Actual Flying Rotax Installs

[Zack]

Hey guys, I just wanted to update you on how my firewall forward is proceeding. I'm using an MT propeller with a 13" spinner, so my cowling needed radical work to accommodate this. I had a local university scan my firewall forward so I could digitally design the cowling. If anyone is interested in the file please let me know. There was a cost involved in getting the scan.

[Zack]

I noticed the 912iS has different oil return line crankcase locations than the 912ULS. Please see page 195 of the ULS installation manual and page 156 of the iS installation manual. The mounts will interfere with a standard AN fitting into the crankcase. I told Sonex Tech support and I'm sure Kerry and Mark weren't too pleased :) I don't have a solution to this yet.

Update: This is what Mark and Cris at Sonex had to say "The banjo fitting is a Vibrant Performance 11535 - It’s a 16mm x 1.5 banjo bolt to -8 AN. Here’s the link to Summit: https://www.summitracing.com/parts/VPE-11535 "

[Zack]

I did some research on oil coolers, and compared the large Rotax oil cooler to some Made in the USA Earl's oil coolers (Earl's coolers are cheaper than the stock cooler). I thought my research might help others. The Earls have a roughly square design like the stock Rotax, plus two long and short coolers that have that have >35 sq in of area and may work. I figure slightly larger can be fixed with tape over the fins. I compared the large size oil cooler because the 912iS runs leaner than the 912ULS. The 912iS installation manual identified how much heat the radiator and oil cooler must reject, measured in Kw and BTUs. One of their BTU conversions is incorrect, I forget which one. The Earls coolers say they reject less heat than the Rotax, despite being 33 percent thicker. I can only assume this is a function of the average airflow in the aircraft versus a car.

Rotax large oil cooler P/N 886 015
Width (mm / in): 180 7.09
Height (mm / in): 131 5.16
Depth (mm / in): 40 1.57
Frontal Area 23580.0 36.5844

Earl's UltraPRO Oil Coolers 361-219ERL
Width (mm / in): 163.5 6.438
Height (mm / in): 146.1 5.75
Depth (mm / in): 50.8 2
Frontal Area 23882.9 37.0185

Earl's UltraPRO Oil Coolers 361-413ERL
Width (mm / in): 282.6 11.125
Height (mm / in): 100.1 3.94
Depth (mm / in): 50.8 2
Frontal Area 28279.0 43.8325

Earl's UltraPRO Oil Coolers 361-810ERL
Width (mm / in): 358.8 14.125
Height (mm / in): 76.2 3
Depth (mm / in): 50.8 2
Frontal Area 27338.7 42.375

Update: Mark and Cris at Sonex are going to experiment with an oil cooler in the nose and dual radiators in the side exit air vents. I'm also going to go with the nose location, but a centerline radiator.

[Kai]

I’ve finally got some cruise numbers.

Airframe: Sonex Legacy #0525 standard gear dual stick, first flight may 2005; accumulated flight hours presently 605.
Engine: Edge Performance EP915ECI (Rotax 912 ULS refinement), max output 120HP/5800 rpm/29,92”Hg. A/F ratio 12.8-13.2, presently 12 hrs tt. Engine is still loosening up and rpm readings very slowly creep upwards.
Cooling: Split radiator up front, on each side of red gear housing, combined grid size as for R914. Oil cooler- the largest size Rotax suggests- installed centrally up front, below gear housing. Cooling air exits under cowling as per plans, plus side outlets.
Prop: Sensenich wood/glass 2 blade fp 64x82 with conical hub for Sonex. Standard Sonex scull cap spinner.

Note: Sensenich prop first had to be dynamically balanced. It is a true cruise prop, at climbout from home field it allows the engine to turn 5200 rpm with initially 29.92”Hg MP (remember:efi- no venturi pressure drop.) VSI then reads 1500’/min. WOT static ground home field 5050 rpm/29.92”Hg MP.

Combo weight: 309 kgs plus 40l fuel and one fat flier. CG empty at 20% aerodynamic chord (forward limit)
Note: very quiet late afternoon, little or no convection, headwind component apprx 5 kts.

