Very Very lucky escape.........

[smittysrv]

Lost Prop Video - WOW!

Pilot Kevin Eldredge in "Relentless", Prop explodes.

Lost Prop - Relentless mayday 9_14_2010_slow motion.mp4

[Fake Sealion]

Fortunate that the prop debris didn't do terminal damage to the tail plane & fin
rendering the aircraft uncontrollable.

[Deeday]

Video embedded:

[NutLoose]

See film

YouTube - Relentless mayday 9_14_2010.mp4#!

1) Oil cooler fitting broke
2) Oil pressure went to zero
3) Prop went to flat pitch
4) Engine over-revved big time (sound delay is due to distance)
5) Some engine internals broke through crankcase, seizing the engine
6) Blades broke from hub and departed; hub departed as well
7) Resulting engine shake broke three of the four engine mount tabs
8) Pilot deadsticked (er, "sans-sticked") to safe landing on runway
9) Cowling fire after landing was quickly doused by Reno fire crew, saving the plane

[OnApproach]

the over revving would send a shiver down your spine!! well controlled

[BackPacker]

Well done.

I'm wondering though - could the same thing happen to an average spamcan?

Suppose you're doing a normal cruise speed at full power (just after leveling off at your desired altitude, right before you reduce power to cruise for instance) and lose oil pressure at that moment. Prop goes to fine pitch with full MAP so you overrev the engine. But would that overrevving be so severe to cause damage to the engine internals, and to cause the prop blades to come off? Or do you have time to pull the throttle back before it causes any serious damage?

Obviously the loss of oil pressure will cause damage after 20 seconds or so, but this video suggests that it all happened in under a second.

[JW411]

A similar happening took place at Shoreham a couple of weeks ago. Happily, the pilot was uninjured but the aircraft is a write-off.

[Jan Olieslagers]

I think this kind of mishap can only happen with a constant speed prop, fixed or ground adjustable will not go flat in case of oil loss.

As for what happened: in another discussion, it was rightly argued that the sound is several seconds behind the image - which may change the interpretation.

[NutLoose]

Slow motion version here shows just how much departed from the front end.

At about 15 seconds into the film

YouTube - Relentless mayday 9_14_2010_slow motion.mp4

[SNS3Guppy]

I think this kind of mishap can only happen with a constant speed prop, fixed or ground adjustable will not go flat in case of oil loss.

A fixed-pitch propeller is already "flat." When a prop goes "flat," it means going to the low pitch stops, or in other words, going below the governing range...which is the same as becoming a fixed pitch propeller again.

While going to low pitch will result in a higher RPM, what causes the RPM to go off the charts is loss of the propeller...not simply going to low pitch. Lose the prop and the engine will over-rev.

A propeller should not permit an engine to go over redline RPM during a static runup. In flight, however, a propeller's ability to exceed that RPM varies with airspeed. At higher speeds, higher RPM's are achievable.

[Mark1234]

Perhaps I'm being naieve, but the only bit that strikes me as *really* scary is that 3 of 4 engine mounts broke. Deadstick ok, but if that big heavy thing up front departs the airframe you're seriously stuffed - makes a bit of a mess of the W&B! I do wonder about the order of 5,6,7 too..

Other interesting thing is that this is a reno racer, I'm slightly surprised that they don't adopt similar systems to many aerobatic aircraft in having the prop fail coarse. They're probably far more likely to have this sort of failure than just about anyone else - big power, max rpm, and some very stressed engines.

[BackPacker]

A propeller should not permit an engine to go over redline RPM during a static runup. In flight, however, a propeller's ability to exceed that RPM varies with airspeed. At higher speeds, higher RPM's are achievable.

That's what I meant. I wonder if there's some certification requirement or something that would prevent a catastrophic overspeed up to Vcruise, Vmo, Vne or whatever, assuming the prop at the fine pitch stops and max MAP.

Or is it simply that all bets are off once the engine exceeds redline RPM?

Other interesting thing is that this is a reno racer, I'm slightly surprised that they don't adopt similar systems to many aerobatic aircraft in having the prop fail coarse. They're probably far more likely to have this sort of failure than just about anyone else - big power, max rpm, and some very stressed engines.

Good point. Those Reno racers probably have enough horsepower to go around and get a decent rate of climb on full power, even with a prop at the course stops. (Whether a go-around is a good idea when you've lost all the oil is a different question though...)

[NutLoose]

Not purely a racer but seems to be 99% one, never saw that and I looked Guppy.

Relentless Air Racing Team Official Site

[smo-kin-hole]

Not just the racers...

I had a friend that lost one of three blades (foreign prop shop job) on a Cessna 206 with a Continental 520 at normal cruise. He shut it down within seconds, but it also broke 3 of 4 engine mounts. He ditched off Belize City. Not a good day.

[englishal]

Seems quite common at Reno....From a pilot's perspective !

