GPH H-list

GPH 346 - Comments and 'Nuggets of Wisdom' From Users

Last change: 12/30 - new entries at top of list.

Some GPH owners and how they have thier machines set up... Gunnar Nilsson, Stockholm, Sweden
OS .46 FX, JR388, JR4231 servos (JR511 on throttle), SPCM rx (NER-649S), 1300mA bat., CSM gyro (use heading lock most), Fuel 20% Aerosynth,10% nitro, Pitch: Max throw: -7, +4, +10, Normal: -4, 5.5, +9, Idleup2: -7,+5.0,+8

billludwig (at) Bill , Tucson, AZ, USA
OS .46 FX w/carb mod, Arcamax HH gyro, Hitec Servos, JR8103, PCM rx, 1100 mAh rx batt., BC-6 glitch counter, Vic's Fiberglass blaes, Pitch:  -5 & +10, Hatori Muffler, Byron 20/20 fuel Mike Davis
Two identical GPH 346s with OS46Fx engines (no mods yet).  TG carbon blades (585mm, 140 gram) symmetrical.  Futaba 8UHF radio systems, PCM, 9202 servos except tail on 9203.  CSM gyros and BC-6 glitch counters.  Both have 2 oz. Header tanks. Hatori muffler.  ARC products tail pitch slider upgrade.  Hirobo blue elevator swing arm system. Steve Cass, Tucson, AZ, USA
OS .46 FX w/carb mod, Arcamax HH gyro, Hitec Servos, JR8103, PCM rx, 1100 mAh rx batt., BC-6 glitch counter, Vic's Fiberglass blaes, Pitch:  -5 & +10, Hatori Muffler, Byron 15/18 fuel Lee Bry, USA NY Westchester
OS 46fx, JR 8103, Gyro Arcamax PI gyro w/JR2700, Glass Blades, Belt Tail Drive Vince Deller, York PA, USA
OS .46 FXH, JR8103 FM, Hitech servos (4)455's, (1) 525 on tail, FMrx
1100mA bat., PG-o1T gyro (single rate), Odonnel 15%, Pitch:Normal: -4, 5.5,
+9, Idleup1&2: -7,+5.0,+8 Tauseef Tahir, Illinois, Attending school at Illinois College of Optometry
11+ years RC, 11+ airplanes, 4+ helis, HAD: Shuttle ZXX, Kyosho concept EP, Kyosho Nexus Deluxe, HAVE: GPH and X-Cell custom, Flying GPH, JR 8103, Rx battery hanger 9 1400 or the JR 1100, OS .46 fx, Morgan cool power 10% probably maybe 15%, $99.99 pizeo gyro Gerry Yarrish, Work for Model Airplane News last 8 years, first flew helis in 1976, (Du-Bro Tri-Star) followed by the Du-bro Shark, learned to crash real good:-). Worked up to a GMP Cobra with a Bell Jet Ranger fuselage in 1981. Dropped out of helis for a long time but lived for Larry Jolly's heli column in MA mag. Got a Nexus this year to relearn the rotary hobby. Having lots of fun, just getting back into forward flight.Will be reviewing the GPH346 (belt drive tail rotor system) soon in MAN. Love the GPH (Great Performing Heli). Enya SS .50H, JR 8103, 531 servos and NEJ 900 gyro. Steve Woodrough - I own, and have only owned, 2 GPH Helis.  One has about 20 Hours on it; he other has about 15 Hours. Both are set up identically. Stock GPH, 2 oz header tanks, OS-46FXH, CSM Gyro, Futaba 8UHP Hendrik H, Boise, Idaho
OS .46FX, Fut 8UHF, Arcamax PI gyro w/2700G option, Fuel 15% Cool
Power, 2 ounce header.  Bench set up: Normal: -4 5 9, Idle up 1: -4 5 9,
Idle up 2: -9 0 9.  Battery checker and belt drive.

Bill: I was recently plagued with the elevator not centering after flying around. I was constantly having to retrim elevator. We suspected the Hitec servo was at fault until we changed it and the problem stayed. It was actually the 'Elevator Torque Lever Pivot' (part #403-235 on page 66 of the manual) slipping on the shaft. The shaft NEEDS A FLAT ground on it for the set screw!!!! All GPH owners, do yourself a favor and make this mod NOW! It could easily caused a crash. This is not an isolated case as another, almost new, GPH at our field had the same problem.

Bill: After 40 hours, the autorotation clutch is slipping too much and the
tail rotor almost comes to a stop during some autos.

Mike Davis: IMHO, the constant tail is too tight on the GPH when it is
first put together.  After numerous flights, it becomes lightly coupled and
the tail still drives on power failure but will also turn a lot easier.  When
first assembled, it's like there is no one way bearing or slipper, more like a
direct and constant connection.  They recommend putting grease on the
o-ring.  If you wanted more tension, you could put a shim on top of the
bushing that fits between the o-ring and the bottom of the slipper clutch.

