3) TRANSMISSION DRAGS FRAME WITH IT 4) TAIL … Installation.pdf... 2015 Page 1 THE EFFECTS OF TORQUE ON THE TAIL ROTOR ... transmission back into position and ... of side force to

JUAN RIVERA HELICYCLE BUILDER LOG #2

MAIN TRANSMISSION PREPARATION AND INSTALLATION

www.Helicycles.Org 30 June, 2015 Page 1

THE EFFECTS OF TORQUE ON THE TAIL ROTOR DRIVESHAFT AND THE FRAME

I like to understand what I’m doing before I start drilling holes in my helicopter, so I’m going to spend

some time thinking about the effects of torque on the orientation of the main rotor transmission and

the tail rotor driveshaft. My goal is to have both in perfect alignment during flight – not while the

helicopter is sitting on the ground…

1) TRANSMISSION TURNS MAIN ROTOR CCW2) TORQUE REACTION TWISTS TRANSMISSION CW3) TRANSMISSION DRAGS FRAME WITH IT4) TAIL ROTOR AND FIN EXERT COUNTER FORCE TOWARDS RIGHT5) TAIL BOOM FLEXES TO LEFT AS VIEWED FROM TRANSMISSION TAIL SHAFT LOOKING BACKWARDS.




My drawing on the previous page illustrates the interesting challenge of installing the main rotor

transmission so that the transmission tail shaft is properly aligned during operation. The tail shaft not

only serves as the input to the transmission, but also drives the tail rotor driveshaft. For smooth and

reliable operation it needs to be in line with the T/R driveshaft. The drive pulley also needs to be aligned

with the engine pulley when in flight – not while on the ground.

To get this right we need to consider all the forces acting on the Helicycle in flight. The transmission

main shaft turns the main rotor counterclockwise, and since the rotor blades create drag, it takes torque

to turn them. This creates an equal and opposite reaction, so the transmission housing wants to rotate

in the clockwise direction. Since the housing is attached to the frame, it applies this clockwise twisting

force to the frame, which slightly deforms, causing the tail shaft to move to the left (clockwise rotation)

in relation to the surrounding frame elements. The frame is kept from spinning around by the tail rotor

and the vertical fin which exert an opposing force towards the right. Since the frame is flexible it stands

to reason that the tail section is also flexed during flight from its static position.

B.J., the inventor of the Helicycle and founder of Eagle R&D, tells us that the maximum torque design

limit on the transmission input shaft is 160 ft.lb. From that we can derive a number of values:

Input torque limit to the transmission: 160 ft.lb

Transmission gear ratio: 4.875:1

Main shaft torque limit: 780 ft.lb (input torque multiplied by gear ratio)

Moment arm: 11.5 feet (main shaft to tail rotor distance)

Maximum anti-torque force at tail: 68 pounds (780 ft.lb. divided by moment arm length)

I know that the transmission tail shaft is torqued in a clockwise direction. My simple analysis shows it,

B.J. says so, and testing that I did on my first Helicycle confirms it. That means that the transmission

coupling to the tail rotor driveshaft isn’t going to be where it is when sitting on the ground. It will be a

quarter of an inch to the left. When I install the driveshaft I’m going to take that into account by

removing the right hand transmission mount and aligning the transmission with the tail rotor gearbox

input shaft using my laser. I’ll install and align the driveshaft and the bearings before offsetting the

transmission back into position and replacing the mounting bolt. On the ground the forward driveshaft

section will be very slightly out of alignment, but it will move into perfect alignment once the ship is in

the air… or will it?

The tail rotor gearbox won’t be where it is on the ground either. It will be pushed off to the right by the

anti-torque side force. Should I account for his?

I applied approximately seventy pounds of side force to the tail while a helper stood on a skid, and I saw

a deflection at the tail of about half an inch. I used a laser boresighted down the axis of the transmission

tail shaft to make that measurement. Unfortunately, I’m not really recreating the conditions that exist

in flight. I need to hold the transmission in a rigid position – not the skids. However, I don’t think the

test is totally meaningless since it shows that the frame is fairly stiff. Even if the test was completely

valid what can I do with this information? I assume that the tail will flex along its full length like a

banana. When lining up the transmission tail shaft with the tail rotor driveshaft I can’t just point the tail

shaft to where I think the gearbox will be in flight. I need to align it with the forward end of the

driveshaft. If the shaft is flexing then those two are not the same. Net result of this exercise – ignore

deflection in the tail.




