Gear up landings and prop position

[nels]

Everyone seem to think it is best to position your prop so as to avoid a prop strike during a gear up landing. I've thought about this a lot and it seems to me the only hope you have of not having a prop strike by positioning the prop is with a two blade prop. I don't think there is any sweet spot with a three blade? I also think a crankshaft has a better chance of survival if the prop is spinning when any of the blades hit the ground. The impact on a two blade is once very 180 degrees and a three blade is once every 120 degrees. The nose is coming down at a given rate no matter which blade you are running so a two blade is inherently going to be more damaging than if it were a three blade. I would think if the impact was entirely against one blade, if the engine was stopped and blade down, a bent crankshaft would be more likely. Likewise, if the prop is spinning, torsional damage is less likely with a three blade over a two blade as impact load per blade is less than a two blade.

Does this make sense?

Edited February 14, 2016 by nels

[jetdriven]

44 minutes ago, nels said:

Everyone seem to think it is best to position your prop so as to avoid a prop strike during a gear up landing. I've thought about this a lot and it seems to me the only hope you have of not having a prop strike by positioning the prop is with a two blade prop. I don't think there is any sweet spot with a three blade? I also think a crankshaft has a better chance of survival if the prop is spinning when any of the blades hit the ground. The impact on a two blade is once very 180 degrees and a three blade is once every 120 degrees. The nose is coming down at a given rate no matter which blade you are running so a two blade is inherently going to be more damaging than if it were a three blade. I would think if the impact was entirely against one blade, if the engine was stopped and blade down, a bent crankshaft would be more likely. Likewise, if the prop is spinning, torsional damage is less likely with a three blade over a two blade as impact load per blade is less than a two blade.

Does this make sense?

 

44 minutes ago, nels said:

Everyone seem to think it is best to position your prop so as to avoid a prop strike during a gear up landing.

Nobody with any though process about this nor anyone with a professional pilot mindset thinks this is a good idea.  In fact it's one of the absolutely stupidest ideas in aviation, and despite the mountain of evidence against the practice, it simply will not die.  

[Hank]

52 minutes ago, nels said:

Everyone seem to think it is best to position your prop so as to avoid a prop strike during a gear up landing. I've thought about this a lot and it seems to me the only hope you have of not having a prop strike by positioning the prop is with a two blade prop. I don't think there is any sweet spot with a three blade? I also think a crankshaft has a better chance of survival if the prop is spinning when any of the blades hit the ground. The impact on a two blade is once very 180 degrees and a three blade is once every 120 degrees. The nose is coming down at a given rate no matter which blade you are running so a two blade is inherently going to be more damaging than if it were a three blade. I would think if the impact was entirely against one blade, if the engine was stopped and blade down, a bent crankshaft would be more likely. Likewise, if the prop is spinning, torsional damage is less likely with a three blade over a two blade as impact load per blade is less than a two blade.

Does this make sense?

This would make sense if the engine is seized, but even then, some rotation is likely. This will mitigate the force exerted on the crankshaft. But running or not, it will be hard on the crankshaft.

[201er]

1 hour ago, nels said:

Everyone seem to think it is best to position your prop so as to avoid a prop strike during a gear up landing. I've thought about this a lot and it seems to me the only hope you have of not having a prop strike by positioning the prop is with a two blade prop. I don't think there is any sweet spot with a three blade? I also think a crankshaft has a better chance of survival if the prop is spinning when any of the blades hit the ground. The impact on a two blade is once very 180 degrees and a three blade is once every 120 degrees. The nose is coming down at a given rate no matter which blade you are running so a two blade is inherently going to be more damaging than if it were a three blade. I would think if the impact was entirely against one blade, if the engine was stopped and blade down, a bent crankshaft would be more likely. Likewise, if the prop is spinning, torsional damage is less likely with a three blade over a two blade as impact load per blade is less than a two blade.

Does this make sense?

No it doesn't cause isn't the most common cause of gear up prop strikes either negligence or because the engine is near TBO?

[Marauder]

1 hour ago, nels said: Everyone seem to think it is best to position your prop so as to avoid a prop strike during a gear up landing. I've thought about this a lot and it seems to me the only hope you have of not having a prop strike by positioning the prop is with a two blade prop. I don't think there is any sweet spot with a three blade? I also think a crankshaft has a better chance of survival if the prop is spinning when any of the blades hit the ground. The impact on a two blade is once very 180 degrees and a three blade is once every 120 degrees. The nose is coming down at a given rate no matter which blade you are running so a two blade is inherently going to be more damaging than if it were a three blade. I would think if the impact was entirely against one blade, if the engine was stopped and blade down, a bent crankshaft would be more likely. Likewise, if the prop is spinning, torsional damage is less likely with a three blade over a two blade as impact load per blade is less than a two blade.