The GPH concerned belongs to my son, as he's the
expert pilot! He uses it as a 3D machine, and was unable to achieve a
setup which gave a good tail lock in backwards flight with the wire
drive. Everything else was fine, but as soon as any fast backwards
flight was attempted, the tail would screw out.

I even tried swinging the tail rotor round on to the other side, so that
it acted as a "pusher" instead of a "puller" (more efficient, in
theory!). I had to move the gears round in the gearbox to preserve the
correct rotation of the tail blades (lower blade advancing), but it
still wouldn't lock. Then we got the belt drive kit, and it provided an
instant cure! The tail rotor gearbox on the belt drive version is
identical to the proven Shuttle unit, and works extremely well. It will
now fly backwards as fast as you like, while remaining locked solid.

I rest my case!

I wouldn't call it a complete design failure, as for normal flying, its
fine. However, extreme aerobatics show its weaknesses.


The bolts on the center hub come loose easily. Loctite them
and CHECK every few flights. Some people change to bigger
size head screws for better tightenning. Also, if you have a
crash, best to replace with new screws or they will break
and part of the screw will be stuck in the hub and you'll
need a new hub.

Bill: Happened to me too.

The cap screw holding the main shaft ( bottom one) comes off a few
times despite the nylon nut!!! One in midair and the other
was luckier when he picked up his heli and the head just
came off the heli!

Bill: Mine sheared off!! Someone suggested using a bolt that has a solid
shank that fits almost all the way through the auto hub, instead of having
threads inside the hub. Probably a good suggestion.

A little loctite needed at the clutch bell and top bearing.
Eventually this won't hold and overtime the clutch bell will
wear out inside the bearing. This is the usual source of
funny squeaking noise.

Tail gear set is very fragile. Change even if you have a minor
touching of the tail  blade to the ground. Visual inspection
may not detect minor cracks.

Change to metal stabilizer control arm as it is known to
break easily.

The screws holding tail gear box case
to the boom will be loose if you take it out a few times. I just
use a bigger size screw when that happen.

Oh, another important thing... glue pin 2509-003 to the
plastic part 0404-023. It was known to come loose.

I use oil (Triflow or something good)
to lubricate the wire in the tail. Grease will become
sticky with time and lots of energy will be lost to overcome
this friction.

The covering on the blade should be reheated as they are
very loose. Punch a pinhole at thevery tip and drop cyano in.
The covering at the end comes offeasily otherwise with
minor hit to anything.

Bill: This is more trouble, but I remove the covering and put about
eight coats of clear lacquer on the blades.

Miked: While the head is pre-built by the factory, do not trust that
they understand the utilization of LockTite. Remove the screw holding the
round stop plate, put thread locker on it, and re-assemble. Same for the
screws inside the small bearings on the top of each of the yoke side plates.

Miked: You will find that the time will come where the self tapping screws on each
side of the boom holding the tail gearbox will fall out. Use a small amount
of slow CA on each screw and they will never fall out. You can still get
it apart easily.

Miked: Try this: Pull one end of one of the rods from the x-lever to the elevator
servo arm. Move the servo to one extreme end of travel. Match the pulled arm
up with the ball on the lever. If it isn't a perfect fit the push rods are
out of symmetry. Go to the other extreme and repeat the test. Do the same
tests on the rods going from the x-lever to the elevator lever.

Miked: Be certain to check the aileron control arms. At maximum throw they should not touch
the side frames. Do this at max collective and min collective to be certain.
Do the same test to be certain that the rudder control rod doesn't rub the
aileron control arm at both max and min collective and at all rudder
positions. Even a very slight and occassional touch will cause massive
radio glitching.

Miked: If you fold the blades back to a blade holder on the boom to transport, be certain to
pop off one of the pitch links from the head to the blade. There is stress on
these links when you fold the blades back and they can bend easily.
Symptoms will show up in tracking when you go to fly.

Bill: Another solution is to have your throttle at about 1/4 when you shut off your receiver. This sets the pitch to where no binding will occur.

Gunnar: I followed up a rumour of blade throwing. I got the following
explanation; It's very important to glue the plastic blade roots to the
blades. The manual says cyano but one can preferably use Araldite
(or other 24 hour epoxy). Yes, but of course you say. Hmm, it seems like some
people did not want to glue since the blade roots are bought separately and
its extra work. So my answer is no blade throwing unless you neglect necessities.

Bill: Also, you MUST remove the plastic blade covering under the blade roots prior to gluing! Thick CA is ok, but epoxy is better - allows more time to soak into the wood.

