E-3120 flat root spring tubes

[DC21]

We’ve carried out repairs to a fair few flat root blades on the E-3120 now. I thought the community might like an insight on to the inner workings and issues of the E-3120 flat root spring tubes.

The E-3120 uses a spring tube assembly to allow/control blade pitch in the event of a rotor overspeed. This system helps to limit the rotor speed (55-60rpm) by creating stall on the blades.

There have been many spring tube failures on the E-3120, mostly on the flat root blades. Often this will result in structural damage to the blade.

The pictures below show the Gen 2 flat root blade spring tube. This has been less susceptible to failure than Gen 1, but I think it is only a matter of time before these fail. The major difference between Gen 1 and Gen 2 is the attachment block for the blade pin. Many Gen 1 flat roots have failed where the rod enters the block. Gen 2 is probably less vulnerable to this sort of failure.

The central load bearing rod has two springs around it, these spring are compressed and held in side the spring tube. The rod, springs, and tube are all rubbing against one another. Over time these components will wear, the spring will weaken, and ultimately the mechanism will fail. It is also possible the blades might start pitching/stalling early, resulting in reduced power out put.

Outer spring showing rubbing on spring tube and inner spring.

Rod showing rubbing marks from inner spring

 

[kill]

Do these cause a loud thumping noises like the round routed blades that Endurance's directors would pretend that weren't audible? Even tho they often sound like a clay pigeon shot being held!!!!

 

[DC21]

Thumping is more likely hub wear allowing the blade to move up and down on the nyloil sleeve. Blade spring noise would be more tuneful!

 

[unczbobz]

Thumping is more likely hub wear allowing the blade to move up and down on the nyloil sleeve. Blade spring noise would be more tuneful!

You know I have seen a Gen 2 block snap of a rod which was shocking to see, only good thing about Gen 2 spring tubes is that they are contained within the tube 8 times out of 10 compared to Gen 1

But definately agree the thumping noise is more than likely what Dc was saying, called blade drop, there are 2 different solutions for it, varies from O and M, you got the ability to drill and bush the hub with new pins or drill and install expanding pins both procedures will need to replace the bronze bush on spring tube block unless the block is badly worn and then you will need new spring tube

 

[DC21]

I think the only reason we haven't seen more gen 2 failures is age, it is just a matter of time.

The gen 1s tend to fail on fatigue where the rod enters the block, where as gen 2 tend to fail where rod passes through the spring tube through wear, or were inner spring is binding on the rod. Both have springs that are buckling due to being over compressed.

Even if you don't get rod failure, the spring are weakening due to wear - this bizarre spring inside a spring arrangement - springs binding on each other. That means you start to get partial spring tube deployment, which in turn increases wear.

 

[unczbobz]

I think the only reason we haven't seen more gen 2 failures is age, it is just a matter of time.

The gen 1s tend to fail on fatigue where the rod enters the block, where as gen 2 tend to fail where rod passes through the spring tube through wear, or were inner spring is binding on the rod. Both have springs that are buckling due to being over compressed.

Even if you don't get rod failure, the spring are weakening due to wear - this bizarre spring inside a spring arrangement - springs binding on each other. That means you start to get partial spring tube deployment, which in turn increases wear.

Completely agree, but on the other hand I have seen new Gen 2 spring tubes go bang in 3 weeks from refurbs, but their nyloil washers they use between block and tube also wears causing premature deployment too

CR tubes are slightly better but I have seen premature wear on them with the same nyloil washers

Saying that how’s your new redesign on spring tubes, it’s been what about year and half to 2 years since first set installed ?

 

[DC21]

Yes CR have issues and time will see increasing issues. Fidgetting doesn't help.

To date the design is performing well, 12 months in.