Does this make sense?

No it doesn't cause isn't the most common cause of gear up prop strikes either negligence or because the engine is near TBO?

I was always under the belief that the insurance companies prorated the amount of time on the engine and didn't pay you the full rebuild cost. Isn't that the case?

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[wpbarnar]

For the OP question "does this make sense" ?   It doesn't make sense to me why someone will put himself and passengers at much greater additional risk to possibly save the insurance company a little money.

Based on NTSB data, landing under power is much safer than incidents when the pilot attempted to land without power.  A good recent article based on actual data illustrated the stupid stuff that happens when the pilot chose to shut the engine down prior to the gear up landing.

Be focused on touching down at the slowest  possible speed, perfect alignment with the runway, and for a safe evacuation.  Nothing else!

Bill

 

[carl]

11 hours ago, jetdriven said:

Nobody with any though process about this nor anyone with a professional pilot mindset thinks this is a good idea.  In fact it's one of the absolutely stupidest ideas in aviation, and despite the mountain of evidence against the practice, it simply will not die.

I think this is a great idea .

manufactures should make a switch , yeah,in the shape of a horizontal  propeller, when you get ready to land you throw the switch and the prop stops perfectly horizontal.

They could position this switch directly under the gear down switch, in a kind of landing grouping arrangement so you don't forget. 

And maybe a lighted straight bar that flashes when the prop has stopped. just as a redundancy.

 

[carl]

But really I think this question is more about the engineering principles of F=ma while spinning vs stopped ,which is a interesting question.and not about gear up landings .I have no idea

[cnoe]

Previous poster said:

I was always under the belief that the insurance companies prorated the amount of time on the engine and didn't pay you the full rebuild cost. Isn't that the case?

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I believe that insurance pays for a tear down inspection and engine costs directly related to the strike but provide zero reimbursement for any refurbishment. But it can substantially reduce the cost of an OH if the engine is getting long in the tooth by covering $8-$10K of the total engine-work bill. With an otherwise healthy mid-time engine many would opt for the (all expense paid) TDI only.

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[mooniac15u]

Trying to save your prop and engine during a gear-up landing is a fool's errand. You'd better believe the FAA will have something to say about your decision making if you shut off your engine and then fail to make the runway.

On the other hand, the emergency procedure for a gear up landing in the POH for my M20J includes:

"When sure of making landing area:  Fuel selector.....off"

 

That is presumably more about preventing a post-landing fire.

When I had to make a gear-up landing in my M20D I shut off the fuel when I crossed the runway threshold.

[dlthig]

Many years ago on the day that was supposed to be my first lesson, a Lance had a stuck nose gear and my to be instructor and I watched his landing, If I recall correctly, he had a two blade prop and did shut down the engine. However, he didn't get it positioned quite right and bent a blade. I don't know what else became of the incident. I didn't give it much thought at the time. Since then I've had a few more ideas. I think the idea of stopping the prop and saving the engine sounds good, but it doesn't fit into my risk-reward matrix very well. You'd better know what you are doing and you don't have a mulligan if you decide to shut down the engine. I'd guess that most of us fly out of GA fields that aren't 10,000'. I'm also willing to guess that most major airports would rather you go somewhere else to gear-up your airplane and not shut down their runway. Run the checklist, phone a friend or whatever, but backing yourself into a one-way corner unnecessarily usually isn't a good idea. Let the insurance figure it out. I'm a big fan of using superior judgement and avoiding the use of superior skills. 

[FlyDave]

Being that most of us have never landed an airplane gear up and, as such, don't know exactly what to expect, you should be completely focusing on getting the airplane on the ground in one piece, stopped and yourself and passengers safely out and away from the airplane.

I can tell you that if I ever have to land gear up (gawd, I hope I never have to do that!!!!) I sure a hell won't be thinking about saving the engine.

[bonal]

Really can't see any reason to add to the problem of a gear up. Once I knew it was up and stuck I would make contact with all that-need to know if I wasn't at home and had ample fuel I would fly home trying every thing I could to get a green light reducing fuel for weight and safety and then make the best approach and landing I could with the engine doing exactly what it does on all the previous landings I have made. Unless you practice shutdown over the numbers and then play with the starter to align the blades to get framilier with how things go I think would be real stupid to try for first time in a real emergency. Now if I ran it out of gas and my gear stuck then why not and once you get down safe turn in your cert and find a new hobby

[Andy95W]

5 hours ago, mooniac15u said:

When I had to make a gear-up landing in my M20D I shut off the fuel when I crossed the runway threshold.

