Can you damage a prop in-flight?

[beasly]

Dis-allowing the obvious of bird-strikes, etc.....

Can you hurt a prop in flight?

I would imagine that within A.C published performance limits, this would not happen.
That said, I don't know that.

(caveat, it has been nearly 2 years since I have flown so my POH knowledge is not there right now)

Some scenarios I have experienced:

• In a Seminole, props forward to slow from +100 KTS to blue-line--slows you down real quick.
• Emergency descents...the air starts turning the prop faster than the engine is turning it.

Being conservative by nature, I am cautious about those two things I posted--but I have experienced them. I don't know if I am hurting the prop or not.


On : this thread there is a discussion about props breaking the sound barrier.


Finally, Prop care is not really emphasized in my experience beyond knicks and prop length limits in the single and twin POH's I have studied. Counter examples are Flaps and engines with have a lot of restrictions

Is a good working definition that the prop is tougher than the airplane, the aerodynamics it can produce and any stuff the engine can produce?

Can I damage the engine/a.c. by mis-managing the prop?

 

[ppragman]

Dis-allowing the obvious of bird-strikes, etc.....

Can you hurt a prop in flight?

I would imagine that within A.C published performance limits, this would not happen.
That said, I don't know that.

(caveat, it has been nearly 2 years since I have flown so my POH knowledge is not there right now)

Some scenarios I have experienced:

• In a Seminole, props forward to slow from +100 KTS to blue-line--slows you down real quick.
• Emergency descents...the air starts turning the prop faster than the engine is turning it.

Being conservative by nature, I am cautious about those two things I posted--but I have experienced them. I don't know if I am hurting the prop or not.


On : this thread there is a discussion about props breaking the sound barrier.


Finally, Prop care is not really emphasized in my experience beyond knicks and prop length limits in the single and twin POH's I have studied. Counter examples are Flaps and engines with have a lot of restrictions

Is a good working definition that the prop is tougher than the airplane, the aerodynamics it can produce and any stuff the engine can produce?

Can I damage the engine/a.c. by mis-managing the prop?

I think that if you were diving at 180kts and you jammed the prop full forward you could overspeed momentarily, which could potentially cause damage, but I doubt it.

 

[meritflyer]

In the airplane I currently fly, there's not a whole lot to the prop managament as it's turbocharged and generally left > 2500 RPM to keep the turbo spinning appropriately.

However, in my aircraft (Mooney 231), it is not advisable to put the prop to below 15" of MAP as the prop ultimately drives the engine which is undesirable for a variety of engine cooling reasons (as you mentioned during your emergency descent example). This is more of an engine management consideration rather than a prop though.

Lastly and possibly the most critical element is over-speeding the prop which can place undue stress on blades, hubs, and shanks. Over-speeding can cause excessive stress on the engine crankshaft and counterweights while exceeding the aerodynamic limitations of the prop itself. This issue [over-speeding] is quite possibly one of the most important operational considerations in prop management.

In several airplanes I've flown (GA), there's actually a limitation to slow throttle movements at a certain indicated airspeed. Hope that helps a titch.

 

[Chucco]

As far as the propeller itself goes, I have only heard of cases where the propeller disintegrates in flight and I don't recall the reason being mis-managed prop settings. However I have been warned about (hence never experienced) leaving the manifold pressure higher than the rpm setting in light singles and twins (seminole, arrow, bonanza, etc). I'm told it can severely damage the engine to put that much torque resistance on it for more than a minute or so (similar to what meritflyer is saying, I believe). I guess the problem being that the oil pressure is going to red line eventually?

Slowly putting the prop full forward during cruise at 100+ would be the opposite situation then, where the engine would have decreasingly less torque resistance from the propeller. I think I'll agree with ppragman there and will say that the governor is going to catch that overspeed before any real damage occurs. That is unless you quickly jam the prop forward like some of my students like to do!

I'm not so sure about the emergency descent scenario. That's a good question. Maybe no matter what the throttle is set at, if the engine rpm is enough to operate the oil pump for lubrication and pressure to the prop governor then the engine shouldn't get any damage? Except for shock cooling I suppose. What do you guys think?

 

[Roger, Roger]

Perhaps if you have one of those engine/prop combos that has a bad resonance range and you unwisely persist in operating there (any certificated aircraft will have that placarded so you really shouldn't be able to do it unwittingly). Otherwise if you have a governor failure and overspeed the snot out of it, though I think you'll take out accessories and even engine internals before you'd take out a not-previously-damaged (i.e, un-cracked) prop.

 

[USMCmech]

As far as the propeller itself goes, I have only heard of cases where the propeller disintegrates in flight and I don't recall the reason being mis-managed prop settings.

There is nothing you can do from the cockpit that will cause a prop blade to break in flight.

However I have been warned about (hence never experienced) leaving the manifold pressure higher than the rpm setting in light singles and twins (seminole, arrow, bonanza, etc).

