HELICYCLE BUILDER LOG - Welcome to Helicycles.Org Rotor Scissors.pdf · I wish I had a...

JUAN RIVERA HELICYCLE BUILDER LOG #2

TAIL ROTOR SCISSORS

www.Helicycles.Org May 23, 2014

Well, there goes my baby, N750G, to its new home is San Diego. I immediately purchaed another kit so

I’ll have something to do. As with the first one, I’ll be jumping around and not necessarily following the

order of the video’s. That’s because some components are not here yet, and any work done is progress,

so the main thing is to stay busy. Most of the time it pays to proceed in the order suggested, but many

of the smaller subassemblies can be done in any order. With this kit I plan to use all the lessons learned

from building the first kit, and incorporate a number of modifications and enhancements that were not

practical to retrofit to my first Helicycle. Here’s a list:

Bigger skids because they look cool and I think the ship will look more substantial

Instrumentation I customized with UMA where I am now a dealer – Most indicators now have

alarm settins that are available on the rear connector as well as colored silk screened arcs that

are tailored to the Helicycle. All the alarms go to the Annunciator circuit (see below.)

A two-probe fuel quantity totalizer so the indicator reads accurately

A main rotor torque telemetry system

A master warning annunciator system that will monitor 16 paramters automatically

A bigger windsheld for greatly improved visibility

Nav/Position/Strobe LED lighting, LED landing lights, and instrument lighting

My 55-Amp alternator modification to power all the goodies metioned above


TAIL ROTOR SCISSORS


All projects have to start somewhere and I decided to machine my tail rotor scissors. I always try to do

the best job I know how, and not rush. As a result it took me two days to fabricate these two pieces.

I created an AutoCAD drawing from the factory sketch. The top view is rotated so that the horizontal

axis is the bottom edge of the part instead of the center line of the bolt holes. This saved me the effort

of milling one long side. That meant that each bolt was at a slightly different elevation, but with a mill

this is not a problem.

The factory sketch calls for a 3⁰ offset in the axis of the slotted hole at the top of the drawings. After

reaming the bottom end of the hole (labeled ‘Pivot Point’ in the bottom drawing) I can achieve that 3

degree axis offset by rotating the pieces around that hole until the far right edge moved 0.419 inches

down. This is one of the great strengths of a CAD program – you can figure these sorts of things out. So

I simply made a stop that distance away, loosened the clamps, rotated the parts till the end touched the

stop, and then clamped them in the new position. At that point I could move my mill table up the

vertical axis 0.250 and ream the upper end of the slot. Then it was a simple matter to clean up the area

in the middle and I was done with that slot.


TAIL ROTOR SCISSORS


I wish I had a metal-cutting band saw, but I

don’t, so I either have to get out my hack

saw or mill straight cuts by making many

multiple passes until I get through the

material, and then slowly closing in on the

edge. In this picture you can see the

scribe line I made and my progress as I

sneak up to it. I align the material by eye

using an edge finder. Once I get where I’m

going I can clean up the edge with my

deburring wheel and/or a file.

I drilled and reamed the three bolt holes first and then pinned the two pieces together with AN-3 bolts.

This insured that the two pieces will be identical.


TAIL ROTOR SCISSORS


In this picture I’ve reamed the bottom end of the 3/8” slot (left arrow) and I’m going to reposition the

material to align the vertical axis of my parts 3 degrees off axis (per the factory drawing) by rotating the

material around the reamer until the right hand edge has moved 0.419” and contacted the block I have

positioned for the purpose (right arrows.)

I reamed that big ¾” hole as I got into that area and it will serve as the inner radius on the arms once I

remove the excess material.


TAIL ROTOR SCISSORS


Once all the parts were cut

to shape the next step was

to round the ends. I wanted

to make an accurate radius

and insure that the holes

were in the center.

I clamped a bolt into my mill

vice and offset the two

pieces with a stack of

washers. Then I fired up the

mill with this burr installed

and manually swept the

work from side to side while

slowly moving closer to the

burr until I had the radius I

wanted. Then I touched up

the edges on my deburring

wheel.


TAIL ROTOR SCISSORS


Here you can see the 3

degree offset slot and the

finished end.

Here are the two finished

pieces ready for bending. I

have no good way to bend

them other than clamping

them in a vice and giving

them a thump with a

mallet. I’ve got way too

much time invested in

these to mess this up so I’ll

hold off for a while until I

think of a better way.


TAIL ROTOR SCISSORS


All modern digital printers are extremely accurate dimensionally. Here you can see that the center

marks for the holes in the drawing line up exactly with the actual part. I take advantage of that often

and cut out parts in paper to fit check them prior to actually fabricating the part.

If you’re wondering why the dimensions don’t match the factory drawing it’s because I rotated the part

to make the bottom match the mill’s horizontal axis instead of the holes. In this orientation the middle

hole is 0.050 higher than the right hand hole and the left hole is 0.075 higher than the middle hole.


TAIL ROTOR SCISSORS


I don’t have a break so I have

to do my bending using my

mill vise the old fashion way.

I stuck a thin piece of

aluminum sheet at the bend

axis to help radius the bend

and then bent the part by

thumping it with a leather-

covered piece of wood and a

mallet.

I can check progress with this

really useful digital

protractor that I picked up

used on eBay. It reads out in

tenths of a degree.


TAIL ROTOR SCISSORS


I checked my work with this protractor and worked cautiously to avoid overshooting.


TAIL ROTOR SCISSORS


After making the first

bends I stopped to

examine my work. So

far, so good…

The next step worried

me because the exact

point where I clamped

the pieces in the vise

would determine if I

came out where I

needed to be, and

trying to determine

how the thickness of

the material would

affect the outcome

was something that I

wasn’t comfortable

with. I had to trust the

CAD dimensions I

came up with and

press on.


TAIL ROTOR SCISSORS


After clamping the

pieces on the vice

at the location

determined in my

drawing all I could

do was to make

the second bend

equal to the first

so that the end

was vertical and

hope I had the

correct offset.

You see my wood

scrap and the

leather glove I

used to protect

the metal from

dents. The digital

protractor says

this one is as good

as I can make it. I

hope this works…


TAIL ROTOR SCISSORS


The bends all worked out very well. I may need

to tweak them just a bit to account for the

washers later.

But I’ve run into a slight problem - the Slider

Assembly has two flats machined where the

scissors mate up, but they’re too small.

I’m either missing something here, or those flats

are too small. I also seem to be missing the

bushings that should fit inside the slotted holes

to account for the difference in the outside

dimension of the AN4 bolts (0.250) and the

inside dimension of the slots (0.375) so I’ll have

to stop and wait for some clarification.

HELICYCLE BUILDER LOG - Welcome to Helicycles.Org Rotor Scissors.pdf · I wish I had a...

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