Power Systems - OS Max GT15HZ - An In-Depth Look

[carey shurley]

OS Max GT15HZ

Overview

After almost a year of anticipation, OS Max has released their first official entry into the gas powered helicopter engine market with the GT15HZ

Thanks to Hobbico and OS Max I've had the opportunity to work with this motor for several months, and now that its officially available I want to go through it in more depth and show more details about it.

When I first saw the GT15, I assumed it was "just another" glow conversion. Almost all of the model glow engine manufacturers have tried to do this............and for the most part failed. So I was pretty skeptical and even wrote an opinion about it back in May of last year HERE

As I indicated in that opinon, if anybody could make this work I thought OS could. Well they've done a pretty good job with it and I think in the right application its going to introduce more people to gas powered helicopters!

I'm going to show some photos of a production motor, then some of the internals and discuss applications for it

Heres another photo of the production motor in its standard form (no muffler), you can see the Walbro 1067 carburetor and the mixture adjustment needles


Production GT15 - left side

on this side you can see the throttle/choke posts as well as the ignition trigger sensor and timing ring


Production GT15 - Right Side

Here are the english instructions for setting up and running the motor

Operating Instructions - English


here's the included OS IG05 ignition system, its very small and runs on 4.8-8.4 volts. It can be connected to the same battery as your on board system is using. It has a rated usage of 750Mah at 14K rpm at 6 volts. The plug cap fits tightly over the plug and has a straight cap which makes it easier to fit into many models


OS IG-05 EI system

Here's the optional Powerboost pipe, designed specifically for this motor, its a lower backpressure version of the popular pipe


Optional OS Powerboost - GT15

for those who need a more compact muffler, OS offers this cast aluminum silencer, its very similar to most OS muffler, its quite loud and produces less power than the powerboost pipe.


Optional E4051 Silencer

Internals

The GT15 crankcase is custom made for this application, it includes a cast mounting flange for the carburetor which includes a bi-directional pump port (more on this later). This is a typical gas helicopter setup using a composite isolator block to reduce heat transfer to the carburetor. Notice that the gaskets and the isolator have two holes so they can be easily installed

If you're familiar with Walbro carburetors, they include an internal fuel pump easily capable of pulling fuel 2 ft or more. The pump uses crank pressure pulses to operate which is why having a port aligned in the case is important. If you want to know more about the internals of the Walbro carb, take a look HERE


Walbro carb components

Another area thats different from a normal glow motor is the addition of this timing ring on the front of the motor. It uses a magnet/sensor arrangement similar to that used by governors. The magnet has to be precisely placed in order to fire the spark at the correct time so its installed in a ring that mounts on the front of the crank. OS has made is simple to keep this properly aligned, due to the way the alignment pin fits, this can only be assembled one way


Ignition timing parts

Here are the parts that look more familiar, the piston, rod and cylinder. Don't be fooled though, they've been custom designed and toleranced for the characteristics of gasoline. Note the connecting rod uses a roller bearing in its bottom end.


Piston/Rod/Sleeve Parts

couple of other differences in the crank case, note the hole at the top where I've removed a threaded disk that seals this.

On the prototypes, the piston pin could be removed through this hole simplifying removal of the piston and sleeve. This is because the lower end of the rod is attached with a threaded keeper. However on the production models the hole in the sleeve is no longer there so there doesn't appear to be any purpose for this disc

There is also a larger rod cavity to allow the larger rod lower end to fit. The bearings are standard OS 91 bearings. I don't expect the normal corrosion problems here because gasoline does not absorb water like alcohol does.


Inside the case

Carburetor Orientation

I've talked about the carburetor being reversible. There are a couple of reasons for this:

• throttle servo alignment - its mounted on one side or the other of the model
• cooling fan interference - because of the size of the carb, there may be fan interference

here's an example of how the fan can interfere, this is a Raptor G4 fan. You can see with the carb in its std position there is a problem


Raptor G4 fan position

other fans fit perfectly, Here's the Whiplash fan, it will have plenty of clearance even after its fully tightened down.


Whiplash Fan Mounted

so here's how the carburetor mounts in its std position


Carb - Std Position

you can see here the relationship of where the fan will mount to the carb


Fan/Carb Positon - Std

when the carb is flipped around, it looks like this:


Carb - Reversed Position

now you can see here that a much larger fan can be fitted without interference.