The oversquare myth again. Totally false. follow the settings in the POH, and forget the myth of matching your RPM and MAP.

I think I'll agree with ppragman there and will say that the governor is going to catch that overspeed before any real damage occurs. That is unless you quickly jam the prop forward like some of my students like to do!

Agreed, always be smooth and gentle when dealing with your engine.

I'm not so sure about the emergency descent scenario. That's a good question.

If it's an actuall emergency I could care less about taking care of the engine or prop.

Maybe no matter what the throttle is set at, if the engine rpm is enough to operate the oil pump for lubrication and pressure to the prop governor then the engine shouldn't get any damage?

If the engine is running at all, then the oil pump is providing all the lubrication it needs, regardless of what the pilot does.

Except for shock cooling I suppose.

Unless you are deliberately TRYING to, you will never exceed the maximum drop of 50 deg of CHT in under 60 seconds.

What do you guys think?

I think that you are like many CFIs who don't understand what is really going on under the cowling (neither did I at one point). Please do some serious research before passing these myths along to your students.

 

[jhugz]

I think that you are like many CFIs who don't understand what is really going on under the cowling (neither did I at one point). Please do some serious research before passing these myths along to your students.

:clap: Let 'em have it.

 

[ppragman]

Unless you are deliberately TRYING to, you will never exceed the maximum drop of 50 deg of CHT in under 60 seconds.

Not so fast there. Having played with the digital CHTs that were installed in the IO520Fs, I've seen some 50 degree drops happen fairly rapidly with only slight power reductions, but the temperature has to be sub zero at the surface. Be gentle with yoru engine, and nothing too bad can happen. Don't be too aggressive.

 

[dasleben]

Only a concern if you retract flaps in the flare.

 

[ppragman]

Only a concern if you retract flaps in the flare.

Lol.

 

[kiloalpha]

Only a concern if you retract flaps in the flare.

Roadhouse.

 

[Chucco]

I think that you are like many CFIs who don't understand what is really going on under the cowling (neither did I at one point). Please do some serious research before passing these myths along to your students.

:clap: Let 'em have it.

I'm aware that I don't know exactly what's going on under the cowling. I tried to write my two cents with that in mind.

...I have been warned about...I'm told it can severely damage...I guess the problem being...
...That's a good question. Maybe...
...What do you guys think?

I'll try not to teach anything I'm not sure about. Putting that aside, lets discuss this a bit!

About that oversquared myth: I've seen cruise settings for 23" and 2100 rpm. So I understand it to mean that in that airplane, in that configuration, there wouldn't be any undue stress on the engine, and hence the BS about oversquare. (BTW, didn't Charles Lindbergh demonstrate that as a fuel saving tactic to a bunch of P-38 pilots in WW2?) But is there still a concern for having the throttle advanced with the prop lever at low rpm? Am I incorrect in thinking that has to be bad? Or is it just that on a smaller scale it won't affect the engine?

 

[Douglas]

Dis-allowing the obvious of bird-strikes, etc.....

Can you hurt a prop in flight?

If you overspeed your prop (talking governor failure), you could damage (cause failure of) your prop by taking it past its limits.

It sounds obvious, but I'm certain that in an RPM overspeed, many would think in only terms of it being hard on the engine.

 

[Patrick]

As far as the propeller itself goes, I have only heard of cases where the propeller disintegrates in flight and I don't recall the reason being mis-managed prop settings. However I have been warned about (hence never experienced) leaving the manifold pressure higher than the rpm setting in light singles and twins (seminole, arrow, bonanza, etc). I'm told it can severely damage the engine to put that much torque resistance on it for more than a minute or so (similar to what meritflyer is saying, I believe). I guess the problem being that the oil pressure is going to red line eventually?

Slowly putting the prop full forward during cruise at 100+ would be the opposite situation then, where the engine would have decreasingly less torque resistance from the propeller. I think I'll agree with ppragman there and will say that the governor is going to catch that overspeed before any real damage occurs. That is unless you quickly jam the prop forward like some of my students like to do!

I'm not so sure about the emergency descent scenario. That's a good question. Maybe no matter what the throttle is set at, if the engine rpm is enough to operate the oil pump for lubrication and pressure to the prop governor then the engine shouldn't get any damage? Except for shock cooling I suppose. What do you guys think?

Go back to internal combustion engine school. The oil pressure is not "going to redline" because you left the prop forward and changed "torque resistance." Oil pressure is dictated by the speed at which the oil pump is driven (which in our case, is engine RPM), the thickness of the oil (both the actual viscosity rating of the oil and the temperature it is at) and the resistance to flow within the engine (the size of galleries, orifices, bearing clearance, etc). Also keep in mind that many different engines read oil pressure at different places in the engine, which can have an effect on the number that the gauge reads.

