RADIO CONTROL HELICOPTERS
Dan Williams, 27 Treeline Dr., Liverpool NY 13090; E-mail: [email protected]
Winter maintenance and timing
Is everybody enjoying winter? Yeah, right! This issue will come out sometime in January, smack in the middle of winter. I'm writing this in October, so I have no idea how the winter is going to shape up. I do know one thing: there's not much outdoor helicopter flying going on in February and March in the North.
Now is a good time to get radios out for repair and tuning. I used to work for a small radio-repair shop, and I know for a fact that people don't think about getting their equipment tuned right now. The first warm day in spring or late winter usually brings them out in droves and the backlog goes out several months. If you don't want to get caught up in the rush, do it now!
Battery care
Earlier this year I took my Intrepid 46 out for a spin. I hadn't touched it in quite a while. I did a once-over mechanically and freshly charged the batteries (Ni-Cd's). After approximately 30 seconds into the flight, things started to go wrong. I was getting tail-rotor twitching, and then the engine was going to idle — it was going into fail-safe. I still had enough control to autorotate the helicopter and shut off the engine. I went over and moved the controls and was getting sluggish response. I checked the battery pack and, lo and behold, it had lost a cell. That was close!
I went home and cycled all of the installed batteries in my shop. I also found a failed cell in one of my 9Z transmitters. The moral of that story is: do some battery cycling during the winter months. It won't guarantee a failure-free season, but it's better than doing nothing.
- Several good battery cyclers exist. I used an ACE Digipace for many years; it discharged at roughly 500 mA then charged at the C/10 rate and had an auto-trickle rate for pain-free cycling.
- I used the FMA Direct Supernova 250S (www.fmadirect.com) most recently; it's my current favorite.
- If a battery is more than three years old, replace it. Helicopters are expensive and batteries are cheap.
ViperHead test — setup
I recently had the opportunity to fly with a ViperHead-equipped YS .91 engine installed in a Vigor CS helicopter. Ray Stacy of Performance Hobbies (Webster, New York) had just started getting ViperHeads in stock after Curtis Youngblood's visit and success with them. We decided to make a head swap in Ray's Vigor CS and compare power and flying characteristics before and after.
The day we picked for the experiment was nice: temperature in the 70s with low humidity, so we weren't unduly influencing the test with extreme weather. The engine was tuned correctly for the conditions. The YS .91 had a Youngblood Muscle Pipe II for exhaust, and we were using Morgan Cool Power fuel with 30% nitromethane. Ray had modified the cooling shroud to accommodate the glow-plug location(s) on the ViperHead.
Each of us made flights with the Vigor. It's great to be able to experiment on someone else's helicopter—especially when he buys all of the parts to do the testing! We wanted to feel the power characteristics and find a maneuver that would load the engine so we could compare the modification.
We found that a good, solid "rainbow takeoff" (take off and climb out with a lot of pitch, roll to inverted, and immediately upon flying inverted pull full negative pitch to do an inverted climbout) causes a slight reduction in engine rpm on the stock head. It was subtle since the YS .91 already has tremendous power. Bogging with this engine usually means you've done something wrong or are doing something more extreme than I'm capable of right now.
ViperHead installation and observations
I proceeded to change over to the ViperHead. I was able to gain good access to the head without dropping the engine — we just removed the fan shroud and all head bolts were accessible from the rear.
When we removed the old head, there was a distinct odor of cotton-candy fragrance in Ray's fuel. I don't know what that stuff is made from, but I don't think I want it in my fuel.
The shim that comes with the ViperHead is slightly thinner than the stock YS shim. I followed the instructions and used the shim that came with the head, though James O'Neal later told me required shim thickness might vary with fuel type, engine, and engine age. We may have to experiment with shims depending on the situation.
A close look at the ViperHead showed some unique characteristics. The combustion chamber is roughly round, similar to the stock head. There are two glow-plug locations:
- The main glow-plug hole is slightly forward of the center of the combustion-chamber dome, toward the front of the engine. This required a slight modification of the fan shroud.
- The second glow-plug location is rear of center and tipped toward the rear at quite an angle. This didn't pose an access problem in the Vigor, but in some helicopters it could.
The instructions recommend using a cool plug in the main location and a hot plug in the rearmost location. This spawned a search through flight boxes because most fliers use hot plugs like O.S. #8 or Enya #3. Cool plugs include O.S. #A-5, Enya #4, and Enya #5. We didn't have a cool plug on hand, so we used two hot plugs (one O.S. #8 and one Enya #3). Curtis Youngblood commented that it didn't seem to make much difference whether a hot or cool plug was used.
James O'Neal said the cool/hot plug combination is more for FAI-style flying and helps smooth the hover. We ran with what we had and buttoned things up for a test flight.
Flight impressions
There is no need to connect both plugs to the glow starter at the same time for starting; the main plug can be used alone. We started the engine on the main plug and it had a completely different exhaust note. When we touched the glow starter to the second plug, the exhaust note changed again and idle rpm rose — it had a great sound even at idle.
At the flight line the engine spooled up the blades with no trouble, although it seemed to be running a bit richer than before. Up in a hover it was definitely richer but had a vastly different exhaust tone than before the modification. It probably could have used some needle tweaking, but that didn't detract from the performance so we left it alone.
After a couple of circuits, all seemed well. Ray launched the Vigor into a rainbow takeoff and as soon as it was inverted and got negative pitch, the engine rpm went up. It was obvious there was much more power available! The engine wasn't loaded by anything we threw at it. The model was peppier, engine performance was extremely crisp, and control response improved.
I haven't flown much with one of the 90-size big-block engines; my machines use 60-size small-blocks. I took off and flew circuits with airplane-type maneuvers and found the model more responsive. I had to get used to the extra power, but it was impressive. I flipped the model inverted and took off vertically and it launched without changing a note. Stationary flips caused the Vigor to climb as I did them. The response was instantaneous — the helicopter seemed to dance in the sky with the extra power.
Fuel ran low all too quickly. The engine probably could have been leaned a bit for improved economy; fuel mileage may end up slightly lower with the new head, but it's too early to tell — more testing is needed.
Since the initial testing we also tried the recommended hot-plug/cool-plug combination. There was no noticeable difference in performance for our 3-D style flying.
Recommendations and contacts
I highly recommend talking with James O'Neal if you're having difficulty getting your particular setup to run properly. With different fuels, plug preferences, and various engine ages, he can help with plug and shim combinations. He has a wealth of knowledge to share.
- Contact James O'Neal at AMI: (256) 776-0879
- More information: www.oneals.com/ViperHead.html
In all, the ViperHead modification is a worthwhile improvement at a reasonable cost. It definitely complements the Muscle Pipe II, and with the gearing and setup of the Vigor, I now understand why Curtis flies with it and recommends it. I give it the "Dan-o thumbs up"!
Closing notes
A club sent me a letter and some pictures describing some of its activities, so next month I'll do a short club profile. I also got to take a first look at the new Hirobo Scud 50 EVO, so I'll pass along some information about that as well.
If it's sitting on the shelf looking pretty, it's just getting dusty. I'll be back next month. MA
Transcribed from original scans by AI. Minor OCR errors may remain.
