Marty d's CH-701 build log

[skippydiesel]

3 hours ago, nomadpete said:

Thanks for a number, Skippy.

As a starting point I plan to put a air temp probe under the cowl. And in the exit stream.

That will give an idea of what is happening. Any other ideas?

Hot air leaving the cowl is not important. Heat around the ignition modules & the voltage regulator (VR) is. Put your thermocouples in these areas.

 

If possible either mount your VR in a known cool area or consider fitting dedicated outside air duct onto the VR.

 

You should also consider insulating all fuel lines /fittings in the engine bay, to minimise the chance of fuel vaporization/vapour lock.

 

Shield the underside of the carbys from exhaust pipe radiant heat. You can make shielding using ductile aluminium flashing, supplied by any good hardware/building supplier (even Bunnings Aerospace).  Fix in place with double wrap safety wire on exhaust and or cable ties on carbys (Alternatively purchase Rotax carby drip trays - they do little if anything about drops from the carbys but do act as good heat shields, better looking as well.).

 

I "Silastic" /glue exhaust wrap to one side of the flashing for extra insulation and safety wire it around a hose where it is in close proximity to the exhaust system .

 

If you are fitting an airbox (Rotax or other) consider ducting outside air in, more efficient combustion/power. The down side of this is greater chance of carby icing  - need carby heat or heated inlet manifold rings.😈

[Marty_d]

First engine run with cowling on. 

Completed the glitch list fixes and blanked off half the oil cooler.

Ran for around 15 minutes (didn't have my phone with me but Hobbs meter went from 0.5 - 0.8). Kept it around 2300 until oil temp hit 50 degrees, then up to 4000 for mag tests.

At that point I found the ropes I'd tied the main gear to a fence post weren't as securely knotted as the should have been - luckily she was pointing uphill!

CHT gauges showed 120 and 105. Oil got to 90 over the run but no higher. Oil pressure stayed around 4 and fuel pressure 3 with pump off.

After the run the cowl was warm in spots, mainly near the front exhaust headers. Not too bad though.

Checked oil level when warm and added around 300ml.

Quite happy overall.

[Blueadventures]

13 minutes ago, Marty_d said:

First engine run with cowling on. 

Completed the glitch list fixes and blanked off half the oil cooler.

Ran for around 15 minutes (didn't have my phone with me but Hobbs meter went from 0.5 - 0.8). Kept it around 2300 until oil temp hit 50 degrees, then up to 4000 for mag tests.

At that point I found the ropes I'd tied the main gear to a fence post weren't as securely knotted as the should have been - luckily she was pointing uphill!

CHT gauges showed 120 and 105. Oil got to 90 over the run but no higher. Oil pressure stayed around 4 and fuel pressure 3 with pump off.

After the run the cowl was warm in spots, mainly near the front exhaust headers. Not too bad though.

Checked oil level when warm and added around 300ml.

Quite happy overall.

You burped engine to check level before top up?

[Marty_d]

21 minutes ago, Blueadventures said:

You burped engine to check level before top up?

Hmmmm not sure if I fully burped.

It was still very warm when I checked the level so the prop would only have stopped 5 minutes prior.

[Blueadventures]

2 minutes ago, Marty_d said:

Hmmmm not sure if I fully burped.

It was still very warm when I checked the level so the prop would only have stopped 5 minutes prior.

All ways burp the oil from sump into the can then check the oil level.

[Marty_d]

Will do. I think I was nervous about rotating the prop when the engine is warm (even though the key was out of the ignition and the kill switch off).

Edited Sunday at 03:44 AM by Marty_d

[BrendAn]

3 hours ago, Marty_d said:

Will do. I think I was nervous about rotating the prop when the engine is warm (even though the key was out of the ignition and the kill switch off).

Hit the starter for a few seconds with mags off  that will burp it 

I always did it by hand until an instructor showed me that trick

Edited Sunday at 06:57 AM by BrendAn

[facthunter]

The slower you turn it, the More effectively it Burps. With a Low hours Motor that technique would not be very effective.. The rings seal too well. The oil return relies on Blow by.  Keep a firm grip of the Prop Blade or the compression May injure you. Nev

[BrendAn]

It works fine unless you have the combo mag and start  key switch 

[facthunter]

I didn't come down in yesterdays shower. What do Rotax recommend?  You also GET to FEEL the compressions. The Blowby pressures the Crankcase, not the revolutions. The SLOWER it turns the better.  Nev

[BrendAn]

52 minutes ago, facthunter said:

I didn't come down in yesterdays shower. What do Rotax recommend?  You also GET to FEEL the compressions. The Blowby pressures the Crankcase, not the revolutions. The SLOWER it turns the better.  Nev

I know it's not the recommended way but it works the same.

I do agree pulling through by hand is the way to check compression.

I ever said you came down in the last shower unless the last shower was a really really really really really really really long time ago 😀

[skippydiesel]

"Checked oil level when warm and added around 300ml."

 

There is a danger you will not be getting an accurate oil level reading

 

I believe Rotax advise checking oil level when cold.

The technique I have adopted, is to do the "burps/gurgles" when oil is hot, usually after flight. The oil will flow more readily when hot, so forcing oil from the crankcase to the reservoir/tank, happens very easily.

At the next pre flight check- Cold engine (oil) will usually "burp" within a full prop rotation. The small amount of oil, that has accumulated in the crankcase, will now be in the tank - Check Oil level.😈

 

6 hours ago, Marty_d said:

 I was nervous about rotating the prop when the engine is warm 

It It is not possible to hand crank a Rotax 9 to sufficient speed/rpm for the engine to start. This combined with the recommended slow cranking, to achieve a good "burp" makes it impossible for the engine to start.