With respect to engine damage, as long as the engine is spinning and there is oil to be pumped, the engine is getting plenty of lubrication, whether at 30" or 10".

Regarding "manifold pressure." In every other facet of the internal combustion world, this is referred to as "manifold vacuum" (which is what it really is) or as "boost," if in a forced inducted (turbo or supercharged) engine. However, it's all the same thing, as it just depends on what scale you put on the gauge. Aviation chooses to call it manifold pressure, mainly to make power setting charts useful, however, do understand that in a normally aspirated engine (like your Seminole), that "manifold pressure" is ALWAYS vacuum.

The myth of "operating over-square" is exactly that. It is, in fact, more efficient to operate at a higher manifold pressure and lower RPM. There is also less engine wear to be had at a lower RPM. Look at the POH for many turbocharged aircraft, and note that it is not uncommon at all to cruise at 32" and 2300 RPM.

Remember that the prop is an airfoil, and during flight, will be kept in rotation by a combination of engine power and aerodynamic forces. Below a certain power setting (both manifold pressure and RPM) for a certain airspeed the prop is actually driving the engine, causing negative thrust (and this is why it's imperative to feather a dead engine's prop). As you increase prop RPM at low manifold pressure (say on short final), you are INCREASING resistance (if you want to think of it that way) on the engine by allowing the prop to create more drag, which is why the airplane slows down (assume manifold pressure and aircraft pitch and configuration are kept constant).

It IS possible to shock cool an engine. Mind you, it needs to be pretty cold OAT to do it, but if you go from cruising at 32" in your Navajo with a CHT of 400 and you chop the power to 15" with the OAT being 5C, you will cool those jugs VERY rapidly, and metal never likes that.

These engines appreciate being treated nicely. That means smooth inputs, and gradual power changes. However, nothing that you do as a pilot will cause damage to a properly functioning, properly maintained prop.

In closing, I would recommend that as an active CFI you gain more knowledge on these subjects so that you can properly teach your students.

 

[Roger, Roger]

If you overspeed your prop (talking governor failure), you could damage (cause failure of) your prop by taking it past its limits.

It sounds obvious, but I'm certain that in an RPM overspeed, many would think in only terms of it being hard on the engine.

Possibly, but props are so darn strong I think you'd be really, really unlikely to damage a previously-undamaged one just by overspeeding it. Personally, I think that you'd have stuff like magnetos, alternators, and engine internals get damaged first. Now, if you have a crack in the blade or you get some weird resonance at the overspeed RPM, that MIGHT do it.

 

[Patrick]

Possibly, but props are so darn strong I think you'd be really, really unlikely to damage a previously-undamaged one just by overspeeding it. Personally, I think that you'd have stuff like magnetos, alternators, and engine internals get damaged first. Now, if you have a crack in the blade or you get some weird resonance at the overspeed RPM, that MIGHT do it.

Absolutely engine/ accessory damage first. However, resonance can be a powerful force. I've seen cars snap cranks when the harmonic balancer was removed. If you operate at a critical resonant RPM long enough, you can cause some serious damage.

The Garrett engines specifically note the critical resonant RPM, and this must be avoided (in those engines, however, it is below normal operating speed, but must be factored during shut down/ start).

 

[SpiraMirabilis]

I've seen a dash-8 land after a prop overspeed on takeoff in Denver, it looked fine physically to me and it had to have been going supersonic at the tips at least.

 

[kiloalpha]

The Garrett engines specifically note the critical resonant RPM, and this must be avoided (in those engines, however, it is below normal operating speed, but must be factored during shut down/ start).

Yes, 18-23%. You really don't care much about this speed unless doing an intentional inflight shutdown or startup. Or if you don't see ignition 10 seconds after passing 10% or before 20% on a normal start, then you must abort the start, but thats there to protect from a vibration resonance.

 

[spbrian]

Yes, 18-23%. You really don't care much about this speed unless doing an intentional inflight shutdown or startup. Or if you don't see ignition 10 seconds after passing 10% or before 20% on a normal start, then you must abort the start, but thats there to protect from a vibration resonance.

AND this is not for prop damage, it's internal gearbox within the engine. I want to say that on the 3 bladed arrow that I flew many moons ago there was a caution range for the prop to be operated in, but it was also due to harmonic damage within the engine.

Hitting a bird or taking a lightning strike would hurt the prop, doubt even over speeding a prop would do anything to the typical aluminum props we run, plus have you ever watched an aerobatic show? Those kevlar/carbon fiber props on these planes go through huge ammounts of abuse.

 

[fholbert]

AND this is not for prop damage, it's internal gearbox within the engine. I want to say that on the 3 bladed arrow that I flew many moons ago there was a caution range for the prop to be operated in, but it was also due to harmonic damage within the engine.

Maybe it was a different RPM but the two bladed arrow had the same thing.