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Review: Venture 50 3D ARF

8/9/2004 by Rick Bell

Provider Name:  Model Airplane News

Issue:  July 2004

Copyright:© 2004 Air Age Media

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Page 4: ASSEMBLY NOTES
(continued from previous page)

All shook up

The key to a smooth-operating helicopter is balancing the rotating parts such as the cooling fan, clutch bell, main gear and the rotor blades and using a dial indicator to check the runout (out-oftrue condition) of the cooling fan, clutch and start shaft. Balancing rotating parts is a complicated process and would take many pages to explain; instead, we'll look only at how to use a dial indicator; keep in mind that this is the method I use to check and adjust runout, but it's by no means the only way to do things.

Here are the basic tools needed to check the runout: a heavy, stable metal plate, a dial indicator and a mount to securely hold the engine.

 

The cooling fan is checked first; it's only finger tight on the engine, so adjustments can easily be made. The runout should be less than 0.002 inch.

Why use a dial indicator? Isn't just securely fastening the parts to the engine good enough, especially if the fan uses a tapered collet? Not really; you must remember that the fan and clutch assembly are fastened directly to the engine's crankshaft and therefore are turning at the same rpm. This can be anywhere from 10,000 to 14,000rpm, or even greater. If the runout of these assemblies is greater than 0.002 inch, the bearings and the radio equipment will very quickly fail due to excessive high-frequency vibrations.

Today, most helicopters use a brass tapered collet to center the fan on the engine, however, the Venture 50 doesn't, so the need to check the runout can't be overlooked. Checking runout isn't very difficult, and you need only a few tools. Obviously you need a dial indicator that reads in the thousandths, and you need a way to secure the engine. I use a heavy, solid-steel plate that's 9x9 and 3/8-inch thick so it doesn't move around. I then vertically mount a composite engine mount (to which the engine is bolted) to the plate. This simple and versatile method has served me well.

First, remove the glow plug (you want the engine to turn over easily), and then install the fan loosely (finger tight) on the engine using the prop nut. Secure the engine to the mount so it doesn't move; it can be horizontal or vertical-whichever is more convenient. Position the dial indicator's pointer on the lip of the fan hub. Rotate the fan to find the high spot, and mark it with a felt-tip pen. Now, rotate the fan while watching the dial; if the runout is 0.002 inch or less, you can move on to the clutch. If it isn't, loosen the fan and rotate it 180 degrees; repeat the process and check the runout again. If the runout is less-great! If it isn't, return the fan to its original position and rotate it again, but only 90 degrees this time, and recheck the runout. Repeat this process until the runout comes in.

Once the runout is 0.002 inch or less, tighten the prop nut a little at a time, and check the runout after each tightening. If you apply too much torque, the fan could move. To make sure that the prop nut is fully tightened, remove the engine's backplate and use a wooden dowel or toothbrush handle placed between the housing and crankshaft to prevent the crank from rotating as you tighten the nut. Don't use a piston-locking tool to jam the crankshaft. These tools work by screwing into the glowplug hole, and as you tighten the prop nut, the piston will be pushed against the end of the tool. I have seen people punch a hole in the top of the piston using this tool. Using a wooden dowel or toothbrush handle to jam the crankshaft is much safer.

To give you an idea of how easy it is to do all of this, my Venture took approximately 30 minutes to adjust the runout. After I balanced the fan (about 13 minutes), it took me about 17 minutes to check and adjust its runout. At first, the fan had a 0.005- inch runout. After I had moved things around a few times, the runout was 0.001 inch. The clutch runout was 0.004 inch; after I rotated it 180 degrees, it, too, was at 0.001 inch, and the start shaft was almost perfect. Not too bad for a few minutes of effort! Now if the heli has a high frequency vibration, you'll know it isn't the fault of the engine assembly.

As mentioned, there isn't much to do when assembling the Venture 50 3D; the instructions cover the assembly process quite nicely. So instead of going through it step by step, I'll cover the areas that aren't so obvious.

Because I knew that assembly would proceed rapidly, I first rounded up the components so they would be readily available. The tail boom requires only that it be plugged into the chassis and secured; the tail rotor assembly, drive belt, horizontal stab mount and boom supports are factory installed. Even the nuts and bolts that clamp the chassis around the tail boom have been installed.

