Rotaxaru

[RFguy]

Hi RossK. good !. I will take that advice . any suggested shops that can do this locally you can suggest ? (anywhere  in australia)

regards

 

[BrendAn]

5 hours ago, RFguy said:

"Can't you buy a ready made engine mount for rotax to Jabiru.  It would be lighter than using adaptor plates. "

No - you cant buy a mount, and also every Jabiru is slightly different.....and I dont want to save weight- I need to keep the aircraft as close as possible to the original book. I will add weight if I am low.

I have done the new CG calcs and we'll see how that comes out in a weighing and where I need to add the weight.

 

Marty- I do have 3d cad but this is a 2d requirement. I will just DXF export directly from my CAD application that I am using....

First cut and install will be with ply. we'll see how that looks.

 

Sorry. I wasn't implying there was anything wrong with what you are doing. Just thought a ready made mount would save work.  A lame friend told me someone is making firewall forward kits for 912 into jab.

 

 

[RFguy]

Finally got around to finishing the CAD for the mount adaptor plate.

Off the to fab shop for that 12mm slab of 6061T6. 5005 would have been fine but its what I could get in the size. 

The big holes mate with the Jabiru engine mount with the rubber donuts.

The smaller holes (4) interface to the ring mount

lots of little ones are just utility threaded M5 thru. dont need the rib across the middle but I can always cut it out. 

 

 

 

Edited September 8, 2022 by RFguy

[RFguy]

Well, looks like the drawing is good (Plywood CNC) . Will ponder it a bit then get the ally cut.....

Three pics below

 

 

not holding perfectly aligned/square but you get the idea.

 

 

 

[RFguy]

...The fat spacers ensure the bolts stage square with the plate. next rev I would pin the spacers to the plate, also.

 

 

 

 

 

 

 

Edited October 7, 2022 by RFguy

[Blueadventures]

Nice.

[RFguy]

Next steps:

1) Fit engine mount back onto aircraft. that's a bit of a bastard of a job to get at the nuts behind the instrument panel. 

2) bolt mount, adaptor and rotax  and simulated weight prop  on the front

3) Weigh aircraft- measure CG to see where I am at (I should be *slightly* nose light, still) - this will guide my oil and water cooler and oil tank  locations.

4) slap the cowls on and see how the underside looks for space. The rotax sits lower than the Jab engine because of the gearbox. My mount adaptor is designed to preserve the thrust line precisely. I am expecting some modification because the exhaust is slung under.

 

The prop flange is about 25mm further forward.  This was unavoidable as I needed the bushing spacers between the adaptor and the ring mount because the rubber donuts would get in the way. 

There is good access to the water accessories , alternator/ignition magnets etc through the rear.  

 

 

 

[Blueadventures]

Hi RF if your oil cooler position needs tighter radius connection pipes Rotax sell (at Rotax pricing) tighter 90* bends. I bought these to replace the usual connectors like on the oil can so I could have oil cooler high under the gearbox output prop flange. Looking good.

[RFguy]

thanks Mike. I will see what the local Pytek guys have next door.... so far they've been helpful. there is heaps of room, like tons. room for a turbo ha ha  where the old engine mount is, it will be somewhere in there...

[RFguy]

AS I have been doing my homework on plumbing up the rotax and oil cooling, note well that the rotax sucks through the oil cooler and the install manual specifies that :

"At full throttle (take-off rpm) the max. negative pressure must not exceed 0.3 bar (4.35 psi) at 130 °C (266 °F)"

 

That's the pressure drop through your oil cooler (at 16 litres per minute flow) plus any hoses.

That's not much. I  went with a larger narrow cooler that had pressure drop/flow specifications  . at 16lpm at cst=30  (oil @ 85C) I'll have around 2 psi drop

Many coolers (geometry tends to drive it- long skinny ones are  droppy)  will not make this requirement I found....

While most Rotax are plumbed in 1/2" push on , if you are marginal , then 16mm push-on or  AN12(17.x ID)  might be a good idea- as 1 meter of 12.7mm ID , at above oil numbers is 1.6 psi drop.  say a long run up to the oil can.... chewing into the 4.5 psi margin. Going up to   16mm drops that to 0.7 psi.  AN10 hose  at 14.3 ID is a worthwhile impovement over 12.7mm.

So I will have AN10/12/16mm going up to the oil can.  I also have a oil thermostat in there.  Derale type "Part Number 25719 1/2'' NPT Fluid Control Thermostat". and fit AN ports to some and push ons to another.  the different fittings for oil cooler, can and engine will reduce chances of connection FUs. 

Edited October 12, 2022 by RFguy

[turboplanner]

On 08/09/2022 at 3:53 PM, RFguy said:

Finally got around to finishing the CAD for the mount adaptor plate.

