XSH-60B Thruster
 

Sorry, should have been specific:

What I meant was to ask if anyone knew what the design requirements for the thruster were in terms of directional control power, directional manuever capability or standard, and the like.

Thanks,
John Dixson

Gravimanhttp://www.unicopter.com/1507.jpg
Consider the downwash on this as compared to the downwash from the retreating blades on an ABC Intermeshing or Interleaving.

Who has to design an extra g/box and d/shaft?
________________

Nick,Are you suggesting more KoolAid?
Perhaps the 'Jim Jones' brand. ;)

To get simple about the 1st post;
If Sikorsky (your company) did provide "a 500-hp tail rotor" (safety, durability and strength factors on top of this), one must assume that they felt that the tail rotor could, or would, be operating at near to this 500-hp, on occasion. At these times will not the tail-rotor be drawing 15.5% of the maximum total power?

Dave asked, " To get simple about the 1st post;
If Sikorsky (your company) did provide "a 500-hp tail rotor" (safety, durability and strength factors on top of this), one must assume that they felt that the tail rotor could, or would, be operating at near to this 500-hp, on occasion. At these times will not the tail-rotor be drawing 15.5% of the maximum total power?"

The simple answer is, Yes, as I have repeatedly said, the TR can consume 500HP on occasion, but that the aircraft sees no loss in performance when the TR consumes that power, since the total aircraft (that is the big greasy thing ahead of the tail rotor, Dave) uses LESS TOTAL POWER when the TR is consuming 550 HP, since the main rotor is consuming far less than the increase in the tail power. Therefore, the aircraft carries the SAME PAYLOAD as it does otherwise. Therefore, your belief that there is a 500HP "tail rotor penalty" is bogus.

No wonder nothing you have ever designed has flown! Are you always this thick, or is it something you practice just to get me going?

On these occasions the twin main-rotors also use LESS TOTAL POWER, without having to power a tail-rotor.

Aw Nick that's not fair. When one starts attacking the individual it is usually a sign that they are no long able to attack the topic.


There are many technical reasons why the single rotor should never have become the predominant configuration. However, for a non-technical perspective, here are a couple of selections from the book by William Hunt, Igor's designer and project leader for the XR-4 and XR-5.

• "By the mid 1930's Europe was more advanced in helicopter development than the USA. However, the European models that enjoyed initial success were all multi-rotor types: ....... Not one successful single-main-rotor helicopter existed anywhere. It was just the type of challenge that Igor Sikorsky needed to reactivate his thoughts regarding aircraft that did not need running takeoffs and landings."
• "Another of Igor's talents was his ability to 'sell' his ideas to others." Apostrophes by William Hunt.

http://www.unicopter.com/confused.gif http://www.unicopter.com/confused.gif Is William Hunt saying 'The single rotor became predominant because it was a challenge to do something different, then sell like hell'?

• "1938:-- [Young] Impressed by Igor Sikorsky's film, he concentrates on main rotor/antitorque tail rotor configurations."

Quite naturally, you have a strong bias toward Sikorsky. I would prefer to trust the 'neutral' rotorcraft aerodynamicists. IMHO, Igor took rotorcraft down the wrong road 60 years ago.


Dave

Except that in a Chinook, if you fly side on, you will have to increase power to fly at the same speed because of the huge drag. I'm also guessing even your sleek designs will suffer a bit in this way.

soupisgoodfood,

Theperformance is measured where it is worst, and that establishes the WAT (weight, altitude, temperature) curve in the flight manual. For virtually all designs, that is a still air hover. Once the weight to hover in still air is published on the chart, that becomes what you can legally (and practically) carry.
Were there to be a helo that lost performance in some other mode (imagine one where a moderate hover turn, or cyclic acceleration cost 200 pounds of performance) then that other maneuver state would become the basis of the wat curve. A few Bell helicopters are limited by tail rotor authority and not main rotor hover performance, and for these, the wat curve is "penalized" a few hundred pounds.
For the case where a Chinook (or an S76) has high fuselage drag at 50 knots sideward flight (which is identical to a steady hover in a 50 knot crosswind) if that were a "typical" mission maneuver, the FAA might check that no big performance loss was occurring, and if so, it would have the charts marked accordingly so the pilot would not get in trouble. That is why wat curves have adjustments for doors open, anti-ice on, or other performance changes.

Dave, every helicopter manufacturer in Europe now uses the single main rotor and single tail rotor configuration. If there was a performance disadvantage over symetrical layouts, other than retreating blade at speed, it would have been abandoned by now.

