Recommended twin?

[Brian B]

Tigercat has Amazon 2212 x 1000kv motors spinning 9 x 4.5 CW/CCW on 2200-4s. Tigercat is a pussycat in the air, good step up from beginner. Using Satellite and Aura-5, great little system, especially like auto-lauch. I'm experimenting with a new power train now.

Lighting is a FliteTest laser kit with C-Pack motors, with 3200-4S battery and 10x4 CW/CCW prop set, topped with foam Flitetest spinners. Set up with differential thrust, which is fun. The Lighting flys as good as you'd imagine, but that power train has acceleration that blows away everyone. Not a single pilot at the field, from 3D professionals to gas turbine jet jocks, has not gasped when those efficient FT c-packs rips that thing out my hands on launch!

 

[Brian B]

Bench tested a new drivetrain for the Tigercat. Installed longer and higher-RPM 2217-1250kv motors, with 8x4.5 props. LOTS of pull, 2400gm thrust for 1400gm all up weight! (Didn't measure before the change). If I don't run it wide open the entire time, might work nicely. I'll put in a few flights when weather improves, see if it runs cool enough.

 

[Ranoutofaltitude]

Tigercat has Amazon 2212 x 1000kv motors spinning 9 x 4.5 CW/CCW on 2200-4s. Tigercat is a pussycat in the air, good step up from beginner. Using Satellite and Aura-5, great little system, especially like auto-lauch. I'm experimenting with a new power train now.

Lighting is a FliteTest laser kit with C-Pack motors, with 3200-4S battery and 10x4 CW/CCW prop set, topped with foam Flitetest spinners. Set up with differential thrust, which is fun. The Lighting flys as good as you'd imagine, but that power train has acceleration that blows away everyone. Not a single pilot at the field, from 3D professionals to gas turbine jet jocks, has not gasped when those efficient FT c-packs rips that thing out my hands on launch!

Haha! Thanks. I’m new to electric so this is very helpful. I had no idea you could run such big props on little 2212s. Those things are so cheap too. I have a couple high torque / low rev motors (~2216?) I took out of a quad that someone gave me that would work. I’ve spun 10x4.7 on them with a simple scout, but if there is a breath of wind it’s at a standstill.

I bought 3 noname 3530s with matching ESCs on Ali express that will be somewhat like the C with the intention of putting two in a twin and one in whatever else I build. I do have a C and it’s amazing how efficient that tiny motor is. I also bought a Surpass 3536 with matching programmable ESC to put in the FT MS Spitfire. That might be overpowered. Lol.

 

[Ranoutofaltitude]

Bench tested a new drivetrain for the Tigercat. Installed longer and higher-RPM 2217-1250kv motors, with 8x4.5 props. LOTS of pull, 2400gm thrust for 1400gm all up weight! (Didn't measure before the change). If I don't run it wide open the entire time, might work nicely. I'll put in a few flights when weather improves, see if it runs cool enough.

How are you measuring thrust?

 

[Brian B]

I'll collect it sometime in the P-38, but well over 1:1.
I'm impressed with the 1.7:1 (2400:1400) thrust to weight of my new Tigercat drive train. Didn't collect it before, but possibly 1900gm thrust on the old. Hope to try out today if the club field is dry.

 

[Ranoutofaltitude]

This is my frist twin. Recommendations on power/electronics? I've got a y-splitter for power, but will need to extend it if I store the battery in the nose. Can you also run two smaller batteries in each power pod?

 

[Ranoutofaltitude]

Also, does anyone know of a build guide? It seems mostly straightforward, but I am wondering how to place the six spars.

 

[Brian B]

This is my frist twin. Recommendations on power/electronics? I've got a y-splitter for power, but will need to extend it if I store the battery in the nose. Can you also run two smaller batteries in each power pod?

Check out the Flitetest build YouTube video for the FT Cruiser for electronics details. Don't forget to cut one of the red wires on the ESC y-spitter, so the RX only gets its clean power from one source.

 

[Ranoutofaltitude]

Check out the Flitetest build YouTube video for the FT Cruiser for electronics details. Don't forget to cut one of the red wires on the ESC y-spitter, so the RX only gets its clean power from one source.

Thank you! I will. That advice is probably all I’m missing. Do you double the wing spars flat or on edge?

 

[Brian B]

Thank you! I will. That advice is probably all I’m missing. Do you double the wing spars flat or on edge?

Regardless of which you use, P-38 or F7F, follow their plans. In my folded wing designs, if I need spar strength in the center, I'll go with thin balsa or ply doublers on a single vertical spar, tapering to a single foamboard spar as it tapers outward. Unlike balsa frame wings with a tension-only skin (fabric or film), foamboards handle tension AND compression, so you only need the spar to space out the top and bottom boards and give shear resistance, and the spar does add a lot to ultimate bending strength.

 

[Ranoutofaltitude]

I just had a blinding glimpse of the obvious. The spars probably only go out as far as the underside fold, so they probably fit per the plans. I will add a small plywood center spar as humidity got to my FT Spitfire and I snapped the wing in two.

I posted elsewhere that last night I tested control surface movement, glueing and painting packing tape and it all worked perfectly, so the F7F will be fully taped before painting. That should prevent the humidity issue my Sptifire succumbed to.

For anyone else building the F7F, test fit the nose skin before you try to glue it on. The plans are about 1cm too long. Otherwise it is an incredibly quick and easy build.

 

[Brian B]

How are you measuring thrust?

I mis-read your question. This is what I do, stand plane up on the nose, which works great on twins and pushers. Measure total weight on the nose, zero out the scale (found cheap digital one on Amazon), then throttle up to meaure thrust-only (stabilized with a light touch).
With a good ball bearing and a true spinner, I've done it with a tractor propeller plane once, but sorta scary. Instead, hang the plane off a yardstick, with the scale located halfway out, and use math ratio on mechanical advantage to work out thrust and weights results.

 

[Ranoutofaltitude]

Brilliant. Love it.

 

[Ranoutofaltitude]

Do you put your batteries in the nose or nacelles power pods? I want to put it in the nose so I can solder everything up and leave it. I am sick of swapping power pods.

 

[Brian B]

All my twins employ only a single battery in nose. 3200 4S in P-38, 2200 x 4S in Tigercat, and 2200 3S in the Cruisers.

I'm fond of doing race car themes on my planes.

 

[Ranoutofaltitude]

Love your builds!

 

[Ranoutofaltitude]

Do you have an STL for the nose?

 

[Brian B]

Never was sure which you decided to make. The Tigercat? See attached.

In the forum resources, there are several p-38 STLs.

 

[Ranoutofaltitude]

Yes, sorry. Almost done building the Tigercat.

 

[Brian B]

Good choice to tape up. Except for curvy master-style builds, I'm definitely taping up before assembly on future builds.