Propeller built like a tailrotor. 3

[RoarkS]

Okay so on top of being an engineer and an A&P I also have my Helicopter and Airplane private pilot certs.

So here I am sitting next to the tailrotor assembly of an MD-500. I go for a bit of a walk and I can check out the tail rotor on a Huey. They are basically designed the same so lets go with that.

Now lets go have a look at a constant speed airplane prop... complete mess. Hand me a manual and yes, I can take it apart and put it back together successfully. Stick me in a plane with one... and that "prop" lever had me baffled. I get it manifold pressure, throttle... ehhhh.... what's going on. No idea.

Back to the helicopter... Okay, engine RPM in the green, rotor RPM in the green, Manifold pressure/%torque, TIT... Push more pedal (more pitch) or pull collective... everything goes up. Makes sense. I like it.

So what's stopping me from building a propeller on an airplane, basically identical to a tail rotor assembly, that has a manual pitch control? Is there something obvious I'm missing? Seems a whole lot simpler.

Second to that... Helicopters in their infinite wisdom like to be able to flap or Teter. Way I figure is it takes stresses out of the structure that a propeller would typically fight... and essentially get rid of P-factor?

I see this as a win-win. What am I missing?

I tried to google, but my google-fu failed me.

 

[3DDave]

He's probably posting to get a toe-hold for an advertising blast. They use innocuous posts as bait.

 

[WKTaylor]

OK, guys, my 2-cents...

xxxxxxx

Classic helicopter...

Think of a tail rotor as Sikorsky does: it is a helicopter ROTARY RUDDER for directional control during all aspects of flight. As such it is designed encounter air-inflow thru 360-degrees of aspect. The main rotor system is really 'just' a ROTARY WING that provides lift, fore/aft and lateral [left/right] thrust... and roll. Crazy Huhhh!?!?

A tail rotor system is designed for a purpose completely separate from classic propeller thrust: it provides lateral [side-to-side = left/right] thrust at the end of the tail-boom in various air-flow fields for the purposes of: (A) main-rotor anti-torque thrust in all phases of flight; (A) yaw control [nose-left/right]; (c) thrust for lateral movements [left/right-sliding]; and stability in forward/aft flight [flying forwards and backwards].

In-flight, the thrust variations of the tail rotor are constantly shifting from left-to-right depending of pilot rudder pedal; helo stabilizing inputs; airflow orientation, WEATHER variables [steady cross-wind, gusts, rain, snow, ice, etc]. In most cases the RPM remains relatively constant... in-sync with main Rotor blades for harmonics and vibration... but drive-power and thrust/thrust-orientation can vary widely/wildly.

When tail rotors fail by separating/disintegrating in flight, becoming out-of-sync with main rotor blades or the pitch mechanisms fail, then the resulting direct effects on the drive-train and tail-boom structure can be catastrophic...

xxxxxxx
Now let’s look at [variable-pitch] propellers. They are designed to extract optimum thrust directly from the mating engine at various airspeed, RPM and power combinations. Props can also be designed for ‘zero effective thrust’, to ‘maximum thrust’ to ‘feathering’ under many start-up and flight scenarios. Although they operate under diverse airflow orientations, they are optimized for relatively shallow angles of flow-angles [attack/yaw].

WHEN failure occurs... engine or propeller internal mechanisms fail... that big/high thrust prop then must become feathered and/or stopped to minimize drag and prop-induced aerodynamic instability. In worst case a failed prop can have disastrous consequences on drag and instability if it continues to ‘windmill’ way in front of the acft. Of course, IF a blade fails then the resulting direct effects on the engine and structure can be catastrophic...


Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[enginesrus]

Manual pitch control? Isn't that what the prop pitch lever in a plane is for? Or are you talking mechanical linkage to do the pitch controlling? That would add extra weight and way more complexity. A nice old Hamilton Standard does just fine using hydraulics. And your manifold pressure, rpm comment, is related to the proper design operating parameters for the engine, if its a turbine you won't have to be concerned about manifold pressure.

 

[berkshire]

Enginesrus,
The manual pitch control on a Hoffman prop is done by a lever in the cockpit attached by aircraft cable to a swashplate at the rear of the prop , yes mechanical linkage. It is designed for light aircraft engines up to approx 100HP that do not have hydraulic pumps fitted. Whilst the prop is not cheap it is about half the price of a hydraulic prop.
B.E.

You are judged not by what you know, but by what you can do.

 

[WKTaylor]

While on the subject... the evolution of helicopters was 'rough/dangerous'... and required nerves of steel [and ready-to-go 'WILLS'] for the test pilots.

This video... is well done for the 1970s... Birth of the Bell Helicopter

https://www.youtube.com/watch?v=k562IriqnlA

This validates what Igor Sikorsky stated late in life...

"At that time [1909] the chief engineer was almost always the chief test pilot as well. That had the fortunate result of eliminating poor engineering early in aviation.” – Igor Sikorsky

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[tbuelna]

Maybe this picture might help:

https://www.sikorskyarchives.com/images/image s-66 AAFS/S-66 X 5.jpg

 

[Sparweb]

Wil,
Great video!
Seeing the familiar "47" helicopter come together from model to successive prototypes to the real article is like watching kids growing up in home movies.
Though I did not enjoy the accident scene at 12 minutes, the rest was fun.
The demonstration of a "prony brake" at 13 minutes will come in handy when educating so-called engineers who don't seem to know what torque is.
"There's our first rotor brake" at 16 minutes
Tail-rotor pitch control chain (17 minutes) The UH-1 (medium) helicopters had tail rotor control chains for a long time.
"Brian was the first passenger... even though it's supposed to be only a 1-place machine" at 19 minutes
Useful vibration indicators at 21 minutes. Can't get the name he used. Can anybody name them so that I can look them up?
"we have almost no shots of model 30 ship 3 because it was rather illegally constructed..."

Thank you

http://www.sparweb.ca

 

[Compositepro]

That is a remarkable video. A great example of how engineering and free enterpise works.

 

[RoarkS]

tbuelna Wow... that tilting tail rotor is amazing.

Also another data point for the thread I found out about Beechcraft Roby Propeller. Essentially what I'm looking for.

My only real question left unanswered at this point is still the difference in "bulkiness" of a propeller than a tail rotor.

The UH-1 Tail rotor IS transferring 200hp. So is the prop hub on a Cessna 182. What's the difference?