S-97 RAIDER first ground testing begins

Cool video shows the Raider test it's rotor assembly and tail pusher prop. Cool looking bird:

February 4, 2015 marks the start of bladed ground testing, a major milestone, for the S-97 RAIDER™ program. During the ground runs phase, the S-97 RAIDER team is testing the first of two aircraft prototypes as a completed system for the first time. The team will perform initial ground tests with the aircraft tied down and will focus on verifying correct operation of the propulsion system, drive train, rotor control system and pilot-vehicle interface.

a reply to: Sammamishman

Be interesting to see if they run into the problems that the CH-53K has run into. Nice to see the rotors turning though. Looks like she wants to go.

a reply to: Zaphod58

Yeah it is. I also noticed how quit it is compared to other helos. Most of the noise is from the turbines.

a reply to: Sammamishman

A lot of the noise from a helicopter, after they started bending the blade tips, comes from the tail rotor. This technically doesn't have a tail rotor (at least not in the conventional sense), and since the back blades are rotated 90 degrees to normal, that completely changes the noise signature it gives off.

This may be an ignorant question, but ... what sort of mechanism allows a single drive shaft to rotate two propellers in opposite directions? I'm just assuming it's a single drive shaft, maybe it's not. I'm sure someone here knows.

a reply to: newWorldSamurai

A planetary gear is the most common method. It's a gear within a gear that rotates in the opposite direction, creating a coaxial system.

Epicyclic gearing

a reply to: newWorldSamurai

Nested driveshafts, which are exactly as complex as they sound like they would be. It's why countra-rotating propellors are so rare in both marine and aviation applications despite their obvious advantages in terms of power.

The Soviets/Russians on the other hand seem to have had much better success with their countra-rotating gearboxes, which is why you saw countra-rotating props on more of their submarines as well as all of Kamov's helicopters.

For some reason, American helicopter designers have been especially averse to countra-rotating/coaxial rotorblades, which is why we ended up with the unusual tandem and intermeshing designs of Piasecki and Kaman, which existed almost solely as a means of getting most of the advantages of coaxial rotors without requiring that damned gearbox.

a reply to: Zaphod58

Hey, thanks for the knowledge transfer. Makes sense on a basic level. There's a certain genius in a simple design. Like a differential.

a reply to: Barnalby

Thanks. That definitely seems like a more sophisticated design. I would think weight might be an issue being that you have a wrap an already heavy drive shaft with another one. Specifically with something that is supposed to fly.

Sometimes I'm amazed by the fact that we're not speaking Russian right now. They were so good at so many thing during the cold war era.

a reply to: newWorldSamurai

The advantage of it, with a normal helicopter, is that you don't have a tail rotor, or the associated drive train, hydraulics, etc. The tail rotor causes a number of problems, and has led to many crashes. The disadvantage is in the associated complexity, and increased failure points.

a reply to: Zaphod58

I take it the tail rotor pushes air rearward of the Raider?

If so, that would mean that the majority of the sound from its turning would be issued rearward, and that has to be helpful in terms of not letting everyone forward of its location, know that it is coming.

a reply to: TrueBrit

It's a pusher prop, instead of a counter torque prop like a normal tail rotor. It will give it a much higher top speed than a regular configuration.

a reply to: newWorldSamurai

Counter rotation also cancels out torque, meaning the body isn't trying to rotate in the opposite direction to the way the engine is turning like on a conventional helo. This was also the reason why, once the spitfire evolved into the Seafire 45, with that massive Griffon engine shoehorned into the tiny Spitfire airframe, the Royal Navy fitted them all with contraprops to simplify carrier take offs and landings. It improved handling immensely.

Just curious. Since when did they allow prisoners from Gitmo to be ground crew?

Sorry for the thread drift, I just had to go there with the orange flight suits.

But I do hope this thing is successful. Looks pretty bad ass to me.

a reply to: Zaphod58

Indeed.

So, just to get this straight in my head, a regular chopper requires a counter torque rotor at the rear, to counter the effects of the spinning main rotor, and stop the chopper from beginning to spin itself? I take it then that the configuration of the dual rotor atop the Raider makes this unnecessary, and so the push rotor can be tasked for extra speed, rather than as a main source of stability for the craft?

This should be much easier to stealth out shouldn't it?

a reply to: TrueBrit

Exactly. The main rotor causes so much torque that the fuselage would spin opposite the main rotor, without a counter torque source. If you notice with the counter rotating blades, they're spinning in opposite directions to each other. That counters the torque of a single rotor system. This design doesn't need a tail rotor at all, but Sikorsky went with a pusher prop, that acts like the propeller on an aircraft, to increase the top speed.

The Sikorsky X2, that the Raider is designed off had a top speed of 259 mph, using this design. The FAI world speed record was set by a Lynx at 249 mph. This design is also more stable, as the tail rotor gives you a little wobble when used. That's one reason that the NOTAR design, that used air instead of a tail rotor was incredibly stable.

a reply to: cavtrooper7

No. The main source of RCS on a helicopter is the main rotor. It's essentially a huge solid object to radar.

a reply to: Zaphod58

I am interested to know, how different control of this chopper would be, from a regular configuration.

As I understand it, forward thrust in most choppers, is achieved by tilting the main rotor so that as well as lifting the craft, it provides forward momentum. This leads to some choppers appearing to go around with their noses somewhat tilted downward when at full speed.

I take it that with forward thrust being provided by the tail on the Raider, that the necessity for that is either reduced or eliminated, but I would love to know what the difference in handling is, aside from the obvious stability improvement.

a reply to: TrueBrit

Huge from what I hear. The X-2 was a pilot's dream from what I've read about it. The X2 had a fly-by-wire flight control system, and was capable of a 10,000 foot hover out of ground effect at 95 degrees, which is huge, as well as a 220 knot (253 mph) cruising speed.

The S-97 will contain hub drag reduction, active vibration control, fly-by-wire, and an integrated auxiliary propulsion system. The NOTAR revolutionized helicopters compared to the traditional designs. The Raider is like comparing the Wright Flyer to a jet aircraft.