Gemini V-2 Build

[Maingear]

I ran across this aircraft at the Bearospace Industries website. Spike designed the original and the version 2 Gemini to be a long endurance FPV platforms. With 3 hr duration and a 20 lbs max takeoff weight, it was intriguing. Doing this with two power 15 motors, I clicked the buy it now button. The scroll saw, I picked up at a pawn shop, made cutting out the fuselage plywood a breeze.

Copied from his website:



SPECIFICATIONS:



WINGSPAN: 3200MM 126 INCHES
WING ASPECT RATIO: 10.77 / 1
​AIRFOIL: HIGH LIFT / NON CRITICAL TYPE MAX CO-EFFECIENT OF LIFT: 1.5
WING AREA: 96,000 CM SQ. OR 1488 INCHES SQ.
AIRFRAME STRUCTURE APPROX WEIGHT: 4 LBS, 9 OZ
EMPTY WEIGHT: 7 LBS
MINIMUM FLYING WEIGHT: 15 LBS / 6.8 KILOS
MAXIMUM GROSS WEIGHT RECOMMENDED: 20.75 LBS / 9.4 KILOS
WING LOADING: 23-32 OZ. -SQ. FT - 71-98 SQ. D.M.
FLIGHT DURATION : APPROX. 3 HRS WITH PAYLOAD
RANGE: AT LEAST 12 KM DISTANCE WITH L.R.S.
DISTANCE: APPROX 120 KM LINEAR WITH PAYLOAD
CRUISING SPEED: 40-70 KM PER HR
STALL SPEED AT MAX GROSS WEIGHT: 22 MPH / 35.4 KM PER HR
CIELING: UNKNOWN, BUT VERY HIGH. 20,000FT +
BEST LOITER SPEED: 42 KM PER HR
BATTERY CAPACITY 50,000MAH 3 CELL LITHIUM POLYMER
AMP DRAW AT 42 KM PER HR: 13 -17 AMPS DEPENDING ON PAYLOAD/BATT.
RECOMMENDED POWER: 2X E-FLITE POWER 15 BRUSHLESS ELECTRIC
RECOMMENDED PROPS: 13 X 6 - 13 X 8 APC THIN ELECTRIC 2 BLADE
RECOMMENDED PROP CONFIGURATION: COUNTER/ROTATING INWARDS
RECOMMENDED SPEED CONTROLLERS: PHOENIX EDGE 50 AMP +
RECOMMENDED SERVOS: HS 225 METAL GEAR TYPE FROM HITEC
FLAPS: DUE TO HIGH LIFT AIRFOIL, NONE ARE NEEDED

So here it goes, my first scratch build!

I built on top of the plans for the sides. The bulkheads go in and are to be cut to the fuselage measurements.



Fuselage is roomy


Here is a Nikon D90 in half of the rear bay, good indicator of size.





Had to bend some wood that builds up the ply in the top of the nose. I soaked the wood, then found something close to the shape I needed.


Tail was built by making perimeter, then adding ribs, then placing the 1/4 x 1/2 strips on the vertical stab.


Finished the H-stab, and elevator, will post pics soon.

Need to cut out some ribs! How should I cut the holes in the ribs when I have them stacked?

Justin

 

[Foam Addict]

Impressive start! I'll be watching this!

 

[Maingear]

Major problem! Seems I have a severe balsa allergy. Not sure how to finish the wings if I can't sand more ribs. With a two weeks of vacation including a cruise, my wife has made the project off limits.

Justin

 

[Joker 53150]

A balsa allergy, or balsa dust allergy? Are you using CA adhesive? Many people have problems with that glue, including me. If the dust is a problem there are ways around much of it, but it's a very fine dust and can be a pain. I'll end up with occasional sinus problems from it during heavy sanding sessions, so a dust mask is often used.

 

[Maingear]

Dust, no CA yet - Tightbond II. Used Sketchup and did this instead at 60% power . I'm back on track!
Justin

 

[Foam Addict]

Way to get back on track! I'm kinda jealous of that CNC router..

 

[Maingear]

The 60W infinity bit gives great results!

I am very grateful to have access the machine, cut days off the project. Pun intended..

Justin

 

[Maingear]

I cut rib jigs out of this stuff called "Adams Foamboard". It's only a dollar a sheet and found at Dollar Tree.
I can get six ribs out of a 4" x 36" sheet of 3/32 balsa. Time to glue some wings and fingers together!

Justin

 

[Maingear]

The wings are going together, just takes time.

