I am not knocking any of your upgrades. Or the pilots opinion. Just a fact on this machine does not have mast support and when blades are in perfect alignment to each other no vibrations smooth flying
I have to agree with you..... on the modified Mini-500APU you have.
I looked at your pictures on the other thread for Mini-500 parts. I could immediately see what was done differently.
First, our problem ended up being a combination of design mistakes, each amplifying the other. I knew what to do to correct what was happening, but financially my hands were tied. The Airframes were one of the most expensive and time-consuming items to build, yet that was the main part of the problem, and to redesign it correctly, build all 400 (at that time) customers a new one, even if I sold it to them at my cost, would have put us out of business, and that was not in the best interest of the customer as well. No, I needed a solution that would forever solve the problem, yet would retrofit on what we had and cost as little as possible to produce. That was a butt-load of thinking, designing, and doing, but we did it.
1. For the normal Mini-500, we have an engine that vibrates, so it has to be isolated from the rest of the aircraft. For you, the vibration is not an issue, so you can have solid mounting and drive belts which will eliminate some "soft-spots" we had to have in the classic Mini-500.
2. The way I designed the frame where the Main transmission mounted was wrong in one place. It would allow the 1" horizontal tubes to bend, rather than to put that load into corners. You were able to place more bracing in the area to distribute that load since you didn’t need the idler pully and its mount.
3. The real problem came from the flexibility in that horizontal tube the transmission attached. If you take your fingers and squeezed the main drive belt together in the center, you would observe the rotorhead moving forward and aft, and that was not good.
4. With any semi-ridged two-blade rotor system, it is important that the teeter height of the system will intersect the Center of Mass of the blades during coning. In the beginning, we experimented with the height until we found the smoothest height. However, it was WRONG, and due to the frame allowing that slight flexibility, the misalignment between the teeter height and rotorblades Center of Mass (C of M) alignment during coning, would cause the mast to rock back and forth, radiating down into the frame and causing it to brake.
Now, if the frame would have been more ridge, that would have allowed for the proper teeter height to align with the rotorblades C of M during coning, and that vibration and mast rocking would be eliminated. That is what the mast support corrected, and that is why the mast support includes new teeter blocks at a shorter height so that they will align properly with the C of M of the main rotor system.
With your extra bracing, ridged belts, and more solid engine mounting, and putting blades on that matched the rotor systems C of M, effectively also solved the issue. With what you have, you could have still used the Mini-500 blades and changed the teeter height, and still fly very nice, without vibration.
As for the warp in the Mini-500 blades, this is due to holding the blades straight in the molds while in the oven curing at 250F, and once removed, the aluminum spar will shrink slightly more than the composites, and providing the blades with that slight bow. In reality, this positive load on the blades makes them more ridged.
Also, I did try making a set of blades with the molds warped in the oven, so when the blades came out, they were perfectly straight. Upon flight testing, I found that it took much more spring action to counteract the downward pull of the collective, yet there were no other benefits found from the flight testing. In action, the slight warp of the blades helped to reduce collective pressures.
A different manufactured blade force may react differently, but, this is what we had in the field and this is what we had to make work.
I respect anyone that can make a helicopter fly if it’s their own design, or 98% someone else’s design and they were able to toy around and make some improvements. The one thing I ask of them is to remember that it’s easy for them to come up with even radical modifications that make improvements, “one time”, while I was a manufacturer that already has 500 of the units in the field all over the world have my hand-tied in many ways, and my solutions are much more difficult to design and implement when needing to stay in a budget for yourself and the customer.
You have a beautiful Mini-500APU, one of the nicest I’ve seen.