# Tag Info

## Hot answers tagged tiltrotor

21

This video explains it nicely starting at about 1:20 in. Also see here. This is a pretty interesting article on flying it as well. It really seems to depend on mode but its summarized here nicely, Climbing into the front seats of the Osprey definitely does not produce the most graceful entrance: it requires some contorting around the armrest, ...

21

It is possible to drive the two rotors of the V-22 Osprey from a single engine using a segmented driveshaft connecting both engine shafts via gearboxes: The drive shaft is depicted in blue in the left wing. Source Each engine drives its own rotor and the connecting shaft. If one fails the same rotation speed is maintained, but each rotor receives now half ...

15

Tilt rotors and virtually every other VTOL aircraft with more than one lift rotor (Chinook, K-Max) or proprotor (AW609) must employ a shaft between these lift units, so when one engine is out the other keep the units turning will half power (which doesn't mean half rotations per minute, but half maximum torque). That's why available power reserve on the ...

14

Short Answer: yes. If they could not, they'd likely not get certified One engine can drive both prop rotors. After digging into an old version of the V-22 flight manual, I find a whole pile of tables in the chapter that cover single engine flight. Gross weight and DA and flight configuration informs what the "best" airspeed is for single engine ...

13

This concern was one of the major design challenges in the development of tilt-rotor VTOL craft. In every flying example I'm aware of, it was solved one of two ways: either the engines were embedded in the fuselage and power was transmitted through a common gearbox (much like a twin engine helicopter), or the engines in the wingtip pods were connected with ...

7

In a way, this has been done already half a century ago. When NATO decided to try a VTOL strategy, the Harrier was not the only result. There was even a supersonic VTOL fighter, and it used swivelling engine pods at its wingtips, much like the V-22 does today. It was the VJ-101C, developed in Germany and first flown in 1963. VJ-101C in flight. Note the ...

6

There is a bit of a misnomer here, although the plane runs diesel engines it most likely does not run traditional diesel fuel as you would find at a gas station. Diesel engines can be run on Jet-A which is available far more widely than 100LL at airports outside the US which Ron mentions. There are even some applications for diesel engines in GA as noted ...

5

" However, two Osprey 38-foot rotors weigh 4,654 lbs (JANE's, 1998-9, p. 557.)" this quote is from http://www.freepatentsonline.com/8382030.html That would put the mass of a single V22 rotor at 1050 kg. The quoted source dates from 1998, so some improvements may have been made, but it is unclear to which parts of the rotor this refers, so it's only a ...

5

Well, engines and rotors obey the same laws regarding induced drag (induced power in this case) as wings: larger fan/propeller/rotor is more efficient, but limited to lower speeds. And from that, the advantages should be obvious: Tiltrotors (V-22, AW609) are only a little less efficient in hover than normal helicopters, but they can only go around 300 knots ...

5

The main reason V-22 uses propellers is efficiency. To get high thrust for power, you need to affect a lot of air and that requires a large propeller. The V-22 has huge propellers, closer to helicopter rotors than typical aircraft propellers. This gives it the static thrust-to-weight ratio of more than 2, so even with one engine out it still has more than 1 ...

5

Instead of having a set of contra-rotating proprotors on each side, if you're after decreasing the disk loading, a span increase would also do the trick, allowing wider proprotors. However the Wikipedia paragraph starts by saying: Due to the requirement for folding rotors... The main contributor to its less-than-ideal size is the folding requirement to ...

5

Fan shrouds are a fix for a problem that can normally be designed around in other, more efficient ways. They do reduce tip loses, but usually the tip loses are smaller than the weight and drag penalty of the shroud. The fundamentals of prop/fan/rotor design is that thrust is proportional to the increased momentum of the air flow, but the power required to ...

