pushing on a propellor

Some twin props use oil pressure created by the prop governor to drive the blades out of feather. If the engine fails, the oil pressure drops and the combined forces of big spring in the prop dome and counterweights on the blades move the blades back into feather.

Tom-D said:
I see no problem with placing a full feathering prop on a single engined aircraft, but not the other way around.

the twin with a full feathering prop, has 1 of 2 ways to go to feather, first is a N2 charge that acts as a big spring pushing the blade up to feather opposed by engine oil pressure.

the other is a electric feather pump activated by the cockpit crew.
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OK, I did the gyro calculation for the Hartzell prop on my plane.

The scenario is doing a level turn with 60 degrees of bank at 90 knots. This yields a turn rate of around 20 degrees per second.

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When I push on the prop, my hand is less than a foot from the center of the hub. So, I'd have to be applying over 700 lbs of force to match the torque caused by a steep turn. I'm not gonna sweat it...well except for actually pushing the plane, that requires sweat.:D
 
Actually, part of the hand prop procedure is to try to move the airplane by pushing on the prop (check to see that brakes are on or checks are holding), and once that's confirmed, pushing on it to make the engine start.
 
Is there any concern about accidentally starting the engine while pushing on the prop?

I grant that many things have to happen - bad ground on a magneto, fuel still in the engine (which should have been removed with mixture cutoff), and rotating the prop instead of pushing or pulling on it for the engine to start and may not be very likely.
 
Cap'n Jack said:
Is there any concern about accidentally starting the engine while pushing on the prop?

I grant that many things have to happen - bad ground on a magneto, fuel still in the engine (which should have been removed with mixture cutoff), and rotating the prop instead of pushing or pulling on it for the engine to start and may not be very likely.
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You'd have to rotate it through a compression cycle to get it to start. On my bird that won't happen by accident. Pulling the prop through the compression requires a fair amount of elbow grease.

Maybe Dan could accidentally push or pull the prop through on his ride, given the low compression, tiny engine, and small number of pistons (yes, I think 4 is a small number)
 
COFlyBoy said:
Maybe Dan could accidentally push or pull the prop through on his ride, given the low compression, tiny engine, and small number of pistons (yes, I think 4 is a small number)
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I think hand propping makes me more aware of the prop, pushing, pulling, or whatever.

Even doing work on an airplane, you are careful. The mag switch is not absolute, and fuel cutoff stops most of the fuel -- but there's still a bit left in the bowl.

So I don't casually turn the prop -- ever. I will push on it when maneuvering on the ground, but that's rare. More often I throw a rope around the tailspring and pull it where I want it to go.
 
dmccormack said:
-- but there's still a bit left in the bowl.
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On most carbureted spam cans, the bowl is ABSOLUTELY FULL after you pull the mixture! Pulling the mixture shuts off fuel downstream from the bowl. So your warning is well spoken. A small leak in the fuel cutter-offer will let the bowl fuel leak by. But it is an updraft carburetor....

-Skip
 
Steve said:
Mine has a rod that goes through the nosewheel axle. Works in either direction.
...
It's not like you have no alternative. Even taildraggers have options available to them.

The universal towbars such as those that are manufactured by Brackett work in tension and compression. They have a positive clamping action that will not disengage until you release it.
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I don't want to hijack the thread, but I'm a new owner and would appreciate a pointer to some of these other options. The OEM nosewheel pant for my PA28 blocks the wheel axle; are there "universal" towbar designs that will work with the "towbar flange" above the wheel? What other options are there if the axle is not accessible?

I have considered using a winch to pull the plane from the aft tiedown ring, but there are perhaps even more reasons to shy away from that than pushing on the prop....
 
Jim_R said:
I don't want to hijack the thread, but I'm a new owner and would appreciate a pointer to some of these other options. The OEM nosewheel pant for my PA28 blocks the wheel axle; are there "universal" towbar designs that will work with the "towbar flange" above the wheel? What other options are there if the axle is not accessible?

