CX7 :: [2024-04-24] :: The fastest coax in the West

CX7 means Coaxial Copter, vehicle 7.
I knew for a while that CX7 is somewhat bottom-heavy, and this prevents optimal operation. Installing something at the top - such as a GPS+Compass module - can theoretically improve that a little bit. Or not so little...

[@Ben-Dixey]

Brilliant work, great to see a model of this configuration flying so well. Do you have any thoughts on the stability of the hiller flying platform ? Weight shift by the pilot if I understand it correctly. Amazing they were able to fire a weapon at the same time, you wouldn't have thought it would be that stable.

[@wowthatflies]

The stuff that happened to that craft is precisely what I am investigating now.
They used weight shift in first prototypes, but the particular variation of the Coanda effect from the duct's upper envelope is that when you are at an angle to have some horizontal speed, that speed adds a force that turns the craft back. This was strong enough to end the project even when they added flaps similar to what my models have.
By the way, this is explained pretty well in this old video by RCModelReviews: ua-cam.com/video/0stl1U9evzU/v-deo.html.
CX7 does not have this upper envelope, though what I observed during the entire course of its life, and what I am trying to quantify in some recent tests (not yet published), is very similar to that.
A yet untested idea is that something similar in shape to CX4's tunnel instead can alleviate or at least reduce this effect. This will be tested in some form in the next month or so.

[@Ben-Dixey]

@@wowthatflies Thank you very much for the information and I will watch Rc model reviews video too. 👍

[@Ben-Dixey]

@@wowthatflies Brilliant video explaining how strong the coanda effect is. I've been wondering about the downside to this machine for ages, so great to have an answer! The delackner aero cycle wouldn't have suffered the same effects with rotors that weren't ducted but rotor flap back would have had some effect. I suspect there wouldn't be any rotor flapback with the flying platform but there would be with the aerocycle, same for translational lift.
Not sure if you have seen my channel but I built a full scale coaxial helicopter, the flying platform certainly seems a fun project even if I could only travel at very slow forward speeds.
Look forward to monitoring your progress, models are the way to test.
Do you think mass above the rotor has any stabilising effect ? If you did the same thing but pilot weight shift below the rotor would that be more or less stable ?

[@wowthatflies]

Your projects are nuts! And I think that technically there should not be much speed limitations, unless you resort to very small pitch adjustments.
The mass above the rotor... Well, I had a theory once that the center of gravity should ideally exactly match the center of thrust. But I no longer think this way. The effect from that mass was twofold:
1) it increased the weight by 10%, which increased the hover thrust;
2) it lifted the center of gravity a little, which increased the moment arm of the flaps;
and both of these contribute multiplicatively to the control authority. Whatever the levelling effect comes from in the case of CX7, even if it increased after this change, it was to a lesser extent, so overall the authority improved.

[@Ben-Dixey]

@@wowthatflies makes sense when the CG is higher the control authority is better, like a longer tail on an aeroplane. 👍
I saw this video only recently.
ua-cam.com/video/aD6Om6LoERM/v-deo.htmlsi=0n5i__V6lq9sGdCK
Don't know what happened about it. Interesting the guy thought that coaxial's are gyroscopes. Counter Rotation cancels gyroscopic effects 🙂

[@sukhad2707]

Like a UFO speed 😮

[@wowthatflies]

Still quite loud for a UFO, I think :) But this one can be quite creepy too, if met outside in the darkness...

[@YAPKAIHONG_AEE]

Hi. Could u explaine what going on the vanes to hover the drone?

[@wowthatflies]

There are two vanes/flaps arranged in a "+" shape. The one that comes front-to-back controls roll: when it tilts bottom-to-the-right, the pressure from the airflow causes the drone to roll right. In the same way the vane that comes left-to-right controls pitch.

[@YAPKAIHONG_AEE]

@@wowthatflies can I have yr email or any contact no? Bcs I currently do the same project like yr one, but using Arduino n mpu6050 only. I m not sure the mechanism that I codes it correct or not.

[@wowthatflies]

@@YAPKAIHONG_AEE I think people nowadays use Discord for this kind of chatting, and I can be found there as "maximbuzdalov".

[@YAPKAIHONG_AEE]

@@wowthatflies alright. Already sent. Very Appreciate.

[@AlanSmith-q3g]

Facts😤🫡