3

The purpose of the swashplate isn't to tilt the rotor head. It's to pitch each blade as it passes through various sectors of the disc. In a Stewart platform, both plates rotate at the same time. In a helicopter swashplate, the control plate stays stationary. Rotor blades pass over the stationary plate and sort of follow its profile in pitch. Tilting the ...

3

The cross shaft of the V-22 is normally unloaded. It only takes up the load if an engine fails, at which point everything continues as normal albeit with reduced power. Alternatively, if the shaft is damaged, but you've still got two good engines, the aircraft flies as normal because the shaft isn't being used anyway. On the CH-47, though, the shaft is ...

2

I would say that the complexities of tilting the entire wing are what compelled Bell to choose just the nacelles. By complexities, I am thinking 2 major systems. The first is the flights controls. Based on the how old that image looks, I suspect that aircraft want designed with a fly-by-wire flight controls system if it was even an option. That would be, in ...

2

Like Hobbes said. For instance, after take-off, tilt the thrust 10° forward. The cosine is 0.98 so you only lose 2% of propulsion lift. The sine is 0.17, so forward thrust is 0.17 * total thrust. The craft will speed up until aerodynamic drag = forward thrust: $$T = D = C_D \cdot \frac{1}{2} \cdot \rho \cdot V^2 \cdot S$$  V^2 = \frac{2 \cdot T}{C_D \...

2

Technically, if the tilt rotor flies forwards with vertical rotors, the lift is produced by the wings and forward thrust by the rotors. So let's regard the rotor thrust, whether in horizontal or vertical rotor position. Tilt of the rotor does not affect the amount of thrust produced. The following factors do: Rotor speed. This would remain pretty constant ...

1

Such an aircraft can't exist. Helicopters don't work with a single rotor, they need at least two of them to counter torque. There are several popular designs, including conventional, coaxial, intermeshing and tandem rotors. All tiltrotors operate as tandems in helicopter mode. It's the only setup where both rotors can be placed at the nose, tail or wings. ...

1

The lift of the wing is proportional with the square of the aircraft speed, see the lift formula. That tells you how much vertical thrust you need at each speed. The vertical thrust of the rotors depends on the cosine of the tilt angle, horizontal thrust depends on the sine. The horizontal thrust leads to the speed you can reach at that tilt angle, but ...

1

There is one disadvantage: it makes control dependent on engines running. This disadvantage effectively precludes using it on any aircraft carrying people. Usual requirement for a critical system, which controls are, is that the probability of fatal failure must be estimated to be less than $10^{-9}$ per hour of operation. There are simply no propulsion ...

1

To replace an effective technology, propose a better technology for that particular application. The Stewart platform (as shown) would add both weight and complexity, and therefore cost and potential performance limitations, to a function already accomplished with less weight and less complexity. As @Therac pointed out, tilting the rotor is not necessarily ...

1

In the case of those two particular aircraft: V-22 and XC142, the big difference is not in the fact that the engine nacelles rotate versus the entire wig, it is in the complexity of the propulsion design. The XC142 has conventional engines and props that rotate with the entire wing. The V-22 does not have conventional propellers. It has two cyclic pitch ...

1

Picture source Co-axial rotors are insanely complicated. The V-22 had to overcome many first time problems and is very complicated. Combine the two, and you'll have a bunch of weeping engineers and no product. On a co-axial rotor: Both the rotors need to have their individual swash plates being able to generate collective and cyclic inputs. But one ...

1

Is any reason that is obvious that smaller contra-rotating rotors wasn't adopted. Smaller contra-rotating rotors would not have higher efficiency! The efficiency of lift/thrust generation by propeller increases with the amount of air it affects. But when you put one rotor above another, they both affect the same air, so efficiency is not increased. Contra-...

1

Aircraft design is always the art of finding the right compromise. Even if a feature might promise to increase efficiency in some way, this may come at a great price. If your suggestion were to be implemented, the aircraft would go from having two rotors (which is already a high number) to four. I am not familiar with the specific design, however these are ...

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