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By Flintstone
#1188233
Following my rebuild of the Fury I'd managed one flight, about an hour of circuits. I had set myself some pretty strict limitations so it was a couple of weeks before I felt the weather was right for another go.

Accompanied by a friend (Dave) I pulled the aeroplane out of the hangar, refuelled and conducted a pre-flight inspection before briefing him on hand swinging a propeller. As I did so I considered how mechanically minded he isn't so decided to do it myself. I could still make use of him by having him stand by the cockpit (out of harm's way) and explained to him the function of the mixture knob so if something went wrong he could cut the engine immediately.

The engine started first time and chuffed away as I walked round to the cockpit and Dave. I tried to recap my earlier explanation as to how I would warm the engine, perform checks and run-ups before asking him to pull the chocks but even at idle the propwash made communication difficult so we took two paces to the side. As we did I turned away from the aircraft, bent down to pick up my jacket and heard a loud crack followed by the most silent of silences. I turned to see my aircraft with it's tail in the air and nose on the ground.

Carefully we lowered the tail, switched off the magnetos and fuel and surveyed the damage. About six inches was missing from each propeller blade, the pieces being scattered across the grass. There was a small scar in the soft ground about two inches deep. Not knowing what else to do we gathered up the mahogany shrapnel, put the aircraft back in the hangar and went home.

Over the next few days I sought advice from as many sources as possible. Working in aviation gave me the advantage of being able to speak to over a dozen engineers plus a similar number of pilots all of whom had experience of prop strikes on light aircraft. The engineers of course had seen many so I knew I was drawing from a large pool of knowledge and while at first I had thought an engine strip down inevitable as I spoke to more people it seemed that might not necessarily the case. The engine was at idle (850 rpm), the ground soft and the wooden propeller took the brunt. The majority suggested that a runout check and thorough inspection were reasonable first steps. Obviously if there were any hint of damage it would be engine out time. If no damage then run the engine. If that went well a test flight and if that was satisfactory a structured period of monitoring with oil analysis to look for metal.

Cost was irrelevant, the price of a new propeller was almost exactly equivalent to my policy excess so either way I was going to be £1000 out of pocket. LAA Engineering and my Insurers were happy but unfortunately my inspector wasn't. I fully understood his reasons but it was simply a matter of differing opinions so we parted ways. One of the people I'd approached for advice was Hatz who is of course also a LAA inspector and happened to agree that a strip down might not be needed.

His dial gauge barely twitched when we turned the engine over and with no sign of any damage the new propeller (courtesy of Hercules, thanks Rupert) was fitted. Extensive ground runs were fine so paperwork was submitted to the LAA for a test flight and propeller change. With less than five hours on type I wasn't allowed to conduct the test flight but Roger, who was test pilot after the rebuild, stepped up again. His report was along the lines of "Smooth, vibration free with improved performance in take-off, climb and cruise" which is interesting considering my old propeller was 78x52 and the new one 76x48. The test flight statistics speak for themselves though.

I was almost reluctant to fly again, so worried was I about damaging the aircraft, but last week I chose a calm day and spent an hour doing touch and goes plus a (legal) overflight of home. Nobody came out and waved though, miserable lot. I think I was more relieved after that than after my first Fury flight and can't wait to go again.

What went wrong? There's only 14lbs on the tail wheel with nobody in the aircraft and although I had a procedure in my head for starting the aircraft when alone (bungee to hold the stick back, great big chocks and a stake and bungee to hold the tail down) I only used chocks that day. Why? Because initially I was thinking I had someone to swing the prop and when I made the (correct) decision to keep him out of harm's way I didn't then adjust my plan to one of starting the aircraft alone. Had I climbed straight in this wouldn't have happened but I realised afterward that while we were in the prop wash we were blanking half of the tail plane. As soon as we moved aside, ironically so I could repeat my safety brief to Dave, we allowed a rush of air to flow over the tail and lift it.

If, if, if. If I'd climbed straight in, if we hadn't moved, if I hadn't turned my back........... any one of them would have seen a different outcome but the fact is they didn't. Lesson learned, I have a new propeller in time for summer and providing the oil stays clean we'll be fine. If not then my Insurers will be hearing from me. Either way I've learned my lesson.

Thanks to Hatz and Andy Draper at the LAA for having open minds and being prepared to think laterally. Thanks to Rupert at Hercules for making my new propeller in less than normal time and thanks to Roger for putting himself out and being my test pilot again.
Last edited by Flintstone on Fri Aug 02, 2013 1:36 pm, edited 1 time in total.
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By Lowtimer
#1188411
Much sympathy - your analysis of the proximate cause, the change in airflow over the tailplane, is one I had not thought about before and I am very glad you published your tale, for that reason.

At least you ended up with a slightly better performance, so that's always something which helps you feel better in the long run. Rupert does indeed seem to be the wizard of the moment when it comes to prop magic.
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By Rob P
#1189065
I so feel your pain.

No stranger myself to the bent prop syndrome, but on a much more financially painful (for the insurers) level.

:pale:

Rob P
By Hotelfox
#1190147
Glad you're all sorted now and back in the air. :thumleft:

I'm with Rob, I had the same with a 3 blader years ago, and it was financially frightening, with 12 weeks of downtime.