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Darwin and composites - 2/6/2004 6:02:57 PM   
DHG


 

Posts: 896
Joined: 4/24/2002
From: Denver, CO, USA
Status: offline 		As some of you already know, I recently got "tagged" with a broken prop while bench-running a QM40 engine. Apart from the choice of brand, which I admit was pretty stupid, there were a couple of other factors that you should know about.

First, the fragment went backwards. I had a remote needle hooked up and was standing a couple of feet away, behind the propeller arc. I never spend any time in line with a spinning propeller. Conventional wisdom says the pieces will go either straight out to the side or slightly forward, so I figured I was pretty safe even if the prop wasn't. Strike one.

Second, the main problem seems not to have been design, but material fatigue. This prop had been run before, on the same engine. It started life as a 10" x 6" and was cut down to a 6" diameter. (Why not a QM40 or F3D prop? Shallower pitch, more blade area, better cooling, not-so-sharp edges. Somebody should make a good continuous-strand CF version and sell it.)

The hub looked plenty stout compared to those stubby little blades. The material was glass-filled nylon, basically the same as the gray APC Q500 props we've been using for 10 years now. I know a lot of folks use cut-down APC Q500 props for break-in -- and yet Fred Burgdorf found it necessary to change from glass-filled to carbon-filled for the QM40 props because the gray ones were fatiguing and throwing blades at that speed.

So: misuse one brand, misuse another brand, same difference, the thing to do is start with a bigger piece of material and test carefully, right? Strike two.

By the way, a little bird told me some folks have been thinning down the black APCs in the middle of the blade, leaving the tips alone to avoid detection. Please do not run one of those next to me on the starting line. You don't know the limits of the material any better than I do, and I'm tired of being a test subject.

The only reason there wasn't a Strike Three is that I made a good choice of sunglasses. Run, don't walk, to your workshop and make sure they're at least 0.060" polycarbonate. If not, buy some. Wear them every time you go flying ... a helmet, too. You just never know when stupidity (your own or someone else's) or failure of a critical part can put you in harm's way.

DHG
       Post #: 1

RE: Darwin and composites - 2/7/2004 12:41:48 PM   
Terryoc


 

Posts: 87
Joined: 6/19/2002
From: WerribeeVictoria, AUSTRALIA
Status: offline 		Glad to hear you got away with it DHG . I could not agree more with the sunglasses I wear mine no matter what the weather or if it is real poor light I may change to clear safety glasses and yet other racers still ask why are you wearing glasses it isnt sunny .
I am prepared to lose a finger but never an eye.
Terry

(in reply to DHG)
       Post #: 2

RE: Darwin and composites - 2/8/2004 7:58:38 PM   
Lefty-RCU


 

Posts: 29
Joined: 7/17/2003
From: Broomfield, CO, USA
Status: offline 		Duane: So much for the Grape-Vine. I heard about your prop failure from Delponte in Oregon last week, the local news seems to be lagging behind. So give us a report on your eye condition. since one eyed guys get a one lap lead, I hope you don't get that AD.

Regards

Bryant

(in reply to Terryoc)
       Post #: 3

RE: Darwin and composites - 2/9/2004 4:50:58 PM   
DHG


 

Posts: 896
Joined: 4/24/2002
From: Denver, CO, USA
Status: offline 		Terry,

Isn't it ironic, if I hadn't been so worried about fingers I wouldn't have to deal with the eye at all. But those razor-sharp little F3D props give me the willies. Can you say "Cuisinart"?

I might just go ahead & mold up a continuous-strand break-in fan with rounded edges. Perhaps no one would want such a thing from me, after this ... but then, who'd be more motivated to make a good one?

Bryant,

Thanks for the good wishes ... eh'll be bock.



Sky Borg

(in reply to Lefty-RCU)
       Post #: 4

RE: Darwin and composites - 2/14/2004 2:47:03 AM   
Terryoc


 

Posts: 87
Joined: 6/19/2002
From: WerribeeVictoria, AUSTRALIA
Status: offline 		Hi Bryant
Its funny how different people see things differently . I see the F3D props as quite large and in my 6 years of racing have never seen any one get hit .
Its our 1/2a props that scare me small sharp and 29 000rpm on the ground with the neddle 1" behind the prop. A few guys have been hit by these and the props never broke and they got bit several times.Check the photo that is a F3D and a 1/2a prop the 1/2a prop get a little off diameter yet and the last 1/4" of prop ends up tapering from 20 thou to 10-15 thou.
At least the cuts are always clean and easy to stich but there is always a car accident just before they see you at the hospital and you miss the days racing.
Terry

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(in reply to DHG)
       Post #: 5

RE: Darwin and composites - 11/18/2004 7:14:27 PM   
js3



Posts: 1142
Joined: 1/30/2002
From: Arvada, CO, USA
Status: offline 		Hey Duane,

Would you mind giving us all an update on the status of your eyesight? I've linked to this thread from the clubhouse and thought it would be nice to hear your prognosis some months later.