YouTube - Reno Air Race Unlimited 1991 Lancair Prop Failure

[Adrian N]

Losing the prop rather messed up the engine..... or vice versa.

[SNS3Guppy]

Not purely a racer but seems to be 99% one, never saw that and I looked Guppy.

Never saw what?

Or is it simply that all bets are off once the engine exceeds redline RPM?

The RPM isn't the only factor; it's not that simple. Crankshaft and propeller harmonics play an important factor, as do engine internals, such as crankshaft counterbalances (which can become detuned or fail at higher speeds. The propeller's aerodynamics change as tip speeds exceed critical mach, or in other words, enter mach effects; when they go supersonic. The propeller begins to flex and move in ways that it didn't at sub-compressibility speeds.

Generally speaking, RPM limits on aircraft engines are propeller limitations, not engine limitations. That is, aircraft engines are capable of operating at much higher RPM's, like most piston engines; propellers are not.

In the video, the overspeed is almost certainly not the result of the propeller's pitch flattening, but the result of loss of the propeller. The noise you hear is indicative of a prop loss; lose the prop, and the engine overspeeds.

Engine test stands utilize full size propellers, or test "clubs," which serve to produce cooling air but also to put a load on the engine. Take away the propeller and the engine can overspeed itself rapidly to destruction...especially in the absence of oil.

If a blade separation causes an imbalance, then the resulting vibration can rapidly damage even the strongest mounts, or damage the engine at the locations to which the mounts attach. Some aircraft utilize steel cables to keep the engine attached to the airframe, even if it breaks the mounts, strictly to keep such a massive weight loss from occurring in flight.

[cambioso]

Following the fatal Owl racer crash in 1971 (caused by the propeller breaking, and the engine departing the airframe) all of our UK Formula 1 pylon racers were required to be fitted with a restraining cable around the engine (attached seperately to the airframe) to prevent such an engine departure.
We used metal racing props with known vibration bands that we had to transition through rapidly whilst increasing or decreasing power.
The racing props gave us a good 15-20 mph advantage over the wooden jobs, but they were bloody scary to sit behind!
We used wooden props for the ferry to and from the races!

[Unusual Attitude]

Speaking of F1 racers I was looking back through the log books of my Cassutt which has done quite a bit of racing in its time. Interesting to see some of the noted RPM readings on the 0-200 engine, lots of '3400 rpm for 10 or 30 mins' entries and a couple of '3650 rpm for 10 mins' right before the engine spat a piston.....! (a normal 0-200 is max 2750 RPM!) Saying that it was at about 1600hrs when it died so it did well to last that long....

[Pilot DAR]

some certification requirement or something that would prevent a catastrophic overspeed up to Vcruise

The design requirement you're thinking about would be this one:

§ 3.421 Variable pitch propellers with constant speed controls.

(a) Suitable means shall be provided at the governor to limit the speed of the propeller. Such means shall limit the maximum governed engine speed to a value not exceeding its maximum permissible take-off revolutions per minute.

(b) The low pitch blade stop, or other means incorporated in the propeller mechanism to restrict the pitch range, shall limit the speed of the engine to a value not exceeding 103 percent of the maximum permissible take-off revolutions per minute under the following conditions:

(1) Propeller blade set in the lowest possible pitch and the governor inoperative.

(2) Engine operating at take-off manifold pressure with the airplane stationary and with no wind.


Notice the "stationary" element of the requirement. If the aircraft is moving, there is a presumption that the pilot will remove the power as required to maintian the RPM within limits. If the aircraft is already operating at a high RPM, or very fast (at a much coarser pitch). If at coarse pitch and high power an overspeed is inevitible with an oil loss, because the prop will probably go to fine pitch before the pilot can control the RPM. In any case, the time available to prevent an overspeed will be very short.

It is possible that the aircraft in the video (not a design I recognize as certified) did not have a propeller engine combination which met the certification requirements, so it's sort of comparing apples to oranges to compare this situation to a certified aircraft.

I had a prop overspeed once in a Cessna 340, right after takeoff. It only went 150 or so over red line. By pulling the propeller lever all the way into the feather gate, I was able to get the RPM back below red line, flew the circuit, and returned. Everything else was fine, it just needed a replacement governor.

During my time working at the engine overhaul shop, we had several engines come in with had suffered runaways, though again, not too far over red line. In several cases, this was determined to have been the result of the 15W50 multigrade oil having viscosity breakdown, and the governor not being able to control the RPM at high power. My O-200 suffered a similar problem with viscosity breakdown, but as mine is a fixed pitch prop, the only indication was a loss of oil pressure. This repeated twice during the next two 10 minute flights, each of which were only conducted after hours of cooling off, and just to get the plane home. As a result of my experience, and those of the other pilots, I have never used that grade of oil since. Straight garde only for me, and appropriate preheating in the winter.