Scott's Hirobo GPH-346 Page

Last updated: August 22, 2001.

Here are some pictures of my Hirobo GPH-346. I bought this helicopter in kit form, on October 5, 1999 from MTA Hobbies in Torrance, CA. This is the belt-drive version. It is powered with an OS 46FX-H engine, a Hirobo "GT" muffler (Hatori), and an Enya #3 glow-plug.

I'm using a Futaba R148DF receiver that I had on hand from one of my airplanes, Futaba S148 servo for throttle, S9202 for collective, elevator & aileron, and a S9205 on the tail with a Futaba GY501 AVCS gyro. All of this is powered with a 4.8V 1700maH Sanyo SUB-C battery pack.

I use a Futaba 9ZHPS as my transmitter.

October 21, 1999 -- I've decided that I'm going to continue to chronicle my GPH-346 much the same as Bill Ludwig did on his excellent page. These pictures show it mostly completed and nearly ready to fly. Since this is my first chopper, I've made a few mistakes here and there, but it's the fixes that make mine unique.

You can see the pitch arm and balls are not original. This is because I accidentally used the rod for the pitch arm for the throttle, and the throttle arm was too small. I fabricated this one from 2-56 rod and Du-Bro ball ends. This is actually more rigid than the original setup.

You can also see in these pictures that I upgraded some of the servo arms to aluminum. Just a personal preference here, purple wasn't my first choice but you get what's available.

Left Side Left Front Right Side Right Front Boom Servo Gyro Mount Pitch Arm Pitch Ball T-Fuel Filter Left Side with Canopy & Heather & Hannah

October 24, 1999 -- We were going to fly today, but I'm having problems understanding the Futaba GY-501 setup instructions. (click here for 9MB PDF file) I've decided I'm NOT going to use the Heading Hold feature until I'm more comfortable hovering and controlling the tail, so I just want to use it as a standard dual-rate gyro. The manual has me doing programmable offset mixes and it's confusing me. Also, the rudder stick is only functional for about 25% of it's travel on each side of neutral. There is enough we don't understand that we're not going to fly today.

October 25, 1999 -- I finally figured out the Gyro and now have it set for standard dual-rate using switch F for high and low. Now I understand what they were trying to do with the programmable mixer, I just went about it a different way for now. The gains are set for 20% and 60% as a starting point.

October 31, 1999 -- Today will be the day. I went over to my buddys house and we double checked the pitch curve and maximum pitch. We tied on some training gear that Robert had built for his old Kavan (1982-ish?) and headed for the flying field, which is a local rec-center soccer field.

After some further checking, Robert found a couple of loose ball-links. They probably wouldn't have come apart, since they were screwed and loctite'd, but we fixed them there at the field. Further checks and we were ready to get things rolling. My friend Jeff and his son Jeffrey had joined us and took video of our trials.

When we attempted to start we found the engine was flooded. Once we got past that we started it up and carried out in the field. Robert did some testing to familarize himself with my radio, as he went to the dark side and is using a JR 8103. Seriously, I don't have a problem with JR, I just started with Futaba and am happy with what I have now.

Okay, triple check and we're ready to see what happens. As soon as she got light on the skids the tail, in a BLUR, whipped counter clockwise. We tried it again with the same result. After checking the stick deflection/tail rotor direction we determined that I had the gyro direction wrong. A quick change of GDIR and we tried again.

The first time off the ground was about 1/2 second. Robert said the stick was WAY too sensitive. I made a quick change and she was in the air hovering about 6" off the ground. We noticed the head speed was a little fast, and there wasn't much lifting potential. Long story short, I didn't have enough pitch at that throttle setting. A few changes over the next couple of hours and it was working much better.

I had read about problems with the mixture on the OS 46FX-H engine. I had decided to myself that I wasn't going to make any changes until I had witnessed the problem on MY engine. Well, let me tell you, we fought mixture problems through all six tanks of fuel. As has been stated before, DO THIS MODIFICATION to save yourself lots of headache.