Thanks,

_____________________________

John
I feel a lot more like I do now than I did earlier!

(in reply to Terryoc)
       Post #: 6

RE: Darwin and composites - 11/18/2004 10:51:47 PM   
DHG


 

Posts: 896
Joined: 4/24/2002
From: Denver, CO, USA
Status: offline 		Still got a wobbly spot right in the middle, and the rest of it is like looking through a cloudy fish bowl. My right eye was never much good anyway so it's no great loss, but at this point any further recovery will be slow at best. Think Christopher Reeve here. The retina is part of the central nervous system. Maybe it'll keep gaining one or two percent per month, or maybe in 5 or 10 years I'll be able to squirt some embryonic stem cells in there and be good as new. But meanwhile, there is a silver lining: My distance vision has actually improved. Without the right-eye input, I no longer have to worry about double images, and my left eye is razor-sharp. It's like flying using a telescope.

Sure am glad I had those glasses on.

(in reply to js3)
       Post #: 7

RE: Darwin and composites - 11/19/2004 6:08:08 AM   
StregaFlyer


 

Posts: 53
Joined: 7/28/2004
From: South Beloit, IL, USA
Status: offline 		Duane,

Glad you are alright.. That's a scary scary thing having props come apart.. Glad you are alright, it could had been much worse..

(in reply to DHG)
       Post #: 8

RE: Darwin and composites - 11/21/2004 3:30:13 PM   
Bill Vargas



Posts: 1542
Joined: 1/6/2002
From: Team Coldies, CA, USA
Status: offline 		I found this on a post flight inspection after my 3rd heat of the Race yesterday,,,

BV

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_____________________________

If it ain't leaking oil, then something's wrong,,, USMC, RETIRED!

(in reply to StregaFlyer)
       Post #: 9

RE: Darwin and composites - 11/21/2004 3:51:35 PM   
Duane-RCU



Posts: 417
Joined: 5/5/2002
From: Arlington, TX, USA
Status: offline 		Isn't it odd how the eye seems to be a "magnet" for stuff? I can't really say I've ever been hit in the forehead, cheek, chin or nose with stuff. But don't have eye protection on, and guess the first place something goes! Even wearing my safety glasses, I've had dirt and other junk make it in. Am I the only one that's noticed this? Did your glasses break and the piece make it through?

(in reply to Bill Vargas)
       Post #: 10

RE: Darwin and composites - 11/22/2004 5:53:10 PM   
DHG


 

Posts: 896
Joined: 4/24/2002
From: Denver, CO, USA
Status: offline 		Duane,

Oh, it was FAR more impressive than that. The sunglasses didn't shatter, otherwise I'd probably be dead. The propeller piece dented the front of the lens, which folded in half (breaking the frame) and shoved into my eye like a blunt knife. It didn't puncture the cornea but dislodged the iris and lens behind it, causing a condition called "hyphema". When the ER docs saw that, they called the ophthalmologist immediately and bundled me back into the ambulance for a trip across town. But none of that was permanent damage. The nasty part was the sonar "ping" through the vitreous humor (eyeball gel) that transmitted the force from the point of impact in front to the retina in back.

It's the same kind of injury racquetball players used to get when they would wear those goggles that didn't have lenses, just a padded ring around the eye. If the ball hit just right, it would squeeze through the ring and deliver a blunt smack on the front of the eyeball. It doesn't sound bad, but it is, because of that "ping" effect.

Bill,

Good thing you changed props. I want to say that Fred Burgdorf is extremely conscientious with his materials and manufacturing on those APC props -- they are far, far better than anything else on the market, so I have learned since the accident -- but nothing is foolproof. Add up the factors of horsepower, vibration, run time, and tiny nicks or flaws, and sometimes those sunglasses are your last line of defense.

Duane Gall
RCPRO

(in reply to Duane-RCU)
       Post #: 11

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