Fan/Carb Positon - Reversed

Its also possible to use spacers between the timing ring and your fan if the carburetor orientation you need for your throttle servo doesn't allow for proper fan clearance. This will add fan clearance but keep in mind that this pushes the motor lower in the frame. Your setup will need to allow for that

As you can see the carburetor position can be easily adapted to your model either for throttle positioning or cooling fan clearance.

What other changes are needed?

The most common is modifications to the cooling shroud to allow clearance for the carburetor

So what can this be installed in?

OS has targeted this as a replacement for a typical 90 size glow motor. The goal is to make a few modifications to the airframe, change the fuel plumbing to something gasoline tolerant and go fly

................more to come

[Universe]

Originally Posted by carey shurley

Almost all of the engine manufacturers have tried............and for the most part failed.

NGH, DLE, MVVS and ??

[brw0513]

Webra had the 91 P5 Hi.

[martin_]

Very interesting, I can see it have a bridged exhaust port.

I thnk this motor can be easily modified a bit more, there is enough room on the sleeve.

[cyberjoeone]

Great heli for this engine!

[carey shurley]

I don't know much about the 600 DFC but I suspect it will require extensive modifications to fit a GT15 into it

The Fury 55 project uses a 90 size clutch, bell, fan, shroud and engine mount and required a frame redesign to fit all of that

[cyberjoeone]

Or maybe a T-rex 700N DFC with a 600 tail boom and 600mm blades, will do the trick!

[Universe]

spark plug pipe http://www.os-engines.co.jp/2013/gt15_plugatt/

[ranma103]

Im about to put one of these in a kasama srimok the gear ratio is in the 8.25:1 mark a 12t pinion with 99t main gear.

Sent From My Galaxy S3 Using Tapa Talk 2.0

[carey shurley]

Plug Cap Attachment Procedure

What they are showing here is critical. If the cap doesn't seat properly, the EI system will arc somewhere, including backfeeding through your receiver/FBL system. I haven't seen it kill the electronics but I have seen it cause a reset........................which of course kills your model

[rbort]

I have seen it cause a reset........................which of course kills your model

Does that mean it went in??

Bummer...

-=>Raja.

[carey shurley]

actually no, I was very lucky I discovered this with my normal pre initial flight testing back with the prototypes

however its important for folks to check this, otherwise it will end badly

[fastflyer20]

Carey the link to the plug cap procedure is not working

[carey shurley]

sorry about that...........fixed

[Intrepid175]

Originally Posted by carey shurley

I don't know much about the 600 DFC but I suspect it will require extensive modifications to fit a GT15 into it

The Fury 55 project uses a 90 size clutch, bell, fan, shroud and engine mount and required a frame redesign to fit all of that

Can we assume that means there might be a Fury 55 gasser in the mix, maybe even a conversion kit somewhere down the road? I know the possibility has been discussed but I haven't seen anything on it lately. Carey, I'm very much looking forward to reading the rest of what you have to say on this engine. Thanks for all the hard work!

Fly Safe,
Steve R.

[msallua]

Originally Posted by carey shurley

here's the included OS IG05 ignition system, its very small and runs on 4.8-8.4 volts. It can be connected to the same battery as your on board system is using. It has a rated usage of 750Mah at 14K rpm at 6 volts. The plug cap fits tightly over the plug and has a straight cap which makes it easier to fit into many models

Hi , Someboy can confirm if the ignition system can be connected to the same battery as your on board system.is using?

Thanks in advance

[phillhague]

Best to use a separate battery pack for ignition don't know the reasons for it but that's what I have always done in gasser planks and will be running a separate pack on my GT15HZ powered Helix GT600 heli.

[carey shurley]

I can only say I've run every EI system I've ever run on the same battery pack as everything else

it does need to be high capacity and you do need to keep an eye on the charge state. The EI systems eat it pretty good

[Sowa]

+1, running both my GT15HZ heli's on one rx pack. I get 2 flights out of a 2100mah 2s LiFe, or 4 flights off my 2s 4000mah lipo. Keep in mind those are 14min flights.

I have noticed I experience less voltage sag with the 2s lipo, it does have a much higher c rating.

[msallua]

I have a 700N DFC without engine, Can I do 3D flights with this engine OSGT15HZ ?, I need special gear ratio?
Thanks in advance