4 Blade Rotor System for two place machines

[skyguynca]

Ok, for those following the original thread........I have dropped the lead/lag hinges, flap hinges........way to much complexity and especially expense. I know people have tried the two teetering system stacked....problems with hooks-scissor effect (what ever you want to call it) because of one set of blades wants to slow down as they move fwd and aft positions and the other two want to speed up and they come into the upwind/downwind positions. It was suggested to allow the teeter bolt to move a bit in a elastrometric bearing to absorb the loads, lead/lag hinges....well a bunch of ideas (and I do thank everyone for their suggestions because without them I would not have found the answer I am looking for). My head is not anything new I have just given it the ability for the uppper and lower blades to swing fwd and aft of each other independently 15 degrees which should alieviate the scissor effect problem. It is a very inexpensive answer that should last atleast 100 hrs before the buffers need to be replaced and 500 hrs for bearing replacement. Oh and there will be two buffers and 4 bearings, total cost for those pieces should be about $150.00. I have already made the complete head from wood to check for fit and movement and I am very satisfied with it so far. Hopefully during the next month (my girlfriend in Canada visiting relative for christmas, I have till Jan 1st) I will make the test head from 6061t6 aluminum and mount it on my test vehicle. Actually the test vehicle is a 1982 small toyota pickup. I will run it down the run ways here as fast as I can to test the system. I will have a cyclic in the cab to put the head through its paces. I am going to make a cheap set of plywood blades with steel spars to use for the first 4 blades. The airfoils won't have to be great, just good enough to spin and produce lift. Once I have enough high speed runs and have tested it out and no problems then onto flight testing. Which means I got to build a two place machine. I will post pictures and info on how it goes on my website once I start the ground run phase.

[skyguynca]

OH, forgot one thing. I have not put it in stone yet but it will either use two lock pins or two bolts that will unlock the upper head and allow it to turn to match the lower blades so it will not occupy more space than a standard gyro with two bladed head.

[Victor Duarte]

David ! great ! i am hungry to know more !
just one thing : i read D. Degraw used 2024 instead of 6061 on his hub.. do you have the answer why ?
i also went back from a 3 bladed and i am on a simple 4 bladed and adresses the sissors effect and the need for lead lag.... i will tell more..
go on ! post pics of the mockup please...
thanks

[skyguynca]

I think he used 2024 because the stresses in a articulated hub are more than what I will see. We use 6061 in our teetering heads and my loads won't be anymore than usual compared to the teetering head. 2024 is also harder and alot more expensive. I have taken care of what I believe to be the normal effect of the two rotor systems together and the scissor effect. The wood mock up doen't show much different than a stacked system, it is closer inspection and movement of the two that revels its operation. I will post video of the aluminum head in operation when it is assembled.

[PW_Plack]

David,

This will be an interesting approach to solving ground resonance, too. Even if the two sets of blades got out of relative position by 45 degrees, they'd still be balanced.

Your crude test blades will have to be pretty uniform to assess balance issues, right?

[quadrirotor]

The approach seems OK! :)

[skyguynca]

That is one of the main reasons for the head design, to make ground resonance a non-issue, one blade can not move out of balance, only two blades can but then they are still balanced because each one moves toward or away from a different blade, so the angles between two sets can change but only equally.

[quadrirotor]

I am eager to see how you manage to keep the too rotors in the same plane!

[skyguynca]

One rotor is about 2.5 inches higher than the other and the top teeter bolt is only 7 inches above the roll pivot in the head so hopefully the control forces will not be any higher than they are with the standard 2 place head. I think it should work pretty well but we will see when I start testing it.

[Jim]

The first picture is of Magni's 4-bladed system and the second, I think of Ernie's

Jim

[skyguynca]

Yep, Ernie had cracks form in the trailing edge of the blades near the root, no one really knows how Magni's head is doing, no press or information.

[Screw]

Screw-In

Did Ernie find or fix the problem. Does he sell them?

Screw-Out

[skyguynca]

No, he dropped it and went to the springs that allow the single teetering head to shift and dampen vibrations on the two blade system he sells

[Jim]

David,

You say that you have a wood mock-up of the hub. Any photos available?

Jim

[skyguynca]

No, but I can take some when I get back into my shop. Will probably be Sunday or Monday.

[Jim]

Thanks!

I really look forward to see what you are doing.

Jim

[skyguynca]

Ok, here are a couple of sample drawings of the new head. They are not to scale and do not reveal the rotation of the upper part of the head. Just to let you know the upper teeter is only 2.3 inches above the lower teeter so stick forces should not be higher than a single seat. The drawing also does not show the acurate clearances for the upper teeter assy for its rotation but you get the idea from the drawings. The aluminum head, well I have cut the stuff for the upper teeter assy, right now I am still looking for a double bearing two seat head so I won't have to make all the parts for this head. A few people have said that they have one but just need to find it. So if any of you guys have one to sell at a reasonable price let me know. I am very anxious to get this project on to the testing phase. The dampening material seems to work great in the mock up head and I can move the upper assy 20 degrees fwd and back from center, this should relieve any stress in the blades and attachment points and should allow everything to fly in its plane without any undue vibrations. Also resonance should never be a problem in a head of this design either. When you get thru flying you will have to remove the two stop bolts for the upper assy (requires one socket wrench) and then the upper blade system will rotate 90 degrees to center over the lower blades for ease of storage. Of course you will have to have some foam blocks and velcro straps to tie the blades together so there is no bumping or denting.