Once she was trimmed, Robert commented "Hey you've got a sports car here!" and asked me if I was ready to fly. It should be mentioned that I have never flown a R/C Helicopter before! I spent pleanty of time on my CSM simulator, but never the real thing. As I raised the stick, I watched it get light on the skids, applied a little right cyclic, some more pitch, and I was up in the air. I had a tendency to stay very close to the ground, and everytime I got the slightest bit nervous I brought it back onto the grass. I should mention to all of you new pilots that if I did not have the training gear on there I probably would have destroyed the chopper. Mostly because of my "sliding" landings that are possible with wiffle balls but impossible with skids. I never "hit" the ground hard, but sliding landings are another reason for training gear!

My next flight, I got a little braver, and was about 2 feet off the ground when a big gust of wind came along and she went about 10 feet in the air. I panicked and dropped the collective and it started falling, to which I panicked again and added collective. You got it, PPIO, Panicked-Pilot-Initiated-Oscillation. I was able to get it down okay and handed the controls back to Robert. As he was bringing it back towards us the wind changed and it touched the ground. It wasn't hard, but the vertical tail-fin touched the ground. We saw parts flying off the tail. Further checking revealed that the tail-fin, the tail-rotor blades and the tail pitch-slider were all broken. It looks like the tail fin flexed into the path of the rotor blades. See the pictures for a visual.

Broken Vertical Fin - Left View Broken Vertical Fin - Right View Broken Tail Pitch Slider

November 1, 1999 -- With the advice of my internet friends, I called Ron at Rick's R/C Helicopters and ordered an aluminum tail-pitch slider, carbon-fiber tail fins, and some replacement Hirobo tail-rotor blades. It wasn't until late this evening I noticed the tail-rotor shaft was also bent. It's more than .030 out, which I'm sure is unacceptable. I'm going to attempt to straighten it myself.

November 2, 1999 -- Well, the tail-pitch slider is out of stock, so I'm grounded until it comes in next week. Probably a good thing, since Thursday is my 10th wedding anniversary, and Saturday is my oldest daughters 4th birthday. I'm still going to sneak to the flying field with Robert to see his ZXX fly. I did the OS Carb mod mentioned above. I hope I did it right, you can see a picture below.

OS 46FX-H Carb Mod

November 8, 1999 -- The tail-pitch slider, fins, and rotor blades showed up today from Rick's. Ron was also nice enough to send me replacement bolts for main-shaft that has been noted could be a problem. I picked up a new tail-rotor shaft locally and started to put things together this evening.

It is becoming obvious to me that the belt-drive version of the GPH is the bastard child. Everything comes for the shaft (wire) drive version, and in some cases there is no mention of differences. Luckily, I was able to retrofit things to work on my bird. You will see in the pictures below, there were several modifications that had to be made.

After reassembling everything I noticed that the tail-gear housing was a little loose on the tail boom. I decided not to do anything but ask for advice on the H-List. Once that's been corrected, I think I'm ready to fly again.

Aluminum Tail Pitch Slider Carbon Fiber Tail Fins My Helper this evening! Tail Fin Gap Tail Fin Mount Tail Gear Completed Tail Gear Completed - Top Tail Set Completed

November 9, 1999 -- A couple of folks on the H-List recommended using a piece of electical tape on the boom before placing the housing on, and then tightening it down. I'm going to do that. Also, I was looking for a replacement pitch lever when I finally realized that the tail gear housing is exactly the same as the Shuttle ZXX. The little pin on the new pitch-slider is what keyed me in, and there are pleanty of replacement parts for the Shuttle series tail gear. I'm toying with the idea of trying some of the replacment parts.

