|Aug 07, 2011, 02:57 AM|
Henschel HS-129 B3 76" scratchbuild EPP
After the succesfull (2nd) maiden of my Nemesis Air Racer I decided to build another big EPP-foamie: a Henschel HS-129 B3 - the grandfather of all modern gunships.
The version B-3 was equipped with a huge 75mm Pak under the fuselage to destroy any known armament of 2nd WW-tanks - and the barrel is a perfect landing-skid
I will build her ~1/8 scale but with a ~10% enlarged wing with a wingspan of 1920mm (75,6"). The fuselage will be carved out of two massive 60mm (2,4") EPP RG20-sheets, the nacelles of three 40mm (1,6") ones. Two carbon-tubes D10x0,5mm will reinforce the fuselage. The wings will be hot-wire-cutted (profile: Clark-Y) and the tail-surfaces made of flat 10mm (0,4") sheets (sligthly larger than scale to improve carefree handling). The spar of the wing-center-section is an upright 3mm ply-sheet with 3x0,6mm carbon-profiles on top and bottom and wrapped with glas-fibre-tape.
wing span: 1920mm/ 75,6" (scale would be 1770mm/ 69,7")
wing area: 52,32dm˛ / 811inch˛
fuselage length: 1230mm / 48,4" (witjout gun barrel)
MTOM: less than 2,5kg /<5lb
engines: 2xDyamond C3536 1290kV
controller: 2xDyamond 40A and Turnigy 5A-UBEC
accu: 3sFlightmax 5000 20C or 3sFlightmax 3000 40C - depending on CG
servos: 9x HXT900 (2xaileron, 4xflaps, 2xelevator, 1xrudder)
RX: Corona 8Ch
TX: Graupner MX16scan
edit: she is completed (1st pic) and awaiting her first flight (much more pics in post #53 @page 4)
...also some pics of the original, drawings and a pic of a very nice finished plastic model:
|Aug 07, 2011, 11:39 AM|
...started with the fuselage. Had to cut a lot of channels and slits for all the spars and cables. Also cutted an accu-bay and a seperate bay for the RX.
The front reminds me on the muppet show...
|Aug 08, 2011, 02:44 PM|
...cables, cables everywhere
...soldered the harness today. 9 servos, 2 engines and 2 controlers had to be wired - an almost infinite work - but now it is done! (sorry, forgot to take pics of the wing- and nacelle- harness)
|Aug 09, 2011, 01:22 AM|
wing and fuselage spars, ribs and bulkheads
...layed out the inner structure of fuselage and wing: the fuselage will be reinforced by two CF-tubes (10x0,5mm), connected together by two 3mm, 5layer ply-bulkheads which will also carry the barrel of the gun. The barrel is detachable and slides into a 12x1mm GF-tube. The accu-bay is backed by a 0,3mm GF-box with 6x6mm Balsa triangles in the corners.
The wing spar is made of soft 3mm 3-layerd cottonwood and two 3x0,6mm CF-beams glued on top and bottom. To absorb shear-forces the hole spar will be wrapped with GF-tape at an angle of 45°. At the disconnection point the spars will be connected by 8mm GF-rod inside a 10x1 GF-tube in the front and 3mm steel-rod in a 4x0,5mm brass-tube at the rear one.
The center section is enclosed by 3mm cottonwood ribs with 10mm Diameter magnets.
|Aug 10, 2011, 12:16 PM|
...made the skeleton of the fuselage and center section. Its all glued with UHU endfest 300 which needs about 12 hours to cure completely. So all the glueing was made in improvised rigs to prevent distorion.
It was done in 3 steps:
1st: attaching the rear bulkhead to the three spars
2nd: glueing on the forward bulkhead
3rd: installation of the two wing spars
The final skeleton is very stiff and light - just as it should
Can you identify the skeleton inside the rigs on the pics below?
|Aug 11, 2011, 12:15 AM|
Thank you for the compliment!
I will only paint the foam - this is the lightest and most durable way (as long as I am the pilot, cause only every third landing hits the strip). Also havent found a way to cover EPP - most materials dont last for long and wrinkles occour.
|Aug 13, 2011, 12:38 AM|
...prepared the skeleton for integration. To absorb shear stress I wrapped the wing spars with fibre-tape at an angle of +-45°. Also added a layer at 90° at places of higher stress: begin and end of CFK-tube and connections to the fuselage bulkheads
Then I glued in the skeleton. I used PU-glue which expands during the curing, so I covered the symmetry plane of the fuselage with tape and only let the areas for the skeleton uncovered. After the curing I cuted away the expanded glue:
|Aug 14, 2011, 01:22 AM|
2nd half of fuselage
...attached the second half of the fuselage: the outlines of the fuselage and the areas beneath the skeleton halfs are glued with UHU-POR and the skeleton itself is lubricated with PU-glue.
A bit of theory, tips and tricks:
The PU-glue expands during curing and fills the gaps between the skeleton and the fuselage. If the symmetry plane would be lubricated with PU-glue too, the expanded glue would cause the halfs to drift appart and a deformation of the fuselge would occour. So this parts are glued with contact cement. But the UHU-POR causes an airtight enclosure of the PU-glue which only cures in combination with water vapour - so it is important to lubricate the hole skeleton with a bit of water before applying the PU-glue. This ensures a complete curing and durable bonding of EPP and wood/carbon without deformation. Sounds much more complicated than it is during the assembly.
Also cutted the outline and servo-cutout of the vertical stabilizer and finally test-fitted the wing center sections - looks nice yet
|Aug 14, 2011, 09:44 AM|
United States, WI, Fond du Lac
Joined Sep 2008
Looks like a very strong, light weight assembly.
If you are worried about PU glue expansion pushing the halves apart, why not cut a shallow channel in the halves for the excess glue to expand into? Are there internal channels for the tail servo wires?
|Aug 15, 2011, 01:58 AM|
There are already numerous channels in the fuselage:
-along the fuselage to the tail servos
-from the TE at the fuselage-outsides inclined to the RC-bay (aileron and flap servos)
-from the backside of the forward spar inclined to the rc-bay (controler)
-from the frontside of the forward spar to the accu-bay
-from the gun vertical to the RC-bay
-from the machineguns to the accu-bay
So I dared to drill lot more holes for the expanding glue. Beside that if the glue expandation is restricted, its density increases and therefore the bonding between the CFK/wood parts and the EPP.
...I started to scarve the naccelles. They are made from three layers of 40mm EPP RG20 sawed by a scroll saw. The outer layers are identical, the middle one has some cutouts for the motor and below the wing to save weight. The front is also made from a 40mm EPP-sheet sawed by a scroll saw. To get the correct transition to the wing sections of the negative cutouts of the wing-fabrication are glued in place.
Finally I scarved the form by a knife and sanded the surfaces with 80 and 120 grain abrasive paper.
Attention for all super-scalers:
I made a non-excusable mistake: only the first versions of the HS-129 had oil coolers with elliptical cross section - the -B3s (with the 7,5cm PAK) had rectangular ones!
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