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Ending Swashplate
Link Confusions


By Mark Fortune


Make sure Left side and Right side pushrods
from bellcrank to swashplate are the same length.

   Well, the flying season is now in full swing. I have attended 4 funflys in the last few months and am leaving in a couple of days for another. It’s always good to see what everyone has been working on over the winter months. This year started out really exciting! Leaving the flying site on Saturday of the Birmingham, AL FunFly, I was nearly involved in a major accident. My traveling buddy, Al Warfield, was not so lucky and took a direct hit into the mobile hobbyshop trailer he was towing. Al and I are both OK, but I’m sorry to say that others traveling on that same road that night can’t say the same. Thanks to all who stopped by and helped us unload Al’s trailer and all the RC goodies he had inside. Even more thanks to “X” who offered us his home for an overnight stay before we started home early the next morning.

Here is a tool that will allow you to check that
the swashplate is level and for interaction
between the collective and cyclic system. It
sit on top of the swashplate and is used to
check if the swashplate remains level while
is moving along the main shaft.

The small electric heli’s are very popular and growing every day. I have seen several of them flying, over the past few years, but honestly, they all looked like they were struggling just to hover. Some of the types I saw fly would get airborne only long enough for something to fail and crash. After a while, I just simply stopped watching them flying. However, that changed during the Huntsville, AL FunFly. I’d heard of the TRex series of small heli’s, but never really paid them much attention to them. Well, these little machines had performance like a 90 powered machine! Clearly, this design was far and above the great unwashed masses of the electric heli’s I’ve seen fly previously. Not only is the performance there in the T-Rex, but parts are amazingly cheap! You can check around some of the heli shops for prices, but here are a couple of examples: Main rotor blades $34.00, Main gear (2 pcs.) $10.50, Feathering shaft (4 pcs) $6.00, Flybar (2 pcs) $4.00. This reminds me when Miniature Aircraft introduced the X-cell series of helicopters in the 80’s. There was a lot of performance, unique combination of proven parts design, and replacement parts were cheap, as compared to what was already on the market back then. I’m hoping I can get a T-Rex 450SE up and running for a review.

I met an interesting guy named Darrel Sprayberry at the Huntsville, AL FunFly. Some of you may know him as well. He recently placed first at the Weak Signals Show in Toledo, OH in the helicopter static display. He has some interesting thoughts on electric powered helis. All of his models are electric powered. Now I’m not still talking about T-Rex or even 30 sized machines. His models are 60-90 sized machines. The cool part is that they’re not electric models by design, but were converted from glow powered versions. He was telling me how he uses electric motors and toothed drive belts to convert his models. I’m hoping he will give us more info on his conversions in the future.

This is a tool I made to assist in checking
that flybar is level. It can beused for many other setup
and building steps too.

Set Up continued ... A couple issues back, I left you with a model whose control linkages from the servo to the bell cranks were all the same size and parallel to each other. Now, we have to connect the swash plate and ultimately, the rotor head to these linkages.

As an overview, here is how everything should be set: Servo end points set as per the manual for CCPM, or if using mechanical collective control - 100%. All sub trim and radio trim should be at zero or neutral. All mixing should also be OFF and collective pitch curve should be a straight line from -10 to +10, and with end points set to 100% for high pitch and 0% for low pitch. Collective stick position should be in the middle or 50% position.

Ok, so where should the swash plate go? Well, the swashplate and washout unit should be considered as one “unit”. Since the washout arm links are not adjustable, the distance between the swashplate and the washout unit remains fixed. With that in mind, it’s best the swashplate and washout remain joined when centering the swashplate/ washout unit for setup.

