Not sure that vibration would cause that. It would have to be violent vibration like the plane literally shaking in your hand to cause control issues.

Sounds like maybe you were tail heavy or maybe pulling up before it had enough airflow over the control surfaces.

Ducted fans don't have the same amount of thrust as a prop does so your plane might have been struggling to get on step. If you pulled up even a little, it would have been stalling causing the wild out of control flight you had.

The problem is definitely vibrations. Put the Skyfun back together after the crash and performed a bench test. As I approached wide open throttle the red light flashed and then went solid and then the elevons started to go full left and right and then switch back again erratically. When I throttled down the elevons went back to their normal positions.

Then I installed the vibration system that comes with the FY-30 with no improvement.

Then I used some Zeal foam to isolate the FY-30 and now the red light only flashes intermittently during wide open throttle but the elevons do not behave badly anymore. Wonder if this means it is safe to fly?

In the manual it says if the red light is solid then the vibrations are too much but it doesn’t say what it means with the light is flashing.

Any observations about this?

Thanks,

ecworks

Maybe the solution is to minimize the vibrations, rather than treating the symptoms.
Are you running a quality motor with good bearings and low tolerances?
Is your propellor balanced well?

Originally Posted by ecworks

The problem is definitely vibrations. Put the Skyfun back together after the crash and performed a bench test. As I approached wide open throttle the red light flashed and then went solid and then the elevons started to go full left and right and then switch back again erratically. When I throttled down the elevons went back to their normal positions.

Then I installed the vibration system that comes with the FY-30 with no improvement.

Then I used some Zeal foam to isolate the FY-30 and now the red light only flashes intermittently during wide open throttle but the elevons do not behave badly anymore. Wonder if this means it is safe to fly?

In the manual it says if the red light is solid then the vibrations are too much but it doesn’t say what it means with the light is flashing.

Any observations about this?

Thanks,

ecworks

Originally Posted by TheCure

Maybe the solution is to minimize the vibrations, rather than treating the symptoms.
Are you running a quality motor with good bearings and low tolerances?
Is your propellor balanced well?

Eflight 80mm ducted fan. Quality stuff. Never balanced a ducted fan blade.

Sounds to me like you are experiencing high speed vibrations.
You should give dynamic balancing a try. There's at least a few threads around here on it.
What about including a (better) vibration dampening fan mount?

Never heard of vibrations causing the elevons to glitch like that. Are you sure it's not a receiver issue? Maybe a receiver brown out issue caused by the BEC not keeping up the voltage under high load from the motor?

If it's not receiver brown out then maybe the vibration could be shaking the servo connections loose?

In any case high vibration is bad for the motor and plane. When motor/blades are vibrating a lot, the motor will actually draw more power which might be pushing the limits of your ESC and/or battery. Also it will eventually kill the motor bearings.

Originally Posted by cjbucher

Never heard of vibrations causing the elevons to glitch like that. Are you sure it's not a receiver issue? Maybe a receiver brown out issue caused by the BEC not keeping up the voltage under high load from the motor?

If it's not receiver brown out then maybe the vibration could be shaking the servo connections loose?

In any case high vibration is bad for the motor and plane. When motor/blades are vibrating a lot, the motor will actually draw more power which might be pushing the limits of your ESC and/or battery. Also it will eventually kill the motor bearings.

Using a Castle 10amp bec

Too late (for now) to dampen the EDF motor mount. Hot glued it in.
Managed to control the jitters by using Zeal padding in layers on top and bottom and then tuning down the gain on the FY-30. It flashes slowly but no eratic elevon movement so far.

Originally Posted by ecworks

Too late (for now) to dampen the EDF motor mount. Hot glued it in.

Rubber o-rings work miracles when you put them between motor and motor mount.
Tested on more than one plane.

Finally got the FY-30 to play nice with the Skyfun ducted fan.
Used a variation of the Milti-mod (see below) and lowering the gain on the FY-30.
Now it just blinks slowly when throttling up but no more erratic elevon movement.