Ambient field temp: 24 centigrades
Ambient field pressure: 1022 mbar.
Field elevation: 38’ (!) amsl

Track: 45 degrees magnetic
Altitude: 3000’ amsl.

1)
Rpm: 5050. Mp 22”Hg
ASI: 126 kts (gps gs 122 kts)

2)
Rpm: 5550. Mp 27”Hg (wot)
ASI: 147 kts (gps gs: 143 kts)
Note: it has been explained to me that this would translate to apprx 152 TAS at wot.

Note: I hate TV screens, so the panel only sports steam gages- brand is Aviasport. The tach, however, does not promote exact readings: too fat markings.
Note: while barely acceptable for hot (scandinavian) summer conditions, the cooling system as a whole will be outside Rotax specs during winter. As of present day, oil temp will not rise above 70C. Coolant stops at 65C. What will happen at -10C ambient, keeps me awake!

This original posting has been edited, and will be again as further numbers become available.

Thanks
Kai

[Zack]

Thanks for posting those number Kai!

[Kai]

Further to the oil cooler research above, I would like to chip in with the following:

1)
Most automotive oil coolers are designed with passages intended for pressure feed. This makes the passages fairly narrow. The Rotax recommended brand is adapted for suction- the oil pump sucks the oil through the cooler; wider passages. The pressure drop through an ordinary automotive oil cooler could become an issue (oil pump cavitation).

2)
Most automotive oil coolers are designed with a cooling grid intended for airflow generated by dynamic air pressures attained by cars. This results in grid spacings which are narrower than desirable for the faster aircraft. This again could result in cooling efficency issues. To overcome this the Rotax recommended coolers often have wider grid spacings than several makes intended for cars.

Thanks
Kai

[Zack]

I wanted to share an update on my cowling. I'm going with a MT propeller with a large 13" spinner, and the stock cowling with the "skull cap" style cowling would have required a lot of custom work. I visited a composite shop in Kansas that walked be through the process of design, gantry CNC mold cutting, fibers, resins, the whole works. It was very fascinating and I learned a lot, but unfortunately that shop was unable to help me. I found another, Mace Aviation in AZ, that was willing to take on the job and was understanding regarding my budget. I contacted a local university who came out and did a 3d scan of the firewall forward plus a foot or so of the windshield and fuselage. This cowling is based on that scan, and it should be adaptable to any B series Sonex or Waiex.

The radiator is fully ducted. We selected a forward tilt to give us room in the rear for an exhaust. I'll be using the standard Sonex side cowling vents to create negative pressure for the air inlets and oil cooler. Mark from Sonex is currently planning on two radiators in the side cowling vents instead of this approach. It will be interesting to compare the results when we're done. The other thing Mark is thinking about is a NACA duct to feed engine intake air. I had planned to pull intake air from inside the cowling, but I could retro fit the NACA duct later if I choose.

[Zack]

The larger spinner and redesigned cowling will really change the profile of the aircraft. Mace Aviation created a 7 page PDF slide show I can share with other views, but I'm not sure the best way to post it.

[Zack]

Kai, that was very helpful information regarding the oil coolers. One thing that confused me was that the Rotax oil coolers dissipated more heat energy than the automotive coolers. The Rotax cooler dissipates 34,121 BTUs/hr (calculated) while the comparable Earl's cooler dissipates only 13,000-17,500 BTUs/hr (published). Perhaps this is due to the slower air the automotive cooler is exposed to, and it would be higher at aircraft speeds? In any case, after doing the research I settled on the Rotax oil cooler. I thought the research could be helpful to others considering different options. One thing that could have fooled me was unit conversion. Even Rotax goofed there!

[Skippydiesel]

Casey,

When replacing the oil in the tank we are supposed to do this with the aid of compressed air: do not exceed 1bar/15psi!, the manual says.

T

Remember : Murphy lives!

Thanks
Kai

Incorrect - I have been changing the oil in my Rotax 912 ULS for 11 years - the only time additional air pressure is required, is when you do a crank case (complete system) oil removal. For all other changes you, Burble/burp your engine by hand, just drain/replace the tank oil (nominal 3 litres), check for oil pressure (short non ignition crank) - that it.