Robbe Modellsport Amplitude prop and fuselage failure mid flight.

I thought I would share this video to show the moment one blade of my folding prop snapped off mid flight and the subsequent vibration severely cracked the fus. You can here a crack 1min 23sec into the flight when the broke. I got the Amplitude down as safely and quickly as possible to find one prop blade missing, the motor protruding from the fus with the wire only stopping the motor coming out fully.
Very lucky incident and nearly a lost motor and potential loss of my Amplitude

[@hotliner2872]

The Amp is a great plane, as is the Limit Pro, even in stock PNP form (tho she is more fun with real power). I saw this video and thought you had a factory fail (i.e. a stock airframe cracked from normal use), but now I see your point. Your prop was likely damaged in an earlier landing, it is rare they just fail, it is very easy to get complacent but a solid pre-flight check avoids these issues. Not that I have not lost planes to rushed pre-flights :-), not lecturing, just pointing out for general awareness. That said, if you have the PNP version... Robbe uses C-clips to hold on props in the PNP models, where anyone else (GM, RFM) uses bolts or screws to hold folding props on spinners. The C-clips suck, I lost a limit pro to a tossed C-clip causing a prop to depart, under full throttle on a Neu 1110/P29 so it pretty much just instantly blew apart the nose, and so she was then tailheavy and you know the rest. Great instincts on your part to catch the issue, not discount it or try to 'test power', and land immediately. Other than the C-clips, the balsa spar in the vert stab is weak, as is the saddle between vert stab and fuse. I used to pre-patch the saddle area with a 12x25mm carbon panel, just sand through the paint and epoxy it on. However this does drive the CG back, so in my current incarnation I just reinforced the balsa spar in the vert stab. I think this is the root cause of tail cracks, once that balsa breaks the shear stress cracks the tail.TBD on outcome, only 3 flights on her in this form.

[@All_things_RC.]

Many thanks for your response and great info. With this being a HOT liner I am thorough with my pre flight, pre and post flying session checks. However these will not pick up the micro stress fractures that are inevitable with such forces & loadings. These are not just confined to the prop or drive components but the whole air frame. I am grateful for the comment on cracking at the base of the vertical Stab, these have become visible on on my Amplitude after the last outing. As you suggest I have covered the last 3cm of the fuselage and and leading edge of the fin with carbon cloth & epoxy. As yet she is un-flown since this mod. I have achieved the CG by going from a 2200mah flight pack to a 3800mah pack. My main concern now is what will give next with the extra wing loading? Probably my nerve 🫣🤣

[@shozzy69]

Hell of a crack glad it came down ok

[@tomfpv1982]

Has it damaged the wing as well? Have you had many flights with it, Reason i ask im finding it hard on landing do u use crow Ta

[@All_things_RC.]

The only damage to the wing was jell coat damage from the prop half strike. I have had around 50 flights wit the Amplitude and one other incident where the wing tip caught a solid tuft of grass and cracked wing skin. This is the repair you can see in the wing. Re the crow brake setting I have 5mm up on the ailerons and 40mm down on the flaps. As you will see the model lands at a brisk walking pace.

[@sundayfloater2926]

I´ve made a thousands of flights with different planes even with much stronger Hotliners up to 5.000 W. Never had any problems with props so far. May be your prop was not balanced correctly? And astonishing is how weak this original (?) motor for this PNP plane is. This plane definetily begs for a geared setup.

[@All_things_RC.]

It's not only the props the motor and fire wall came out of the fus. Yes out of balance props and vibration will cause this king of problem. The props are high quality balance checked by the manufacturer, hyperflight and myself and the props were fine. Looking at the fire wall edge there was only 4 spots of glue on the whole surcumfrance. I have now glued the original fire wall back and put glue gussets front and back and the model flys great.

[@tomfpv1982]

If it cracked for no reason and u have proof id be asking for a replacement

[@All_things_RC.]

The prop failure was the reason for the cracked fus. One half of the prop broke off causing an unbalance and vibration through the airframe. I immediately cut the throttle but the few seconds was enough to damage the structure.

[@iwontreplybacklol7481]

Balance the props on a .01 gram scale at the very least. Check vibration levels on bench runs before putting it in the sky.