Marty d's CH-701 build log

[bexrbetter]

3 hours ago, Moneybox said:

That's the sort of accuracy I expect with Autocad but I have trouble with Sketchup.

 

 

Maybe it's just me but If I try to select a point of couple of intersecting circles, I cannot accurately select the intersection.

 

 

I understand your issue: While it is true SU doesn't have 'true' circles, when you click on 'circle' icon, the next thing you do is type the number of sides you want and press enter. Default is 24 sides, but I usually use 96, staying with divisions of 12, but just tested 960 and it was no problem. The more sides the larger the file of course. 

 

Thanks Marty, surprised to see you're still at it, many give up in shorter time, such tenacity, well done!

[skippydiesel]

Marty-D,

 

I am concerned about the management of your Rotax. 

 

It seems, from all the questions, that you are not referring to the Rotax manuals, rather advice from well meaning persons on this Forum.

 

Rotax have detailed instructions on priming the oil & coolant system (including specification for coolant type) fuel /oil pressure, etc etc.- stick with this if you don't want to risk expensive engine damage.

 

Further there is the Rotax Owners Forum https://www.rotax-owner.com/en/rotax-forum where the latest manuals are available,  Rotax specific discussion and  Rotax  mechanics.😈

[Marty_d]

Pulled the plane out again this morning and did another start - thanks to @nomadpete the oil pressure gauge is now working.

I bought a small fuel tank (generally used for working on motorbikes when the tank is off) and suspended it on one side of the fuselage going into the wing tank inlet to the header, put a couple of litres in then switched the line to the return barb for running.  (Forgot to take a photo sorry).

 

Ran it for about 10 minutes.  Look like the oil TEMP gauge is not working now, so will have to try to figure that out.  (or ask Peter to help which is more likely to result in success!)

 

Kept it at 2000rpm for most of it, after running around 5 minutes at 2000 and with the oil pressure stable on around 3.5 bars I increased throttle to 4000rpm for around 30 seconds, then tested magneto drop individually.  Then back to 2000 for another few minutes.  Idle with throttle pulled back as far as it'll go is around 1800rpm, at that point oil pressure is reading just under 2 bars. 

At the end of the run the CHT's are showing around 75 degrees on one gauge and just on 50 degrees on the other.  I'm assuming the lower temp is on the front cylinder, will have to trace the wiring on that (and then label the gauge!)

I need to tighten up a few nuts in the oil system, there's a slow drip from the bottom nut and I think also the oil cooler connections.

 

The other problem is one of the main gear tyres went flat - it always had a very slow leak but now you can hear the air whooshing out of it when you take the pump off.  I reckon the valve stem has a leak where it joins the tube - will have to undertake the painful process of replacing that (it's a Savannah wheel which splits, I've heard they're painful!)

[Moneybox]

8 minutes ago, Marty_d said:

Pulled the plane out again this morning and did another start - thanks to @nomadpete the oil pressure gauge is now working.

I bought a small fuel tank (generally used for working on motorbikes when the tank is off) and suspended it on one side of the fuselage going into the wing tank inlet to the header, put a couple of litres in then switched the line to the return barb for running.  (Forgot to take a photo sorry).

 

Ran it for about 10 minutes.  Look like the oil TEMP gauge is not working now, so will have to try to figure that out.  (or ask Peter to help which is more likely to result in success!)

 

Kept it at 2000rpm for most of it, after running around 5 minutes at 2000 and with the oil pressure stable on around 3.5 bars I increased throttle to 4000rpm for around 30 seconds, then tested magneto drop individually.  Then back to 2000 for another few minutes.  Idle with throttle pulled back as far as it'll go is around 1800rpm, at that point oil pressure is reading just under 2 bars. 

At the end of the run the CHT's are showing around 75 degrees on one gauge and just on 50 degrees on the other.  I'm assuming the lower temp is on the front cylinder, will have to trace the wiring on that (and then label the gauge!)

