That's not a bad price compared to UK rates. Equates to GBP 175 /hr, some places in the UK charge up to and over GBP 200/hr (CAD 450/hr).

You just need to remember how worthless our dollar is.

Re Jed A1's comment,

I have never seen R22 hire in the UK at over £200 ph, dual instruction is normally around that figure excluding VAT, but self fly hire is normally £130-£140 exc VAT.

are we sure we are not comparing applies and pears here!

If a *much* easier-to-fly helicopter, could be built.

1/ Then more people would get a pilot's license, for this helicopter.

2/ Then more people would rent and buy, this helicopter.

3/ Then there would be larger production runs, of this helicopter.

4/ Then the price would come down, for this helicopter.

5/ Go back to 1/ :eek: and repeat.


Just a dream. :) http://www.UniCopter.com

[ 04 September 2001: Message edited by: Dave Jackson ]

Well the kiwi and ozzie dollar are 40% and 30% more worthless than the Canadian right now. In Taupo NZ you can get a R22 + 17000hr instructor for $350hr....and thats pricey.
On the east coast of OZ you can can expect to pay around 300 - 330hr.
The cost of aviation downunder is substancially greater with the increased distance from the USA. It doesn't stack up.

Dissymmetry of Lift & Robinson
 

The subject of Dissymmetry of Lift has been brought up a number of times over the last few months. For the fun of it, I presumptuously claim that in forward flight, there is no such thing as symmetry of lift and therefore the phrase 'Dissymmetry of Lift' is without meaning.

This argumentative position has been put on the web page http://www.unicopter.com/0994.html because of the sketches.

I also feel that this may (or may not :eek :) have relevancy to the Robinson rotor head.

To: Dave Jackson

Hopefully Nick Lappos is on holiday and he won’t read this. If you look at the problem as you have defined it you are probably correct. However you have overlooked a few things. In order for a helicopter to fly in a stable state once cyclic input has been made there must be no dissymetry of lift. If the pilot makes a change in cyclic input he will create a dissymetry of lift and depending on your point of view or where you live the disc will move to the commanded position due to either aerodynamic precession or, gyroscopic precession. Once the disc arrives at the new commanded point the system has equal lift distribution across the disc.

The only time dissymetry of lift comes into play where the pilot did not command it is during transitional flight during speeds from 0 to 20+ knots. This can result in transverse flow effect and blowback (flapback) with both conditions being corrected by input on the cyclic. Once the helicopter reaches the desired forward speed the lift distribution across the disc is equal.

Two things allow this to happen. One is that the blades have a negative twist, which equalizes the lift distribution across the blade span. The second thing is the introduction of cyclic pitch. In order for the helicopter to fly forward, the pilot will decrease the pitch in the advancing blade and increase the pitch in the retreating blade. Although the induced relative wind is higher on the advancing blade the blade has decreased in pitch. The retreating blade induced relative wind is less but the pitch on the retreating blade is higher. If the helicopter is in a stable speed and direction and the pilot makes a change in cyclic position the respective pitch changes will be input and at that time there is a lift differential. I believe that this creates a lift differential across the disc and results in a perturbation of the rotating disc and gyroscopic precession moves the disc. Other people believe it is aerodynamic precession but in either case the disc will move to the commanded position. Another thing to consider is flapping and the delta hinge effect. When the blade flaps up for any reason the delta hinge effect will reduce the blade pitch and counter the upward movement of the blade. The opposite is true when the blade flaps down.

I don’t know if this adds to your argument or not but it is my story and I’m sticking with it.

To Lu:

>Once the disc arrives at the new commanded point, the system has equal lift distribution across the disc.

This is the very position that I am arguing against. The following is a summation of this argument.

1 To negate roll; the CCW moment of the advancing blade must equal the CW moment of the retreating blade.
2/ Moment = lift x arm length.
3/ The center of lift is closer to the teetering hinge on an advancing blade then it is on a retreating blade.
4/ Since the arm length is less on the advancing blade, this blade's amount of lift must be greater.

In other words - There must be equal (but opposite) moments on the advancing and the retreating sides of the disk, and therefore there cannot be equal lift on the advancing and retreating sides.

Lu: Don't you just love Robinsons?!!

"depending on your point of view or where you live"

I think that's quite funny! :D

Here we go again.

My contribution will be limited this time, firstly to point out that angle of attack is affected by changes in relative airflow and blade pitch angle is only one factor determining angle of attack. A blade experiences a whole range of relative airflows across its span, even before its helicopter moves into forward flight. A standard vector diagram explains this.

As Lu pointed out, modern blades are usually built to include washout but this is towards equalising lift along the length of the blade. It is NOT done for any reason connected with symmetry of lift across the rotor disc.

