Titan T51 crash

[The_Eric]

Saw this on Jaun Browne's channel last night. He's saying that the engine over sped which led to a hub failure and ultimately to a crash from the forced landing attempt, but many comments are suggesting the opposite - that the hub failed which decoupled the engine from the prop which allowed the high revs.

How can this happen? If the engine is coupled to the prop via the reducer box, how is it able to over speed to the point it could cause damage? It sounds like it wasn't radically over powered at about 300hp. Wouldn't the engine be basically "matched" to the prop in terms of load and power? Is there a governor system to limit rpm while allowing wot when power is needed?

 

[Danno]

Think it was hub failure, then overspeed due to the failure. Things break. Home engineered break more than real engineered ?

 

[The_Eric]

I'm not sure that this qualifies as "Home Engineered". He may not be Boeing, Airbus, Lockheed or others, but he's been doing this for many years and I'm guessing that the T51 has a fair bit of engineering behind it.

 

[Cujet]

I'm sad to see this, the T51 was a really neat plane. Many of us know that experimental amateur built aircraft have 5-6x the crash rate of type certificated aircraft and mechanical failure is a major factor. Unfortunately, this ends up being another negative statistic.

If I understand correctly, this was a 4 blade Whirlwind experimental constant speed prop. These props typically have a 5 year/500 hour teardown inspection schedule, which many people IGNORE. I've flown behind Whirlwind props many times, and found them to be less than perfect. The picture below is a plane I've been in many times. What bothered me about the prop is that I could see the tracking of the blades was imperfect. So, while the balance was technically OK, the prop blade tips all followed a visibly different path and there was always a minor shake.

Not once have I seen a Hartzell, MT or McCauley prop display such poor blade matching and tracking. MT props are not my favorite, but even those guys get the tracking thing right.

As always, had this plane used a 300HP Lycoming coupled with an MT or Hartzell, this would not have happened.

 

[The_Eric]

I'm sad to see this, the T51 was a really neat plane. Many of us know that experimental amateur built aircraft have 5-6x the crash rate of type certificated aircraft and mechanical failure is a major factor. Unfortunately, this ends up being another negative statistic.

I got the opportunity to see a T51 being built/repaired at a local builder shop. That particular one had been started by the customer and when it ended up on their doorstep, there were several glaring safety issues with it from the owner's handiwork. They put a fair bit of time into it and ultimately the owner wanted to take it and fly it out or haul to another builder. (I don't remember the whole story) They weren't about to let that plane go out the door with their name attached to it like it was so IIRC there was some paper signing and so on.. That particular one was powered by a 3.0 Honda V6

 

[BusyLittleShop]

I gather all 4 blades were jettison at once which is more desirable
than a single blade loss and resulting out-of-balance will be of such
a huge magnitude that it might tear the entire engine off the airframe
and ruin any hope of control flight...

 

[ms21043]

Prop overspeed? Not sure how that propeller system controls blade angle, but you absolutely do not want to go below the low pitch stop in flight. If for some reason it did, the prop will overspeed uncontrollably. The engine will be driven by the prop. On the ground you'll hear the blades going supersonic, the engine rpm going to the moon and kicking rods out and finally the prop hub, if not able to take the tremendous load, will fail releasing the blades.
Not saying that's what happened, but prop overspeeds are very dangerous if they can't be controlled.

 

[Cujet]

I believe the prop let go before the overspeed. However, you'd think that the engine would have a rev-limit programmed to prevent excess engine overspeed as that could overstress a prop. Any properly designed constant speed prop has a low pitch stop that allows continued safe flight at redline.

Many pilots don't understand what happens when prop control is lost. Typically the low pitch stop is the lowest blade angle that will provide enough thrust at maximum engine RPM to keep a plane above stall speed. There have been many crashes where prop control is lost, and the pilot did not understand to set the engine right at redline and fly the airplane low airspeed.