In the real world: how much power is lost in the Kmax from blade vortex interaction through lower blade tip? It must be pretty noisy.

Trivia:

Someone once mentioned that to minimize vibration the Chinooks flew sideways when aircraft were taking off and landing on aircraft carriers. The combined speed of the carrier and the head wind would probably be around 50 kts.


Graviman,

A response to your first paragraph:

Can you please show me any research work that has been done on the pros & cons of symmetrical configurations over the past 60 years?

If not, could this be the reason? Bilateral Symmetry

A response to your second paragraph:

Why will the "lower blade tip" on the Kmax rotor configuration experience more blade vortex interaction than that of any other 2-blade rotor?


Dave

to Grav's point, over 95% of the helos ever built have a single main rotor and a tail rotor.

That means either that the single MR with TR is the reasonably best configuration, or 95% of all helo designers know less than Dave. I wonder which is right.....

Tandem Rotor Note
 

Hi Nick . Guess no one has any info re the Piasecki Seahawk's directional controllability spec, maybe because there is none to be had?

Just for fun ( well not quite "just" ), here is a tandem rotor anecdote with a strong subliminal message:

Just out of flight school in 1963, I was able to convince a pilot at the Test Board down at Ft Rucker to check me out in our one and only CH-21C. he had just returned from a tour in the Mekong Delta flying H-21's with the 121st Trans. Co. I think it was.

Anyway he showed me a technique to get that machine to climb when the trees were getting bigger in your windscreen and there wasn't any additional power to be had. On takeoff, he had me accelerate to 60 kts or so at about 40-50 ft altitude, stabilize there, then advising to lock the collective in position. There was a tree line at the edge of this stage field and as we were getting ready to make a hole in it, he told me to ease in some left pedal, thus getting the rear rotor out from under the downwash of the forward rotor. Magic; we climbed over the tree line with ease.

Here, John, look at time :47 to :59 and note that there is FULL rudder deflection in a gentle hover turn, as well as a normal landing. I think the yaw control is near nil.
Note later in the flick that the nose is going over fairly rapidly - not enough stabilizer.

I don't know what they were shooting for in yaw control, but I can see what they ended up with!

http://www.youtube.com/watch?v=Q5ihDwz5l7s

Regarding the tandem's power losses that you can cure with a 90 sideslip, Mark Vineberg of the Mil Bureau always told me the "Vantikeryl" (sp??) was the best configuration - a side by side tandem. He said the rotor interference was non-existent. Kamove built one once:
http://avia.russian.ee/vertigo/ka-22-r.html



http://www.aviation.ru/Ka/Ka-22.jpg

Nick says; And, you know for a fact that these are the only two options?


I previously asked the reasonable question; This question is still awaiting an answer.


The only two evaluations of the intermeshing helicopter that I know of, are;

The Prewitt Aircraft Company;

• In 1948, the Prewitt Aircraft Company, a U.S. company with no reason for bias, evaluated and conducted twenty hours of flight-testing on one of the two remaining Nazi Flettner-282s. "The performance of the helicopter was found to be very high, ...".
• In addition, Prewitt recommended "That all eligible and interested helicopter organizations be permitted to have their pilots fly this helicopter." Prewitt's grandson mentioned that he did not know of any US helicopter company that took up this offer to fly the craft.
• This is additional information from my copy of Prewitts 146 page report.

The Rotorcraft Aerodynamicist W.Z. Stepniewski has done comparative analysis of the;

• The Single rotor, Winged helicopter and Tandem evaluations, which are in his published book.
• The Cold-jet-driven, Single rotor and Synchropter w/ ABC comparisons, which are hand-typed with additional hand-written information, probably in preparation for publication. Stepniewski's conclusion was that the Synchropter-ABC was best.
• This is the public information about this (previously?) unpublished material.

Nick, come to think about it, you may be correct. I possibly do know more about bilateral configured rotorcraft than 95% of the helo designers.

Thank you for the recognition. http://www.unicopter.com/RollLaugh_2.gif

Dave

Ya know I wonder how it would compare if one were to use Sikorsky's old idea of the swiveling tail rotor like on the H3 prototype, on the Blackhawk. You could have all your tail rotor control bennefits and turn that 500HP tail rotor into a pusher prop! Of course to get the best of it you would still have to have the stub wings which is a downer in the hover but obviously that doesn't seem to be slowing anyone down from spending money on the speedhawk program.