I need to tighten up a few nuts in the oil system, there's a slow drip from the bottom nut and I think also the oil cooler connections.

 

The other problem is one of the main gear tyres went flat - it always had a very slow leak but now you can hear the air whooshing out of it when you take the pump off.  I reckon the valve stem has a leak where it joins the tube - will have to undertake the painful process of replacing that (it's a Savannah wheel which splits, I've heard they're painful!)

 

Split rims are usually easier, just make sure you release all the air, valve out, and break the bead before you split the rim. There will most likely be a rubber sleeve to prevent you pinching the tube on assembly however a tiny bit of air in the tube can help prevent that.

 

Ps: Inflate the tyre very carefully, they don't take much air.

Edited Sunday at 05:37 AM by Moneybox

[IBob]

Hi Marty......all sounds like progress!

FWIW:
My front CHT always read lower than the other one: probably inevitable given the position of the sensors.
I think Rotax now recommend initial warmup at 2200RPM, dropping back to 2000 after a few minutes. And my 912 always felt better at 2200 when cold.
And I'm not sure about 1800 as the min setting. Mine went lower than that, which was kinder to the engine/gearbox when finally stopping (no big clunk). I set my idle jet and throttle stop as per the Rotax manual, it's quick and easy and one of them was out on a new engine, so worth checking.
 

[facthunter]

The Motor has essentially NO Flywheel whatever and won't be Happy at Low revs particularly cold. The carbs are NOT Phased evenly.  Nev

[rgmwa]

Mine will idle down to about 1450, but I don't go below 1800 unless stopping the motor. It also helps to cut one magneto at about 1800 and wait two or three seconds as the motor slows before cutting the other one. It stops with less of a clunk. A 2000 rpm idle is a bit slow when the engine is cold. I usually run it a 2200-2300 initially. 

Edited Sunday at 06:12 AM by rgmwa

[facthunter]

Stop the Motor when running as slow as Possible. 1 Switch OFF wait, then Cut the second.  Nev

[skippydiesel]

47 minutes ago, IBob said:

Hi Marty......all sounds like progress!

I think Rotax now recommend initial warmup at 2200RPM, dropping back to 2000 after a few minutes. And my 912 always felt better at 2200 when cold.
And I'm not sure about 1800 as the min setting. Mine went lower than that, which was kinder to the engine/gearbox when finally stopping (no big clunk). I set my idle jet and throttle stop as per the Rotax manual, it's quick and easy and one of them was out on a new engine, so worth checking.

 

On cold start up, my 912ULS goes to 2500pm - 2700 rpm . I reduce the "choke" by 1/2 and the rpm comes back a little. After a few moments I remove all "choke" & rpm drops to about 1800 and I increasing, with throttle, to 2500 rpm.

 

As engine warms, rpm rises - I reduce throttle to maintain 2500 rpm, until oil temperature reaches 50C.😈
 

[Blueadventures]

5 hours ago, IBob said:

Hi Marty......all sounds like progress!

FWIW:
My front CHT always read lower than the other one: probably inevitable given the position of the sensors.
I think Rotax now recommend initial warmup at 2200RPM, dropping back to 2000 after a few minutes. And my 912 always felt better at 2200 when cold.
And I'm not sure about 1800 as the min setting. Mine went lower than that, which was kinder to the engine/gearbox when finally stopping (no big clunk). I set my idle jet and throttle stop as per the Rotax manual, it's quick and easy and one of them was out on a new engine, so worth checking.
 

Yep; they recommend 2200 or a little higher about 2300 to ensure smoothness.  Some engines can be a bit rough running at 2200.  This is mainly to reduce effect to gearbox plates.  (Also not ever mentioned is that rough running of engine results in the scuff marks on the carb piston slide sides, due to the carbs shaking.  Any marks are not detrimental to the carb performance.  So in short best after start to be at 2200 rpm minimum then after a few minutes increase to say 2500 to get to recommended lowest temp for take off.