was Mark mis-drilling a hole in the main frame. But worst than that he gets it so hot the drill was glowing! By his own admission this seriously compromises any heat treatment carried out locally and left the local steel work very hard. More importantly - very brittle and highly susceptible to fatigue. The answer - I bit of uncontrolled DIY heat treatment! I threw my hands up in the air! [This of course may be controlled or a procedure provided - it didn't give that impression on the program though.]
Furthermore, some of the section that were drilled clearly gave little or no access to the inside of the tube/section for deblurring, this provides a mechanism for crack initiation/propagation. They are building in flaws. [Seemingly, based on the program again]
Weight
As has been mentioned before on PPRuNe, the Rotorway is rather under powered, this is for two reasons, firstly it is a rather poor rotor system (aerodynamically) so that 150HP is non being used very well. [Or should I say the rotor system is optimised for low production cost and ease of repair!]
Secondly because of the apparent choice of processes in the manufacture of the components, then large safety factors will have been applied to ensure safety and hence large weight penalties incurred. Note, did you see the size of the pedal castings and the cyclic and collective clevices!
Simple nuts and Self locking nuts
I also felt that assembling with plain nuts and then reassembling with self lockers offers the opportunity for the builder to use the wrong nuts in the assembly and hence have the thing shake to pieces in mid-air. Also I only saw one means of lock the mechanical fasteners. Hmmm
Plus's........
That’s all rather negative, what about the good side of the machine......
It looks rather nice - better than a R22 it has to be said.
Its dirt Cheap [for a helicopter]
It’s well equipped for the price - everything you need for VMC flight except radio & transponder.
Skids are bolted to the frame so if you bend them you can replace them and not the whole airframe!
Supposedly fly's nicer than a R22
Wire locking - Important nuts in the chain wheel were retained by wire-lock to protect against ingestion into the chain following a shear-failure. Good.
Cheap
Cheap
The general configuration of the machine seems quite neat also, and it has a very trendy instrument console layout.
CRAN
