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Gohbee Aviation Stinger 30-90 > Gohbee / TZ / Raptor 90 Heli with BME modified G90 Gas Engine

Ringo Ranger
Senior Heliman
Location: Honolulu, Hawaii

What a world gas powered rc helis. I received my g90 gas conversion from chief aircraft. We'll, I'm breaking in with a 16:1 ratio
hehehe guess what? It started like a pop corn maker. It did run
but I have to remix fuel to 50:1. Raptor 90se is in transit, I don't think for a glow 90 for it. while waiting for rappy 90se gotta
break in my supertiger gasser 90 and familiarize a gas engine for it.
we'll, let's see what we can do. let's join hands and open and share our thoughts for this wonderful hobby.

aloha!

FUTABA 14 MZ of course!
Rappy 50
OS 50 SZh
9252's
401's
Vblades
Align 450 XL carbon
Align 430L
etc...

04-03-2006 Over year old.

SkateFreak
Key Veteran
Location: Cambs UK/Luton

Hey all.
I'v been following this post for a while now but i cant seem to tell how much power this engine has...
Is it equivelant to an OS90 in power, above or below?

Any thoughts would be great

-Jvr

Non-3D heli pilots are planker spys trying to bring down the heli community from the inside - Topher

04-03-2006 Over year old.

Franconia2
Heliman
Location: Shrewsury, MA

Power

The G90 conversion does not have the power of a 90 nitro, its more like a 70. I don't think any gasser will ever have the "punch" and quick response of a nitro in the way a deisel engine does not have the same response as a gasoline engine. Different engines for different appluications.

That said, every engine has its place, the G90 can handle most 3D with authority, it will be tough to do tic tocks and other hard stick banging moves, but for most flyers, it has enough power.

Dave

04-03-2006 Over year old.

AnnihilaT
Key Veteran
Location: The Netherlands Force: The Dark Side

Franconia, could you maybe give an indication what kind of throttle settings you are using so i have some kind of comparison?

A day without sunshine is like, well, night.

04-03-2006 Over year old.

HOMEPAGE

Franconia2
Heliman
Location: Shrewsury, MA

Throttle settings

I'm at work (don't tell my boss) but as I recall Normal mode is 8,35,50,68,92. This produces a constent 1630 headspeed with the following pitch curve: -3,-3,1,5.5,9, hover at 3/4.
will post the actual curve tomorrow.

04-03-2006 Over year old.

AnnihilaT
Key Veteran
Location: The Netherlands Force: The Dark Side

Ok that tells me what i needed to know. I am also at between 60-70% throttle to get a decent headspeed at hover and just wanted to know if that was normal for this engine. I found a 91T main gear from TZ and am using the 12T pinion so i may have a bit lower ratio at 7.58:1. How did you set your throttle curves? By ear in the air or negative pitch on the ground?

A day without sunshine is like, well, night.

04-03-2006 Over year old.

HOMEPAGE

Franconia2
Heliman
Location: Shrewsury, MA

Throttle Curve

Sounds like you are in the ballpark. As I continue to lean it out and get it running with more power, I find a lower throttle curve seems to work better. The engine seems to run better and happier under a contant load. This weekend I slowly lowered the throttle curve without much impact to the overall headspeed but it ran better and had something left over when you punched the throttle.

I set the headspeed on the ground at 1/2 stick, then guessed at the 3/4 stick point and set the radio. A friend checked the headspeed at a hover and made the final adjustments.

The tail started kicking to the left for the first time this weekend. A lower headspeed (1630) minimized the problem but in IDL2 at 1720 it kicks like a mule. Too much to control. ITs a kick and always to the left, increased/decreased gyro gain has little affect on it. This only started recently. Any ideas?

04-03-2006 Over year old.

AnnihilaT
Key Veteran
Location: The Netherlands Force: The Dark Side

Belt or drive shaft for the tail? Which platform did you use again? Rap 60?

A day without sunshine is like, well, night.

04-04-2006 Over year old.

HOMEPAGE

SkateFreak
Key Veteran
Location: Cambs UK/Luton

Hey.
So does that mean throw the G90 into a 60 and tic tocks will be achivable?!

Not that i'm saying they wont be achivable in a 90 by a skilled pilot

~ Jvr

Non-3D heli pilots are planker spys trying to bring down the heli community from the inside - Topher

04-04-2006 Over year old.

AnnihilaT
Key Veteran
Location: The Netherlands Force: The Dark Side

SkateFreak,

There are only 3 people i know of that have tried this and i am one of the, franconia is another, and a guy in the Czech Republic. Most of us are still in the testing phases so noone will be able to answer your questions until they have more time to test and fly. If it interests you and you have the money just try it.

A day without sunshine is like, well, night.

04-04-2006 Over year old.

HOMEPAGE

Franconia2
Heliman
Location: Shrewsury, MA

Belt Drive

I running a Hirobo Freya X-Spec with Belt drive. I had a OS70 in the machine that ran fine, before installing the G90. The first 20 flights showed no problems with the tail. It started on Friday and I can't seem to fix it. I continue to lean the engine as the plug is still black, but less than when I started.

Throttle Curve,

Anni,
Checked my radio this morning, the throttle is set lower than my previous post stated but its in the ballpark, 8,32,45,60,89. Basically 60% at hover.

04-04-2006 Over year old.

AnnihilaT
Key Veteran
Location: The Netherlands Force: The Dark Side

Franconia,

I now have two other problems im running into. This thing is really starting to get a bit annoying actually.

Problem 1: The muffler keeps getting hot and loctite heats up and bolts holding it to the engine vibrate loose. How are you dealing with this or is this not an issue for you? Are you using the stock muffler or an aftermarket pipe?

