Rotor rpm in a hard turn?

Since the audible phenomena I think of as 'blade slapping' tends to occur during tight turns, is this a direct result of loading up the blades?

Guys it's not the RPM of the rotor that's important, it's the tip speed of any given rotor that is important. With Dragon wings, it is important to keep the tip speed out of the high sub Mach numbers.

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Since the audible phenomena I think of as 'blade slapping' tends to occur during tight turns, is this a direct result of loading up the blades?
The sound comes from each blade chopn the others wake in an area of the disc thats 'helicoptering' through oversped.
IOW, its AFTER theyv been loaded, and they are spin'n back to normal rpm.
You can make them wop at a constant load, but its abit more involved than just loadn and unloadn.

Ernie thank you for your note of caution with Dragon Wings. A question if I may.

With my Dw's in straight and level at my anticipated max AUW of 620lbs (lowest with 1gall remaining would be 566lbs) at 500' with 23'DW's I would expect to be getting a rotor RPM of approx 373 RRPM, a tip speed of 450 ft/sec and a disc loading of 1.49.

This is a reasonably high RRPM, (because I am at gross weight). If I were then to enter a steepening turn and begin loading the rotors I would expect to see an increase in RRPM as the perceived AUW (as seen by the rotors) increases.

At what point (RRPM wise) am I beginning to venture into the danger zone ie the high sub Mach numbers you are talking about?

I begin this question at my expected nominal max AUW (at low level of 500') because I want to try to define what will be at the edge of my proposed test envelope for my particular gyro. We presently have an empty weight of 350lbs, I weigh 210lbs, and I have a fuel capacity of 10 galls

Later I would wish to explore/define the safe envelope at higher altitudes.

I certainly do not wish to be yanking and banking at the higher gross weights as one would only be up there if you wanted to go cruising/cross country and needed the extra fuel/range, however it does help to know where the gyro's limits are whatever the configuration of the gyro.

Thanks Birdy. I do not hear it myself with the helmet and earphones on, but have been told about it by others after I have been doing maneuvering which involves steep turns.

At present on the Bensen here in England I do not have a rotor tach. I do on the Hornet in the US however it was not working the last time I was out there.

I intend to be doing some flying on the Hornet and hopefully will have it working when I get back over there trying to work out all my speeds and safe envelope.

Well, that'd be around mach .6 At the 130'ASL I was at. If numbers are right I fly at 575lbs., and at 540rrpm I loaded the rotor by 2.275g's. So, not a high mach number.

To get to mach .75 on a 23' set would be 670rrpm and a load weight of 2011lbs. Which, would be a 23' set with a AUW of 665lbs pulling 3g's.

Probably be safe to say, the chances of that are slim.

OK Phil so at my AU weight I would have to well up towards 670 rrpm to be approaching any sort of danger area, if I read you correctly?

3.25g's at your AUW Leigh, and that's just to get to mach .75, in the 550mph range. Different airfoils experience compressibilty at different speeds, but most are in the upper 500's. I've never pulled as much load as Saturday and that was a mistake. I can't imagine how to sustain more than 2g's without outside influence. The pull of the rotor, as I came out of the updraft, was enormous. To get 1.5 times that for 3g's, you'd have to pull up into a tornado.

Im pretty sure the rotor 'falls through' long before you get to 3Gs.

Sorry Birdy, not familiar with that expression.

What do you mean by the rotor 'falls through'?

Hi leigh

Not exactly sure this is what Birdy means, but as I view it, it would be like a jet intering a max performance turn at such great speed it goes into a high speed stall, or in other words is pulling so many G's it loose "traction" or lift and "falls through"

Tony

Air compressablilty means you can only exert only so much load ona rotor before it falls through with quick cyclic changes.

High speed stall, or where one has exceeded the ability of airflow to maintain it's path over the airfoil and it separates breaking down lift.

I buy that, it is routinely demonstrated that the stall speed increases in a steeply banked turn, and when loading the rotors in a turn that is exactly what one is doing. In a fixed wing aircraft we can calculate the stall speed using angle of bank and AUW.

With Dragon wings, it is important to keep the tip speed out of the high sub Mach numbers.

Click to expand...

Since rotor RPM is directly linked to this I go back to my origional question to Ernie, is there an approximate rotor RPM that indicate where the Dragon Wings are approaching this danger zone, or tip speed to be used as a limit? The rotor performance chart will allow us to calculate this if we knew an approximate tip speed where the problem begins to become apparent and this would vary with rotor diameter and weight.