Off the to fab shop for that 12mm slab of 6061T6. 5005 would have been fine but its what I could get in the size. 

The big holes mate with the Jabiru engine mount with the rubber donuts.

The smaller holes (4) interface to the ring mount

lots of little ones are just utility threaded M5 thru. dont need the rib across the middle but I can always cut it out. 

 

 

 

Beautiful CAD work.

[facthunter]

RFg if it can pull over 4 psi of suction you should have a safety bypass and also line the hose with a long coli of wire to stop it closing up and starving the engine of oil. Put that sort of vaccuum on your hose and see what happens. Nev

[RFguy]

Nev, yeah I will ensure it is specified.  there is in fact another little tidbit in there , for those who wouldnt realise that the negative pressure limits on the hose are important : 

"OIL HOSE REQUIREMENTS: Main oil pump (Oil circuit, engine) At negative pressure of -500 mbar (-7.25 psi) and a oil temperature of 150 °C (302 °F) the oil lines must not collapse."

 

that and another I added to Skippy's topic, oil can too high and the can will empty will go through the crankcase bearings into the crankcase. oil too low and the oil filter will drain into the can and starve the engine of gallery pressure at start  until the filter gets full.... 

post script:

Well I cannot find ANY hoses with negative pressure specifications, there are some suction rated hoses in hydraulics, but they are all low temperature ish. 

I imagine the larger the ID for a fixed wall thickness, the more likely the collapse would occur.  I will talk to a couple of the local suppliers.

Edited October 12, 2022 by RFguy

[RFguy]

oh yes does exist
https://hoseflex.com/wp-content/uploads/2020/03/2022-1-PHF-Catalogue_Page_121.pdf

 

etc etc.  would need to determine chemical compatibility.
Of course other people dont have this problem (or do they?) . The short lengths between the cooler and the pump and the oil thermostat would be 1/2". that's the high neg pressure side. the long line up to the oil can is low negative pressure. 

 

OH NEV- just re read what you wrote- put a spring IN the hose. yes. right. problem solved.

https://aeroflowperformance.com/af450-12-supp-inner-support-spring-12an-hose

 

 

Edited October 12, 2022 by RFguy

[jackc]

Some time ago I was looking at this for my Rotax 80hp in the Aeropup.

 

https://infinityaerospace.com/product/other/pre-oiler-and-back-up-engine-oil-pump/

[RFguy]

Remember this is not like an engine that mob who sell that refer to !

This is a dry sump.  and put you oil tank such that  the level is somewher between the filter and the jounrals and the oil should stay in the tank and not migrate.  just crank it without magnetos on and watch the oil pressure ? 

 

The 15W40 (rotax oil) is much better flowing at 0 deg C compared to W100, also.

and I would recommend against using corrugated hoses anywhere. The math says they are bad for flow.

Edited October 12, 2022 by RFguy

[RFguy]

moved back to Cowra from Temora for Rotax install.. Thanks Thruster88 for your invaluable experience and assistance. (pictured) 

 

Edited October 16, 2022 by RFguy

[jackc]

Sorry for dumb question but, what happens to 24 rego for your conversion?

[kgwilson]

Usually it is changed to E24 (experimental).

[RFguy]

Calculating my engine mount bolts and tensions....

1stly, I choose AN bolts, they're well specified, can choose precise grip length, and metal lock nuts are available. AN bolts have a reasonble tension gap between yield and ultimate tensile strength. They're not brittle like a 12.12 , more like a 5.7 etc

 

Total grip length required :

* 12.7mm Adaptor Plate thickness

* 45.0mm spacer thickness (the role of the spacer is to ensure the bolt stays in tension not shear on the plate), and for clearance of the Jab suspension donuts and starter motor needs about 43-45mm.

* 37.0mm : minimum length of the four of the  8mm ID tubes through the ring mount. 

*1.6mm x 3 (three washers 0.062") . one of these washers is between the aluminium spacer and the 8mm ID tube as a LOAD spreader.... otherwise the pressure on the spacer from the end of the tube would exceed the ALuminium compressive strength) 

=99.5mm total.  That is what I need for GRIP LENGTH

This is (99.6 - 76.2)  =3" + 23.3/25.4 inches = 3.9173" , or 3"  and (0.9173/( 1/16" )) = 3" and 14.6/16  which need to choose the next lkower to ensure we can pull thread with some margin - so next lower is 13/16"

Looking up the AN catalog - nearest bolt size is 3" 13/16" , this is an AN5-42. 

Local supplier has AN5-43... these are 3 " 15/16" grip - total 100.01mm. too long. nothing an extra 62 thou (1.6mm) washer wont fix for the moment even if that isnt perfect. 

 

Now, these are long bolts,  bolt stretch at tension will be significant, let us calculate the likely bolt stretch to determine if our grip length is too long.

