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adamjedgar

DLE 200 Dropped throttle, catastrophic redrive failure

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Posted (edited)

Hi guys,

had not long taken off in the DLE 200 a few days ago when I noticed I had a brake line wrap.

I usually fly with brake toggle in the palm of my hand and throttle over the top of it (was trained that way). 

I gained a little height, and in the process of swapping the toggle/throttle configuration around so I could then unwrap the brake line, I dropped the throttle.

That in itself was nothing more than an inconvenience initially as I was directly above a golf course and so I decided to simply land on the golf course and sort out the dropped throttle issue once I landed. As soon as I touched down, the throttle was swallowed by the propellor (not sure exactly where is went through but I think It was through cage netting), wrapped itself around the upper redrive pulley, revved the engine temporarily, then instantly stopped then engine when it pull tight, causing the re-drive to snap in half and the propellor and upper bearing house to separate from the engine and bury itself into the ground behind me on the golf course fairway.

I am amazed that the cable being swallowed by the propellor has snapped the redrive housing in two...I would never have expected this could happen. 

 

I have thought of a couple of future modifications

1. ensure that all my paramotor units always have a secondary kill switch that is not also mounted on the throttle

2. a bungie to prevent dropped throttle from being able to go against cage netting and possibly through it

 

 

 

DLE Broken Cage.jpg

DLE Broken Redrive Housing.jpg

DLE Propellor and Broken Redrive Hub.jpg

Edited by adamjedgar
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Owch!
I don't think the cable broke that bracket in any tourniquet style event:

Something got between the belt and the pully (doubt it though)
The massive imbalance of the broken prop at high revs hit a resonant sweat spot (Possible but there is a more likely cause)
The shock of the prop hitting the cage at high rpm would have sent a HUGE force through the bracket in the opposite direction to the strike.

If you decide to weld it, it might be worth adding a plate so that if the main welds fails, the plate will give enough to unload the belt but not enough to allow another prop strike.
You can afford an extra bit of weight on such a light motor :) 

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Ah that sucks.  Hope it can be welded.  How do you find the DLE200 in general?

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Posted (edited)

Its not possible for this prop to hit the cage down there unless the frame is deformed at least 100mm (4 inches)...its a cage for a 1350mm prop and this prop is a small one. so the prop strike happened after the redrive failure had already happened.

 

The failre was definately caused by the throttle cable wrapping around the upper pulley and belt, there are no other witness marks on the cable anywhere near on the frame so its entirely centerred around the redrive itself...its incredible  really. Im pretty pissed off that the redrive housing failed so easily, its clearly not designed well enough. Having said that, it is what it is! Im not going to weld it, aluminium castings dont weld particularly well for this kind of application...i would rather just replace the redrive housing with a new one.

 

The DLE engine itself is great. I have never had to touch any carby setting on it since it was run in over 100 hours ago. Its always the same, hot or cold...flick on choke, wind over a couple of times until it pops, turn off choke, it fires up instantly. Its electric start only, i would prefer if it also had a secondary pull starter.

 

I dont like the mufflers on it at all, they are crap but light i suppose.

Its a little low on torque and horsepower for a 200 (21hp), i think it also uses more fuel than my simonini mini 2 plus, but very reliable.

I am going to throw a carbon fibre prop on it after this, that should make a huge difference...the timber one is a bit low on thrust, pitched in the wrong rev range for the engine (on the edge of the power band at cruise with trimmers closed on my wing), is noisy and annoys the bystanders a bit.

Edited by adamjedgar

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1 hour ago, adamjedgar said:

Its not possible for this prop to hit the cage down there unless the frame is deformed at least 100mm (4 inches)...its a cage for a 1350mm prop and this prop is a small one. so the prop strike happened after the redrive failure had already happened.

Ah... tricky!
I've had rubber mounts give by at least 50mm (clipped prop on a stumble)
I would assume the cable pulled the frame into the prop (or prop into frame)
If you follow the path of force... From the prop hub, the cable would pull lengthways "along" the re-drive bracket, it would be a straight on tug of war between the frame, netting or carb cable fittings and that thick re-drive bracket.... which one do you think would win and why?
My money is on the bracket being stronger than any of those three buy a factor of 20+

Maybe something did get under the belt... I could see that snapping the bracket.

