e-Hawk 1500 ARF “build”

[Mucksmear]

It’s an ARF so not a lot of actual building but that’s ok. I saw Scott’s e-Hawk maiden flight at the Berkeley Marina and was generally impressed enough to ask my son if he was still planning to build his - we didn’t see how that would be possible so I’m jumping in.

Didn’t really like the transparent magenta so that had to come off. With the covering removed it’s interesting to see how a factory build quality compares to hobbyist build quality. Easy enough to address most of the gaps, missing glue and inconsistencies in LE shape, etc in an otherwise fairly neatly built airframe. The covering job was actually very good.

Stock calls for 3 servos (aileron via torque rods and ruddervators). I will go with 2 wing mounted aileron servos and a single elevator servo. No rudder, she has minimal dihedral anyways.

 

[Wayne]

It is interesting to study the build methods at the big ARF shops. Each person has a task, then the model moves down the line. The covering folks are like PROS! Guess you would get good pretty quick at a place like that.

 

[Mucksmear]

Yeah, I found myself thinking about how the individual assembler’s motivations are so totally different than ours when building. Trained for the specific task, with the minimum necessary context to do the job efficiently and properly. I was noticing the neatness and consistency of the seam overlap on the covering. The goofs and problems in general are a result of the high assembly speed winning out.

 

[Konrad]

I've seen videos where the gal covering the model has final inspection authority prior to covering. (I assume all steps down the line are able to reject work up stream). She had a sanding block to correct minor build quality issues. Her skill with the iron and heat gun were a joy to watch.

Truth be told these ARFs are better built than 90% of what we see built by hobbyists. Those of us in the upper 20% can see how we would do things better. But take a look at what passes for a built model at any swap meet or hobby auction and you can see why ARF as so popular. They really are better built than most hobbyist built models regardless of plant throughput (speed).

Great idea updating the control set up to a modern 2 aileron servo set up. With today's great light weight servos adding 4 servos can add a lot of options to the flight profile of even this small 60".

 

[Mucksmear]

I sheeted in the bottom of the servo bay and cut some simple 1/16” ply servo frames/hatches. The servos will be glued to the hatch with the servo horn sticking out thru the slot. The hatch will then be screwed onto the ply frame.

I needed a servo wire conduit that was big enough to accommodate the servo connector. For custom diameter tubes, in the past I’ve wrapped a brass tube with wax paper and spiral wrapped it with a strip of glass cloth and then soaked it with CA.

Since this is definitely non-structural I thought hey, what about just using tape? Blue painters tape spiral wrapped sticky side out, with about 1/8” overlap. A second wrap in the opposite direction this time sticky side in. Seems to work well enough. The tape shouldn’t delaminate since it’s stuck sticky side to sticky side. No glue, no curing no waiting, cut to length with scissors! The lightning holes in the ribs are narrow wedge shaped so for this one I taped two brass rods together side by side and wrapped the tape. The end result is an oval cross sectioned tube (but the doubled up tape is just squishy enough that it will conform to different aspects too).

 

[Mucksmear]

Pic 1-3: first wrap, sticky side out. A small scrap of tape is used at the starting point to anchor the reversed tape to the brass tube.

Pic 4-5: second wrap, sticky side in and opposite direction. Press around and along the tube to make sure the two sticky sides are nicely stuck together.

Slice off/peel away the first inch of wrapped tape at the starting/anchor point to free up the rest of the tube and carefully slide it off the brass.

Pick 6: trim to length

 

[Mucksmear]

I've seen videos where the gall covering the model has final inspection authority prior to covering. (I assume all steps down the line are able to reject work up stream). She had a sanding block to correct minor build quality issues. Her skill with the iron and heat gun were a joy to watch.

Truth be told these ARFs are better built than 90% of what we see built by hobbyists. Those of us in the upper 20% can see how we would do things better. But take a look at what passes for a built model at any swap meet or hobby auction and you can see why ARF as so popular. They really are better built than most hobbyist built models regardless of plant through put (speed).

Great idea updating the control set up to a modern 2 aileron servo set up. With today's great light weight servos adding 4 servos can add a lot of options to the flight profile of even this small 60".

Yeah the quality is actually pretty high overall and considering the speed at which they crank them out and the price point (especially this one). If any of us were on the assembly line we’d be fired for taking too long and fussing and nit picking, etc.

 

[Wayne]

I never would have know it was a tape tube if you had not shared. Good solution.

Keep up the great work Elliot!

 

[Mucksmear]

The stock ailerons are center beveled and attached with CA hinges. I’m changing this to top hinged so I squared-off the aileron LE by removing the double bevel, adding a strip of 1/16” balsa and sanding to a new single bevel. I cut off the servo-end of the torque rods with a Dremel tool/cutoff wheel and then slid the torque rods out.

 

[Konrad]

Very nice. I too like the facing of strip ailerons as I find it helps control the warping of the aileron.

Would you explain what is going on with the tooling/fixturing? I find this is key to that quality of build you mentioned earlier.

 

[Mucksmear]

Very nice. I too like the facing of strip ailerons as I find it helps control the warping of the aileron.