November 13, 1999 -- We flew about two tanks of fuel through the chopper today. Several issues from the tail parts upgrade. First, and most important, was that I installed the belt going the wrong direction. Duh. Once that fiasco was over, we got it in the air again. Still needs more pitch, and the radio travel was at max. I changed the length of the pitch-rods and that gave us what we needed. I flew again, several short hovers, this time caught on tape. (clips will be here when I get my firewire card re-installed)

A new problem has surfaced. There is a vibration when the engine is running but no other parts are moving. I had some problems removing the one-way bearing for the starting shaft when I removed the engine for the carb mod, and I think I may have bent something just enough to cause vibration. I didn't think of this until we had wrapped it up for the day, so I'm not sure how to check until it's running again. Ideas anyone?

Another problem seen for the first time today was radio glitching. I don't have a glitch detection device, but watching some of the quick, uncontrolled movements of the chopper, there is something causing problems. More to follow after I do some testing on the bench. Possibly the carbon-fiber fins I installed?

On to the good news. The carb mod worked exactly as advertised. While I'm not into FFF yet, it was an easy task to get the mixtures set this time. I can't stress enough, DO THE MOD. Why hasn't OS addressed this obvious problem?

November 22, 1999 -- I didn't get to fly this weekend, but I did get my digital video capture card working again. Here is a clip of my early stages of hovering (I think this is my third or fourth hover). !!Warning!! It's a 17MB, 43 second clip. I haven't learned how to compress it any more, but will replace this clip with a smaller one when I get that figured out. (click here for 17MB MPG file) You'll see the glitch reported above when the camera is zoomed in on the chopper -- watch the tail shoot left. Note: This clip uses the Microsoft MPEG4 codec which doesn't work properly in older versions of the MS Media Player. Use this link to The Codec Zone for a variety of fixes to multimedia players.

January 2, 2000 -- I've had the tail pitch lever off while taking some measurements to attempt fabrication of an aluminum replacement. I've missed flying during this time so I put it back on today. I also moved the throttle linkage to reduce throttle a bit without affecting the pitch or throttle curve in the radio. Robert came over just before dark and we fired it up in my small front yard. Just enough to get things dialed back in and ready for the next day of flying. The rotor speed seemed much better this time.

January 9, 2000 -- What a day! Got several flights today, after a new glow plug was installed. This was in a cul-de-sac in an industrial area, and there was a little breeze that turned into a few gusts. A good learning experience for me. Had to make some major changes to the tail->pitch mixer. Also, Robert tried to fly it without the training gear and we found that there are several balance issues to work out when I'm ready to try it without the training gear.

I got **VERY** lucky today when BOTH screws for the damper on the rotor head came out! All of a sudden the helicopter pitched up and I corrected thinking it was wind or something. However, I had a hard time controlling it and put it on the ground for Robert to check out. He took it for a very short flight and confirmed that something was wrong. I actually found one of the screws and washers in the cul-de-sac. Grounded until I find another screw and washer. Here's what it looked like:

(click here for video clip)

On the plus side, the throttle sounds much better, it might even be a bit too slow, but certainly better than it was before. Also, mixture is about perfect and there were no problems with the engine.

January 22, 2000 -- After talking to my friends on the H-List, I found that the GPH rotor-head design is prone to those damper screws coming loose. I used some loctite and made sure they were tight today. I also went over every other screw just making sure everything was ready for flying again soon.

January 23, 2000 -- Another fun day of flying. Grama watched the kids so Kim came with Robert and I to watch and video us flying. Robert hadn't flown his chopper in several weeks, so we started off with him getting back into the swing of things with a properly tuned ZXX.

I realized when we changed the glow-plug a couple of weeks earlier that I had inadvertantly used and Enya#4 instead of the #3 we normally use. That in addition to a new brand of fuel caused a few mixture setting issues. We also dialed in the hover head speed to right around 1500RPM. I probably got two tanks of hovering practice. Robert says I'm starting to "get ahead" of it, but I've still got a lot to learn.