Now I’ll move from thinking and planning to prepare the transmission for installation…

FACTORY LUBRICATION LINES

To prepare the main transmission for installation I modified it to accept a Robinson R22 self-sealing chip

detector (separate write-up.) I also removed the factory-supplied oil lines, plugged the ports, and had it

painted.

After a long pause while I worked on other projects, I began to reinstall the oil lines and prepare to

install the transmission in the frame. As I was doing this, something caught my eye… Closer inspection

of the flares on my factory oil lines showed that something wasn’t quite right with the flares.

The ends of the tubing were jagged and

cracked and the interior surfaces were badly

scratched. It’s likely that these flares

wouldn’t seal at all, and they all looked as if

they might fail completely in flight. From

the looks of these flares I doubt that these

tubes were inspected at Eagle. This is not

good!

Here’s a look in the end of one of those oil lines. Not only

is this a complete mess, but there appears to be loose

debris inside the tube.

There’s a lesson here. Don’t trust anyone with your

aircraft parts and always carefully inspect everything

before installation. You’re the builder and you bare the

ultimate responsibility for the quality and suitability of

the components, and for the workmanship that goes into your ship.

Based on the poor quality of the factory-supplied tubing I decided to scrap them and make my own. I

was surprised to see that the interior of my first test flare also showed a lot of scratching. I found that

the surface of my flaring tool was scratched. After buffing it with a Dremel tool the flares looked much

better.

NOTE: Don’t try to use an automotive flaring tool as the angle is incorrect for mating with AN aircraft

fittings.




NEW LINES FABRICATED AND INSTALLED

Here’s a look at one of my flared tubes after I

repaired my tool. The scratches on the outside are

where the tool grips the tube and don’t damage the

tube.

Here’s the left side of the painted transmission with my oil lines installed.

1) This is the lubrication fill line and breather. Once installed the transmission is buried behind the

fuel tanks and this port will be inaccessible.

2) This is the sight gauge. The level should be half way in the window.

3) This is the transmission oil temperature sensor. I’ll terminate these wires with a Deutsch

connector.




Here’s a view of the right side showing the oil filter housing (#4.) A flexible braided line will go from

the port with the red plug to the output port of an external oil cooler. The flex is important since

the transmission and the oil cooler are attached to different locations on the frame, and the frame

flexes.




Looking at the left side again, you see the output of the oil filter feeding the critical lube points.

6) Main shaft bearing

7) Input shaft bearing




The bottom of the transmission is shown here.

8) This is the self-sealing Robinson R22 chip detector. You can see how I installed this in another

write-up.

9) This is the transmission oil pump. A braided line will go from the port with the red plug to the

input of the external oil cooler.

10) This is the drain port. A Tygon tube will connect to a valve at the bottom of the ship where the

line is accessible.




Here’s a closer look at the line feeding the main shaft bearing. It has to avoid the transmission web,

below and to the left, and also the plastic fitting for the feed line.

Many years ago I was a line maintenance mechanic for United Airlines. I remember seeing a stainless

steel hydraulic line that had been partially abraded through by a soft rubber hose. The hose was coated

with a film of hydraulic fluid had some grit, and although it was much softer than the stainless steel

hydraulic line, it managed to wear halfway through. The culprit was high-frequency vibration. It

reminded me of some lifer in prison slowly trying to cut through his bars with his shoe laces. The moral

of my little story is that I try to avoid letting wiring fluid lines touch anything that could cause abrasion.




This is that loop labeled #7 on page 6. It’s another example of a line that I don’t want to touch anything.

It extends inside of the main pulley, so it has to be close to this flange. Since I balanced my pulley

assembly with a blob of epoxy in the inside of that main pulley I needed to check for ample clearance as

it comes around.




MOUNTING THE TRANSMISSION

The transmission is now

mounted in the frame and

secured with one bolt on the

left side. Per the procedure, it

will now need to be properly

oriented to account for the

twisting caused by torque when

under load. The idea is to bias

the orientation of the input

shaft towards the camera so

that the shaft will be properly

aligned during flight – the

torque reaction will twist the

tail shaft away from the

camera. (The strap is a backup

so I don’t drop the transmission

during this project.

Notice that the right hand

transmission mount is not

drilled at the factory. The

builder does that using a center

drill once the transmission is

properly aligned. If ever there

was a case for following the old

carpenter’s saying of, “Measure twice and cut once” this is it. Many mistakes can be easily corrected

when building a Helicycle, but this is not one of them. That right hand mounting hole has to be a tight

fit, perfectly round, and in the correct location. It’s also very important that the frame mount be

perfectly aligned with the transmission housing, with no interfering welds, paint blobs, or other

obstructions. In my case it isn’t, but I’ll get to that later.

