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FTFC19 Tron Legacy One-Man Light Jet by DamoRC

DamoRC

Well-known member
Mentor
#42
Damage report:

Maiden Damage.JPG

Left battery pod totally off - I must remember to return that divot to the field.
There is a crack in the left pylon at the v-tail.
Right pylon totally off, just held on with the wires.

All of this is repairable I think.

Here is a gif of the second launch

Second Launch Slow.gif

Looking at this in slow-mo I am beginning to thing that this is just a lack of power problem (oh, and I could have tried a little harder, the throw seems a little timid).

I would try moving the CG back a bit and see where that gets you.
Yep - although I like to maiden nose heavy, I may have overdone it this time. On the thrust angle, this is a profile pic marking the supposed thrust line from the EDF (horizontal line) and the CG position, which is essentially where I am gripping the model for launch. I would not expect to be able to feel "push over" from the EDF with this setup which I why I suspect that the EDF and thrust tube could be off, with the thrust exiting the tube pointing downward, creating a torque around the CG. But looking at the vid of the second launch, I may be imagining this because the plane didn't look like it was nosing down significantly.

Thrust Line.jpg

Have you considered a bungee launch to get her up to speed quickly?
Yep - this could be a good option - lack of launch speed is probably killing any attempt to get her up. Only concern is that once up, if I am still significantly underpowered, then I just come down again.

What is the next step to make this fly?
Given that I have no idea if this shape / configuration will fly but I do know that it is significantly underpowered, and the fact that I can't really change the former, but can do a lot with the latter, I think the next step is to add gobs of thrust. Options for this are:
(a) Add 2 x NTM2826 1200Kv motors wearing 8x4.5 props to the front of the battery pods - these can run off the same 4S supply as the EDF and provide 5 lbs (!) of extra thrust
(b) Remove the EDF and add the motors described in (a)
(c) Remove the EDF and add a single pusher to the rear ( the E-Flite Motor 10 that I run on the Tigercat will give me just under 4.5 lbs thrust on 3S with a 12x4 prop).

It also might be worth my while, if I pull the EDF, to do some glide testing.
 

jfaleo1

Junior Member
#43
Add the two motors and go for it. What is there to lose😀

About the pushover. I had the same feel on launching the Quinjet but it turned out to be of no consequence. On that model my EDFs are above center line a lot and are still zero thrust angle, so I did expect it but it did not nose over at all. I don’t think that looks like an issue for you either. Seems to me a ground/bungee start to get airspeed, or more power is needed. A higher lift airfoil may help or possibly flaps to increase camber until you are up to speed.
 

Namactual

Well-known member
#44
It also might be worth my while, if I pull the EDF, to do some glide testing.
That is a sound plan. Same with the prop power.

Looking at the launch, it looked like it may have yaw'd a bit from the toss. I agree that it does not look to be a thrust angle nose down, I would say the issue is the awkwardness of the grip. I also agree that having a better T2WR, it probably would have powered out of that.

Not a bad toss, just not enough thrust combined with an awkward grip.
 

DamoRC

Well-known member
Mentor
#45
Build post is complete (what a job that was, its a bit of a slog to read through, sorry).

Haven't made much progress with the plane. I did pull the EDF because the next version will be prop powered. Not overly happy with this option as I think the props will not really fit the look of the plane. One option is twin props at the front of the battery pods - this might give me the option to mount the battery in the fuse instead of in the pods and, if I can keep it to 1 x 2200mAh 4S, this will save 1/2 pound. Second option is a single powerful pusher. I have the motors and props for this, but I might have trouble getting the plane to balance if I hang a large motor on the rear end. I'll do some mockups once I fix the airframe.
 

DamoRC

Well-known member
Mentor
#46
Quick update

The repairs are pretty much done. She's a little rough (and probably a little fragile) but good to go I think. With the airframe back together I did some mockups of a pusher configuration (I really want to avoid twin motors at the front from an aesthetics viewpoint). Looks like I can get the E-Flite Power 15 950Kv motor ("borrowed" from the Gee Bee R3) hung on the back and get her balanced with the twin 4S batts in the front. With this setup she'll be a tad over 4 pounds. On the Gee Bee, this motor wears a 9x9 prop for speed. But for the Light Jet, all I care about is raw thrust so I put the motor on the thrust stand and tested a few props on 4S. Used 2 x 2200mAh 4S in parallel to mimic the available power and ran tests to cover 50%, 75%, and 100% throttle. Increased the prop size (limited by what I have on hand) until I started to hit 40A-ish

Results at 100% Throttle

Prop

Thrust (lbs)

Current (A)

Power Input (W)

RPM

9 x 9

3.35

43.4

651

10684

9 x 6

3.83

31.2

477

12000

10 x 6

4.51

32.4

486 (est)

11830

11 x 6

5.49

39.6

590

11029



So the 11 x 6 is really tempting at almost 5.5 pounds but I am going to have to check what the prop overhang at the back will be. I think she will still be a handful to launch and if I can avoid ripping my knuckles to shreds with the pusher prop that would be nice. Also considering a couple of fins attached to the underside of the tail that would hit the back of my hand before the prop does.