Before installation, be sure to twist the drive belt 90 degrees clockwise (when looking at it from the front) before you slip it over the drive pulley. The boom supports are attached to the chassis, and the boom is pulled back to tighten the drive belt. The tail fins are attached to their mounts, and I applied the decals to them before installing them. I installed the tail-rotor pushrod next, and I sanded it so that it would slide more easily in the boom-mounted pushrod guides.

Before you snap the ball link on the tail rotor bellcrank, take a few minutes and adjust the pushrod so that it will move with the least amount of resistance. That completes the mechanical assembly of the heli except for the installation of the engine and servos. I told you there wasn't much to do!


Engine and fuel system.
To power the Venture, I used an O.S. 50SX-H ringed engine. The engine is screwed to a castaluminum mount that is then secured across the chassis with the engine head toward the rear; this provides easy access to the glow plug. Before installing the engine in the chassis, I dial indicated the cooling fan and clutch assembly (see "All shook up" for details on this important step). After the engine/cooling-, fan/clutch-assembly is dialed in, the engine and the engine mount slides into the chassis after the carburetor is removed. JR must have changed the mount after the instructions were written. The pictures show 3x30mm bolts and locknuts being used to secure the engine to the mount, when in fact, 3x12mm bolts are used; the engine mount has been threaded for the shorter bolts. Before the fuel tank (which has already been installed) and the engine can be plumbed, the 2-ounce header tank needs to be installed; it's simply bolted to the left side of the chassis. Adding the header tank to the fuel system is easy; the feed line from the tank goes to the upper nipple on the header tank, and the feed line from the header tank goes to the carburetor. Muffler pressure pushes fuel from the main tank to the header tank. Besides increasing the fuel quantity on board, the header tank improves engine performance and consistency and provides an easy way to see how much fuel is left.


Radio installation.
The swashplate requires 3 servos to drive it, and these all must be the same. I used JR DS8231 digitals because of their precise control and excellent power. The servos are mounted within the chassis; I routed their leads inside the chassis as well. After the servos have been installed, the manual becomes your best friend; it provides detailed instructions on how to set up the CCPM system. If you're using a JR radio, choose the pages that apply to your radio and follow the instructions to the letter; you can't go wrong. The chassis has a molded-in battery compartment under the front of the receiver-mounting tray. I wrapped my receiver battery in foam rubber and placed it in the compartment. I also wrapped the receiver in foam rubber and placed it on the mounting tray. The tray has a bunch of molded-in lugs so that you can wrap rubber bands around them to hold the radio equipment in place-a very smart setup. For those who haven't dealt with a CCPM setup before, here are some pointers to get you started:

• All CCPM servos must be the same make and model.

• Initially, the travel adjust values (ATV) for the CCPM servos must be the same. If not, unwanted pitching and rolling of the swashplate will be created during collective pitch inputs.

• The throttle/collective stick and swashplate needs to be in the center of its travel during initial setup.

• The servo arms must be exactly horizontal. Minor adjustments can be made using subtrim to center the arms.

• All pick-up points on the servo arms must be the same distance from the center of the arm.

• The swashplate must be level fore/aft and left/right when the servo arms are centered. Adjust the swashplate pushrods to level the swashplate. Do not use subtrim; subtrim; this will upset servo-arm centering. Then follow the instructions for your particular radio to set up the pitch and throttle curves.

• Final details. All that is left is to trim the windshield, attach it to the canopy and apply the remaining decals. The cut lines on the windshield match the canopy very well, and four small screws secure the windshield. The canopy has molded in recesses where the muffler resides, so I decided to cut them out to provide cooling air for the muffler. I really like that the muffler is enclosed; it reduces the risk of burning yourself by touching it.

 
Four guides support the tail-rotor pushrod. They wrap around the boom, and a single screw.   For a smooth-running heli, all rotating parts should be balanced. Here, the cooling fan is being checked out on a Robart High Point balancer.

IN CLOSING
The JR Venture 50 3D ARF is one impressive helicopter. Its aerobatic prowess is unmatched by any heli in the .50-size class, and it's a logical step up from a .30-size heli. What little assembly there is goes quickly and easily thanks to the simple mechanical layout and tiny parts count. The icing on the cake, though, is the outstanding instruction manual; it goes far beyond most other heli manuals and isn't overly technical. Whether you're a novice, intermediate, or expert heli pilot, the Venture 50 3D gives you a lot of bang for your buck!

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