 

Despite the above, you should always assume the prop to be "live" Keep your body to one side/away from the prop ark when hand rotating😈

[Marty_d]

Haha - I decided to Google whether it was better to check oil level when warm or cold, because I'm sure I read somewhere that it's better to check warm.

What this did do was confirm my belief of never trusting AI - check out the highlighted bit:

 

[facthunter]

Never turn the Prop backwards. Nev

[rgmwa]

It takes fewer rotations both when the oil is warm and if you move the prop slowly. Don’t trust Google for advice but you can ask it where to download all the Rotax manuals for free. 

[IBob]

14 hours ago, Marty_d said:

Haha - I decided to Google whether it was better to check oil level when warm or cold, because I'm sure I read somewhere that it's better to check warm.

What this did do was confirm my belief of never trusting AI - check out the highlighted bit:

 

Marty, I recently searched the thermal conductivity of wood.
In the same paragraph, AI stated that thermal conductivity is higher in denser woods (makes sense), it then stated that denser woods are preferred in building due to thermal insulation properties.
It then changed it's mind yet again in the next paragraph.
What this illustrates is that, while the thing is writing English (so appears logical), it is not actually in any way checking for logical consistency in what it writes.....(

[skippydiesel]

Marty-d,

 

A Warm/Hot oil check will not give you an accurate indication of oil contained within any engine.

 

WHY -

• Hot engine oil will not have drained fully ie a significant quantity will still be adhering to all the components/inside of the engine.
• Adding oil to a hot engine reading may result in overfilling ie result of a false low level reading.
• This is unlikly to cause damage, as excess oil will be "blown" out of the engine.
• May cause you to record higher oil usage that actual - Rotax specify (from memory) Maximum 0.06L/hr

 

In all my (limited) experince I have never heard of advice to check engine oil quantity on a hot engine (this may be diffrent for marine engines where I understand some engines have oil changes while running).

I do know of at least one automatic transmission, that required the oil level to be checked hot, proscribed movements of the selector mechanism & with the engine running - completely diffrent requirements.

 

As for Google/AI - Rotax publish very detailed/comprehensive manuals for the care & feeding of their engines - why put your trust in a dodgy AI system??

 

Join Rotax Owners Forum for quick access to all manuals, trained technicians and Rotax advisory publications https://www.rotax-owner.com/en/rotax-forum

 

😈

Edited yesterday at 02:30 AM by skippydiesel

[IBob]

As pointed out by others above:
1. Burping the Rotax relies on blowby to pressurise the crankcase and push the oil back. That being the case, you are no better off pulling it over briskly: you are actually better to linger in the compressed state, so maximising blowby.
2. You can't hand start a Rotax. The reason for this is that the power for the ignition comes only from little dedicated stator coils and the engine has to be turning over very briskly for these to generate sufficient power. Having said that, one still reflexively checks 'mags off' before pulling it over....

Edited yesterday at 04:29 AM by IBob

[nomadpete]

18 minutes ago, IBob said:

2. You can't hand start a Rotax.

and that's when the fight starts

 

 

 

Edited yesterday at 04:47 AM by nomadpete

[IBob]

Okay, that's a revelation!

[BrendAn]

2 minutes ago, IBob said:

Okay, that's a revelation!

i would say its a more of a revolution😀

[IBob]

That is a 912 UL, with a lower compression ratio.
I never tried, but I'm doubtful I could pull a 912 ULS over that briskly.
Still, I stand corrected!

[onetrack]

Well.... he did swing that prop very briskly!

[Marty_d]

6 hours ago, skippydiesel said:

Marty-d,

 

A Warm/Hot oil check will not give you an accurate indication of oil contained within any engine.

 

WHY -

• Hot engine oil will not have drained fully ie a significant quantity will still be adhering to all the components/inside of the engine.
• Adding oil to a hot engine reading may result in overfilling ie result of a false low level reading.
• This is unlikly to cause damage, as excess oil will be "blown" out of the engine.
• May cause you to record higher oil usage that actual - Rotax specify (from memory) Maximum 0.06L/hr

 

In all my (limited) experince I have never heard of advice to check engine oil quantity on a hot engine (this may be diffrent for marine engines where I understand some engines have oil changes while running).

I do know of at least one automatic transmission, that required the oil level to be checked hot, proscribed movements of the selector mechanism & with the engine running - completely diffrent requirements.

 

As for Google/AI - Rotax publish very detailed/comprehensive manuals for the care & feeding of their engines - why put your trust in a dodgy AI system??

 

Join Rotax Owners Forum for quick access to all manuals, trained technicians and Rotax advisory publications https://www.rotax-owner.com/en/rotax-forum

 

😈

I don't rely on AI, in fact I despise AI. That was an illustration of how AI is completely untrustworthy.

I don't know about you, but I find the Rotax manuals incredibly hard to navigate especially as they're usually in PDF with no direct navigation links.

Therefore I don't think it's unreasonable to Google "Rotax 912uls check oil level hot or cold" in the hope that there's a link somewhere to a reputable source.

Unfortunately all the user groups - Rotax-owners, Vans air force etc - have opposing points of view on the issue.

[BurnieM]

What I do with all other engines is check the oil level when it is cold and full to the mid point in the dipstick range.

 

Warm the oil up (but not too hot) before draining.