Today was also the first day we flew with the canopy installed. We were always making so many adjustments in the past that it didn't make sense to keep the canopy on. It's a little easier to see but I long for a nice fiberglass canopy like Bill Ludwig put on his GPH. After I finished my flying, we took the training gear off and Robert flew it around a while so I could take some 35MM pictures of it in the air. All in all a nice weekend flying.

March 3, 2000 -- Some pictures from January 23rd. We haven't had any flights in a while. With all the local Berlin concerts, and our trip to Lake Mojave, there just hasn't been any time to fly. Sigh.

Robert & Scott getting ready to fly GPH in air GPH in air

April 2, 2000 -- Robert, Duane and I went for a quick flight today. We went to a new place that was close to my house. I didn't bring my training gear so today was my first day to fly without them. Hmm, that gear is really narrow! :-) It was kinda windy but I got three short flights in and was quite pleased with myself. I learned that I need to get the RPM's up a little bit because it was evident that when I pull pitch out I'm loosing too much head speed. It's a little scary when you're dropping and there is a lag time before you can keep it from falling. Will work on mixing more throttle before my next flight. That annoying tail twich was back again. I need to solve that! Came home with everything I went with...a good day!

Between April & November -- Well, a lot happened over the summer. I hit just about every Berlin concert in California, and we made a couple of trips to the river to ride waverunners. I didn't get any flying in since the April 2, flight. I did upgrade the tail rotor assembly to an all-aluminum setup, and installed a carbon fiber pushrod. I'll add some pictures as soon as I get some time.

November 11, 2000 -- My uncle Terry, Robert and I went and flew a bit today. First time since installing the new tail gear. Robert took it up and trimmed it out for me, and I took just a short flight. Getting back in the hang wasn't too hard, just like riding a bike (with training wheels). I was totally nervous the entire time, and mostly right on the edge of control.

December 9, 2000 -- Had a great time flying again today. Practiced a bunch of take offs and landings. Decided to dial-out the trims and fix the mechanical linkages. Also changed the gyro to allow me to try heading hold mode for the first time.

December 15, 2000 -- What a deal. Robert's new job he gets every other Friday off. We found a huge field that we had to ourselves. We dialed in heading hold mode today. Pretty neat, got to ask some questions on the h-list as this is really new to me. Robert had me spend a LOT more time doing take-off's and landings. He is working on me getting the training gear off, and I actually flew my last tank without the training gear. I got 4 tanks of flying in today.

December 16, 2000 -- Ran three tanks through again today, no training gear again from the start. Spent a lot of time practicing orientation to the left and right. My buddy Mark and his wife Liz from Washington State stopped by to watch. It was nice to see them again. Only slightly added pressure to not screw up royally. Got the gain set just right on my gyro. Can't wait until next week!

December 23, 2000 -- I made a few changes over the last couple of days, including a new 1600mAh sub-C battery pack, receiver, and a base-loaded antenna. I went to install the new battery and antenna, and found the receiver was kinda fuel soaked. I just replaced it with an identical R148DF that was in one of my planes.

I was trying to eliminate some tail twitching and a noise. We tightened the belt tension but the noise and twitch is still there. It's kind of a "Brrrp" and a tail movement in unison. Haven't figured it out yet.

This was also our first time trying my idle-up1 setting. It seemed to be just about perfect on the first try. Excellent. Got to get some pictures scanned and up here, maybe this weekend.

February 13, 2001 -- The updates are coming less frequent, but I have been flying on a regular basis. I've flown about 4 gallons through to date and have been sneaking into forward flight. I'm still pretty weak from left to right, but am doing okay from right to left.

I also upgraded to a Futaba 9ZHP-WC II radio.

August 22, 2001 -- Couldn't pass putting this picture on the web right away. What a perfect ending to a perfect day.

Questions, comments? Please send me a message at

Are you a fan of my favorite band, Berlin? Check out the Berlin Fan Page.