I thought the M20D had fixed gear?

[mooniac15u]

5 minutes ago, N1395W said:

I thought the M20D had fixed gear?

They came from the factory with fixed gear but almost all have been converted to retractable.

That day I was wishing I still had fixed gear. 

[M20F]

One day with a lot of altitude and an airport in close proximity go out and try to make your prop stop, it isn't exactly an easy task.

[Andy95W]

2 hours ago, mooniac15u said:

They came from the factory with fixed gear but almost all have been converted to retractable.

Sorry, I should have put in a . There are so few left that haven't been converted a lot of people don't realize it actually had fixed gear from the factory. 

[Raptor05121]

On 2/13/2016 at 6:00 PM, mooniac15u said:

They came from the factory with fixed gear but almost all have been converted to retractable.

That day I was wishing I still had fixed gear. 

Why didn't the gear go down? Was it an electric?

[Shadrach]

On February 13, 2016 at 6:54 PM, M20F said:

One day with a lot of altitude and an airport in close proximity go out and try to make your prop stop, it isn't exactly an easy task.

I've done it in the Mooney. It's not hard, but I recall the stall horn chirping a bit about the time the prop stopped. I had an instructor demonstrate this in an Aeronca Chief years ago...in Indiana...in February...oil congeled and the prop would not turn even in a dive at 135MIAS. He executed a perfect dead stick landing on airport, but it was a good example of what not to do in an airplane.

[mooniac15u]

1 hour ago, Raptor05121 said:

Why didn't the gear go down? Was it an electric?

No, it was manual gear. It was the first flight after some maintenance on the gear. The right main gear jammed and in the process of trying to put it down a retraction tube failed. After that the right main gear wasn't going anywhere. 

[marks]

Nels, this is a truly silly question.  Keep things under control and simple.  Don't give up the control the engine gives you.  Back in 2004 when I suffered an engine failure and fire in hard IFR conditions I chose to land gear up and was lucky enough to find a golf course.  The prop kept turning cutting up chunks of earth and helped absorb energy to slow down the plane ending up the very shortest landing distance of my life.  Both blades were bent far back and I wouldn't have ever wanted it any other way.  Life is too precious to give the slightest concern to a prop or crankshaft. 

[jetdriven]

Wow, that sounds scary.  Glad it turned out.  What happened?

[Mooneymite]

I remember way back in Navy flight training, a T-34B had a gear extension problem.  The instructor landed the airplane and just before touch-down he bumped the prop into the horizontal position on short final.  He was hailed as a hero and pilot-extrodinaire.  As I recall, the airplane was back on the flight line in a day, or two.

As a tax-payer, I appreciated the effort to save the engine.  As a pilot, I was in awe of the soft touch down and presence of mind to bump the starter.

I guess it depends on your degree of success whether it's a good idea, or a bad idea.

[marks]

Byron, The NTSB accident report was Oct. 15th 2004.  I had a hot mag and the IA who fixed it failed to reconnect the fuel pressure gauge and rerouted the fuel line out of place.  He had to remove the fuel line to reach the left mag.  As a result fuel was spraying like perfume into the engine bay and when the exhaust manifold got hot enough POOF!  I could feel the "poof" in my ears, and the fire burned the leads to the spark plugs and killed the engine.  The worst part was that the fire also burned the main vacuum hose so I had to make a U-turn over Nantucket Sound with partial panel in order to make it back to land.  I used to commute most every day from Martha's Vineyard to Hyannis on Cape Cod and back.

[Guest]

19 minutes ago, marks said:

Byron, The NTSB accident report was Oct. 15th 2004.  I had a hot mag and the IA who fixed it failed to reconnect the fuel pressure gauge and rerouted the fuel line out of place.  He had to remove the fuel line to reach the left mag.  As a result fuel was spraying like perfume into the engine bay and when the exhaust manifold got hot enough POOF!  I could feel the "poof" in my ears, and the fire burned the leads to the spark plugs and killed the engine.  The worst part was that the fire also burned the main vacuum hose so I had to make a U-turn over Nantucket Sound with partial panel in order to make it back to land.  I used to commute most every day from Martha's Vineyard to Hyannis on Cape Cod and back.

Scary story, glad you're alive to share.  A question comes to mind, was there a fuel pressure indication on pre start checks?

I've had a fuel line on the inlet to the engine pump which came loose in flight.  When I turned off the boost pump the engine quit due to air being drawn into the pump.

Clarence