Angle of Bank and G loading

interesting.....the most I've felt in a gyro was an abrupt pullup, well actually a vertical fall with a stick input to pull out and a much delayed reaction. When the rotor finally caught it was a really hard flare. I don't know that it was any more g's than in a turn, but I was near zero before the flare, so it seemed like more.
 
A rotor tach is a good first approximation “G” meter.

Rotor RPM varies as the square root of “G” ratio. At 2 “Gs”, rotor RPM will increase by a factor of 1.414 over straight and level.

For that reason, gyroplane “G” loads are unlikely to exceed 2 “Gs”, rotor tip speed runs into compressibility and simply won’t go any faster.
 
And what happens then? Is that the reason why the maximum bank angle for the MTO-03 is given as 60 degrees?
 
Many of the specifications and limits, particularly component lifetimes, are numbers pulled out of a hat.

When a rotor runs into compressibility and refuses to turn faster, it can’t develop additional lift and mushes through a turn.
 
Again, the rotor as limiting factor.
It gives me the impression that, the rotor is our gardian angel up there.
Heron
 
Now that is interesting Chuck, and comforting. I assume 2G max is with the standard rectangular two-bladed rotor. Would abrupt G-loading increase with more solidity-ratio, like larger area blades or more than two blades? I believe it would….when I think of the rotor disk as being a solid plate compared to two blades.
 
Everything’s a tradeoff. More blade area would permit more “Gs” but either tip speed will be too low to permit high forward speed or else with pitch lowered for higher tip speed, the excess blade area is excess baggage to be dragged through the air.

Tip speed is roughly 66 x square root of blade loading (fps, pounds and square feet) at the most appropriate pitch setting. Cierva settled on a blade loading of ~35 lb/ft² as the most appropriate value. This gives a tip speed of ~390 fps and allows a top speed in the range of 100 mph.
 
I have pulled/jerked 3.5G on a G meter while playing around solo in my s X s A/Command trainer.

Aussie Paul. :)
 
The trig formula and the relationship between RRPM and G-load both apply to steady-state, level turns. Obviously, because of both the limited available extra power and compressibility, our ability to do level, steady-state steeply banked turns is very modest. No way any gyro can execute an 80-degree banked turn without slowing down, losing latitude, or (almost certainly) both. The formulas don't apply in the case of sinking turns, since the rotor then isn't generating enough lift (not thrust -- lift in the sense of thrust-that-opposes-gravity) to hold the machine up anymore.

So the real-world, steady G's that we can produce aren't that high, even in a steep bank -- BUT --

The designer of a gyro airframe must consider momentary loads as well as steady ones. A sharp, sudden updraft, for example, does not increase RRPM in the short run. Instead, it increases the AOA of the blades in the short run. This can produce short-duration G increases larger than the ones we can obtain in the long run. Lift is directly proportional to AOA.

Jim Vanek has cited results from a recording G-meter in the neighborhood of 4 G. These instruments capture events of very short duration. Jim's findings tend to justify the FAA's strength requirements for utility aircraft (I think theirs is +4.4G).

I'd design around a load limit of +4 - 4.5 G, with a safety factor of at least 2. If you crunch numbers on the primary structure of a Bensen, you'll find that it meets or exceeds this standard.

The interesting game is how to allow for fatigue. For example, 6061-T6 goes from an ultimate tensile strength of something like 40,000 psi for a one-time event down to 13,000 or less for a few million cycles. Cycles add up quickly in rotorcraft.
 
Vance if you looking at how strong to make the airframe, then a look at FAR 27.337 might help. It is for certification of helicopters but is a starting point.

http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=c8d479c50338730f14d770aebc937868&rgn=div8&view=text&node=14:1.0.1.3.13.3.247.7&idno=14

27.337 Limit maneuvering load factor.

The rotorcraft must be designed for—

(a) A limit maneuvering load factor ranging from a positive limit of 3.5 to a negative limit of −1.0; or

(b) Any positive limit maneuvering load factor not less than 2.0 and any negative limit maneuvering load factor of not less than −0.5 for which—

(1) The probability of being exceeded is shown by analysis and flight tests to be extremely remote; and

(2) The selected values are appropriate to each weight condition between the design maximum and design minimum weights.
 
...The interesting game is how to allow for fatigue. For example, 6061-T6 goes from an ultimate tensile strength of something like 40,000 psi for a one-time event down to 13,000 or less for a few million cycles. Cycles add up quickly in rotorcraft.