I have considered using a winch to pull the plane from the aft tiedown ring, but there are perhaps even more reasons to shy away from that than pushing on the prop....
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Yes, you can purchase a towbar that will attach the the nosewheel strut just above the pant. Your aircraft should have come with one. If you are a tall gentlemen you can probably push the aircraft with the tow bar alone. If you are a little squirt like me, you'll probably wind up pushing on the prop so you can see where you're going. If done with a modicum of care it will harm exactly nothing.

Welcome to the exciting world of Cherokee ownership.
 
Jim_R said:
I have considered using a winch to pull the plane from the aft tiedown ring, but there are perhaps even more reasons to shy away from that than pushing on the prop....
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Just as with the pushing on the prop business, if done with reasonable care, you can town the plane into the hangar with a winch without doing harm to it. The forces acting on that tiedown ring during a wind-storm are going to exceed what you can create by towing on a even surface (this does not apply to some of the plastic planes with a glued on tail-skid, those will be damaged by pulling horizontally).
 
Am I understanding this right? This thread is about airplanes, right? I remember a frictionless plane formula being something like F=mgsin(theda). Granted the bearings aren't frictionless. But, pushing a 2500 pound object up a 5 degree incline only takes about 200 pounds of force. These things (airplanes) were designed to break away from the pull of the Earth's gravity...slowly in a Warriors case. I hear that sometimes, if you control the descent properly, they don't end up a mangled pile of metal when they get back down to the ground. :rolleyes2:

Seriously though, the only way you are going to bend the prop manually is if you hit it on the edge with a hammer! You certainly aren't going to do it with 200 pounds of squishy man palm. :dunno: Same with the tie down loop. If you break the tie down pulling on it, to move the plane across level ground, it was already broken.
 
Several years ago a guy here at my home airport tried to fly his Pitts through a chain link fence at the end of the runway. The plane was relatively bashed up but flyable except for a bent prop blade on a two blade aluminum Hartzell. The guys here put about ten feet of pipe on the blade and got a couple of big lads to push on it to bend it back until it looked straight. There was a crusty old WWII P51 ace here that took a brief look at it and said he'd fly it. And he did - all the way from Annapolis back to the factory in Afton Wyoming where they replaced the prop and rebuilt the engine amongst other things.

If you move it around by the root of the prop, it's never gonna know you were messing with it unless it's one of these new hotsy snotsy LSAs that have styrofoam plastic covered props. Those things look pretty flimsy to me.
 
Skip Miller said:
On most carbureted spam cans, the bowl is ABSOLUTELY FULL after you pull the mixture! Pulling the mixture shuts off fuel downstream from the bowl. So your warning is well spoken. A small leak in the fuel cutter-offer will let the bowl fuel leak by. But it is an updraft carburetor....

-Skip
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Dan's airplane has no cutter-offer. The mixture control, if his carb has any at all, is a back-suction affair that requires venturi vacuum to hold back on the fuel in the bowl. At idle there's no venturi vacuum and the mixture control does nothing. He, and I, shut off our old airplanes by turning the fuel off. The engine runs for awhile on the fuel in the bowl, but there's a tiny bit left when it quits. It's the fuel in the bowl's low spot that can't get into the jet. The low spot is to trap any bad bits that get past all the filters. It gets drained at annual time. Or it should.

Dan
 
Dan Thomas said:
Dan's airplane has no cutter-offer. The mixture control, if his carb has any at all, is a back-suction affair that requires venturi vacuum to hold back on the fuel in the bowl. At idle there's no venturi vacuum and the mixture control does nothing. He, and I, shut off our old airplanes by turning the fuel off. The engine runs for awhile on the fuel in the bowl, but there's a tiny bit left when it quits. It's the fuel in the bowl's low spot that can't get into the jet. The low spot is to trap any bad bits that get past all the filters. It gets drained at annual time. Or it should.

Dan
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Exactly.

:cornut:

(I asked my A&P if we could rig a mixture on the bird. he just laughed...)
 
I've always thought the "don't push the prop" rule was a sub-part of the "always assume the mags are hot" rule... :dunno:
 
Pilawt said:
One of the popular events at the Grumman owners' group (American Yankee Association) gatherings is the contest to see who can push his or her airplane backwards along a prescribed path most accurately, without a towbar.

It ain't easy, folks. :D
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I can imagine...