 

[gabrielete]

Wow that's big.... impressisve wings

 

[Maingear]

Sketchup was so fun to work with when I drew the wings for the laser cutter, I decided to try to cut the fuse out of 1/16 ply.
Justin

 

[Ocean]

Awesome, I would love to build one of these.

 

[Maingear]

If you do build one read everything Spike has written as well as the videos. Instructions are very thorough. Drawings are well done and there are a few parts that are cut to fit, but no surprises.

Here is a deviation taken from the drawings. Servos stacked in this configuration is not called out in the drawings. I am using a bell crank to make a 90 degree change in elevator rod direction. I will try to configure it where elevator up is a downward stroke for the servo.



There are three 4s 5000mhr batteries with one stacked on top of the three in the nose. I cut off some of the nose gear to level the fuselage. you can see the baack of the servos.




That bell crank will installed just bellow the h-stab (horizontal stabilizer). I purchased, but did not use the carbon fiber in the tail because the two webbing strips of balsa called out to strengthen the vertical stringers worked so well. I may box in both the left and right sides above the servo tray sections as I get the slightest twisting motion when I try to twist the top of the H-stab. I am sure the covering would take care of this and it will not be an issue.


I goofed and burned 1/4" holes rather than 1/8" for the gear. I drilled out the main gear attach holes to match. Also laid rubber between the main gear and the main gear attach block. I have plenty of room for one 3s 2200mah for video with these 4's.


I deviated again by cutting the top of the vertical stab in line with the balsa webbing. I omitted the top section's balsa and used the ply only. I figured the ply was stronger. The cut's location was a mistake because I didn't realize balsa was to be installed before the ply, but everything worked out well. If you see the plans some time, you'll will see what I mean.


What's left? wing training edge, ailerons, wiring, static runs, taxi test, sanding, then covering....... All I like is finishing up!

Justin

 

[Foam Addict]

That's enormous! Very sharp balsa work though, it looks like it'll fly superbly.

 

[Maingear]

Thank you sir! I have been taking my time, but forgot to glue the top of the H-stab where i cut it and inserted the plywood. It does not flex when glued! When the empennage has the vertical stab installed, any movement to the stabilizer moves the fuselage.

I deviated again when it came to steering the nose gear. I used a 10KG servo (22lbs) because I do not have access to improved runways. The gravel and tangly bermuda grass this plane will encounter should not be a problem.


I drilled two holes, then connected them with by whittling. Epoxied a bracket that was cut out of some 1/4" ply. I drilled pilot holes, but need to find a screwdriver that can reach that last screw....



Epoxied in the bracket that the bellcrank is attached to.



Neutral


Down


Up


Justin

 

[cranialrectosis]

Geeeeez this is a monster!

What kind of glue are you using?

 

[Maingear]

I started using titebondII, but got no penetration; the joints were brittle and separated when handled. I started using Loctite CA, then switched to a generic medium CA, local hobby shop generic. Critical structures and attachments are 15 min epoxy, that takes hours for the matrix to set some reason - but it does cure!

I forgot to point out the 1/8 ply doublers in the steering servo pic. First, look at the wire gauge on that servo! I have shielded cat 5 cable for the servos, but the size of these wires will make me double strand for the load to the stand alone BEC.

Secondly that wire is touching one of the 1/8" ply doublers cut out to strengthen the battery compartment. All I had to do is crop the side panel to make the section I needed, then change the speed of the cutter from 1/16 ply speed to 1/8 ply speed. In the end I need to incorporate the profile of the battery brace with this doubler, to make one piece.

Other goofs include - placing all the holes I needed in the nose for the gear, have the laser cutter perfectly making the part, then installing 180 degrees out of position. Side effect of working after everyone has gone to bed, I should have been sleeping too!

Another deviation I would like to point out is the additional top; and bottom cross bracing at fuselage station 29 (29" aft of bulkhead 1) in the rear cargo bay. The original design is clear of these braces to accommodate large cargo. My needs are strictly video related so I have no need for this option, but will keep the access panels for ease of structural inspections.

Justin

 

[Maingear]

We had an open house at the makerspace. Here are two pics, HStab is covered.
Justin

 

[dodgebob]

I had no idea the wing would be that big looking at the fuselage pic

 

[rcpilotacro]

I too grabbed me the plan from Spike, exceptional person to deal extremely prompt to say the least. Last night got the plan printed, both on the paper (For cutting) and on a flex printer for working on a table. Just the printing costed me a bomb