# Tag Info

34

Old propeller airliners were much more prone to "bumpy" ride than modern jets, for one major reason: they flew lower. When I was in my early teens (almost fifty years ago), I flew several times aboard a Beechcraft 99, a low-wing, twin turboprop feeder aircraft with (IIRC) 14 or 18 seats. Unpressurized, and most if not all seats have a pretty good ...

34

All three sentences make sense to me. Firstly, the shape of the propeller is such that it cork screws through the air. The cork screw motion pulls the propeller and the plane through the air The cork screw reference here is to say that with every revolution, the propeller advances through the air, pushing more air behind it. A nice visualisation of that ...

26

It is so you will see a circle when they are turning. Without contrasting bright tips turning propellers are invisible, and pose a grave risk for someone who is deaf, wearing heavy hearing protection, or distracted by other noises.

25

How did we switch from talking about a blade's angle, to caring about its RPMs? Because of the engine. A piston engine will only run well in a narrow range of RPMs. Going too fast means lubrication may break down, resulting in excessive wear, incomplete cylinder filling and fuel burn, resulting in power loss, increased inertial loads on crankshaft, ...

24

There are two really big issues with tail mounted powerplants with propellers; weight distribution and Foreign Object Damage. Tail mounted engines move the empty C of G aft. This forces you to put the disposable load with a forward bias to compensate, hence the long forward fuselage necessary to put the loaded C of G in the required range. Of course, when ...

19

Yes, if you were riding on a DC-7 or Lockheed Constellation, the planes that the first passenger jets replaced, you would be crawling up the walls if you found a modern jet frightening. Lots of noise and vibration from 4 Wright R-3350 radial engines, that belch great clouds of oil smoke when they start (to me, all the noise and smoke is a symphony, but not ...

19

To enlarge upon John K's answer: At night, the exhaust stacks (visible through the windows!) on the DC-7C glowed red-hot and the exhaust gas itself glowed blue and pink as it flowed back along the engine nacelle, flickering all the way to the trailing edge of the wing. This scared the heck out of me in 1960 while flying from LAX to Copenhagen via Winnipeg ...

18

The inner portion of the blade is protected by a self-adhesive PU-strip, unless the blade is equipped with a de-ice boot. The outboard edge as you can see in the very lower-right corner is protected with a stainless steel erosion sheath. Since the inboard section is slower (radial speed), its protection is a lighter polyurethane-strip/tape. The Extra 300's ...

17

Note that the report says "derived from witness marks on the preload plates", so the investigators did not use witness marks on propeller blades to determine the blade angle. This might have been possible, as scratches and the deformation of the blade tip do, to some extent, manifest blade angle, but you would need to take into account the speed at ...

17

The prop control sets the engine RPM. Moving it forward allows the governor to flatten the blades, which results in a lower angle of attack. In fact, in certain circumstances the AoA goes so low that it actually becomes negative, meaning that the airflow is moving faster through the propeller than the propeller is moving forward. This is like running around ...

16

Sure, this is not only possible, but even has some advantages over single-plane propellers. The catch is you ideally want the two to spin in opposite directions to cancel out torque and vibration. You're building a contra-rotating propeller: Pictured is a Sun Flightcraft contra-rotating gearbox kit for Rotax 503 and Rotax 582 engines. Although more ...

15

We can count more than 15 blade-images in that short arc of revolution of the propeller, so there's no way that each one corresponds to an individual firing of a cylinder. Perhaps there is a resonant vibration involving a slight twisting of the blade, and the sun angle is such that this produces a strobing effect. The suggestion of a 300 rpm variation ...

12

If an elliptically-shaped aerofoil gives the optimum lift distribution … I interpret this as an elliptically shaped wing, because only then the question makes sense. Propellers are similar, but not identical to wings. Dynamic pressure varies along blade span. The outer sections needs less chord for the same lift compared to inner sections. Propeller blades ...

12

It's done sometimes, for ultralight aircraft and paramotors. Like this:

12

Because engine RPM is the variable in the feedback loop. If you did have a nice big knob to directly set blade angle, how would you know when to adjust it, to what setting? You would need to have a feedback signal, like IAS, and a graph that indicates knob setting. No way to verify if you have adjusted correctly, and you’d be very absorbed by the process ...

