Oops, I did it again...........570 Goblin Style

[jc23cl]

Originally Posted by Doug Darby

If the sensor hasnt moved then it almost has to be the ignition box... Are the sensor magnets still in place?
All your weird engine reactions almost has to be from firing at the wrong time.
I have seen nitros "kick" and run in reverse... Not even sure this engine can do that...
The only way I diagnose these things is to just start replacing parts one at a time...
Not scientific or cheap but its all I know how to do... Sorry...

Thanks Doug,

I have fortunately a loaner GT15HZ Ignition system I can try (thanks Jockstrap).

If it fires as before, I'll buy a new one.

We would have to be confident its the Ignition module wouldn't we ?

I'll get a new start shaft in tomorrow night and fire it up, fingers crossed !

Doug I'll get back to you then, as mentioned I need to be convince I'm at least "in the ball park" before proceeding down any other path.

Thank all, Joey.

[Sowa]

Stupid question, did the pin fall out that clocks the magnet?

[Doug Darby]

Glad you have a spare to try...
not stupid at all Mike... Possible...
No Worries Joey... One step at a time.

[gta18]

Cheap solution but would be tedious is put the classic contact point for ignition timing and coil.


Have you Tried turning the crank by hand and see where the spark actually comes in during the stroke?

While the spark plug is pulled out.

[Sowa]

Originally Posted by mitsudriver274

Stupid question, did the pin fall out that clocks the magnet?

The thought crossed my mind that maybe Joey did some work that required pulling the clutch and hub off.

[jc23cl]

Hey Guys,

When diss-assembling to change the fan shroud, it doesnt require touching the clutch assembly. The magnet is captive and has not been touched.

As mentioned I get a good strong spark, but from all suggestions the problem is pointing at the coil module.

I'll replace it tonight, as I get a couple of new starter shafts delivered today, and .... well, I'll let you all know.

Thanks again all, Joey.

[brw0513]

Hiya Joey. Glad to see you're pressing on with the project. I know your going to feel great when you finally nail this thing.

I remember one of my lecturers telling us that getting a spark plug to fire outside of the engine is not a particularly good test of the health of an ignition system. What is missing in that scenario is the pressure that occurs within the cylinder. The higher pressure makes it much more difficult for the spark to jump the gap - it needs much more energy. IIRC the spark plug gap has to be opened up to 3x its usual gap to be a fairer comparison outside the engine.

I don't know for sure, but I highly suspect the ignition module that OS supplies with the GT15HZ is equivalent to the one that gets supplied with the Evolution engines:

http://www.evolutionengines.com/Prod...odID=EVOG10300

That ignition module comes with the bonus of a tacho output.

[jc23cl]

Ok, Guys........

Here we go.

Sunday lots of flying ! Lots to talk about and decisions to be made.

Firstly I am certainly embarrassed (almost ashamed) to have discovered that ALL my Ignition problems have originated from Incorrect spark plug gap !!!!

It wasn't until Carey (thank you sir) mentioned that my spark plug should be 22 thou or 0.55mm. Mine was actually 0.1mm ! I can only speculate that the plug at some point rolled off my bench and landed on its end. Cant remember this happening specifically, but crap falls of my bench all the time. It's just Ignorance on my part that even looking and CLEANING the plug I did not think twice that the plug gap was really small. OK I now know

As soon as I re-gapped to 0.55mm, re-assembled the engine fired and Idled beautifully.

NOW.....Sunday morning 17deg, sunny started the Heli, took off and flew circuits.
Temp did not go above 127 deg's !!!! Flew 3 tanks for the next hour. FUN FUN FUN.

Late afternoon, 21 degs, overcast, again temps did not go above 135 degs !!!

Tuned and played with needles to get a really nice crisp BRAP, BRAP sound and flew it HARD !

On full collective climbouts for 5 seconds, in Idle up temp rose to 135 degs, as soon as I stopped climbing temps dropped almost Instantly back to 130 degs.

Tic, Tocs and Rainbows same story. HAPPY, and FUN !

OK......so what's the catch, it has taken many hours of testing, designing, assembly and dis-assembly to find that this motor in at least the 570G configuration requires a mod !

I have found that temp rise has been highly dependant on the modification of the Bell mouth on the carb ! Yep, that little bit of a funnel at the mouth of the carb !

I have reduced it twice by cutting and filing (15 min.s work), it is now reduced to 3mm from the shoulder of the throttle body. It's very soft aluminium, and files easily. It looks machined with a couple of slow even file strokes.

Note that, I am not convinced that the motor requires this bell section, as it flew as well without it. Or at least my skill level didn't notice any difference.

I can only speculate that the "shadow" it created greatly reduced available cooling.

I have not modded the shroud since last time and even with a huge open hole for the original bell venturi, the cooling is working well.

Now guys......this is all the Info I have. The AXIAL cooling seems to work, and work as hoped. BUT it comes with a catch as mentioned above.

The BETA kits I had made will mostly be scrapped as I want to make some small but Important mods, mainly around ease of maintenance and assembly/dis-assembly.

So....need to hear from you all....do I finalise the AXIAL concept OR now try a radial version (which I am keen to do, as I have some Ideas there also)

Now is the time to decide whether the added weight, complexity and cost can be reduced with a more traditional approach !