After reviewing the construction video I believe that it may be in error, or at least it’s a fairly crude

procedure. In the video B.J. says to follow these steps:

1) Stretch a string from the tail shaft to the center of the rear tail rotor gearbox mounting hole

2) Rotate the transmission counterclockwise until it is offset by ¼-inch as measured at the first

driveshaft bearing mount. You are to do this by extending a straightedge from either side of the

tail shaft and measuring across to the string.

Flight testing and measurements that I made on my first ship showed that the tail shaft, as measured

half an inch forward of the large nut, moves a quarter of an inch clockwise under load. Of course the

entire frame flexes and my reference point was the small vertical frame tubes on either side of the tail

shaft area. That first bearing mount is forty two and one half inches from the point where I measured

the quarter-inch deflection (see the drawing on the next page.)




As you can see in the drawing above, if the tail shaft deflects a quarter of an inch, an extension of that

shaft at the first bearing mount is going to deflect 1.19 inches.

Comparing the factory method with this is not as simple as it looks since the string moves with the tail

shaft as you rotate the transmission. I found the factory method difficult to do and subject to all sorts of

errors – the steel rule flexed and flopped around, I got different result depending on exactly how I

positioned the rule on the tail shaft, and it was difficult to hold the rule steady while attempting to

measure the distance to the string.

After attempting to compare the string method with the laser alignment method that I intend to use, I

came to the conclusion that the results appear to be similar. It’s impossible to know what offset B.J. was

attempting to achieve since that string moves with the transmission. It’s like a dog chasing his own tail.

With my method using a laser, I can very accurately set the offset exactly where I want it and I can

explain exactly how I’m doing it. With the factory method there is no direct correlation between the

quarter-inch offset to the string, and the amount of transmission deflection.




MY TRANSMISSION ALIGHMENT PROCEDURE

I know from the testing

that I did on my first

ship that the shaft

moves 0.25 inches

under load in a

clockwise direction as

measured just forward

of that large nut (left in

this picture.)

I’m using a boresight

laser that was designed

to line up the sights on a

pistol. I fabricated a

housing to just fit into the end of the tail shaft and hold the laser (white arrow.)

The first step in my alignment

procedure is to center the laser on

a target at the tail rotor mounting

location by adjusting the

transmission (picture at left.)

By rotating the tail shaft while

observing the laser spot, it’s easy

to tap the end slightly to reach

perfect alignment. When the dot

remains in the same place as the

shaft is turned, the laser is

boresighted. This is where I want

the transmission when under load.

As you can see, there is a vertical

misalignment that cannot be

corrected. The weight of the tail rotor assembly and fins will flex the frame down very slightly, but not

nearly enough to bring that dot up into the middle of the tail rotor gearbox mounting hole. Since I can’t

change it, I’m not going to stress over it. The couplings at either end of the driveshaft are designed to

handle some angular misalignment, which I calculate to be 0.67 degrees.




Now that the

transmission is

centered on the T/R

gearbox mount using

the laser, I taped a 6-

inch ruler across the

first bearing mount and

lined up the 3-inch half

way point on the ruler

with the laser dot.

Going back to the

drawing on page

eleven, I rotated the

transmission

counterclockwise on

the one mounting bolt

until the laser dot was

offset by 1.19 inches.

That will give me that

0.250 inch offset that

I’m after at the end of

the tail shaft.

The only remaining

step is to drill the right

hand mounting hole

into the steel frame

using a center drill.

You use the existing

mounting hole in the transmission as a guide and come up from below. The center drill is smooth along

its length so that it does not cut into the much softer aluminum transmission housing.




MOUNTING THE TRANSMISSION

The actual drilling of the right hand

transmission mounting hole in the frame is

anticlimactic. You simply insert the #4

center drill through the transmission

housing hole and drill into the frame

mount. I lubricated the shank of the drill

to minimize friction with the housing and

made a special point to try to stay

centered in that hole while drilling. As you

can see, the center drill has a pilot drill at

the point to get the hole started.

These drills have a cutting tip on each end

and come in different lengths. I chose a

four-inch length.

Wear safety glasses when drilling!