Tauseef: I did the mod the GPH so
I can remove the engine in 10 min! Take out the shourd and fan and all,
line up the fan in the center and draw it's outline, and cut out the
bottom of the shroud so the fan can slip in and out. Now, you can leave
the shroud in, but wait, you will have to make the hole slightly
bigger on the top to, so the clutch can go through it.. I now only have
to remove the 4 mount screws, the muffler screws, the carb, link, and a
few lower screws and the whole engine drops out.. like the shuttle
pretty much (I think?!!?)

Tauseef: Did you dial indicate your start shaft?? I
have not, I do not have a indicator, I know I should but????

Gunnar: No. Did check with my importer, he is flying a lot (since 25
years) and says he never bothers with alignment.

Gunnar: Do be careful with the starter. The importer said some people
have broken the start shaft up to the "one-way" bearing connector. Means
you have to buy a new clutch.

Tauseef: The gear is toooooooo narrow, if you find this a problem, remove
the aluminum skids, put the plastic legs in a pot and let the
water boil for about 20 minutes, and then put the alumimun
skids back through and place something heavy on them. They will bend-
let them totally cool off, and wa-la your landing gear is wider and will
(should) stay that way! it worked great on mine!
You can also boil your gear for about 20 min to fix it if it wobbles to.

Gunnar: Its narrow but usually not a problem. With a rough engine
(like when running it in) and the heli is new you have to be careful.
I had no problems (after 4 tanks) so will see in the future with

The tail rotor drive wire can wobble and cause vibrations.

Gunnar: YES, do put on oil/grease. I didn't grease mine and still no vibrations
after about 5 litres fuel through. BUT, I will put in a steel tube like
Tauseef suggests.

Tauseef: The NEXUS DELUXE guide for the tail rotor wire slips right into
the plastic thing in the boom of the GPH and the wire will not flop
around now.. use Triflow Teflon oil.

Bill: Do oil. The instructions say "NO. use grease", but a manufacturer rep. said
that really means put on grease on the wire!).

Gunnar: On right hand side there used to be a M2.6 bolt going into the shaft.
Today the shaft is threaded M3. My heli was supplied with the bolt rather than
the "U-nut" indicated by the manual (my only deviance).

Gunnar: The engine sits low. For OS46FX leave out the extra washer and set
the tapered collar directly onto the front bearing. E.g. Hatori 444 still
needs a little filing. Also do change the nyloc nut on the side frame to a
thin nut (set with green loctite).

Not in manual: Clutch must have a small vertical clearance (0.3 mm) so push
the engine up and then lower it just a little. Metal needs room to expand.


Bill: Sand the fuselage with 220 wet paper before applying the decals. Also seal the decal edges with some thin cyano with a small artist's brush.

Gunnar: I only rinsed and washed mine with dishing soap in very hot water.
Still fine after nine tanks but we will see.

Christian Nord was having trouble with the main gear teeth breaking repeatedly.

Mike Davis: I have 2 GPH's... and never this.  Did you look at the tail drive gear... is
it missing a tooth perhaps or have something clogged in it?  This is way to
weird.  Do you have a free running tail system?  How about at servo
extremes, nothing binding it up anywhere?  Did you check the teeth on the
clutch bell?  All there?  Is the clutch running freely and smooth?  How
about vertical play in the clutch, main gear, tail drive gear?  Any chance
they can slip up or down?  Do you still have the driven tail set up?

Tom Retzinger: Make sure that there is no slop where the hardened sleeve of the
autorotation clutch mounts on the main shaft.  The sleeve should grab the
mast tight, with no play, so no shock can develop.  Also, put some
lightweight machine oil down in the one way autorotation bearing, so it
will grab quickly, without any delay when you turn the bearing backwards.

   Lastly, replace the cheap plastic main gear with the heavy duty machined
one made of Delron.  This is the gold part from the Shuttle, and is
somewhat expensive from Hirobo.  You can get essentially the same gear from
either Hobbies and Hellis, or CENTURY, for less.  You do not need the whole
unit, including hub.  You only need the new Delron replacement gear

    If you think that the stock plastic gear is bad now, wait until it gets
cold out, then you will be able to spit out teeth several at a time!

Larry: I had this problem for a while and mine was caused by two things. First, the
tail gear was comming loose just a little, I cured that problem with Loctite
green. The I found the other problem, which was the tail support tube and
come loose from the mount. This would allow the boom to flex on hard
landings. Your's maybe flexing during some of your flying. It may be that
something else is causing the flex. One thing I did notice about the main
gears, is that they would be missing one tooth, then one more tooth about
90-110 degrees from the first. I think this was caused as the boom flexed up
and down.

Christian: Thanks for your input. I will try all and see what helps. Another idea
from a friend is that it is the autorotation unit that is slipping and
when it catches the mainshaft the jerk breaks the teeth. I have greased
the oneway bearing at assembly but I will now clean it up and mount it
with oil only and see if this helps.


Gert, 30/09:
Can someone give me information on how to change te main gear 77T in a hirobo GPH 346 Where do i have to start with unscrewing Gert

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