...especially if a "cycle" can be a 2/per vibration on a mast. (42,000 cycles per hour at 350 RRPM.)
 
Paul-> ...especially if a "cycle" can be a 2/per vibration on a mast. (42,000 cycles per hour at 350 RRPM.)

Interesting figure Paul, so far I had the impression that rotor design follows the rule of "If we have enough margin of saftey on ultimate then fatigue will be all right".
That's actually the rule by which rail cars have been , successfully(!), designed for quite some time. Has anyone ever proposed a load spectrum for fatigue design of a rotor?
 
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vance I've read greg grimmengers articles religiously and I'm trying to convice myself my gyrobee isn't stable lol! when I pull the power off from altitude I tend to hold back pressure just a bit, about 30 mph. then I add full power near the ground and my airspeed rises rapidly, not sure if I'm moving the cyclic or my bee is becoming unstable at speed but at full power the nose doesn't try to rise and climb! chuck bee is my bee unstable lol, I'm sure it not! low airspeed and it acts like a powered parachute, climbing and descending with power!
 
Well Chuck, after many iterations of varying spec.'s and compromises, I have found that your ~400 fps tip speed advice was always a good place to start for the best efficiency. A low inertia rotor can have a problem with high coning angles at this tip speed however, unless the blade CG is moved outboard with tip weights and so I configured my blades for a 2.5° max coning at gross weight (at normal cruise speed)….don't like high coning rotors. This does make for a rougher ride and so I added .5G and ended up with 2.5G max for smooth maneuvers.

I surmised that adding 1G would take care of the abrupt maneuvers and bumps with a two-bladed rotor and this 3.5G jives well with what Paul reported. But Doug stated that Jim has seen 4G loading and that would probably black me out. Now Jeff comes up with this FAA document (I don't know how he finds this stuff) that says to stress for +3.5G / -1G load factor. My UL project is stressed for +/- 3.5G, plus a +1.5G safety factor (+5G -3.5G). Because I am using all glass in this loaded structure, I don't need to be very concerned about fatigue but some safety factor is a good thing. I agree with Doug on a safety factor of at least 2 when using aluminum. I don't know about Vance, but you guys have helped me out and I thank you!

Juergen - In "Design Classroom", Bensen said that Sikorsky Aircraft factors of safety on fully articulated rotors were normally at 1.25 to 1.75 over max design stress. I'm sure that would be just find, but personally, I would tend to gasp with each bump in the sky……

Hmm….after reading my above statements….I seem to have the meditative veracity (some would say the down-right gull), to say these ideas in a way that I consider, somewhat informative…..although I can see where they may be construed by some as contentious. I blame it all on my perceived out-of-the-box project ;).
 
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Coning angle remains constant as “G” load increases. The increase in rotor speed vs. load keeps it so.
 
I too am mused by people who recon they can get big +Gs ina gyro.
Iv dun most things ina gyro that a gyro can do [ cept loops, iv never seen a cow do one, so i havent had to] and i even rigged a G meter to staisfy my interest, only to find i couldnt get it past +2 1/2.
Pulln out of dives, power on, power off, abruptly and gently, the highest i ever saw was 2 1/2.
But i know how to make a gyro 'fall through', and i think this, along with airs compressability is wot makes it impossable to exceed much past +2.
 
If I understand this thread correctly if you were to pull out of dive and exceed about 2G the gyro will continue along its line of flight until the airspeed decreases enough that compressibilty eases and a postive rate of turn will develop.

Is this a concern and are there any side effects of compressibility like slowing the rotors or reducing drag. Is it possible to increase you rate of descent when you try and pull out of dive and come up against compressibilty.

Would the recovery be just to ease the stick forward slightly to reduce th g load and accept a shallower recovery or wider spaced turn and if you had plenty of room can you just ride through it knowing at some point the g load will reduce and you just fly out as normal.
 
A rotor tach is a good first approximation “G” meter.

Rotor RPM varies as the square root of “G” ratio. At 2 “Gs”, rotor RPM will increase by a factor of 1.414 over straight and level.

For that reason, gyroplane “G” loads are unlikely to exceed 2 “Gs”, rotor tip speed runs into compressibility and simply won’t go any faster.

Is there a way of working this backwards, ie using the max rpm you can get, to work out approx G's ?
 
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