Most high-wing nosedraggers with struts are pretty easy... push on the strut and nudge the nose wheel with your foot to steer. :D
 
PittsDriver said:
Several years ago a guy here at my home airport tried to fly his Pitts through a chain link fence at the end of the runway. The plane was relatively bashed up but flyable except for a bent prop blade on a two blade aluminum Hartzell. The guys here put about ten feet of pipe on the blade and got a couple of big lads to push on it to bend it back until it looked straight. There was a crusty old WWII P51 ace here that took a brief look at it and said he'd fly it. And he did - all the way from Annapolis back to the factory in Afton Wyoming where they replaced the prop and rebuilt the engine amongst other things.
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Sounds like that P51 pilot's luck was holding up nicely... but I guess you'd know if it was going to work or not during the runup. :D Personally, I don't think I'd even entertain the idea, especially if I suspected the prop had been "repaired" this way before.

I met a young CFI during my search for a flight school years ago who told me he'd quit one school when he went out to preflight a plane and the school's owner was out there "repairing" the prop with a hammer. He turned around and went home. :D
 
rottydaddy said:
I met a young CFI during my search for a flight school years ago who told me he'd quit one school when he went out to preflight a plane and the school's owner was out there "repairing" the prop with a hammer. He turned around and went home. :D
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There is an NTSB report from Alaska where the air-taxi pilot went out to pick up some hunters and 'q-tipped' the prop during a nose-over on the gravel bar he was landing on. As the accident report noted rather dryly 'the customers observed the pilot beating the prop back into shape using a rock':hairraise:.
 
weilke said:
There is an NTSB report from Alaska where the air-taxi pilot went out to pick up some hunters and 'q-tipped' the prop during a nose-over on the gravel bar he was landing on. As the accident report noted rather dryly 'the customers observed the pilot beating the prop back into shape using a rock':hairraise:.
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Gotta do what you gotta do.... :)
 
Dan Thomas said:
The low spot is to trap any bad bits that get past all the filters. It gets drained at annual time. Or it should.
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A good question to ask your mechanic after Annual... "So how did the stuff from the carb drain plug look? Any water in there? Any grit in the screen?"

And... if you still think they're BS'ing you, "What kind of thread seal compound did you use when you put it back in?"

If they look at you dumbfounded, find another mechanic.

It's also an excellent indirect test of your fuel selector OFF position in Cessnas.
 
dmccormack said:
I think hand propping makes me more aware of the prop, pushing, pulling, or whatever.

Even doing work on an airplane, you are careful. The mag switch is not absolute, and fuel cutoff stops most of the fuel -- but there's still a bit left in the bowl.

So I don't casually turn the prop -- ever. I will push on it when maneuvering on the ground, but that's rare. More often I throw a rope around the tailspring and pull it where I want it to go.
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Good call. And on my airplane, at least... there's absolutely no accessories or engine or prop components that can be harmed or damaged by turning the prop backwards, if it absolutely must be turned.

Backwards, the magneto bendix gear doesn't engage, and simply can't fire.

But those who turn them forward seem to not mind handing their life over to the whims of an 18-gauge ground wire through the cheapest ignition switch Cessna could buy that passed Certification in 1975.

There's a lot of old-wives tales out there about various things people say can be damaged by turning them backwards. Dry vacuum pumps being one of them. It's generally not true. Know your systems before applying to other GA aircraft. I only know mine. ;)

"Don't let anyone you know turn a prop unless you're willing to hang out in the ER waiting room to see if they survived."

That pretty well covers it, even hand-propping. Hand-proppers probably already agree that they already signed up for that sad duty if the worst happens... the rest of us... think about it.
 
denverpilot said:
Good call. And on my airplane, at least... there's absolutely no accessories or engine or prop components that can be harmed or damaged by turning the prop backwards, if it absolutely must be turned.
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Unless you are flying a Rotax 912/914. The operators manual says in about 100 or so places never turn the prop backwards. As I recall, it has something to do with oil and lifters.

Backwards, the magneto bendix gear doesn't engage, and simply can't fire.
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The starter typically has a Bendix (except Rotax - they have a Sprag clutch). Mag's don't. Perhaps you are thinking of the impulse coupling? (Rotax doesn't have those either).