Have fun but don't upset the moderators, eh?

p.s. Without symmetry of lift across the disc the aircraft would roll over, as Cierva discovered many years ago. We now have the luxury of flapping hinges to allow symmetry of lift to occur.

[ 30 October 2001: Message edited by: ShyTorque ]

Dave,
You are of course right, but only because we actively balance the lift with cyclic, and some rotors help as well with flapping to relieve the differences in lift.

The term is useful in understanding what the aerodynamic environment is as the aircraft moves into forward flight. :D

To: Dave Jackson

If there were in fact greater lift on the advancing blade as opposed to the lift on the retreating blade you would have a problem. One response indicated that the helicopter would roll to the left, which is partially true. The situation you describe is akin to retreating blade stall. I am about to say what might incur the wrath of many of the participants on these threads but the helicopter would tend to roll left but immediately thereafter, the disc would blow back just like in retreating blade stall. The aerodynamic reaction would be to roll left but the physical rules in effect would cause the disc to flap back due to gyroscopic precession or if you use the terms G’day or bloke the movement is caused by aerodynamic precession.

Aw Nick; Your agreement has stopped any chance for a good argument :) ; except from Lu, of course.

Just joking Lu.

------------------------------

To Lu:

An analogy is that of a 200-pound father and his 50-pound son on a seesaw (teeter-totter). The weight on the father's side will be greater then the weight on the son's side, but the seesaw will be in equilibrium because the father is sitting closer to the teetering point.

Nick has correctly inferred that the above analogy is only part of the story, since a rotor system is not as rigid as the plank on a seesaw.

To> Dave Jackson

“An analogy is that of a 200-pound father and his 50-pound son on a seesaw (teeter-totter). The weight on the father's side will be greater then the weight on the son's side, but the seesaw will be in equilibrium because the father is sitting closer to the teetering point”.

Which argument are you making? Is there a differential of lift across the disc, which results in a stable disc as, described above or is there a differential of lift that has an aerodynamic reaction which in turn perturbs the disc and results in a change in disc position? In your argument in order for the disc to be commanded to a new position the father must either move closer to or, further away from the teeter position. This movement would be analogous to cyclic input. Once the disc has become stable in space or to use a technical term rigid in space other than gusting loads the only way the disc can be moved is by the input of cyclic control.

The basic tenant of helicopter design is to have an equalization of lift across the disc. The way I learned it this was accomplished by the application of cyclic control, which decreased the pitch on the advancing blade and increasing pitch on the retreating blade. Initially this differential of pitch across the disc would cause the disc to move by either gyroscopic forces or aerodynamic forces. Once the disc is in the commanded position the differential in pitch across the disc will compensate for the differential in the induced relative wind thus making the disc stable.

To be continued.

To Lu;

> Which argument are you making? Is there a differential of lift across the disc, which results in a stable disc ....<

Yes!

A helicopter in forward flight and with no perturbation will be experiencing slightly more 'lift' on its advancing blade then the 'lift' it is experiencing on its retreating blade. The reason that the disk does not tip to the left is that the 'center of lift' on the retreating blade is further from the teetering hinge then is the 'center of lift' on the advancing blade.

The difference in the two distances is the crux of this argument, and this difference can be seen in Figures 5 & 6 on http://www.unicopter.com/0994.html
_______________________

Going back to the seesaw analogy;
The moment of the father is 200 lbs x 2 feet = 400 lb-ft.
The moment of the child is 50 lbs x 8 feet = 400 lb-ft
In other words; the moment on each side is equal but the weight (or lift - in the case of the helicopter) is not.

Therefore to be absolutely precise;- 'Symmetry of Moment' not 'Symmetry of Lift'. :eek:

I seem to remember seeing video of a Helo with just one rotor blade and a dirty great big counter weight on the other side! How does that fit in with all this? :D

Carb icing caused R22 crash
 

And, take note Lu, no mention by the AAIB of 18 degree offset being a factor! ;)

Just oldfashioned carb icing which is a universal problem with piston engines, in fixedwing as well as rotary.

With deepest, deepest respect and sympathy to those involved.

I'd rather be in an Enstrom anytime. Fuel Injection, high inertia rotor and more substantial cabin and skid structure.

P.S. Knowing somebody involved in this accident I know how upsetting this has been. Please don't take my comments as being callous, that is not how they are meant. I'm just pointing out the merits of a safer (in my opinion) machine.

Note the possible role of carb heat assist in all this.

Real nuisance - the control's never where you left it, and it may have a tendency to lull you into not checking the carb heat continuously and actively. Especially a problem when it is fitted only to some aircraft.

Sad sad incident :(