Now that the right hand mounting hole is drilled I can mount the transmission in the frame for the first

time. I used my trusty Genie Lift by tying a line to the top of the rotor shaft and pulling it up through the

main shaft upper bearing. It comes up at an angle so I padded all the surfaces that would scrape paint

as it was raised.

Once in position I secured the two mounting bolts and then the attached the transmission lift strut

assembly.

At that point I stopped to take a few pictures and update this write-up…




Oops! One benefit of taking all these pictures and writing up my work is that I catch errors. The picture

on the left shows the main shaft bearing lube line (#6 on page-6, and top of page 8.) I only noticed that

it was rubbing against the left hand lower tank when I looked at this picture. I fabricated another line

that loops under the fill hose fitting instead of trying to sneak between the hose fitting and the

transmission web (picture on right.)

Finally, I set up my dial

indicator and did a

preliminary mounting of

this main rotor top

bearing using this and fat

washers. That got the

runout down to about

±.005 which is not good

enough for a final

installation, but will do

for the moment.

Once I complete the

installation of my 55-Amp

alternator I can final-

install my pulley assembly

and teak out the radial

runout. That will come

later.




TAIL ROTOR DRIVESHAFT ALIGNMENT

OK. We know that the tail shaft flex coupling is going to move to the left one quarter of an inch in flight

(clockwise rotation.) The traditional build procedure is to align the tail rotor driveshaft with the

transmission offset one quarter of an inch to the right (counterclockwise.) The net result of this

approach is that the driveshaft will be in alignment with the transmission while the helicopter is on the

ground, and slightly out of alignment in flight. This makes no sense.

My plan is to remove that right hand transmission mounting bolt, point the tail shaft at the input shaft

of the trail rotor gearbox, align the driveshaft, and then return the transmission to the offset position.

This way the driveshaft will be slightly out of alignment on the ground, but aligned in flight where it

counts. It’s time to gather some data and do a few more calculations…

After drilling and deburring that hole I again centered the transmission tail shaft with the tail rotor

gearbox mounting hole using the laser.

Then I used AutoCAD to draft the tail rotor driveshaft mounting clamps and filled the center area with a

quarter-inch grid. Working from back to front I taped the CAD drawing into place and noted the location

of the laser dot using a felt marker.

Once again I stretched a string from the tail shaft to the center of the T/R gearbox mounting hole. I

mounted a fresh copy of the bearing clamp to each bearing hanger after cutting a slot to allow the white

string (below) to pass through. I used the previous step with the felt marker to locate my cuts.

REAR MOUNT LOOKING AFT FORWARD MOUNT LOOKING AFT

There’s the two bearing hangers The rear bearing will be offset about an eighth of an inch up and to the

left from the center position (as viewed from the front.) The right one is perfectly centered but it will

need to come up about an eighth of an inch. The bearing clamp mounting holes are oversized so no

filing of the frame supports may be necessary. I won’t touch these mounts until I get to that part of the

build, but it’s good to know the frame is very close.




Its forty inches from the rear bearing mount to the tail shaft. All the flex in the driveshaft will take place

in this forward section when the transmission torques clockwise.

Looking at the forward coupling first, I know that the vertical misalignment is 0.67 degrees on every

ship. This is built into the way the frame and the transmission are configured. If that 40-inch first

section is displaced a quarter of an inch, then the angular offset will be 0.36 inches – only half of the

vertical offset. Since the Helicycles in the fleet are not experiencing any problems with this flex coupling

I think we can disregard it as a potential problem. Plus, I’m not adding any additional flex or bend to the

driveshaft – I’m just moving it from occurring in flight to occurring on the ground.

That leaves the driveshaft itself to consider. But again, I’m not introducing any new flex – just changing

where it occurs. The three sections of the driveshaft are bolted together at the bearings with two

crossed AN3 bolts on either side of each bearing. It’s possible that constant flexing at that first bearing

could eventually oval out those bolt holes, but the flex in that first section should be spread along the

full length of the tube. Either way, those forces and that slight flexing will exist and there’s nothing I can

do about it.




TRANSMISSION INSTALLED – TIME FOR THE ALTERNATOR…

Normally I would close this out and switch to another document file, now that I am moving on to the

alternator. But they are so tightly linked that I thought I’d discuss the preliminary steps involved in the

alternator installation. I have a separate document with all the details, but I’ll cover the first part again

here.

These are CNC machined mounting plates for the 55-Amp alternator conversion. They mount to the

frame on one-inch standoffs that are attached to four modified shaft collars via the four ¼-inch holes

you see. The larger hole at the left is for the field circuit breaker.