But those who turn them forward seem to not mind handing their life over to the whims of an 18-gauge ground wire through the cheapest ignition switch Cessna could buy that passed Certification in 1975.
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Falling while getting out of the bathtub is a very common accident.

There's a lot of old-wives tales out there about various things people say can be damaged by turning them backwards. Dry vacuum pumps being one of them. It's generally not true. Know your systems before applying to other GA aircraft. I only know mine. ;)
"Don't let anyone you know turn a prop unless you're willing to hang out in the ER waiting room to see if they survived."
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Or at least video the attempt so you can go viral on youtube.

That pretty well covers it, even hand-propping. Hand-proppers probably already agree that they already signed up for that sad duty if the worst happens... the rest of us... think about it.
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Flipping the prop ain't exactly rocket science.
 
Capt. Geoffrey Thorpe said:
Unless you are flying a Rotax 912/914. The operators manual says in about 100 or so places never turn the prop backwards. As I recall, it has something to do with oil and lifters.

The starter typically has a Bendix (except Rotax - they have a Sprag clutch). Mag's don't. Perhaps you are thinking of the impulse coupling? (Rotax doesn't have those either).
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Since when is there a Rotax Engine on my aircraft? :D And I quote... "On my aircraft..."

You're correct on the impulse coupling. I had the starter spring stuff on the brain.

While we're on props... some folks asked at systems class this weekend about the MT props on 182s...

The comment from the A&Ps was... "Sure if you don't mind shipping it back to Germany every time you get a serious rock ding."

I guess (haven't looked it up yet) that there's some pretty strict limits on those composite props... there's a very small amount of damage a typical prop shop or A&P can fix, then you ship it back to the manufacturer.

Think that completely convinced me to stick with aluminum. Sheesh.

Then the conversation turned to 2 vs. 3 blade on the 182... and every person with a 3-blade on their aircraft said they'd suffered a cruise speed loss, as did the A&P guys say that as well. You gain in climb performance, though.

Go figure... the big "old" aluminum 2-blade is efficient, can be fixed, and if you at least crack into the prop hub from time to time to make sure it's not headed south, and then reseal if it's in limits to a point, it can usually be rebuilt before it destroys itself.

I bet some smart cookies with slide rules in their pockets thought about that before she ever rolled off the assembly line. :thumbsup:

I'm liking "simplicity" more and more. :)
 
denverpilot said:
Since when is there a Rotax Engine on my aircraft? :D And I quote... "On my aircraft..."
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Oops, I missed that.

But if you want we can bicker about props... One of these days, when I have done about a million other things that need to get done first, I'm gonna make a new prop for my ride out of the proper propeller material. Wood. :tongue:

Right now it has one of those ground adjustable plastic bladed ones with the big clunky hub that has to create a ton of drag...

Oh, the previous owner used to push / pull on the prop to move it all the time. I just find it more convenient to use the chunk of rope around the tailwheel...
 
weilke said:
Well, unless they need a 'new ferrule' or some other part that has to be whittled out of a block of aluminium by some of the elves at the MT factory ;) .
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I did not imply that you would get immediate turn around, only that you don't need to ship the prop to Germany. I like my MT prop but it was a PITA to get serviced, even in Florida. MT changed the management at the Florida shop a few years ago so it might be better now, maybe not.
 
flyingcheesehead said:
It's kind of pointless when your service ceiling is under 3000 feet, and running LOP would only get you from 4 gph to 3.8. :D
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I've been thinking of rigging a mixture control on the Porterfield. I suspect that being able to lean will actually improve the climb rate at altitude and the service ceiling. Probably help the cruise speed above 3000 MSL as well although it's more fun to cruse a bit lower.
 
weilke said:
There is an NTSB report from Alaska where the air-taxi pilot went out to pick up some hunters and 'q-tipped' the prop during a nose-over on the gravel bar he was landing on. As the accident report noted rather dryly 'the customers observed the pilot beating the prop back into shape using a rock':hairraise:.
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Very irresponsible. Everybody knows you're supposed to take a hacksaw and trim off the distorted part, same amount for each blade. :thumbsup:
 
steingar said:
Yes, you can purchase a towbar that will attach the the nosewheel strut just above the pant. Your aircraft should have come with one.
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Sorry for the confusion. I do have the original towbar, but I too have trouble pushing my plane backwards, up a slight grade, over bumpy asphalt, then over the door rails into the hangar, while trying to steer. As someone else put it, it's tough to push on that towbar without it jumping out of the flange. A towbar with a more positive attachment mechanism would be nice, but I don't think the "universals" will work with the front wheel pant installed.