With the main rotor head installed in it’s proper position on the main shaft, push the swash plate/washout unit up until it bottoms out against the main rotor head block or in the case of mechanics, like the Hirobo line, to the adjustable mixing base driver. Now, using a small ruler, measure the distance from the bottom of the swash plate to the top of the main frame. Next, deflect the swash plate full over, either left or right, until it bumps against the mainshaft. Lower the swash plate/washout unit until it either touches the side frame or the washout unit is within 3mm of disconnecting from the drive pins. Being careful not to change the position of the swashplate/ washout unit on the mainshaft, level the swashplate and measure the distance from the bottom of the swash plate to the top of the main frames. Subtract the distance of the lowered swashplate position from the raised swashplate position. Example: swashplate/washout unit raised=63mm. Swashplate/washout unit lowered=18mm. 63-18=45. This means there is 45mm of usable travel for the swashplate/washout unit. Since we are interested in centering the swash plate for equal travel, we will need to divide the 45mm of usable travel in half. 45/2=22.5. Now, raise the swash plate until there is 22.5mm between the bottom of the swash plate to the top of the main frames.

Evening at IRCHA 2006

Measure the distance between the link ball on the swashplate and the link ball on the bell crank, center to center. Make a pushrod this exact same length and install. Repeat for each bell crank that attaches to the swash plate. This is the same method used when the bell crank is eliminated and the pushrod connects directly to the servo. This is also tremendously useful for checking ARF helicopter’s linkages to be sure they are what they should be, as well as a method for double checking the manual’s dimensions of a kit heli.

Next, with the swashplate/washout unit centered along it’s travel on the main shaft, measure the distance between the swashplate ball and the fly bar control horn. Make two pushrods this same length. Make sure the flybar is correctly installed at this time. This means that the flybar is centered in the main rotor head and secured in that position. Also, the flybar control horns are parallel and “in-plane” to each other and are also secured. Don’t worry about the paddles for now. We’ll take a look at them later. After you’ve double checked you pushrod lengths, install the pushrods on the swashplate and flybar control horn balls.

Now, there are only two pushrods left, but they are certainly two of the most important. These are the pushrods from the swashplate to the bell-mixer to each blade grip and from the bell mixer to the fly bar. It’s important the relationship between these two pushrods is established from the beginning. It is possible to get the correct pitch readings at one location, but the relationship between the pushrods is all wrong. Ok, here’s how to get them in the right position. You can make some rough measurements between the swashplate ball and the bellmixer ball, and the flybar and the bell-mixer ball. Once this is complete, make two pushrods each for these two lengths. Install one each of these pushrods. Don’t worry about the other blade until after you get one side right. Transferring measurements over is a whole lot easier than trying to remember what side you were just working with.

Once you have the first
pushrod to the proper length, duplicate this length
for the other pushrod going to the swashplate.
Be sure to record this length for future reference.

Next, with the servos, bellcranks, swashplate/ washout unit still centered, lock the flybar perpendicular (90 deg.) to the main shaft. Some manufacturers sell flybar locks for just this purpose. I made a tool for just this reason. It will allow you to see when the fly bar is perfectly level. Hint: use a small piece of Saran Wrap between the bell-mixer ball and the ball link. This will provide just enough interference fit to hold the flybar in position. With both pushrods connected to the bell-mixer, check the bell-mixer to see if it’s level and adjust it if necessary. This is made easier by placing a small bubble level on the bell mixer. Place a small amount of grease on the bell-mixer to aid in holding the bubble level in place. Next, install the rotor blade in the main rotor grip. Be sure blade is parallel to the feathering shaft while in the blade grip. An easy way to get this right is to disconnect both bell-mixer pushrods from the swashplate and flybar. Rotate the blade back or forth within the grip until the blade will no longer flop around by itself when released. When the blade grip will stay put, carefully tighten the blade grip bolt to keep it there.

I’ll stop here for now. The very next part of this setup process will be determined by your flying style.There are some digestible bits that you should go back and re-read anyway. Next time I’ll tell you how to set your pitch according to your style.

So until then ... go attend a funfly somewhere! If you don’t know the answer to something, a funfly is a great place to find it. Look for sponsored pilots. They are there to help you ... that’s why the manufacturers send them there!