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-   -   Danger Warning (https://www.rcuniverse.com/forum/beginners-85/7211802-danger-warning.html)

aa2dd 03-11-2008 09:10 PM

Danger Warning

Hello guys ... I had an experience today that I want to pass on for only general information. I was flying my U Can Do 60, with a Saito 125 and an APC 16x4W prop. In the middle of my third flight, something flew off the plane. before you could blink an eye the engine started screaming (running out of fuel) and then quit. All happened in a time frame of 4-5 seconds at most... The plane immediatly started tumbling end over end. The plane landed on the ground upright!!!! After a search, we found the engine, 100 feet or so from the plane. It appears that one blade broke off the prop, in flight, and then tore the front end off the plane. destroyed the cowl, tore the fire wall into pieces, and generally ripped things apart. My point is not to whine or look for sympathy, stuff happens, ..... but to let beginners, and also long time fliers be aware that it is dangerous to fire up an engine and then throttle up to full throttle with pilots standing along side. I see it happen frequently, engines being run up with no concern whether pilots are in line with the prop or not, and pilots not being concerned that they are in danger. This could have just as easily happened on the stand as in the air! The prop in question had not been struck on the ground that i remember, but it had many dozens of flights on it. I do not know if they "wear" out, if they have a safe life span, or what happened. It tore apart up close to the hub, actually under the prop nut washer. it was not a clean break, but looked as if it had pulled apart from centrifugal (S) force. I do not know what the rpm limits for these props are. The last time I measured the rpms with this combo, it was turning about 9200-9500 static. Can't recall for certain, but it did not seem unreasonable to me. Again, this is only a "for what it's worth information."


carrellh 03-11-2008 09:34 PM

RE: Danger Warning
APC's recommended RPM limits are 190000 / diameter = limit
Here are the figures for 9 through 24 inch diameters
9 = 21111
10 = 19000
11 = 17273
12 = 15833
13 = 14615
14 = 13571
15 = 12667
16 = 11875 ** I'm pretty sure you did not overspeed the prop
17 = 11176
18 = 10556
19 = 10000
20 = 9500
21 = 9048
22 = 8636
23 = 8261
24 = 7917

I think your prop failure was just one of those "stuff happens" moments. Occasional reminders of what actually does happen are probably good to help us stay aware of the risks associated with our hobby. We don't need to be afraid of our stuff but we do need to stay aware of the fact that it can hurt us.

RCKen 03-11-2008 09:39 PM

RE: Danger Warning
1 Attachment(s)
Always stay clear of the "Danger Zone" when an engine is running.


j.duncker 03-12-2008 12:03 AM

RE: Danger Warning
Although you were only turning 9500 on the ground this engine prop combo will unload quite dramatically in the air. 12000 plus will be attained in a shallow dive.

It is also worth remembering that high compression 4st engines like Saitos give a prop a hard time esp at low rpm full throttle spool ups.

If you were flying 3D stuff with lots of throttle action this might be a contributory factor.

P.S. I am off to have a VERY close look at the APC 16x4W fitted to my OS 120 AX.

KI8FR 03-12-2008 02:28 AM

RE: Danger Warning
when I do a pre flite I take a good look at my prop. every time before I start the engine. You never know if it got hit or bumped. It could have hapend on your way there. or when you put your wing on and not know it. Look at the prop good. Make sure that it is soled with no cracks.

Sorry for your loss


Mode One 03-12-2008 04:37 PM

RE: Danger Warning
Was there ever a prop strike in the history of this prop?

aa2dd 03-12-2008 06:46 PM

RE: Danger Warning

I fly lots of low, slow, 3D type flying. Normally flying between idle and half throttle. I am always bumping the throttle up and down" It is a wonder the throttle ratchet on the tx is not worn out!

I do nto recall a prop hit, but that particular prop had a long life span. It may have "kissed" the grass/ground. I do nto recall it happening, but at my age, I have trouble remembering this morning.


bkf1970 03-12-2008 07:03 PM

RE: Danger Warning
Hey Guys. APC props are good props and work well for many engine/airframe combinations. However, I have heard that they have a tendency to crack at the hub. Pylon racers who use APC props know this.
It is a good idea to get in the habit of doing a pre-flight inspection of your plane at the begining of each flying session. Before you install the wing, start at the front of the plane and work your way back, being sure to check the fuselage, tail and landing gear for any damage to the structure or covering. Check the prop, prop nut, spinner, engine mount and bolts, firewall, muffler, fuel lines, filter, throttle linkage, battery, reciever, antennea, switch, servos, servo arms, servo mounts and screws, connectors, pushrods, clevises, control horns, hinges, control surfaces, wheels and wheel collars. Then check the wing and it's servos, linkages and contol surfaces. Then install the wing and do a radio check, make sure all the controls work and are going the right way, this also a good time to do a range check. I know this alot of stuff to remember and check but once you get into a routine it gets easier and it just may save your airplane someday.

F-15 Fan 03-12-2008 08:04 PM

RE: Danger Warning
Its like a turbine wheel in a jet engine, the centrifugal forces can rip them apart. It only takes the smallest crack, and over time the crack grows until it fails near peak RPM. Its similar with a prop.

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