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Some tip-jets move their rotors by running jet engines on each end of the rotor. Obviously there must be some ways to supply fuel to those engines through a rotating body. How is this accomplished?

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There are pipes inside the blades which connect the engines to a rotary seal inside the main rotor head assembly. That seal allows fuel to be pumped into the blades from a port outside the main rotor head. Such seals are used in a variety of mechanical engineering applications where a fluid, usually lubricating oil, has to be provided to a rotating piece of machinery.

One example which you can probably find a cross-section of on the web is the method of using oil under pressure to change the blade pitch of a constant-speed propeller.

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  • $\begingroup$ Would you mind to elaborate how a seal is accomplished in the main rotor head? $\endgroup$ – Mys_721tx May 10 at 4:44
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    $\begingroup$ as a simple example, imagine a round shaft with a shallow groove cut into it. the upper and lower edges of the groove are fitted with O-rings. Between them, a hole is drilled in the groove into the side of the shaft reaching to its centerline. Then another hole is bored down the axis of the shaft to intersect the first hole. the shaft thus fabricated is set into a hole in a solid block with a hole drilled through its side coincident with the groove location on the shaft. if oil is pumped in through that hole, it fills the groove and flows in the first hole in the shaft and up the second hole. $\endgroup$ – niels nielsen May 10 at 4:53
  • $\begingroup$ I never understand people's description of mechanical things, but the example in your comment is very well written and easy to understand. $\endgroup$ – Wayne Conrad May 10 at 14:32
  • $\begingroup$ @WayneConrad, thank you for that. For a short while in my previous lifetime I was a technical writer, so I guess it paid off! $\endgroup$ – niels nielsen May 10 at 17:16

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