Master Airscrew Blade Separation?

First guess would be flutter...........

Are you sure it wasn't flutter? Had you lost a blade, the model would literally shook itself apart. FYI, I've never heard of a blade on a MA flinging itself off.

Weird. I have never had a blade separate from the rest of the prop where the ground was not involved in some way during the fact. I agree that it would seem likely that the engine would rip itself off the plane before impact. I have seen prop blades fly quite some distance after contact with Mother Earth tho.

I had a MA 3 blader shed a blade on my Ziroli C-47 a couple of years ago. The engine (a G-38) departed with the firewall with a bang. Didn't know exactly what happened until I flew the plane in closer. As a testament to Nick's designs and the fact that the '47 has the engines fairly close to the centerline, I managed to bring the plane around the pattern and make a (normal?) landing. Even had to make turns into the dead (missing) engine to stay away from the pits. I found the blade stuck into the fuselage nose cone....that's how I knew what happened. The other blades were still attached to the hub after the engine was retrieved from nearby woods.Nick hisself was there spotting me and he didn't believe what happened. Mitch

Interesting. The times I've experienced flutter, the sound was more like a kid pretending to be an airplane, ie more rapid and sustained than a doorknock. The one time I lost one blade on an plane, that sounded more like what you hear when a prop comes off in the air, like a baseball card in bicycle spokes(?). The time I lost the blade, I too throttled back immediately after I heard the strange sound. I estimate the reaction time about 3 seconds. The engine stopped running during this period. Fortunately I had enough altitude to make the runway, the plane was sluggish but made a normal landing. I did an inpection on the plane and found that the carb screws had come out, causing the deadstick. Additionally, I found

3 of the 4 bolts holding the engine to the mount had, come out, so had all of the mounting screws for 3 of 4 servos. I was flying a 40 sized plane at the time.

In anycase I'm leaning towards flutter, MA's only seem to break in a crash. One thing I'm wondering though, how is the Tequila in slow flight? A couple of planes I've had snapped so fast, the intial reaction was "radio glitch".

Frank (reply through newgroup please)

Dan, I have. Was breaking in a Magnum or TT (don't recall which ) 91 fourstroke a couple of years ago for a friend. We were using a DynaThrust prop. Well, we did until the engine stopped and was laying on the ground. Found the other blade 10 inches away stuck in the ground. Just freaked us out.

No kidding. Well, I have read so often of the danger of that happening that I habitually make sure never to stand in the plane of the prop arc. Is that an actual term? More aware of the habit with wood props or APCs. Probably the APCs more because they scare the bejesus outta me. The only time I cut myself with one was when I was holding an unmounted engine in my hand and idly just popped the prop. Instant respect!

Dynathrust - yes, they do fail; MA - no

I've never used a Dynathrust, but I've always wondered about them. The material seems to be heavier, less flexible, and more brittle than that used by most other prop manufacturers.

I've seen a lot of manufacturers putting RPM limit warnings on their products lately.

Real Situation: I was at a recent fly-in, watching a 1/4 or 1/3 3D Extra hovering just to the downrange side of the runway. As the pilot throttled up to climb out of the hover, suddenly the engine screamed, quit, and the plane nosed over and crashed, destroying the fuselage. At the postmortem, it was determined the prop (a 2-blade wood prop of some sort, I don't know which one) threw a blade. The blade was found about 50 feet away, broken off at the root. The pilot theorized that, as he throttled up, the blade suddenly had to pull the dead weight of the plane out of hover, the wood couldn't take it, and the prop broke. He maintained a composite prop (assumedly not a Dynathrust) would not have failed.

Any thoughts on this? Dr.1 Driver "There's a Hun in the sun!"

I had an APC shed a blade once right after takeoff. The engine just went "thunk" and quit. I was able to glide it in and land intact, and saw one of the blades was missing. However to be fair, this particular prop had been involved in a less-than-graceful landing and the aluminum spinner was touching the prop blade. I wouldn't think a blade breaking would cause your plane to crash. However, the extreme vibration caused by a missing blade might have an adverse effect on radio components.

Morris

When throttling up, the prop pulls the same load as if it was thrttled up before takeoff. More likely a defective blade.