Note that I "reckon" I can make the cooling as affective without having to mod the carb bell ! This is a hunch at this point but one based in first hand experience.

Note if you guys/we choose to re-design for a Radial version, the fan will be machined Delrin and purpose designed for this motor ( not a Nitro fan drop in ).

So lets hear the verdict gents : D



Thanks again all with help diagnosing my Ignition Incompetence !

[Sowa]

That's a tough one. Do you think a radial fan will work better?

[jc23cl]

Originally Posted by mitsudriver274

That's a tough one. Do you think a radial fan will work better?

I reckon, this motor runs thermally at 130 degs C. regardless of concept.

I'm confident that I can design a radial version that achieves this.

"Work better" is now at least in my mind, reduced parts count, weight and complexity.

Also Mike, I will say (didn't mention it before) that I "flogged" this motor in the spirit of testing. That is half a tank at least, IDLEUP at zero pitch. Motor just revved, sounded good, cooled well.

Has anyone with spirals Installed failed yet ???? that you know of.

Joey.

[Sowa]

Given that both concepts perform the same then whichever is the lightest would be my choice.

To my knowledge there hasn't been any failures with the spiral retainers.

That's pretty impressive, what rpm?

[Doug Darby]

Well some very positive news...
My biggest concern now is what might happen to sustained engine temp when the ambient temps rise up near 40c? If the change from 17 to 21 ambient is linear the motor temp would now be "north" of 160c at 40 ambient...
it probably isnt linear but im guessing well higher than 135...
As for Axial vs radial, weight, parts count and simplicity will always win that argument in my book. I hate to see the beta kits scrapped but changing to a "better" fan design would at least help justify the new beta kit parts...
By this point you have enough quality experience that your "hunches" as to what might work are going to be pretty darn reliable. Couple that with your desire to try the new fan and your answer is simple. Go for it....
As for flying in higher ambient temps, we can find that out when you get a couple beta units running. Even if it does I think there are ways to deal with it in beta form...
As to the carb mods you do now, those are insignificant and can be easily detailed in the first build threads.. Any competent builder can make tyos simple hand mods if necessary. ..
Keep us posted...

[brw0513]

Thanks for the update Joey. Nice work. Maybe that carb intake poking into the vary fast flowing air results somehow in a lean mix and higher temps?

It was 42 deg C in Brisbane on that particular Sunday! It would be good to see how the engine performs somewhere above say 32 deg C.

I reckon if you've gone as far as you think you can with the axial fan arrangement, then give the radial design a go. In my tiny mind it's hard to see that a radial fan would move more air than an axial fan. But maybe there is some magic air velocity anyway that a radial fan can reach. I like the idea of simplicity and low parts count, but the axial arrangement looks rather elegant to me.

Do you know anyone with fluid dynamics software? That might help answer the question?

Can you make two jigs to somehow compare the performance of the axial design versus the radial design?

[Sowa]

Joey, out of curiosity what are the pros and cons of axial vs radial?

I'm guessing, you are already playing with a CAD model of a radial version G570. Any rough estimates on the weight difference between the two?

[jc23cl]

Hey guys,

brw0513; thanks for the feedback : D

I do have access to Fluid Dynamics software, but its an awfully detailed procedure to get a meaningful result. I will just design the fan for optimal efficiency at 14000 rpm. That Involves sweep of blades (forward, radial or backwards) aero foil shape etc.
Fortunately the maths I understand to get close to something decent, oh and beyond that as big as I can get into the canopy.

The jig, yeah its a 570 Goblin : ). Seriously I have thought of it but its just as easy for me to just mount it in the bird.

mitsudriver274; Axial is good for high flow, but suffers poorly with any back pressure ( as I have discovered, albeit empirically).

Radial (depending on blade angle, forward backward or straight radial ) is lower flow but much higher pressure than axial. Suffers much less from back pressure, especially back swept blades.

Weight difference may be 50-100 grams, not a lot.

Carey has suggested that I try one more fan shroud configuration, it has merit (his Idea) so I will try one more. Printing it now, so I will have something to report in the next couple of days.

Thanks again all for the feedback, this is what it takes to get it right, unfortunately.

One last thought, I am determined to get this out, as I truly believe this engine is performing well with the spiral retainers. Hopefully OS get these into future models, I believe they would be doing themselves a great injustice not too IMHO.

Joey.

[Sowa]

50 to a 100 grams is a lot to me!

Although most of you guys will probably agree I'm obsessed with weight.

[brw0513]

It's coming up to Christmas. Should I be placing an order for a Goblin 570 now?

[jc23cl]

Hey Guys,

brw0513...LOL, well one way or another it will come out.

I had a late night, and roughed out a Radial Layout......using a TZ90 Fan shroud and Alu or Delrin ( have to do some FEA) fan, here are the results.

Lets just say, its looking promising.

Note also that I have Include an ALIGN fan (plastic) for comparison (in RED).

Hate to say it IF it works as expected, a hell of a lot simpler. Fingers crossed it can move enough air !


Thoughts anyone ?











Regards Joey.

[brw0513]

Hiya Joey,

Lovely work as usual

I still like the axial fan arrangement the best. It looks like jewellery to me.

The radial arrangement looks good too. But would the airflow be even to both sides of the head? Would it matter anyway?

[fastflyer20]

That looks promising!