Here are the pics. Remember the maiden flight lasted 5.5 seconds and ended badly because of the vibration problem with the FY-30a so it required a lot of plastic (styro) surgery. If this all works I'll probably get another Skyfun and transfer everything over clean. I'll likely cut in two rails on the back as motor mounts and attach the EDF with some sort of rubber o-rings or Zeal material to isolate it from the frame as much as possible.

Currently it weighs in (with a 2800 mah 4 cell batt) at 2lb 11 oz. Max thrust on the bench with the 4s is 2lb 8 oz.
The Eflight ducted fan is set up to run 4 to 6 cells. Should pickup another 1 1/2 lbs of thrust with the 6 cell batt.

2nd maiden flight (?) this weekend to see how it actually flies.

And yes, that is a slotted spoon protecting the 80 amp Eflight ESC.

Looks like an interesting EDF mod! Where does your CG end up being in relation to the finger launching holes underneath the plane? That's a pretty heavy all-up-weight, my SkyFun is very light at about 20 oz. with a 1800 3S battery.

Originally Posted by soundguy63

Looks like an interesting EDF mod! Where does your CG end up being in relation to the finger launching holes underneath the plane? That's a pretty heavy all-up-weight, my SkyFun is very light at about 20 oz. with a 1800 3S battery.

It ain't heavy, it's my Skyfun!

My other Skyfun (Twin motor/prop with landing gear) was heavier and flew great.
All of these planes I've been working on (Twin Raptor, Twin Skyfun, Tri Skyfun) have been proof of concept projects that do get heavy as I try out different things. I guess once I figure these ideas out I'll start from scratch with a new kit and transfer everything over clean and apply all the lessons learned, including weight saving strategies.

For the ducted fan Skyfun a friend and fellow flyer had this Eflight 80mm EDF laying around and loaned it to me to see what could be done with the Skyfun so I'm giving it a try.

Regarding CG, with the 2800 mah batt near the nose it balances out per normal using the finger holes.

Bench tested the Skyfun ducted fan project with a 6 cell (40c) and the Skyfun definitely gained some weight. It is now tipping the scales at 3 lbs 5 oz!

The ducted fan now produces 4 lbs 6oz of thrust with a significant weight penalty.
I think 5 cell will be the sweet spot weight vs thrust wise.

Very cool experimentation! How will you launch this EDF SkyFun? At least there is less risk to fingers with EDF, but will it need a catapult or landing gear?

Originally Posted by soundguy63

Very cool experimentation! How will you launch this EDF SkyFun? At least there is less risk to fingers with EDF, but will it need a catapult or landing gear?

2nd maiden flight yesterday if there is such a thing, 1st flight crashed within 5 seconds because the vibrations scared the FY-30a.

Yesterdays flights went fantastic. Pretty stiff wind (15 mph+) but the Skyfun always loves that. 1st flight flew with a 2800 mah 4 cell (30c) and as I've been hearing the EDF's lack a lot of static thrust when stationary so when it was thrown (a friend threw it for me) it seemed like it might stall but then the EDF started to get "on step" or "on the pipe" and then it gained speed quickly. Seemed to be going 70 -80 mph easily.
It was heavy (2lbs 8 oz) but flew great. Landings were even better. I usually turn in to land at a pretty high altitude and dive steeply with throttle off, flare, and then try to stay in ground effect and float along within a foot or two of the grass until the speed scrubs off. This worked perfectly with a heavy Skyfun and eventually it slowed enough to perform a final flare and then it plopped down and slid maybe 5 feet. A little grass in the EDF but it blew off with a couple blips of the throttle.
The 4000 mah 6 cell seemed too heavy (1.5 lbs by itself) so I'll wait and see what that feels like.

All in all I have to say that the Skyfun + EDF is a great combination. Side benefit: no worries about finger strikes or hitting the prop when landing.

I'll try to record the next flight and post later.