Build Log F-35B Lightning II VTOL - Scale composite build!!!

[capt]

Excellent work! How dod you make the mold? did you use anothe plane?

[cray2602]

Wow, very nice. This is definately the most elaborate attempt at a real VTOL ive seen yet.
Your gyros are working much better than what i have. I left the 40mm fans near the wing roots and moved the batterys to the top of the plank and they worked just fine. The weight was just to low which put the vertical CG to far down. I think i might shelf mine for now and just keep an eye on how yours comes along. I spent all morning tuneing and tweaking my test board with all components installed and just cant get it right. Everything works perfectly but just cant maintain control after an input is given. The correction from the gyros is either too little or too much and they end up oscilating the airframe violently.

Looks like you guys are well on your way. Good luck.

[Hal_The_Hacker]

wow this is the best looking f-35 I have come across so far!

nice work, I will be following this thread closely

[G-force237]

Originally Posted by capt

Excellent work! How dod you make the mold? did you use anothe plane?

Here Capt, a whole thread on how we made the mold
http://www.rcgroups.com/forums/showthread.php?t=891668

Cray are you using rate gain or heading hold gyros? I would think if your plane is oscelating around a point then the gain is set to high? If its too low I would think the gyro would just not correct enough and the plane would roll over? The other thought is maybe there is noise in the system. Before we ordered the SM2 mixers we had tried basic tests with a GWS v-tail (vtailed with raw throttle in the elevator input and gyro corrected ailerons in the aileron input) and found that the mixer could not cope with mixing the high frequency gyro signal inputs with the lower frequency radio inputs. What we saw were jittery 'noisey' outputs from the vtail. it wasnt apparent with the motors as it sounded like the pulsing was caused by minute corrections from the gyro, but after pluging servos in place of the esc's it was obveous that the signal contained a lot of artifacts from the v-tail mixing. This was the reasion we went with the SM2 mixers. They can cope with mixing the high frequency gyro outputs with the lower frequency reciever outputs. So I dont know if you are using any mixers on your rig, but it may be somewhere to look?

[cray2602]

Thats probably what my problem is. I am useing the GWS V-tail mixers and my gyros are set to gain mode. Thanks for the info. Im just gonna sit back and watch how your experiment comes out for now.

[NitroCharged]

Agreed - those GWS and Turnigy V-tail mixers only have a 200 resolution so they are very steppy (therefore inaccurate). The SM2 mixer has a resolution of ~620 and is so smooth - you can't tell it's there.

[foam and tape]

subscribed... i've never seen someone work as quick as you before looks great (probibly going to be the first acutal r/c F-35 to transition from hover to forward flight)

best of luck to ya

[Sky-walker]

Originally Posted by member2006

Awesome I thought that was the real thing

As far as airflow loss, it shouldn't be much of a problem. I've messed around with 90 degree tube bends (1 lb model w/vasa fan 65mm and mega motor 2:1 ) and there doesn't seem to be much airflow turbulence. Just make sure you have the the thrust which these guys seem to have.

I see, but I dont mean the "amount of angle" that is the problem but the smoothness of the bend. I believe that if the 90 degree bend was smooth - (like taking a soft tube or something and bend it)- the efficiency will go without problems up to 88%-90% of the initial thrust of the EDF. But offcourse it is very hard to have a "rotatble tube" and therefore a rotatable swivle- parts-device is better.

[F-111 John]

If it really became an issue of needing every last ounce of thrust during hover, I suppose the center section of the swivel assembly could be curved to maximize efficiency in the hover mode, and just live with the kink in the tailpipe in the conventional flight mode, where the thrust would be less efficient but probably still more than adequate for flight.

[Sky-walker]

Originally Posted by F-111 John

If it really became an issue of needing every last ounce of thrust during hover, I suppose the center section of the swivel assembly could be curved to maximize efficiency in the hover mode, and just live with the kink in the tailpipe in the conventional flight mode, where the thrust would be less efficient but probably still more than adequate for flight.

that might be a good solution but, when the rear part rotates.. problems might occure at the curved place

[cray2602]

The biggest problem i can see is that the front and rear lift points will have different amounts of thrust because the rear fans thrust will lose a certain amount of thrust from the ducting. When throttle is increased the front will generate more lift than the rear and the difference will increase with each increase of throttle. A different way of looking at it is if you had more lift from the left wing fan as oposed to the right wing fan. It would be a challenge to control it i would think. But maybe not, i suspect we will soon find out either way.

[Sky-walker]

playing with c.g should solve this issue

[F-111 John]

Originally Posted by Sky-walker

that might be a good solution but, when the rear part rotates.. problems might occure at the curved place

True, there might be clearance issues inside the fuselage.

[cray2602]

The thrust changes wont be linear with throttle increases, the front and rear fans will vary in thrust output as throttle increases or decreases because of the ducting. What im trying to say is at 1/2 throttle there might be a 6% loss in eficiency at the rear but at 3/4 throttle there might be a 12% loss. But this could be a mute point, a little tweaking or mixing might resolve it if the gyro doesnt. Im interested to see the results with this build.

[bwalt822]

Originally Posted by cray2602

The thrust changes wont be linear with throttle increases, the front and rear fans will vary in thrust output as throttle increases or decreases because of the ducting. What im trying to say is at 1/2 throttle there might be a 6% loss in eficiency at the rear but at 3/4 throttle there might be a 12% loss. But this could be a mute point, a little tweaking or mixing might resolve it if the gyro doesnt. Im interested to see the results with this build.

A gyro should be able to take care of this fact. All the input will be to throttle up to hover higher and the gyro should be able to compensate pitch to make that happen.