After mounting the plate to the frame the next step is to install the pulley assembly and the alternator

alignment fixture. The alignment fixture, along with an alternator surface gauge that serves as a pulley

replacement during installation. The surface gauge exactly matches the dimensions of the drive pulley

but it has threaded mounting holes to allow attachment to the alignment fixture.

The alignment fixture is machined with an offset at the alternator mounting end to exactly position the

alternator to compensate for the clockwise torque reaction of the transmission under load. It also

spaces the pulleys correctly for the Micro-V belt that I am using and insures that the alternator

driveshaft and the transmission driveshaft will be parallel during operation.

Once mounted on the alignment fixture the alternator can be moved up and down and rotated on its

shaft to position it for the two alternator mounting pieces.

I roughed out the half-inch 6061-T6 stock that I will use on a table saw with a carbide blade. Then I

surfaced all six sides of each piece with a fly cutter on my mill.

Since I just completed an installation on another builder’s chip I started cutting the critical mounting

angle using the settings I already had. I knew that each ship would probably be slightly different, and

my mounting angle to the plate was less than half a degree off from the previous ones – probably more

like a few tenths of a degree.




Here’s the

angled vice I

use to

machine the

angles I need

on those

mounts. I

only use it for

this job, so it

stays where I

put it which is

very handy.

Here’s the

small forward

alternator

mount for my

ship. It

attaches to

the plate with

two AN-4

bolts and

locking nuts.




They say a man

with a watch

always knows

the time, but a

man with two

watches can

never be sure.

How true! I

need to know

what this angle

is since I will be

machining the

mounting holes

in the plate at

the same

angle.

Last time I used

a mechanical

protractor but

this time I

decided to try a

photographic

approach using

AutoCAD.

I pasted the picture into AutoCAD, eyeballed two lines to define the side and bottom of the mount (it’s

upside down in this picture.) Then I had AutoCAD determine the angle.

Based on this I will offset my four mounting holes in the plate by 4.6 degrees.

Using AutoCAD again, I sketched out a 4.6 degree angle and included a stack of lines spaced one quarter

of an inch apart vertically. Last step – measure the distance to the intersection of each quarter inch line

with the slope. This is how I intend to get that angle when I drill my holes.




Here’s the mounting plate mounted upside down and supported by a 1/4-inch, a 1/2-inch, and a ¾-inch

plastic rod spaced at the intervals calculated on the previous page. I use plastic so I don’t scratch up the

plate.

I got ahead of myself slightly. As I mentioned, I can move the alternator up and down and rotate it on its

shaft. I mounted the forward mount that I just made, with a fat washer as a spacer and positioned it

where I wanted it to be located. Then I used a quarter-inch transfer punch to make a small mark where

each mounting bolt will need to be located.

Once the plate was clamped as the correct angle I used my laser center finder to precisely center the

drill chuck on my mill directly over each mark. I used a small center drill to start and then worked by

way up to the quarter-inch holes I need in three steps.




Once those two holes were drilled I reattached the plate to the frame and secured the forward mount to

the plate as you see here.

The next step is to fabricate the aft mount. The angle on the foot will be identical, so that is easy to do

with my angle vice. Next step is to use a transfer punch poking through the aft alternator mounting hole

to scratch a line across the aft mounting blank.

I’ll center my hole on that line and slightly above and drill out the alternator mounting hole. Then I’ll

carefully trim the length of that slanted foot until the aft alternator mounting bolt slides in smoothly

with a fat washer as a spacer.

After that I’ll clamp the mount to the alternator and use the quarter-inch transfer punch to mark the

exact location of the two remaining mounting plate holes.

After drilling those two remaining holes I’ll flip the plate over on its back and countersink all four holes

to accept flat washers.

That’s about all there is to my alternator conversion project. Once I have all my metal work done my

parts and the other builders will go off to the plating shop for a satin matte chem-film treatment. Once

the parts come back I can final-install them and add a few more pictures.




Here’s one last picture of the alternator alignment fixture and the surface gauge. Here you can see the

machined offset that accounts for the angular and linear displacement that occurs when the

transmission torques in the frame.

You can read more details on this particular project in a separate document.

Hat’s it until I get the parts back from the plating shop…

3) TRANSMISSION DRAGS FRAME WITH IT 4) TAIL … Installation.pdf... 2015 Page 1 THE EFFECTS OF TORQUE ON THE TAIL ROTOR ... transmission back into position and ... of side force to

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