The slight incline, bumps, and hangar pad lip are also reasons why I shy away from using the winch--that's not a "smooth surface" pull. I have decided to reserve winch use for "in case of emergency" (like if I bung up my leg, back, or shoulder and physically can't push the plane).
 
Jim_R said:
Sorry for the confusion. I do have the original towbar, but I too have trouble pushing my plane backwards, up a slight grade, over bumpy asphalt, then over the door rails into the hangar, while trying to steer. As someone else put it, it's tough to push on that towbar without it jumping out of the flange. A towbar with a more positive attachment mechanism would be nice, but I don't think the "universals" will work with the front wheel pant installed.

The slight incline, bumps, and hangar pad lip are also reasons why I shy away from using the winch--that's not a "smooth surface" pull. I have decided to reserve winch use for "in case of emergency" (like if I bung up my leg, back, or shoulder and physically can't push the plane).
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I push on the inboard part of my prop and steer with the towbar, otherwise I can't see over it. I doubt I could push my aircraft uphill, or offroad, or whatever. I tend to taxi just in front of my hangar before I shut down, thus diminishing the distance over which I have to push it.

In conditions where pushing gets too difficult (mostly snow and ice) I can get an assist from the FBO tug. They do make powered airplane tugs, though like everything else in aviation I imagine they're pricey. me, I'd hit the gym before purchasing one, but to each his (or her) own.
 
I definitely can't push my plane up even the shallow slope right in front of my hangar. And there are no FBO-owned tugs that I have access to. The most valuable item in my hangar when my plane's out of it is the winch. If it's out of commission, I need help getting my plane in.

ObOnTopic: I can push it on level pavement though, and have, much as steingar described, IOW pushing on the prop "root" close to the spinner. Usually, though, I taxi very close to the hangar door and then turn sharply towards the opposite row, stopping close enough to my own hangar door to reach the tie down ring with the winch cable.
 
steingar said:
I push on the inboard part of my prop and steer with the towbar, otherwise I can't see over it. I doubt I could push my aircraft uphill, or offroad, or whatever. I tend to taxi just in front of my hangar before I shut down, thus diminishing the distance over which I have to push it.

In conditions where pushing gets too difficult (mostly snow and ice) I can get an assist from the FBO tug. They do make powered airplane tugs, though like everything else in aviation I imagine they're pricey. me, I'd hit the gym before purchasing one, but to each his (or her) own.
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I have a power tow. Those a kinda pricey new. There are a couple guys by me that picked up old lawn tractors pretty cheap (<$100) and with a mod or two for the tow bar they seem to work really well.
 
steingar said:
In conditions where pushing gets too difficult (mostly snow and ice) I can get an assist from the FBO tug. They do make powered airplane tugs, though like everything else in aviation I imagine they're pricey. me, I'd hit the gym before purchasing one, but to each his (or her) own.
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Watch those tugs. We had one here from Aircraft Spruce and it was hopeless. Could hardly move a Seneca on a bare and dry hangar floor, never mind uphill or on ice and snow. The problem with most is the lack of traction; they just grab the nosewheel and try to move it. A good tug will pick up the nosewheel and place the weight on its driving tires. Id' like a tug that has four driving tires, where we could put chains on two of them for ice traction and the bare tires for the hangar floor.

Dan
 
Dan Thomas said:
Watch those tugs. We had one here from Aircraft Spruce and it was hopeless. Could hardly move a Seneca on a bare and dry hangar floor, never mind uphill or on ice and snow. The problem with most is the lack of traction; they just grab the nosewheel and try to move it. A good tug will pick up the nosewheel and place the weight on its driving tires. Id' like a tug that has four driving tires, where we could put chains on two of them for ice traction and the bare tires for the hangar floor.

Dan
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Yeah, but yer in da great white nord, eh?
 
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