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Posted (edited)

as i said, it is not possible for the propeller or the cage in that location to flex enough for prop to be pulled into the cage (or vice versa). 

If you were able to see the upper re drive pulley, you will notice it has been sliced like an apple core around approx 3 inches of its diameter by the steel throttle cable in a direction parallel with the direction of rotation of the pulley. The belt has also snapped at this point and i could feel the moment when the entire housing failed.

Also, in the scenario Blackburn Mark has outlined, if the housing had failed whilst the motor was still running, then i would have immediately had a runaway engine...ie belt re-drive engines (and certainly this engine) relies on the propeller for its flywheel! As soon as the propeller housing departs the engine say for example due to imbalance, as soon as the propeller housing broke away and flywheel effect is lost, then the engine (which due to throttle cable being pulled was already revving prior to this failure event) would have immediately gone to full throttle with no means of shutting it down, and self destructed internally...which it has not done at all...so that scenario is not supported by the evidence either.

The propeller housing snapped in two because of the sudden stop and massive load caused by the throttle cable jamming in the upper pulley. This immediately stopped the engine dead, and boom...snapped the housing, sending the prop down through the bottom of the frame and into the ground. Definitely, the propeller was also extensively damaged by the throttle hand-grip and cable prior to the housing failure...i felt that at the time.

Edited by adamjedgar

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I have hada close look and this is my engineer view. The base of the frame looks as though the throttle dropped under it, was picked up by the prop, and then pulled the frame in. The throttle cable being pulled in a tight U shape around both hoop tubes is the only way it can be damaged like that.

Now the other end of the throttle cable is more open to interpretation. There are 2 scenarios here. a) the throttle hooked over one blade and was pulled or b) the throttle got into the space between pulley and belt.

My money is on a) because the throttle is not long enough to initially reach the pulley. Having hooked over one blade, the blade would then only be able to rotate probably 1/4 to 1/3 of a turn before it reaches its limit. At the limit the frame squishes, then the pulley snaps off because of the huge and very sudden side load. All the destruction happens in a split second.

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Posted (edited)

Hi AndyB,

I am also leaning towards that outcome as well.

guys with the power of hindsight, i am now wondering whether or not i made the right decision at lowish altitude, in not attempting to recover the throttle whilst i was still airborne!

What would you guys have done in my situation? Would you have landed as i did, or would you have attempted to fish around trying to recover the throttle. Please also keep in mind, the golf course below had a local competition running and there were players on practically every hole on the course at the time. A propellor flying through the air from altitude could easily kill someone, obviously coming off and going straight into ground was a good outcome and where i landed there were no golfers for at least 150-200m.

Obviously apart from the golden rule...dont drop the throttle...

What are the pros and cons of either option (land or recover throttle) at lowish altitude?

Edited by adamjedgar
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5 minutes ago, adamjedgar said:

What would you guys have done in my situation?

I would assume it would be easer to find the throttle than find the off switch (I ought to practice finding the switch now that I think about it) 
My cable is only just long enough to cover the arc of my arm and the net gaps have been closed with extra lacing  (Learned the hard way and lost a prop to a cable//prop-strike)

It doesn't really matter what others might do, you have now had the experience, escaped with all your fingers and toes intact.... What would YOU do in that situation?    :) 
 

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Having gained a little height, as you said, I would have retrieved the throttle.

The question is how much height did you go to? Given the circumstance I think I would have gone to 1000 feet to give a 500 foot buffer before wanting the brakes in my hands again, preferably with the throttle also.

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On 17/07/2020 at 21:58, alan_k said:

Having gained a little height, as you said, I would have retrieved the throttle.

The question is how much height did you go to? Given the circumstance I think I would have gone to 1000 feet to give a 500 foot buffer before wanting the brakes in my hands again, preferably with the throttle also.

Once i dropped the throttle, i couldn't fart hard enough to gain altitude😣

 

So 200 feet was all i had to work with.

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On 19/07/2020 at 09:23, adamjedgar said:

Once i dropped the throttle, i couldn't fart hard enough to gain altitude😣

Hi Adam, I am just going to post this here just in case it is not how you are wearing your throttle, worth watching as good educational video, you may of not been trained this way but hopefully we live and learn and more of us get a better experience out of our flying.  And another point Ian does not make on his video is when used like this if you should happen to drop the throttle their is less slack making it less likely to get anywhere near the prop.

 

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