Thread: Bevel Gears and Helicopters

Alan "C-47" sent me this link the other day and I thought that some of you might be interested in the methods of fabrication and inspection involved in the production of the bevel gear vertical shaft located in the main gearbox of the Eurocopter EC225 Super Puma. G-CHCN ditching incident - Step Change in Safety

It would appear that the Archille's heel of the vertical shaft design is its welded connection. I don't know if this is a conventional means of fabrication of this component or something novelle.

Eurocopter, the merger of the French Aerospatiale-Matra and Daimler Chrysler Aerospace, would have a wealth of helicopter construction experience. Hopefully Alan might be able to provide some enlightenment.

BT

Maybe welding is done for lightness, compared to a bolted-up assembly?
Some small helicopters (Robinson R22) use multiple V-belts to drive the main rotor, which provides lightness, cheapness, safety through redundancy. If a belt fails, remaining ones keep it flying.

Jordan

I think after viewing the method of manufacture of the bevel gears, welding of the shaft is required after the gear teeth are ground & lapped using a generating action.
The only way to reach the gear teeth using this generating action is to fit the shaft after this process & fasten it by welding.
Otherwise the shaft would interfere & restrict the process.
regards
Bruce

I just had to Google up spec's on that craft. With its two engines, its a little over 2,400 H.P. A vast percentage would be going through that gear and that weld. No wonder they inspect it 4 different ways.

Phil

Originally Posted by nadroj

Maybe welding is done for lightness, compared to a bolted-up assembly?

Jordan

Welding of shafts can be very successful if done correctly.

The drive and compressor impellers of all modern turbochargers are heat/friction welded together at final assembly - as an example.

Helicopter drive components are subject to a lot of stress and have a service life. Maybe this one was faulty, or near expirey time ?

The Kamov - 26 Russian helicopter is an extreme example. Driven by twin radial engines linked with an interconnect shaft, the service inspection on this component is weekly

Interesting little chopper though.

http://www.youtube.com/watch?v=DWoxLbO_Nwkamin

Rob

Perhaps it was neglected in some way. Seems odd that and off one could sneak through with so much nondestructive analysis done on the part. Simply not strong enough maybe?!

Originally Posted by nearnexus

The Kamov - 26 Russian helicopter is an extreme example. Driven by twin radial engines linked with an interconnect shaft, the service inspection on this component is weekly

Interesting little chopper though.

http://www.youtube.com/watch?v=DWoxLbO_Nwkamin

Rob

That's cute. I wondered why bother with a helicopter for crop-dusting. But of course - the downwash must help get a thorough distribution of the spray onto the crops.

Jordan

Originally Posted by nadroj

I wondered why bother with a helicopter for crop-dusting.

Not needing a runway would be a big plus, especially if you weren't spraying huge paddocks.

Cool that you can see the blade tip vortices in the spray.

Not cheap to run though.

Stuart

It's a very interesting little chopper - read the wiki on it.

Kamov Ka-26 - Wikipedia, the free encyclopedia

The only helicopter in the world that runs at 95% engine power for most of it's flight regime - due to lack of power.

Helicopter spray units can get into areas a plane can't - eg power lines, trees in the way etc, and can fill up anywhere.

I hope the pilot is wearing a carbon/chemical filter mask as he goes straight through the spray residue on the return pass.

Some good videos on this little unit eg.

HA-MRN, Kamov-26 - smoky cold start - YouTube

Kamov Ka-26 (HA-MPZ) napraforgó vegyszerezés - YouTube

And the technical side:

Kamov HA-MZP életképek... - YouTube

I recon it sounds awesome with the screaming gears and twin radials.

Some of the Russian stuff is amazing. And you can just park it out the back of the house

Cheers

Rob

Originally Posted by nadroj

Some small helicopters (Robinson R22) use multiple V-belts to drive the main rotor, which provides lightness, cheapness, safety through redundancy. If a belt fails, remaining ones keep it flying.

Jordan

They still have a gearbox though, the belts just act as a clutch on motor startup and transfers power from the engine to the main gearbox... They would have two sets of bevel gears in them, one for the main rotor and one for the tail rotor...

OK, thanks RC. I thought it was a low tech alternative to the main bevel.

Jordan

Originally Posted by nearnexus

And you can just park it out the back of the house

Cheers

Rob

I think that would be the case with most small helicopters.
Getting permission to do it regularly might be difficult.

Jordan

Originally Posted by nearnexus

The only helicopter in the world that runs at 95% engine power for most of it's flight regime - due to lack of power.

wow its one engine performance wouldn't be something to look forward to then, still... better than its no engine performance I guess.
About the opposite of a helicopter I saw talked about the other day, its engines where way to powerful for the gearbox so have to be derated by a fare percentage, "which is great" the pilot said "if you lose an engine you flip a switch and get most of the power back". But that wouldnt come cheap.

Stuart

Here's a bit more on it.

Ka-26 Hoodlum

110 kg/hour fuel burn is not too bad. Check out the fuel burn rate for some of the bigger boys below (bottom of page).

https://heliniugini.aero/aircraft-fleet/

Wow, wouldn't want to pay those sort of fuel bills.

Rob

Ah, wukka wukkas! As a fixed wing guy myself, I prefer to steer well clear of them. Too many expensive, life-critical parts.

Having said that, the gearboxes in heli's (moreso these larger, turbine powered, commercial operation types) are designed and manufactured with an emphasis on being able to operate for as long as possible in the absence of oil pressure to lube them. When oil pressure is lost in these glide-like-a-greased-crowbar aircraft, every second counts. As a result, super fine tolerances are required on those gear teeth. Perhaps the idea of welding the shaft was seen as an alternative to be able to reduce the cost of precisely grinding the gear teeth overall? When you're talking about a gear likely worth $50k, reducing the pocket impact could be high on the priority list

Either way, the components are tested through several thousand hours before being certified in the first place, but with over two thousand Clydesdales running through that gear, it doesn't take long for a small crack to both begin and propagate into something more dire. Safety doesn't come cheap

As for croppies, not far from here there's an R44 with a corporate interior - leather seats, shiny trim, you name it - kitted out for spraying. The next owner will be able to indulge his passengers with super-phosphate and urea flavoured martinis on their Sunday flights around the landscape.