Maximum Load Factor on the rotor head.

[Focha]

Hi there,

Can someone tell me what is the maximum load factor on the rotor head of a R-22 and R-44?

Best regards.

[Shawn Coyle]

What kind of load factor- positive G in vertical sense, rolling G?
There are a whole laundry list of loads that the rotor head has to take care of. If you can be more specific, it would help. And are you talking about limit loads, continuous loads, design loads or demonstrated loads or something else?

[[email protected]]

Focha - why, are you planning to loop it??

[500e]

Perhaps he is just thinking of flying one

[lelebebbel]

i've seen plenty of loaded rotorheads. How do you define maximum? ?

[Ascend Charlie]

Ask Nick, but you will probably find that 2.7 is the minimum certifiable. That allows for a level 60 degree turn, plus turbulence, plus a fudge factor.

Then you move up to the BK head where you can pull 3.1 under normal conditions, so the stress level must be over 4 and a bit.

[topendtorque]

Or you could resource some photographs of blades torn, and machinery bent, even life's fragility more than tested;
then ask yourself why on earth would I want to push it, the weight that is, further than what it says , in the book at your feet.
cheeres tet

[mikelimapapa]

Well I can tell you its more than 3Gs in the R-44.......I set off the ELT the other day doing a cyclic climb trying to impress some young students. Not the smartest thing I've ever done, took a second to figure out what that damn noise was

[Heli-Ice]

I was wondering the same for the Schweizer 300C.

Not that I am planning on looping or taking it to its G limits, just that it would be a nice to know figure.

In most aeroplane AFM's the G limits are stated but I have to admit that I haven't seen it in the 300C's RFM. Maybe it is because my eyesight is getting worse from bad

[Focha]

Hi there guys,

Thank you guys for your comments. I'm interested in the positive/negative Gz loads (n=L/W).

Regards.

[[email protected]]

I can't imagine an R22 has enough power to do a level 60 degree turn (2G) at constant speed

However it is not the G at the rotor head that is important, it is the stress felt at the end of the long lever which is the tail boom that is critical - the rotor head drags the fuselage behind it which drags the tail boom and the TRGB and TR. Your rotor system may be capable if producing high loadings with little damage to the rotor but it is the rest of the aircraft you have to worry about.

All the engineering penalties for display manoeuvres on the Lynx took life off the TR and its components - not the MRH.

[Focha]

So you are saying that the most critical parts subjected to stress in a helicopter are TR, TRGB and tail boom? But the most critical part subject to load factors it's the MRH, what I'm saying is that it's the MRH that has to be resistant enough to be punished with all the stress made by the helicopter since it's the MRH that is attaching the RB to the helicopter fuselage. What you are saying is that what limits the stress on the helicopter it's not the MRH but other components?

Best regards and thank you for the help.

[[email protected]]

Focha - no, I'm just saying that unlike a fixed wing where the maximum G loading is based on the strength of the wing/fuselage mounting so excessive G will deform or crack the wings before anything else falls off - on a helicopter you will cause damage to other parts of the aircraft before you get to the point when the rotor rips itself away from the fuselage.

Helicopter fatigue is much more complicated than FW because of all the rotating components and is not simply predicated on the number of cycles of specific G.

[GoodGrief]

When I remember correctly, the max load factor for "normal" category helicopters is 3.3G.

[Pofman]

Max load factor on head.

Certification Specifications for Small rotorcraft - CS 27

CS 27 337 limit manoeuvring load factor = +3.5G to - 1G with a built in safety factor of 1.5.

Obviously could be greater but then heavier and more costly.

When you know that the blade loading at 1G on the 300CBi is 77.29 lb/ square ft then 3.5 x77.29 = 231.87 lb/square ft is asking a lot of the blades and their attachments. Fortunately this can only be maintained for a very short time due to the lack of power.
However,think of your mate who will fly it in a few weeks time!

[VfrpilotPB/2]

Sadly I have flown a R22 that had been overstressed, but the young Fi hadnt remembered to write it up??!!, so I found out the hard way, I endured one of the shortest and most nerve wracked flight in my life thus far, but being a cool dude I didnt throw up or fling my teddy out the cot until after I had landed and changed ma trews! I have not flown a R22 since!

Peter R-B
Vfr

[Droopystop]

So you are tasked with designing the limiting component in the rotor head. You do your maths and determine the maximum load the part is going to see (the design load). You then have to work out how big (and out of what material) to make the bit thereby determine the stress. What is the safety factor used or required by certification authourities?

[Focha]

Hi guys,

Thank you a lot for you knowledge on this one.

@ [email protected] - I understand that, still what I am affirming is that the MR is designed to withstand stress greater than the stress that other components withstand, is my statement correct?

@ Pofman ; @ Droopystop - Droopystop I think what Pofman replied is the requirements for the certification specifications for small rotorcrafts although I don't know the definition of a small rotorcraft, is it max of 3 175 kg (7 000 lbs) and/or less than 9 seats? Is small equal to light? If so than a lot of rotorcrafts are in this class. For example AS 350, so by this required specifications, this means that AS 350 is able to withstand at least +3.5G and -1G? So I guess it's all proporcional to the forces, since the R-22 for example it's in the small rotorcraft category too, it looks more fragile than AS 350, but because it generate less magnitude of forces (less W, less moment, less L, etc) it's able to withstand the same +3.5G and -1G as the AS 350, is my thinking correct?

So, is it correct to say that R-22 is able to withstand +3.5G and -1G (of course just talking about load factors and also not in normal flight conditions)?

Another thing is that, correct me if I am wrong, if you are banked 60º your L has to be 2 times you W to maintain the helicopter at the same altitude (L=W), as n=L/W, in this case n=2L/W, you have n=2G. So is it correct to say that in a 60º turn you have twice the Gs you have in level flight? If so if you pull the cyclic back how easy would you reach the +3.5G?

Best regards to all and thank you for the knowledge.

[[email protected]]

Focha -

I understand that, still what I am affirming is that the MR is designed to withstand stress greater than the stress that other components withstand, is my statement correct?

I am not a helicopter designer but it is the major component of the aircraft so the answer is probably yes.

As far as G loading goes, 3.5G is a lot in a helicopter - the Lynx can be looped and backflipped pulling less than 2.5G so to get to 3.5G from an aft cyclic pull would require a very harsh control input in something like an R22 which has a lot less responsive rotor head.

I used to teach steep turns in the Lynx at 60 deg AoB and yes it is a 2G manoeuvre in its steady state and requires a lot of power to maintain the speed. Pulling back on the cyclic will increase the G in the turn but you will climb and wash off speed an you are very unlikely to get to 3.5G - that would be more likely to be achieved if you tried to recover from a descending turn with aft cyclic without rolling off the high AoB.

[topendtorque]

Sadly I have flown a R22 that had been overstressed, but the young Fi hadnt remembered to write it up??!!, so I found out the hard way, I endured one of the shortest and most nerve wracked flight in my life thus far

vfr
any chance of enlightening us further, clues as to what the stesses were, how you picked it up, what you did in recovery and why and what might have happened had you not?
might be useful to our r22 fraternity
cheers tet