Tandem rotor gyroplane

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joe nelson

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TFF,

I can't get away from thinking, that because of the variation in rrpm, the system needs to be coupled. This will keep the rrpm the same in all attitudes especially in a nose down descent.

The tail will need to be arranged like model #3 for longitudinal stability so it won't swap ends like a Chinook without SAS. By the time all of the fixes are made the model will be so heavy it won't fly, LOL.
 

joe nelson

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Today's tests were at various angles to represent take-off, climb, descent and landing. The aft rotor rpm stills varies at certain negitive deck angles. Would this characteristic be a game changer? Would a full-size gyro have the same flaw or would it disappear in clean relative wind?

Model #4's rrpm is good at 5* nose down to 12* nose up deck angle in front of the shop fan. I'm thinking, that if the model coupled the rrpm would be the same in all attitudes. My theory is, the rotor that is faster will drive the slower rotor during maneuvering that decreases rrpm.
 

joe nelson

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Don,
I keep coming back to the coupled set-up. All of the tests indicated that coupling would improve rrpm in unusual attitudes. Also, the use of gyro-style gimballed head wouldn't be as good as a swashplate controlled head. It'll take a while to set up the gearboxes for the next tests.
 

joe nelson

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Before I disassemble model #4, to install the gearboxes to couple the rotors, I want to test different blade pitch settings. The test has a mast angle of 12* and the blades are now set at -5* instead of -2* previously tested. I'll update the forum when I finish testing the -5* angle.
 

joe nelson

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I've built a teeter-totter jig to test blade angles for improving lift. One unexpected result to this test was the rate the blade's rpm recovered from changing attitudes. The blades being used on model #4 are high inertia blades making them slow to regain lost rrpm. I think, low inertia blades would be a better choice for future aircraft.
 

Topaz

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Perhaps you've already covered this, in which case I apologize, but if you're coupling the two rotors with gearboxes and adding helicopter-style swash-plate control to the rotorheads, it seems like a relatively small step to couple the engine to the interconnection shaft with a clutch and take this to a full-blown helicopter. Seems like you're 90%+ of the way there already, IMHO.

Have you given this any thought?
 

joe nelson

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Topaz,
It wouldn't be as easy as you might think. I have given much thought to doing exactly that, but I keep going back to the tandem gyro. Converting to a helicopter would add approx. 30% more weight to the aircraft in up-rated gearboxes and safety equipment. Dynamically, there's many differences between the two though they look so much alike.

My main goal is to build a simple, low cost aircraft which can be constructed with off-the-shelf components. The aircraft would be simple to maintain and fly. Helicopters, from my experience, aren't easy or inexpensive to fly or maintain. Ultimately, I would like to see a 1000# useful load, 100 kts airspeed and 200 mile range.

One thing that I found interesting, there's no information or studies on this type aircraft. There's a couple of patents that I've found but no information about any aircraft being built before. This may be an indiction of the true worth of this project. There's several studies by NACA and NASA on tandem rotor helicopters but nothing on gyros. One patent took such a shotgun approach to tandems where even the idea of a tandem gyro was patented. Unfortunately, there was no evidence of any model testing was done before it's filing or the author would have realized fault of his design.
 
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Topaz

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Okay, just thought I'd throw it out there. Seems to me that if you've got collective and cyclic control on each rotorhead, and a interconnection with gearboxes, actually driving the rotors doesn't seem like that great of an addition. But then, I don't know a lot about helicopters, either.

You seem to be having a lot of trouble with pitch-related issues with the fore-and-aft arranged rotors, seemingly because of flow interactions between the two as the vehicle moves forward and the flow from the front rotor streams back a bit into the second one. Have you considered going to side-by-side rotors, as in the Focke-Wulf Fw 61 or Focke-Achgelis Fa 223? (pictures below) The Fw-61 arrangement with the front-mounted motor seems like it would be particularly good for a gyroplane.