Max

tail rotor Power consumption
 

Tailrotors only draw power when they are being utilised.
Ie highest demand would be high power setting, High temp/alt, zero speed, opposing a crosswind.

Lowest demand would be high forward speed, tail rotor is just along for the ride and you could quite happily do without the thing completely (until you want to slow down or hover!!

Piasecki XSH-60B
 

"Wow", was my reaction to the video and the thruster exhaust vane angle for a very gentle turn indeed!

Can't you see that machine trying to fly tethered hover performance data? Hope the test pilot is good at maintaining situational awareness while performing a tethered corkscrew manuever.

Chalk Wars
 

Would there be a compressability issue with a full deflection at a slower IAS vs inducted air?

Thinking...wondering...
Just considering if there would be more response at a lesser rudder angle when the forward induced air speed is less?

Is there lift lost due to the loss of the tilted anti torque rotor?

HF

Helofan, it is just difficult to get the air to change direction 90 degrees in the Speed Hawk. The thruster vane is a compromise which ideally does nothing in forward flight, but magically revectors the air at slow airspeed. More parts/mass might help, but then so would a tail rotor.

They might consider cyclic control of the tail fan, as well as collective thust. This would improve the situation, but would still suffer in hover due to low mass flow of air.


Because at 90' and 270' azimuth the vortex shed form the "upper" blade will impact the "lower" blade away from the tip. This means the tip design must be a compromise to avoid excessive drag from vortex messing up the local flow. There will also be audible blade slap.

No one in Europe has done any recent research on lateral symmetry, AFAIK. If you are only considering a cruise of say 165kts then the expense of extra drivetrain/structure mass/cost would put most engineers off. I just don't think the performance benefits are high enough to tempt any one. The increase in popularity of fenestron designs demonstrates this point.

The fact that Stepniewski is discussing ABC means he is considering high speed. That is a different ball game, and the standard has to be against X2.

John,

When I saw the video and looked at it, I wonder if the thruster vane angle is connected to the pedals, or scheduled with airspeed. One means of control would be to have the vanes hard over, and the half-cover thing on the duct, and vary thrust of the propeller in proportion with pedal position. I would still come to the conclusion that yaw power is weak. You can't beat a good tail rotor for yaw control.

-- IFMU

Hydraulic tail rotor drive
 

Instead of a mechanical drive on a "standard" tail rotor g/box, why not have a variable output pump servo controlled or PLC to a hydraulic motor?

There might be more power consumption?

Is it more or less reliable/costly even if it was a component c/o based on hours?

Always wondered.

Hmm can it be poissible to have a hydraulic system be in back up of a mechanical drive?

HF.... back to the bar?

helofan,

Typical hydraulic drives are not very power efficient, they waste about 10% of the power that they transmit, but they are great at putting precise amounts of power on demand in odd places, such as servos and landing gear.

The shaft systems employed for tail rotors are very efficient, usually consuming perhaps 1.5% of the power they transmit (mostly in the gear boxes.)

The rudder in the fan wash of the X-49 does show how marginal the control is, I noted that the rudder slews almost full angle as the aircraft gently accelerates to a side speed of perhaps 10 to 15 knots, in a gentle yaw turn that is perhaps 1/4 the rate needed for operational use, and also when the aircraft settles into a gentle hover from an approach. Since the baseline Hawk family can easily go 40 to 50 knots sideward, this represents a stunning loss of yaw control margin for the Pathfinder.

I also note the extra inertia in the tail upsets the control harmony, note the overcontrolling in pitch in hover liftoff and also during the entry to the "high-is" speed runs. Shows that the pitch sas is wallowing, probably because the pitch axis sas gains are too low for the extra pitch inertia. Also says hat removal of the stabilator and replacement with the ring is not entirely satisfactory. My guess is a full mil qual of the pitch axis HQ would leave something to be desired.

Also, the "177 knots in a slight dive" shows what had been guessed, the drag and weight of the fan assembly probably cost most of whatever advantage the propulsor gives as extra speed. A normal Hawk at 19000 pounds has a max level speed with full engine power of about 156 knots, a slight dive easily gives 170. Ripping the aircraft apart for 7 knots isn't a game-changer.

So far, I would rate the X-49 as a valiant attempt, but little proven. Yaw control = D, pitch control = C, Speed = C-

That being said, hats off to the Piasecki group for doing something, at a time when most R+D is done with Power Point and laser pointers.