Thanks, all, for the information. I had never really thought about flutter (which seems to be the prevailing theory). Don't know that I've really experienced flutter before. Guess I equate flutter with higher speed flight. The Tequila scoots around but not that fast. My Patriot (which, incidentally, had a "2 out of 3 wheels down" landing that day ? not a good day!) flies much faster. So how would I know if there is flutter potential in the Tequila and how might I correct it?

THX again.

P.S. The Tequila is almost back in flying status.

There is flutter in every single airframe. It is more evident in a few and not obvious in others. YOU can discover flutter sources by looking at the control rod while you (by hand) push the control surface from extreme to extreme. If the rod bows, you have found 1 major source of flutter that needs to be changed. Loose hinges is another. Wide hinge lines is another, as is soft balsa on a long control surface and loose attachments to control horns and or servo arms.

Good luck.

Flutter is more of a mystery than a science. All planes will flutter eventually, but most do it at speeds we will never see.

Many things can cause flutter: soft wood, loose hinges, large hinge line gap, unsealed hinge line gaps, not enough hinges, sloppy/weak control linkages, wide control surfaces, no counterweights, weak servo, bad linkage geometry, and a few other things.

Use stiff, straight wood for your control surfaces. Here is not the place to save a couple of grams of weight.

Use tight hinges, Robarts are good, as are Dubro pinned hinges, and of course, properly installed CA leaf hinges.

Make the hinge line gap as small as possible. Attach the control surface, and with the glue still wet, push it tight against the wing (for example). Then flex it both ways the maximum it needs to travel. That automatically establishes the proper gap without excess. Seal the gap with covering material or clear packing tape.

Use plenty of hinges. I don't like to put hinges farther apart than 4", maximum.

Use stiff control linkages. Brace where necessary. Golden Rods are good to use, but MUST be braced not more than 4" apart along the run. Wood rods should be hardwood, and square, not round. Use hard, straight wood. The wire ends should not have any bends, if at all possible. Angle the linkage so you can route the wire out of the fuselage without bending it. Even carbon fibre or arrow shaft rods may need bracing in the middle. Do NOT use "music wire" for linkages. It's MUCH too flexible. Make sure there is no slop in the setup.

A wide control surface will flutter more easily than a narrow one. Not much you can do about that if you need a wide surface, but you can compensate with the other items I'm discussing.

Counterweights are effective for controlling flutter, but are ugly. They don't have to exactly equal the control surface weight and mass distance from centerline, just fabricate what looks about right. That's a science all in itself. :)

Don't skimp on servo power or quality. Enough said there. Metal-geared servos often have more gear slop than nylon gears. I don't have any information on the new composite gears, like Karbonite, that Hitec has introduced. Always use a quality sero. I've had great success with Futaba and Hitec. I've heard that JR is good, but never used them. I've had bad experience with Dad's, FMA, Tower, and Royal servos. Weak, and a lot of gear train slop.

Linkage geomerty. Not many people think of this. Our servo torque is measured using a 1" long arm. If you run a 1" arm to a 1" horn, you will get 100% of the applied force at the control. But let's say you run a 1" arm to a 1/2" horn. Now you have twice the movement, but half the applied force. A 1/2" arm to a 1" horn will give you half the movement but twice the force. That's why I say to not skimp on servo quality or power.

Good luck with it, and keep asking questions.

Dr.1 Driver "There's a Hun in the sun!"

Stiffnes of the airframe and control systems is one factor, and control surface balance is another. Mass-balancing the surfaces so that they balance along the hinge line will prevent surface flutter in most cases. Entire wings can flutter, due mostly either to flexibility or to loose covering. Several fatal FS crashes have been resulted when the fabric came loose on the wing's top surface. I've seen a model do the same; makes an awful noise.

Dan

The two things I have seen that consistently cause flutter are loose linkages and rounded trailing edges.

Root, or proximal cause? I have flutter caused by my Labrador. Maybe even that isn't the real cause. The real cause was carelessness, because I should know better. I entered the sideyard cradling the foamie at shoulder height. Da Gipper habitually greets playmates with a leaping headbutt. I knew that; even the neighbor kids know that. (The rudder cracked through at the control horn. The pushrod was still tight, but quite ineffective. A visual inspection didn't spot the damage. It manifests itself as a strong tail shake in flight. Talk about the tail wagging the dog.)

No mention of whether the blade was balanced or not. And if it was balanced was any material taken off or damaged at the root area? Andy

We can make a box of wood.....FLY!!