Or, since you're going to interconnect the rotors anyway, you might look at the Kaman HH-43:



Since you're still at the model-building stage, this seems like a good opportunity to explore other configurations that might not have the flow-interaction issues you've uncovered with the fore-aft arrangement. There's lots of ways to get the job done.
 

joe nelson

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The bi-rotor aircraft like the Fa 223 and the Fw 61 have a very narrow CG range that doesn't lend itself to carying an internal loads, just sling loads. The intermeshing rotors like the H 43 has the same narrow CG range but it's one of my most favorite aircraft. I would watch Huskies working at Bien Hoa, RVN when I was there. They would routinely refuel at the same FARP we used...cool bird but slow! I would like to test this rotor config. when this model is finished.

There are several bi-rotor R/C aircraft flying called "Twirl". From talking to a local guy, the Twirl has dynamic issues in turns. The inboard rotor slows for some reason but does remain controlable.
 

davh12

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Perhaps an airframe that is a bit longer to allow blade clearence, even 1/8", to eliminate the gears all together?? Would require additional bracing between pylons maybe, but the "columns" of relative wind would be separate passing up through the rotor discs
 

joe nelson

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P9210001.jpgThanks Dave,
Here's some pictures of where I am. These show my teeter totter jig to test lift and if you look closely the blades don't overlap like model#3. Well it seems like my computer isn't cooperating with the picture upload , today.
 

StarJar

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Just browsed this thread for the first time today. I'm very green regarding rotor wings, but I was wondering if there is any data on on Chinooks in autorotating mode that may yeild some information...? Sorry if this was covered earlier, I skipped a few pages.
 

davh12

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It's really strange because I heard that the V22 cannot auto and yet there have been outrigged "lateral tandem" gyos flying successfullly. One thread on PPrune takled alot about chinook. Most say it cannot auto. The rotor hub set is different on gyros vs. helos. Gyros being fixed pitch, but negative pitch close to hub and blade twist/flex positvie pitch farther out from the mast.....Gyro pilots feel free to correct any off the mark info that I may unintentionally put out,.....Joe had a post earlier in this thread about the Piasecki aircraft company that had successfully flown a "X" axis" tandem gyo.

At any rate, it's an intriguing project with unique challenges.




Chinook & other tandem rotors discussions - PPRuNe Forums
 

TFF

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I think there is too much blade twist in the V22, there for froward speed, to allow the blade to be driven well by the airflow. It is a compromise they put up with, and why they are so uptight on single engine operation and all those driveshafts.
 

bmcj

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It's really strange because I heard that the V22 cannot auto and yet there have been outrigged "lateral tandem" gyos flying successfullly.
If I am interpreting "outrigged lateral tandem" correctly, I think you probably mean something like the FW-61 that Topaz mentioned earlier.

fw61-1.jpg

As a kid, I built a radio control model of this that flew well via autorotative action (no power to the rotors, only the tractor engine). Don't ask me any technical questions though, as I built from plans and simply used the pitch and disk angles called out in those plans.

Autorotative... did I just make up a new word?
 

joe nelson

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TFF,
PA190001.jpg

I want to thank you again for the heads-up about the lower aft pylon...it works well! I took my models of the H46 and 47 and measured the angle between the two pylons. I applied this angle to my model and it made a lot of difference in the rrpm.

The V22 can't autorotate like a helicopter. Either engine has enough power to hover or make a soft landing if an engine fails. One thing that is generally misunderstood is the V22 is not a helicopter. It is a "power lift aircraft" that generates lift by the application of power unlike helicopter that generates lift through it's rotor lift. On the other hand, the FW61 is a bi-rotor helicopter and is able to autorotate through a clutch that allows the rotors to continue to turn after a power failure.

BMCJ,

Autorotative is an old word that has been around as long as I've flying helos (late 1960's).PA190003.jpg
 

TFF

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Looks like you are solving the problems. I hope you can get a flying model soon. It will be cool.
 
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