Problem 2: The carburator is also vibrating loose. This is especially worrying because as it vibrates forward the throttle endpoints are changed and it will keep idling higher and higher and then throttle cut no longer works as well. ARGH! Any problems with this as well?

I got another 2 minute hover in today (or less) before i noticed the muffler dangling loose and had to land it. Then throttle cut didnt work so i found the carburator was again loose as well.

A day without sunshine is like, well, night.

04-04-2006 Over year old.

HOMEPAGE

hootowl
Elite Veteran
Location: Garnet Valley, Pa.

Lockwashers?

Member Bog Troll Club #1

04-04-2006 Over year old.

HOMEPAGE

AnnihilaT
Key Veteran
Location: The Netherlands Force: The Dark Side

Lock washers are standard on the engine as it comes.

A day without sunshine is like, well, night.

04-04-2006 Over year old.

HOMEPAGE

PaulH-MA
Veteran
Location: Boston, MA

I attach my muffler using Chris Bergen's method. It works very well:

1. Clean the surface of the exhaust port and the mating surface of the muffler very well. Use a razor blade to scrape any accumulated crud off.

2. Put a very thin coat of red RTV silicone on one of the surfaces, then attach the muffler.

3. Use more red RTV on the bolts as if it were threadlock. Tighten everything up and let it cure for 24 hours.

4. Start the engine and let it warm up. Hover the helicopter for a few minutes, then set it down and kill the engine.

5. Check the bolts. If they are loose, tighten them up.

You can probably use the red RTV on the carb bolts as well. Just make sure that you don't get any in the carb or cover the back pressure holes that drive the diaphram pump.

--Paul

TREX 450
Bergen Intrepid Gasser x2

04-04-2006 Over year old.

AnnihilaT
Key Veteran
Location: The Netherlands Force: The Dark Side

Paul thanks alot for that. Can you point me to a source for this stuff?

A day without sunshine is like, well, night.

04-04-2006 Over year old.

HOMEPAGE

Chris Bergen
Key Veteran
Location: location

The pepboys on the south side of Atlanta has some!!

Sorry, couldn't resist......

What I've been using is just standard old high-temp red RTV silicone, usually found at an automotive parts store, used as Paul stated.

But the bigger picture here are the vibes. You gotta get those under control or the whole heli will suffer, not just the carb or muffler.

Chris Bergen

04-05-2006 Over year old.

MRS
Heliman
Location: Netherlands

Silicone

MFIS,

I have some loctite 5926 brought for you for this problem. Take a look at the website of loctite. It can stand 250 degrees celsius (482 degrees Fahrenheid for the amercans among us)

And we should balance the blades. It's different then a t-rex. 1/2 gram (0.25% of the blade weight)difference at 500mm COG of the blades means 8kg pulling at the head 1600 times a minute! This will distroy youre heli. Yesterday I could not explain, not having the program to calculate it

With a t-rex this is only (also 0.25% of the blade weight --> 0.1 gram) 0.8kg at 1600 and 1.3kg at 2800

This lower pulling force is even on a small heli is easier to compensate by the damping of the head than the 8kg on the larger heli. Blade balance is very important.
I e-mail the program to you.

Marcel

04-05-2006 Over year old.

HOMEPAGE

AnnihilaT
Key Veteran
Location: The Netherlands Force: The Dark Side

Paul, Chris, and Marcel,

Thanks for the advice and help!

Marcel and i got it in the air again yesterday. We ended up modding the bolt that hold the carb in place a bit, tapped the exhaust mount holes for 4mm hex bolts, and used the silicone on the exhaust to engine and as loctite on the screws. Was able to get maybe 5 mins of test hovering done before the engine quit on us. Nothing vibrated loose this time but it appears some dirt got into the carb and was causing the fuel mixture to be extremely rich completely flooding everything and soaking the plug. Also the stock muffler is no good anymore i think. Something has vibrated loose inside of it from earlier flights and im going to replace it with something better. With this machine its been a matter of fixing one thing only to find a new problem. Eventually there will be no problems left to find and maybe ill get to actually fly it!

Anyway the more interesting news is that despite my calculations and against all logic this engine with the gearing i have is giving me 1850RPM on the head right now IN THE AIR and at only about 70% throttle! Marcel tached this while i was hovering. In idle-1 (my normal flight / hovering mode), I have only +8.5 pitch on the blades but this thing was VERY responsive in climbouts without a hint of bogging. This doesnt say much since idle-2 is what i will be wanting to fly it in and that is setup with -11.5 / +11.5 for starters but its shown more power than i was expecting so far. The main shocker was the headspeed. I still cant figure out how at 70% throttle and with SAB 710mm blades on it it could be maintaining 1850rpm with no bog. This would mean that with my gearing the engine would have to be running at a bit more than 14,000 rpm at 70% throttle and holding that with 5-8 degrees positive pitch and slinging the 710mm blades. Does this sound right? I thought max rpm on this engine was 14,000rpm ?

Alot of my vibration issues seemed to be gone when i finally cranked up the headspeed a bit yesterday so this also looks promising.

BTW, Thanks to Bill who PM'd me with the tips about the clutch and its role in vibration. I will certainly be looking into your advice which i believe is very sound as well.

A day without sunshine is like, well, night.

04-06-2006 Over year old.

HOMEPAGE

Malorie
Elite Veteran
Location: Paw squared, MI

With a butterfly type carberator, the throttle is not linear, it is exponential. At about 30 or 40% on the radio, you are around half throttle.

Malorie

Life's a journey, NOT a destination.

04-06-2006 Over year old.

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11864 views

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Gohbee Aviation Stinger 30-90 > Gohbee / TZ / Raptor 90 Heli with BME modified G90 Gas Engine

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