The minimum spec for the bolt  is they yield at 4980 and shear at 5750 pounds.... back in metric - 2259kg / 2608kg. or 22kN/25kN

Working back for the cross section of the grip region, (~ 7.93mm dia) , this amounts to a yield strength of 449Mpa

 

The tension needs to be at least the likely load variation over use. That's pretty low . The bolts will always be in tension unless a bolt becomes loose or stretched, IE JOINT SEPARATION and then it could be all shear if another bolt does same.  The joint must remain in tension during eload excursions.   The weight on the mount is call it 80kg , lets say two bolts end up doing all the work due to some other failure, so we have 40kg/bolt and lets also so this loads are purely tension loads, for the moment  say... aircraft suffers 10G bumps, so there is 400kg on a bolt- . 400kg on a bolt out of 2259kg yield is only 17% of yield ! so that is our minimum tension.  We'll use 20%.

Now! Bolts with combined tension and shear loads have lower limits, and it is possible we might have this scenario in a partial failure mode (joint spearation) . But since we are not up near the limits, we can simplify the requirement.

 

For a 20% preload on these fasteners, about 4400N , this corresponds to a stretch of 43um.  luckily I can measure this to verify tension because I have access to both ends of the bolt. At 50% preload, we are up to 110um (0.11mm very measurable ) . Note that the yield strength numbers are the MINIMUMS. this means that if we measure 0.11mm stretch and the bolt is much higher in strength than the minimum, then we have alot more tension than we expected.

 

Another aspect of the preload is that it pulls the joint together .The 45mm diameter, 45mm long cylindrical solid spacer needs to be kep fast against the plate. Preload tension will assist that. 

 

Consulting AC43.13-7 , using regular nuts MS20365, the maximum torque for a bolt at 40ksi  (something approaching 60% of yield )   is met at ~ 100 to 140 inch pounds.  

 

Dry cadmium plating  with a torque of 60 inchpounds, the lower end of the AC spec ,  will deliver approx 5900N tension.  We wanted 4400N. If we torque to 50 inch pounds, we would have about the desired tension. We can cross check this with bolt stretch monitoring.

 

Let's now check the pressure on the aluminium plate under the standard washer :  0.562" OD,  = 0.248sqinches - 160e-06 sq meters, and a tension of 4400N, provides = =4400N / 160e-06sqM = 27Mpa, well below the 170MPa+  for the 6061T6

 

How about the steel tube through the ring mount- this is a tube welded at each end, a column fixed at both ends.  the maximum loading comes out to some ridiculous number of  newtons.  No issue...

Let's check the shear resistance for the ally plate onto the ally spaces. The cylindrical ally spacer has mated area of 0.00154m2, and a pressure (with 4400N of bolt tension) of 4400/0.000154 = 2.86MPa.  Given the thickness of the spacer (almost square length = diameter) the pressure will be almost uniform and provide same bolt tension/clamp pressure.  The spacer and plate joint should be assembled clean, no lube or contamination in order to provide maximum shear resistance.

 

Note- I am not an aeronautical engineer, nor a qualified mechanical or civil engineer. 
I looked around for a good primer on this for people on the net so they dont have to go through 10 textbooks like me, here is a good one:

https://www.fastenal.com/content/feds/pdf/Article - Bolted Joint Design.pdf

 

 

 

 

Edited October 17, 2022 by RFguy

[BrendAn]

This is an excellent thread for people considering the rotax swap. It's a terrific forum . I learn a lot sifting through all the posts. Keep it up Rf. 

[RFguy]

progress. as known, engine is about 30mm further forward, and the front of the top and bottom cowling needs modifications.  thrust line and centre is all good.

Edited October 28, 2022 by RFguy

[RFguy]

The exhaust ill be custom- that's just what I got.

some weird phone camera image distortion in the side view

 

The oil and water cooler will be underneath. The exhaust and turbocharger will be under and forward of the ring mount. That pipe is heavy. 30mm OD, 1.6mm wall. Wil use corrugated SS hose to connect collector, and maybe see how the collector goes paper thin. the turbocharger has to mount to something. 

 

The front cylinder  cheeks will need to be made a bit wider in the case I reduce compression with cylinder shims. 

 

Edited October 29, 2022 by RFguy

[onetrack]

Quote

The front cylinder cheeks will need to be made a bit wider in the case I reduce compression with cylinder shims. 

Glen, you will have to reduce the compression ratio if you fit a turbocharger, or the increased heat level at TDC will cause pre-ignition - unless you move to a much higher octane fuel.

[RFguy]

yeah ...10.8:1 there is no headroom..  but it's to be a normalizing turbocharger- 100% wastegate  until significant altitude... never more than 30" of MAP.

Turbo will be stage 2..... but it will be designed with location etc in mind....

Edited October 29, 2022 by RFguy