Spectra-G engine faq

[enricovolante]

Hello everyone,

this is my first post on this forum, my name is Enrico and I live in Switzerland. I'm a good friend of Giopapy and together we are the pioneers in Gasser hely for the Italian/Swiss market.

While Gio owns a predator I decided to go for a spectra-g with 26cc Hanson 3D max (+ CSM revlock and stator gator and Raja generator).

After a long break in and several tests (I also toasted a 23 cc) I'm finally able to push hard on my machine. I did noticed that there is a lot of instant power but when the rotor load is constant the engine suffer and the rotor rpm decrease.
As a matter of facts at the second or third tic-toc I've to give up since the tail rotor is not efficent anymore and loose the heading.

At the moment I'm running at 1750 rpm (12500 engine rpm) but in many videos it seems other pilots run much higer.
Since it is not possible to change the gear ratio (actual one is 7.15) with a more suitable one such as 6.5 (I tried very hard to contact MA about this problem but just received generic answers like "just run at lower rotor rpm......") I wanted your opinion about the following changes:

1st option, install an Hanson tuned pipe and raise the engine rpm

2nd option, install a 23cc which has less power but run at higher rpm and most probably at the maximum torque range

3rd option, try to change the gear ratio with some little modification

thanks a lot!

Enrico

[carey shurley]

1st option, install an Hanson tuned pipe and raise the engine rpm


Hey Enrico, the operators guide for the model is pretty specific about not using the G26 with the stock configuration, especially the gear ratio. If you're running long blades and lower rpms for something like AP it will work however you want a 3D config. Long term nothing good is going to happen here in the stock config because of the running characteristics of the motor at high rpm.


2nd option, install a 23cc which has less power but run at higher rpm and most probably at the maximum torque range


Check out the TRM231, its been custom tuned to match the gear ratio and deliver its max power when the rotor head is in the range you're looking for. This is the best option.


3rd option, try to change the gear ratio with some little modification


Some folks have changed the gear ratio to 6.92:1 by using a 90 tooth main gear. You'll have to remove and slot the ratio plates and manually align the gears but it can be made to work. This will let you run the G26 at a slightly slower RPM

Don't forget, the Spectra is quite a bit heavier than a Stratus so its never going to be as nimble but when properly setup, they're still pretty impressive.

The least impact approach for you is it use the TRM231 but there are options.

[enricovolante]

Thanks for the answer Carey,

unfortunately I watched couple of videos, that made me realize I've a problem with the power delivered by the actual power plant.

I'am also considering the TMR but I also noticed that there is a stage 1 so I imagine there is also a stage 2, no?

The easiest solution (and probably cheaper) is to replace the piston and the cylinder head as I did before with the 23 cc unit I toasted (hanson modified)
Playing with the gear ratio is not definitely the best solution, I do agree with you.
Regarding the 26 cc I can't say it does vibrate more than the 23, mine is very smooth. That is the reason I prefer to keep the actual power plant (which delivers almost 1.5 hp more than his little brother).
I really can not understand why MA suggest NOT to install a 26 in this unit, vibrations most of the time is due to wrong carburation or incomplete engine break-in.
On the other side, the model is amazing but considering that MA made everything possible to reduce weight (see 3D.....) , it is completely nonsense that there are no other gear ratio that customer may install.

[carey shurley]

Hey Enrico

There is a TRM Stage III (see posts elsewhere here) thats being tested however its not yet available.

sounds like you've got your plan mapped out, I don't think there's much more I can do to help you right now

[rbort]

Hi Enrico:

Is it possible you have too much throw or you are punching the collective too much? Also maybe you are putting in max collective at the same time you are pulling cyclic?

I can 3D my Spectra-g all day long and I don't have any issues with it. Granted it is heavier than nitro machines and does not "tic toc" as quick, but it can be thrown around in the same fasion just that things happen a little slower.

I'm using the stock gear ratio with SAB 710mm blades and a Century v3 muffler. Rotor rpms I use is 1550 in normal, 1650 in idle up 1 and 1750 in idle up 2.

You should try full power climbout with governor off and have someone tach your rotor (since you don't have a gv-1 with max rpm memory) and see what max rpm you can get with the engine, blades, mixture and pitch settings. Report back this number as it will give me an idea of the power that you have. Make sure to start from a hover and gradually increase the stick to full power then wait at least 5 seconds and 10 if possible to get the rotor speed to increase or decrease from hover speed and settle in the max power.

-=>Raja.

[enricovolante]

Hi Raja,

I saw your videos, your machine appears to be a bit more constant in power delivery.
Every time I do a climb at full throttle/pitch I "hear" a loss in rotor rpm, I'll do the test you suggested me but I have to wait a month before I can touch my heli again (I work abroad,,,, :arggg: )

Anyway, I had my spectra tested by one of our best pilot at our club (he is famous for smooth maneuvers) and he also had the feeling the tail was shifting due to low rpm.
It is anyway possible that I've a high collective throw, probably I've to get used to heavier helis