Gas Helicopter Motors - Part 2 - The Formats Used

[carey shurley]

now that we've covered some history this installment will discuss they formats of motors being used.

PUH Format

From the history discussion its clear that the most popular motor being used to date has been the Zenoah PUH format motor. BTW in case you're wondering, PUH is the designation for Power Unit - Helicopter.

this format motor comes in three stock forms:

• 20cc (32mm bore, 28mm stroke)
• 22.5cc (23) (32mm bore, 28mm stroke)
• 25.4cc(26) (34mm bore, 28mm stroke)

the 20cc uses totally different parts from the other two including a CDI ignition



The 20cc motor is rather new its only been out for a couple of years and has so far only appeared in a couple of models, the Quick Bat and the Century Radikal which are both 600 class models. Unfortunately its been very hard to acquire and they are more expensive than the larger motors. I'm not aware of any new models planning to use this motor. It is overall about 8oz lighter than the larger motors though. Due to its relatively lower power output its not a good choice for the larger 700 class models.

until recently most everything else is based on the Zenoah PUH format motor. As you can see from the specs they have the same stroke with different bore sizes. The motor is delivered with a magneto ignition system, muffler and carb but no cooling system. So each manufacturer has created their fan/hub cooling shroud. Some have been more successful than others, the rather large fan found on the Century models seems to work okay. There was a third party manufacturer also marketing a fan/shroud design that worked rather well but they seem to have since stopped producing it.



a side issue at least in North America is that the PUH motor format from Zenoah has very limited distribution rights. They can only be imported by a few companies and this has kept the supply low and the price high

There have been persistent rumors for over a year that Align would produce a gas helicopter using a motor in this format but not necessarily from Zenoah. Despite a few teaser videos there is no official information that I'm aware of as to whether or not such a model will be produced or when.

the exception to the use of the PUH format has been the Vario and Airstar models, they have been using the Zenoah RC format motor for years.

RC Format


Zenoah RC Format motor


Here you can see the difference in size between cooling fans


here you can see the enclosed cooling shroud on the RC format motor


and this is a typical cooling system for the PUH format motor

as you can see not only does it have the same components as the PUH motor but its also got its own cooling system and its VERY effective. Although the motor is larger and requires a bigger footprint in the chassis, when you put all the supporting parts together it weighs almost identically the same as the PUH motor. So this offers a big advantage to the manufacturers as they no longer have to struggle with getting an oversized cooling system to fit into their models. The motor is physically bigger though and components have to be rearranged.

this motor is also available in a larger displacement:

• 28.5cc (36mm bore, 28mm stroke)

the licensing issues with the RC format motor are different and as a result it is readily available in many different configturations and displacements typically at a much lower price thanthe PUH format. There is also a Zenoah competitor, Chun Yang which have made almost identical copies of the motor.

There are also some confusing variations. The original motors were listed as the G230RC and G260RC. Now there are also the G240RC, G270RC and G290RC. I get a lot of questions about what are the differences. There are a few minor differences but the major difference is that the older 230/260 motors uses only 2 bolts to hold the cylinder on. The newer 240/270/290 use 4 bolts to hold the cylinder on. The big advantage here is that the cylinder seals better to the crankcase and is less likely to develop an air leak.

nonetheless a year ago, I wouldn't have run these motors if you gave me everything I needed to do so. as compared to the PUH format they just look huge!

However in the last coupla years an american company called Helibug started building conversions for TRex helicopters using this format of motor almost exclusively. Eventually I bought one of these and built it. I could have NOT been more surprised. The motors run very evenly, cool superbly and are not any heavier ready to run than the puh format. There are now several versions of these conversions available most all use this motor format. As best as I can tell, this was also the first instance of using the larger 23/26cc motors in a 600 class helicopter

There are rumored to be other manufacturers considering making models available with the motor format as well, time will tell. If so they will have solved the typical cooling problems once and for all.

New Format

There is another option that has appeared in the last year or so. A helicopter company out of Germany/China called RJX produced a model that used a single cylinder 26cc motor made by a company called CRRC. Its a more compact motor with a CD ignition. Earlier this year a couple of conversion kits emerged both using this motor in a 600 class model, the Radikal 20. Since the announcements this has gone rather quiet but I expect by summer time this year we'll see some of these flying.


the 26cc CRRC motor


here is how it compares to the G20 in size

From my perspective the biggest advantage of this motor is that its small enough to install in the smaller class of helicopters but has the same displacement as the larger models require. That presents a great opportunity to improve the power/weight ratio which almost all gas helicopters are penalized with.

there are quite a few other motors similar to this format that can be found on various websites. my experience with several of these in stock form has not been very positive for a number of reasons. I understand folks are having luck with them in airplanes but helicopters have completely different requirements. The motors I have experience with working properly have been highly modified for balance and quality purposes.

Whats next? Thats a great question.

Its likely that at some point these little two stroke motors will cease to exist. Our friends at the EPA don't think much of them and have a way of legislating things out of existence. Seen many new two-stroke motorcycles designed lately? I have seen a couple of four-stroke conversions done by individuals but most of these motors are even heavier that the small two strokes.

