Compound Helicopters

[46Driver]

A few months ago, we had the NHA conference down here in PCola. The Navy has awarded a multi-million contract to Piasecki to further study the compound helicopter concept. Anybody have any info or ideas on the subject? If this thing works, you will have near Osprey performance at a fraction of the cost.

[Dave Jackson]

Personally, I don't think the compound configuration is the answer. It seems inefficient to have the weight and drag of the wings during hover and then the drag of the rotor during fast forward flight.

Two concepts that appear interesting are; Stepniewski's Low Tip Speed Design Philosophy (http://www.unicopter.com/1093.html ) and Sikorsky's Reverse Velocity Rotorcraft (http://www.unicopter.com/1108.html#Sikorsky)

[ShyTorque]

To see one possible answer try:

http://pauldunn.dynip.com/aircraft/rotodyne

[Cyclic Hotline]

The YSH-60F is an H-60 modified with a Vectored-Thrust Ducted Propeller and some wings!

Piasecki YSH-60F story here (http://www.air-attack.com/vtdp.html)

Perhaps they'll call it the H-60 turbo, or the Seahawk GT. :)

Maybe you'll be flying one soon 46driver? :cool:

[46Driver]

I would love to see it - if it works on the H-60, then it should work on the H-53 and the AH-1 - that would be a drastic improvement to the helicopter fleet as a whole. As for the Osprey, I think NASA made it to the moon in less time and with less money than the Corps has sunk into the V-22.......

[46Driver]

Just wondering if anybody has heard anything new on Piasecki's compound helo (or anybody's elses for that matter.)

[NickLappos]

The story is not particularly new, it is as old as helicopters. The rehash of this concept (worked hard and long in the 50's and 60's) is a testament to the ability of Piasecki to get Congress to spring funds, not to the viability of the concept. Like the car that runs on water, the legend that some wonderous improvement is just right there, ready to incorporate, dies hard.

Don't expect the whole truth in a press release, gents! If it were true, the sky would be black with tilt rotors now, except for all those lift fan cars buzzing around making air traffic a nightmare!

Piasecki's machine will go faster, about 20 to 40 knots (cruise at 185K to 205K) but in the process will carry much less, and the result will be a loss of performance, as well as a significant loss of yaw control.

As a guy who flew some compound time above 230 knots cruise, let me toss some thoughts in:

The thruster is a dead weight at a hover, paid for by taking off the tail rotor and using those awful rudders in the slip stream to make some yaw control. This will result in a loss of about 1500 pounds of payload for the aircraft, all no longer available for fuel or pasengers. If the aircraft is held to the same yaw requirements of other military helos (35 knots side flight or more at all hover altitudes and weights) it will loose far more payload, perhaps as much as 50% of the helo it was carved from.

The balanced design will actually fly faster, carry less, and go about the same range as a helo, according to the lessons learned from the dozens of other compounds flown so far. It will not have better fatigue lives (not if it flies faster) and it will not cost less to operate (more parts).


the Pathfinder is in some trouble, read the article (http://www.aviationnow.com/content/ncof/ncf_n82.htm) carefully:

"HOWEVER, DIFFERING VIEWS regarding flight-clearance rules provided by the Navy in April are threatening to make the project more expensive than originally estimated, which could bring down the curtain before the program reaches flight test."

What that really says is that the Navy won't let it fly, because there are too many safety questions, and the contractor wants to bend the rules. The last time that outfit flew an experimental configuration for the Navy, they crashed and killed a test pilot, so the Navy is a bit gun shy.


http://avia.russian.ee/vertigo/sik_s-61f-r.html

http://avia.russian.ee/vertigo/sik_s-69-r.html

[SASless]

Nick,

At the Pratt and Whitney Plant in Florida where you did the testing of the S-69 nee ABC....and after the US Army flight test of the Tilt Rotor...now the V-22 and the ABC at Fort Rucker...did not the prevailing attitude there amongst the Sikorsky Test unit indicate to us that the ABC was a better choice than the Tilt Rotor? My memory tells me that the ABC Test guys felt they had better numbers than the Tilt Rotor and were let down about the results of the competition. Or is my senility playing tricks on me?

[Lu Zuckerman]

What Nick says is true if you make a direct comparison between the two aircraft. However, it is my understanding that the Pathfinder uses an existing airframe to prove the concept not to modify all of the Seahawks. But then again I have been wrong before


The Cheyenne was in fact a compound helicopter and although it had problems in the dynamic system it flew quite well with the propeller providing the thrust.

I personally believe that when you turn a helicopter into an Autogyro it takes on some of the bad characteristics of an Autogyro. That is when the wings are taking the load the main rotor is in low pitch. If the pilot moves the cyclic to maneuver the aircraft the advancing blade will go into negative pitch. The blades have a negative twist and with this twist the blades have a root angle of say seven degrees and the tip is at a neutral pitch. Movement of the controls when in Autogyro mode can result in disaster. IMHO.

:ooh:

[Dave_Jackson]

:D

Lu,

Your point is good, but might do with some elaboration.

Gyrocopters normally have around +1 degree of positive twist. This is because they are optimized for autorotation.

Helicopters designed for high speed have (or will have) reduced twist. The Sikorsky ABC blades had -10 degrees of twist and they said that this would be reduced to -8 degrees on a future blade, to improve high-speed performance.

The ideal solution is to have active blade twist, so that the advancing tip never goes into negative pitch.
___________________

Talking about gyros and fast forward; has anybody heard anything recently about the CarterCopter and it's attempt to break the 'mu' barrier?

[Spaced]

Cater Copter crashed during some flight tests. Busted it up pretty badly too. Landed with the gear up, rotors hit prop, wing hit ground. On their site they said they dont have the money to rebuild it, so they are looking for donations to get it back in the air.

[46Driver]

If I remember correctly, it was all pilot error - he simply forgot to put the gear down.

[NickLappos]

Sasless,
The ABC XH-59 was a great machine, with speed, maneuverability, efficiency and great handling, but it was a bit before its time. It also did not have the high speed cruise efficiency of the Tilt Rotor, so they really did not compete. The ABC is wonderously nimble and also a very high G machine, the Tilt Rotors are typically great at speed, but pretty lame at low speed maneuvering. The two types actually compliment each other.

[Spaced]

46Driver, yeh I read that too. But on their site they state that there was an emergency of sorts, and in the ensueing madness to put it on the ground, they forgot the gear.
From whats on their site it looks like they are grounded indefinately untill they get some $$$$$$$$