I would also like to thank the guys at Magni Gyros, Ernie Boyette and you guys on here for the motivation, ideas and problem solving to get this idea up and running.

[Brent_Brown]

I don't see or know what you are showing but I wish the best for you and I hope to see it fly.

[skyguynca]

It is just the basic head setup. The pivoting of the head was not shown for clarity of the view.

[Jim]

Thanks for the drawings. It makes things more clear. This looks like a good idea.

To make things even simpler, you may want to make the straps on the top teeter as wide as the two vertical teetering plates. Jukka Tervamaki and Magni use two flat teetering plates as you suggest and attach the blades directly to that with (I am not 100% sure) two 10 mm grade 8 bolts.

Remember to build the coning into this!

Again thanks for sharing and good luck.

Keep us posted

Jim

[skyguynca]

I would do as Tervamaki (who sold his head design to Magni and I have all his plans including his fiberglass rotorblades) but I need the room for the head to twist/rotate for the relief of the hooks effect. Thanks for the suggestions. It looks like since I am having so much trouble finding a two place double bearing head without having to buy brand new (got alot already tied up in this project) I am going to make a single place 4 blade to fly first. I have all the stuff to make a 3DRV sitting in my hangar and I have one single bearing head (could use another one though) so I will have to make it the first flight testbed. I figure 18 ft span for the first attempts and see how much lift I get from that.

[Victor Duarte]

David, you're a living book store ;)
make it fly safe (after xmas;)) , i am very curious about the results.
I whish you the best success.
Thanks

[skyguynca]

Thanks, I will be very safe. I hope it turns out to be everything that I wish it to be. I think I have worked out all the problems that were thrown at it with the simplest of remedies I believe. We will see ..........I will post videos when it flies.

[mgbbhc]

These systems have been done before - seePOPULAR ROTORCRAFT FLYING June 1983 p. 19 (Bensen-Brock with four rotors - double teeter system; ROTORCRAFT June-July 1997 p. 4 - Ernie Boyette four-blade system. Photo is is by jim Eich, so either of them will have details. Bruce Charnov

[mgbbhc]

These systems have been done before - seePOPULAR ROTORCRAFT FLYING June 1983 p. 19 (Bensen-Brock with four rotors - double teeter system; ROTORCRAFT June-July 1997 p. 4 - Ernie Boyette four-blade system. Photo is is by jim Eich, so either of them will have details. Bruce Charnov

"There are no old, bold pilots" Carved over the USAAF Officers Club in WWII London

[skyguynca]

yes, but the two systems teetered and nothing else, I know that bensen and brock did them before, I was the one who brought it up again, but mine is different, it allows independent rotation 20 degrees ahead and behind the lower rotor system to relieve the stresses of the 90 degree out of phase accel/decell (hooks joint effect) I know it is nothing new, I have stated that the whole time everyone was telling me it won't work, the blade roots will crack........so I worked through those problems with the help of several people on the forum to find a solution that does work. It was already brought up that the 4 blade requires more storage space, well that was taken care of also by designing in a way to remove just 2 1/4-28 bolts that will allow the upper system to rotate 90 degrees to match the lower system so it takes no more storage than a 2 blade system. So while the 4 blade thought is not new Bruce, the way to solve its problems are..........

[Victor Duarte]

David, for storage, why don't you consider to make a one pin blade grip, remenber, i sent you one, if i recall. with a single rod you can dissassemble them.. If you have dampered the blades, a little disalignment may not be that important.
thanks

[Brian Jackson]

Rather than figuring storage are, I'd me more inclined to take a top-down approach. The big "if" is Does it work? Don't get sidetracked with everyone's proposed criteria. Prove your idea works. You can always refine it later. No sense in puting your energies in if it'll fit into a garage or not if no working example exists.

Sikorsky did a great thing... like you he had a dream but followed it a step at a time. You'll undoubtedly get bombarded with "requests" as if you were a DJ playing records. We all want a personal flying machine that's 100% safe and will never fail and takes no training. As long as gravity exists it isn't gonna happen. So be selective in your pursuits. Remember the phrase "Don't pick a fight you can't win? Consider it.

With utmost and sincerest respect,
Brian Jackson

[skyguynca]

Well I dropped the lead lag hinge because as Mike pointed out it would create more problems than it fixed. I kinda improved on Al Hammer's suggestion of a teeter bolt on the upper head having movement thru a elastrometric bearing. Instead I let the upper head rotate independently 20 degrees of rotation fwd and aft but with a centering dampner to relieve the stresses that everyone else saw while trying the 4 blade teetering hub. So to fold the blades I instead designed in a way to remove the dampner bolts, just two bolts with one 7/16 wrench or socket and then you can rotate the upper blades in line with the lower ones so it does not take any more space to store than your standard gyro, or you can just remove both teeter bolts and take the hub bar/blades off completely. I am really trying to keep the parts count down and the head as simple and inexpensive as possible. I think this will work fine. We will know soon. I really am hoping to get a double bearing head soon so I don't have to make all the parts I need.................come on some one help me out. I have made the upper parts, just need the two place double bearing head now.

[skyguynca]

Thanks Brian, I am walking my path and do welcome all suggestions. The ones that seem to make more work or take away from my project I just leave them to the side. One thing though, with all the suggestions and views I have received from all the different threads where this has been discussed, pictures posted, theories said........I know it would have taken longer, and down alot of wrong ideas to get just this far so I do thank everyone for their input.