Would you explain what is going on with the tooling/fixturing? I find this is key to that quality of build you mentioned earlier.

When re-facing the aileron LE with 1/16 sheet, I support the aileron with the LE pointing up in a block of foam with narrow channels cut into it. The channels hold the aileron steady as well as prevent it from bending out of plane. I used Titebond to adhere the 1/16” sheet so I needed to either use tape or weight to clamp the sheet down while the glue dried. Tape sometimes digs into the crisp squared-off edges so I used weights. Both ailerons were mounted side by side in the foam block and wood scraps were laid across like railroad ties, and then weights placed on top.

I used a plane to rough bevel it close to final angle.

My first thought was to clamp the aileron to the workbench and use a long sanding bar with the correct bevel built in and just run this along the aileron LE but I was too lazy to make a custom sanding bar so I instead clamped my existing square bar to the bench with a shim under the back edge and then slid the aileron back and forth against the fixture.

 

[Mucksmear]

The kit included ply wing mounting plates that delaminated and fell apart in my hands (Edit- top of image 4533 - just noticed the pics are all out of order), no worries - make new ones! It’s a tight fit in that the mounting holes which line up with the pre-drilled holes in the wings are very close to the edge of the wing saddle, especially at the rear. There’s also the FG fillet in the corner edges inside the fuse so the left/right edges of the new plates had to be rounded off. For the rear plate, the blind nut flange also needed to be ground down for clearance.

To get a better fitting shape for the plates I took an overhead photo of the wing saddle and scaled it to size in Photoshop. The new shapes were printed out on paper for a test fit before I cut the real ones from 1/8” ply. Since the front of the wing saddle curves up at the LE, I added a 1/16” ply wedge to the front of the forward plate to get a better fit inside the fuse.

I waxed the m3 bolts and threaded them into the plates upside down from the bottom to aid alignment and clamping during installation. 30 min epoxy and fingers crossed that I didn’t actually epoxy the bolts in place. I reused the original delaminated plates and some m3 nuts to apply clamping pressure while the epoxy cures

 

[Wayne]

Waxing the threads - Is this a paste wax? We tend to use Vaseline, but don't have any hear at the office so end up using some stinky grease. Wax seems like a nice solution. In your experience does it work well?

 

[Mucksmear]

Johnson Paste Wax. I read somewhere online that you could use paste wax and glob epoxy onto the threads and then back the screw out after the epoxy cures leaving behind cast threads.
I had some in the workshop so I tried it. I was planing to use Vaseline but couldn't find it in the house.
The bolts came out really easily, but I don't actually know if I got epoxy on the threads during installation, so I can't say if the wax did its job or not.

 

[Konrad]

I like to use a bar of soap to protect the threads. Not that the soap works any better. But I find it is easier to remove the soap than wax for subsequent repairs (hot water and Simply Green). I don't like to leave wax residues as they more often than not bite me latter down the road.

 

[Mucksmear]

I like to use a bar of soap to protect the threads. Not that the soap works any better. But I find it is easier to remove the soap than wax for subsequent repairs (hot water and Simply Green). I don't like to leave wax residues as they more often than not bite me latter down the road.

Very good point. I probably could also a thin film of PVA mold release.

Just for future reference, I did a quick test and used a paper towel to smear paste wax on the bolt threads and then globbed some 30 min epoxy directly onto it. After it cured I was able to unthread the bolt by hand, leaving behind a threaded hole in the epoxy.

 

[Mucksmear]

Replaced the stock 3 servo tray with one to accommodate the single elevator servo and added a lightening hole next to it just in case that might come in handy later when stuffing in the wires etc.

After a satisfactory dry test fit, I traced the contact line between the tray and the fuse sides with a pencil for a visual guide when dabbing in the bead of 30 minute epoxy. Relatively easy install.

 

[Mucksmear]

Time to start covering. Began with the V-tail. Had planned to hinge the control surfaces at the same time as covering using just 2 pieces of covering, but half way through discovered I had the stab upside down. Normally this wouldn’t matter but in this ARF kit, the stab is provided as one flat piece with a pre-cut V-groove on the top side centerline for the builder to fold the stab into a V configuration (so it matters which side is up).

No problem, just cut the elevator halves off and finish covering the pieces separately and then add the hinge afterwards. 10 pieces of covering instead of 2.

 

[Konrad]

Have you given any thought to V-Tail junction angle? I find that most glider (high aspect ratio wings) respond best with a V-tail inclusive angle less than 100°. As this model looks (visual ref. only) to have a bit undersized tail area a 104° might work well.

Most V-tails are grossly undersized.

Charles River Radio Controllers - Model Design Tips

 

[Mucksmear]

Have you given any thought to V-Tail junction angle? I find that most glider (high aspect ratio wings) respond best with a V-tail inclusive angle less than 100°. As this model looks (visual ref. only) to have a bit undersized tail area a 104° might work well.

Most V-tails are grossly undersized.

Charles River Radio Controllers - Model Design Tips

I have not calculated the tail volume for this but now that you mention it I think I will. I haven’t heard any complaints re elevator authority (there’s an 80+ page ehawk thread on rcgroups).