About slowing down after a landing.

Can the blades of a propeller somehow be rotated
to a reverse or negative pitch, that would aid in slowing the aircraft down ?

or can the rotation of all three blades be reversed to aid in the braking process?

Not a pilot, but yes they can be given negative pitch.

https://en.wikipedia.org/wiki/...able-pitch_propeller

Absolutely. A variable pitch prop can provide forward or reverse thrust.

Yep. I am unaware of any that would do this in flight, but on the ground, its very effective.

RMD

well, when landing, several things slow you down - the rolling resistance of the gear and the runway

also, one might have flaps deployed as a way of increasing the rate of decent without increasing the speed

but yes, you can get variable pitch props and move them into a condition where they're not generating forward thrust and the rotating disk creates a drag force

I don't know of any GA that have a reverse pitch

now that you have provided the nomenclature needed , I have watched a few you tube vids that clear it all up.

thanks

quote:

Absolutely. A variable pitch prop can provide forward or reverse thrust.

No they won't. They will go to a flat or high rpm setting. they will not reverse. A reverse pitch prop can.

Turbo props will have a reverse pitch, but you use that on the ground only, never in the air. You can also put it in beta mode on the ground which is a flat pitch to slow down, which is just before going into reverse. You can even go backwards on the ground in reverse, depending on your engine manufacture.

Actually, MT is making a new prop for single engine aircraft that can now be reversed.

https://www.mt-propeller.com/en/entw/pro_rev.htm

Prior to this, this was only used on twin engine aircraft...at least that I'm aware of.

I've owned a few light airplanes. Yes, the commercial Twin types usually have reverse pitch. It's used kinda like 'reverse thrust' with a jet, assist with slowing.

As an owner, one often thinks about maintenance costs, like light brake use. I usually minimize brake use as able, though use them as called for.

Runway length and where you'd like to turn off factors in. There is often some type of headwind component. Even with a light plane one can 'Aero-brake' once below flying speed. That would be sorta like opening both doors on a car to get some 'barn door' effect.

does the pilot actually reverse the engines ? or do the just re pitch the blades ?
after touchdown.

is there a transmission involved like on an auto ?

Depends on the aircraft.

We manufacture one which is a fixed pitch, one which is positive pitch only, and one which can go negative pitch with weight-on-wheels (very important discreet - lol).

quote:

Originally posted by bendable:
does the pilot actually reverse the engines ? or do the just re pitch the blades ?
after touchdown.

is there a transmission involved like on an auto ?

The blades simply reverse their pitch; the direction of rotation is not changed. As someone above said, there is a "Beta" setting in which the pitch of the blades is basically zero, neither positive (pull) or negative (push) and then there is revers pitch which is negative.

RMD

does a pilot have to get certification to fly planes w/vpb's?

quote:

Originally posted by bendable:
does the pilot actually reverse the engines ? or do the just re pitch the blades ?
after touchdown.

is there a transmission involved like on an auto ?

The engine, whether piston or turbine, does not reverse. It always rotates in the same direction.

Likewise, the propeller rotates in the same direction.

The simplest propellers are fixed pitch, usually either one-piece metal, or layers (laminated?) of wood. Think in terms of an old-fashioned bicycle with no gearing.

Next step with propellers, adjustable pitch. The blades are not one-piece with the hub, but rather the blades are separate pieces that fit into the hub, and the pitch angle can be adjusted.

Simplest of this type is ground-adjustable. Prior to engine start, the pitch of the propeller blade can be adjusted. Fine pitch will allow the engine to achieve higher rpm, kind of like being in a lower gear. Good for take-off and climb.

Coarser pitch will cause the prop to take a bigger "bite" of the air, think in terms of higher gearing for a vehicle. Not as good as fine pitch for take-off and climb, but once established at altitude, it's more efficient for cruise, in terms of speed and fuel consumption.

Next step in complexity are those props that can be adjusted while in flight. These have many variations. Older Bonanzas, for example, had electrically adjustable props. Newer props are typically adjusted via hydraulic actuation. Some older types require the pilot to adjust the prop each time a change is made in throttle setting. Newer types are "constant speed," meaning that they have a governor, so if a change is made in throttle, the pitch of the blades is changed automatically to maintain the same rpm.

Props on most multi-engine airplanes are able to "feather" -- with the engine stopped, the blades can be adjusted past the coarsest pitch, to be parallel with the air stream. This is used to reduce drag on an engine that fails in flight (note that the most common cause of engine failure is an instructor or examiner. ) I believe that some single-engine turboprops also have the ability to feather the prop.

Some props have Beta mode, as has been described by previous posters, is a flat (neutral) pitch.

Continuing past Beta, some props are able to go into reverse pitch, the blades going into a setting that causes the air to be moved in the direction opposite normal flight. This would be used for braking, during the landing rollout.

All of the variable pitch stuff described above is achieved by changing the angle of the propeller blade, where the blade fits into the hub. The engine never changes direction of rotation.

If you have a pilot friend, ask him / her to take you to a local airport and show you a few aircraft with different types of propellers. It's easier to understand when you can look at them, rather than read a description.

Stop by my local airport here, and I can show you some.

Adding: I just thought about this and wanted to mention, helicopter rotors are more complex than airplane propellers. The pitch angle of the rotor blades is variable, and in fact can change constantly during each 360 degree rotation. I'm not a helicopter pilot; there are some here in the forum who can expand on this.

quote:

Originally posted by rscalzo:

quote:

Absolutely. A variable pitch prop can provide forward or reverse thrust.

No they won't. They will go to a flat or high rpm setting. they will not reverse. A reverse pitch prop can.

Why the higher rpm when the prop goes into a flat spin? I always noticed the higher rpm when landing in a 207 and the prop went flat.

quote:

Originally posted by bendable:
does a pilot have to get certification to fly planes w/vpb's?

yes

Like I said before, a variable pitch prop can provide forward or reverse thrust. rscalzo is being ridiculously semantic. Some variable pitch props can go into reverse pitch and some can't. My statement was true then and its true now.

Nobody in aviation refers to a prop that can go beyond beta into true reverse pitch as a reverse pitch propeller, they call it a variable pitch prop. Reading wikipedia doesn't always mean much. Hamilton Standard refers to their propeller that goes into reverse pitch as a "variable pitch" propeller. They are the SME here. If they say its a variable pitch prop, take their word for it.

A flat pitch can produce a very fast rotation because it literally isn't taking much of a bite of the air. It has much less resistance to fight basically. In fact, one of the most dangerous things that a large variable pitch propeller can have happen is losing control of the pitch and the blade driving to a flat pitch. It can and has many times resulted in the loss of a blade followed shortly thereafter by the rest of the prop. Prop overspeeds are very dangerous.

Coolest thing to watch is a C-130 taxi in and then back itself into a hangar.

Reversing prop pitch to slow down in flight is not recommended