12

You can make a case that this was the original way to build airplanes as the Wright Flyer had a forward elevator and rear-ish mounted props extending off the back of the wings. Other than that there have been many designs to incorporate rear propellors. The Bede BD-5 has a rear prop. Burt rutan built various designs with rear mounted piston engines/props. ...

11

Low pitch advantage Power A lower pitch allows the blade to spin faster ($\omega$) for the same torque ($T$). The relationship between power ($P$) and speed and torque is $P = T \omega$, so this means that for the same $T$ we get more power out of the prop when it spins at a faster $\omega$. More power means a higher climb rate. Stall At low airspeed, ...

11

Firstly, any new readings or points of view should be carefully reviewed and compared with current information to avoid these lapses in confidence. As Delta Lima pointed out, "corkscrewing" more aptly describes the combined motion path of the the propeller and the aircraft from a third frame of reference. A good analogy would be "the earth ...

11

This is typical for the De Havilland Canada Dash-8, which is powered by Pratt & Whitney Canada PW100 engines. Other aircraft powered by that engine also seem to have their propellers feathered during shutdown. The propellers are only unfeathered after the engine has started (see e.g. this YouTube video of an ATR 72-600 starting its engines with the ...

10

The stutter would be at 2300/min for a two-cylinder engine (or 2-stroke single). For an 8cylinder engine it would be four times that, or 150Hz or so. For a 1000HP engine the output is about 450J per ignition cycle. Estimating a flywheel effective radius of 200mm and mass 30kg the kinetic energy is around 350kJ and so the stutter would be less than 1%. I’...

8

Let’s take the engine out of the equation to simplify things. In fact, let’s take the prop out too, and consider a very elementary comparison – the old “hand out the window” example... Put your hand out the window when you are driving and feel the drag it creates. Now rotate your hand. Can you feel how there is little drag when your hand forms a “knife ...

8

As stated in comments and Dave's answer, it has been done, but I'm guessing you were thinking about mass produced (successful) commercial passenger planes. Here are a couple of reasons: The propellers on a passenger plane need to be quite big, so they would, for clearance reasons, need quite long and thus heavy pylons. Weight in the tail of a plane is ...

7

You may be overthinking it. The governor will set the blade angle that provides the load on the engine that keeps it from speeding up or slowing down from the setting determined by the spring preload that resists the flyweights. You could connect the governor to a big disc brake in place of the prop and it would work the same. So it sets the blade AOA that ...

7

The different parts of a propellor blade are encountering air moving at different speeds. The tip moves through the air much faster than the parts near the hub, so it's not surprising that the same airfoil is not optimum at all points. The propellor blades also need to be designed to handle the forces caused by rotating at a few thousand RPM.

7

A low-pitch or "climb" propeller takes smaller "bites" of the air and allows the engine to run all the way up to its maximum speed, and therefore produce its maximum rated power setting (don't make the pitch too fine, or the engine will overspeed!). The fuel burn rate will then be at a maximum and you'll get maximum acceleration and climb ...

7

Well, the way a propeller works is a little bit like a corkscrew. There are several similarities: Both machines penetrate a surrounding medium—a propeller penetrates air, and a corkscrew penetrates a cork. Both machines move in a helical path, as seen by an outside observer. Both machines produce a force on the surrounding medium which is approximately ...

6

They are much more prevalent than you think, and have been in use for more than 70 years. Rotax 912 and 914 engines can be installed with electric governors from MT Propeller. Airmaster sells them as well. You may also be surprised to learn that nearly 90% of German operational Luftwaffe aircraft during WW2 used an electrically-actuated propeller system ...

6

Controlling a blade's pitch by its RPMs and Manifold Pressure, to my very uneducated mind, sounds indeed like a very counterintuitive way of solving a problem. It depends on the problem. And here the problem is keeping the RPM and the manifold pressure within design range of the engine. RPM is limited because the acceleration of the pistons is proportional ...

5

A quiet fan is a large fan. (This should be understood in relation to either mechanical power or lift. Of course, a multi kilowatt industrial turbine is way noisier than the fan cooling your computer.) A single large and slower propeller (or two coaxial) instead of 4 or 6 small ones will do wonders, provided one can get good enough automatic pitch control. A ...

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