I get a lot of questions about why aren't their multi-cylinder motors and why doesnt' DA or 3W produce something custom made for gas helicopters. Because of the size and weight (and cost) multi-cylinder motors aren't practical in a 600/700 class helicopter. I have talked to folks at DA before and they just don't see the volume opportunities to spend the money to develop a helicopter motor. So for now the next closest thing is probably motors that have been modified to make more power.

On that subject the next installment is going to focus on the topic of stock vs. modified

The Bottom Line:

to date the PUH format motor has dominated the helicopter market. There are thousands of them in helicopters from a variety of manufacturers. They have been pretty successful but many suffer with cooling challenges

going forward this may change as alternatives are becoming more attractive

[Billme]

"The 20cc motor is rather new its only been out for a couple of years and has so far only appeared in a couple of models, the Quick Bat and the Century Radikal which are both 600 class models. Unfortunately its been very hard to acquire and they are more expensive than the larger motors. I'm not aware of any new models planning to use this motor. It is overall about 8oz lighter than the larger motors though. Due to its relatively lower power output its not a good choice for the larger 700 class models."

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With over a 1000 kits of the Radikal 20 sold, The Zenoah 20 was just in demand, and everyone got a engine...

It is one of the easiest running best engines I have ever had the pleasure to fly and can out perform some 231 machines in the right hands.
Although its not .the ultimate in power, It has its place in the industry as with the PUH, and RC versions if the manufactures design the correct drive train and cooling system for it...

The same with the PUH design, A good cooling system, and drive train, it is still the work horse..It has never got a fair shake till now,...
The puh, and RC versions are same,...RC versions have and also hint as to what is needed for the puh to be successful when its up to the manufacture to realize it. IT has been done, and hope more follow for the sake of the hobby...

I like the conversions, they have filled a important gap, With the new stuff coming every season, its a fun time to be living if you love this part of the hobby...
Nice job Carey

Bill

[rcourtney671]

Thanks Mr. Shurley, that was a very informative write up. It cleared up some confusion I've had over gasoline powered helicopter motors. I currently have the HWC Gasoline Converted Trex 700, Trex 600 and a Radikal G20 helicopter. I lover the long flight times afforded by gasoline engines. I also have a Gaui NX4 nitro that I'm considering converting to gasoline using Gaui's T10 motor. The converted Trex 700 is running a Zenoah G26ei PUH and the Trex 600 a Zenoah G231ei PUH. Sadly I'm having a bit of a problem with the Zenoah G231 and need a new hall sensor and bracket which now seem next to impossible to find. Unfortunately Helicopter World used to have lots of Zenoah parts readily available but now appears to be phasing out helicopter sales and parts for the popular quadcopter market. I've also tried the new O.S. GT15HZ motors on the Trex 600 and Trex 700 and had over-heating issues with all four that I purchased (those were expensive lessons). O.S. seems to make pretty good gasoline motors for airplanes but their helicopter motors seem to need a lot more R&D to overcome the over-heating issues. I followed their written instructions and online videos to the letter and still had heating issues. I've stayed away from the Zenoah RC motors because as you noted they look bigger, bulkier and heavier than the PUH motors; however, after reading your post I'm considering giving the Helibug conversion a shot using the more readily available Zenoah 23 and/or 26 RC motors. My frustration level over the lack of available G231ie PUH parts is such that I could be pulling the trigger on a Helibug conversion kit and RC motor very soon. Thanks again for the invaluable information you posted.

Rodney C.

[gassed]

"this format motor comes in three stock forms:
20cc (32mm bore, 28mm stroke)
22.5cc (23) (32mm bore, 28mm stroke)"

um... having modded these two engines myself... they dont share the same stroke...the 20cc has a 26mm stroke

[carey shurley]

good catch

I wasn't aware they had been discontinued, no longer appear on the husqvarna site and horizon doesn't carry them

[danil]

Dear All

I check after this good thread for the CRRC motor, but I can just find the different one with rear carb. for airplane usage. Can you give some source for this engine? Thank you in advance.

[rcourtney671]

Hi Carey,

Other than the Century Radikal G20, are you aware of any other helicopters on the market that a Zenoah G20 PUH, motor will fit and/or has been used in? With Helicopter Worlds' discontinuation of the Radikal line, I'm trying to find a new home of the Zenoah G20 motor I have. Its runs great and I really don't want it to end up bagged, boxed and put into storage for lack of anything to use it in.

Regards,

Rodney C.

[carey shurley]

Hey Rodney

the only other model I'm aware of that ever used the engine was called the "Bat" which was sold by Irwin Siner. Since he has passed those models went extinct years ago

The engine wasn't particularly popular as it was only marginally lighter than the larger PUH engines but produced significantly less power

sorry, don't have a good answer for you. FWIW I've got a NIB G20 sitting on the shelf as well.

[rcourtney671]

Thanks Carey,

The only thing keeping my Radikal G20 grounded right now are some damaged, plastic torque tube gears. I'll keep searching and hopefully someone still has a few of those bevel gears for sale. Otherwise, I fear the whole thing (with a big bag of spare parts) will be listed for sale at a dirt cheap price . Thanks again.

Regards,

Rodney C.