Marty_d Posted April 7, 2023 Posted April 7, 2023 Seeking informed opinion. An original Rotax radiator is northwards of $700 from Bert Flood. If you google "Rotax 912 radiator" you are flooded with ads from Ebay for replacements, from about $150 - $300. Is the build quality of the original such that it actually should be 2.5 - 5 times the price of an aftermarket item? 1
facthunter Posted April 7, 2023 Posted April 7, 2023 It's typical of Rotax parts. With auto radiators of the aluminium kind.(nearly all of them) the top line Chinese ones are noticeably the best and often have a drain cock which the OEM ones didn't. You'd have to check the actual article but I fit no other kind. Nev 2
Marty_d Posted April 8, 2023 Author Posted April 8, 2023 Thanks Nev - next question - you mention "top of the line" Chinese radiators, do any brand names spring to mind as being better than others?
facthunter Posted April 8, 2023 Posted April 8, 2023 I just go on price and the look of them. I think most have come through Repco so they may have sorted them a bit. Since they are more motor cycle you might try a big show like AMX I think it is. I've also looked at stuff under water/ air Heat exchangers. Nev 1
RFguy Posted April 8, 2023 Posted April 8, 2023 What is the frontal area available, and what will be the climb airspeed , and cruise airspeed ?
Marty_d Posted April 8, 2023 Author Posted April 8, 2023 Big, slow, slow... don't have the figures on me. People with similar aircraft - CH750, Sav - assure me that the standard size is sufficient.
IBob Posted April 8, 2023 Posted April 8, 2023 Savannah S Vx 48-57kts for 450Kg-600Kg Vy 54-64kts for ditto. Cruise 85kts @ 5000RPM 1
RFguy Posted April 8, 2023 Posted April 8, 2023 yeah, so the Sav dimensions are likely suitable. If you have a fast airframe, (more available air pressure) you can save a little frontal area with a triple core radiator. (thicker, higher air pressure drop across it , but more work done per square inch of frontal area) . Most of the motobike radiators, like the Kawasaki Ninja radiator I use for 3300 LCH conversions, $110, have 19mm hoses. Of course you need 25mm hoses for the 'tax, there are many ebay chinese suppliers of rotax compatible radiators. they're probably all fine. $200-$250. Buy a spare if concerned. Carrying a spare is both cheap and light solution to oan otherwise big problem if it fails / gets stoned (the aircraft, not the pilot) . 1 1
Marty_d Posted April 8, 2023 Author Posted April 8, 2023 8 minutes ago, RFguy said: gets stoned (the aircraft, not the pilot) . Used to fly hang gliders with a bloke who'd have a choof before flying. Didn't seem to affect his flying but he did occasionally forget to drop his feet out of the bag before landing. 3 1
trike1 Posted April 9, 2023 Posted April 9, 2023 Just buy Savannah radiator from Australian agent(were about $300) 3 1
IBob Posted April 9, 2023 Posted April 9, 2023 Just back from the hangar. The Savannah radiator has 10 cores and the core area (not including the end tanks) is 250 X 75. 1
RFguy Posted April 9, 2023 Posted April 9, 2023 (edited) OK 10 rows, 8.3mm spacing per row, likely double core (~ 45-50mm thick etc) , and 187.5 cm2. pretty small ! pressure across it must be good. Bob - sure that wasnt the Oil cooler ????? FWIW - The rotax install manual specifies "Experience has shown that with good airflow, a radiator with an area of 500 cm² (77.5 in²) is required for troublefree op- eration.". .. Now, I think that is going overboard unless you are flying at 50 kts..... I think it needs to be about 300 to 400 cm2 minimum. depends on airspeed.... The rotax pulls out alot more heat into the heads from the heavy aluminium cylinders , compared to the Jabiru LCH which the low conductivity steel - the heat is localized. Edited April 9, 2023 by RFguy
IBob Posted April 9, 2023 Posted April 9, 2023 1 hour ago, RFguy said: OK 10 rows, 8.3mm spacing per row, likely double core (~ 45-50mm thick etc) , and 187.5 cm2. pretty small ! pressure across it must be good. Bob - sure that wasnt the Oil cooler ????? Oh darn RFGuy...major brain fade here...but nice catch! Yep, that is indeed the oil cooler, and it's the coolant radiator Marty is wanting. Sorry about that, folks .........( 1
facthunter Posted April 9, 2023 Posted April 9, 2023 They are all heat exchangers liquid to air, I've fitted fork lift radiators to cars where you had no extra AREA and the extra thickness did the job. Oil coolers can be honeycomb and so can radiators. Most today are tube for both.. Oil coolers would be more robust I would think. Nev
onetrack Posted April 9, 2023 Posted April 9, 2023 Engine oil coolers have to be capable of withstanding a lot more pressure than a radiator. They need to be able to withstand at least 150psi, whereas a radiator only needs to be able to withstand about 30psi. The maximum test pressure on radiators is 20psi. Oil coolers also have much smaller inlet and outlet piping, as the flow rates are lower than radiators. Plus oil coolers aren't as efficient at heat transfer as radiators, thanks to thicker materials. 1
facthunter Posted April 9, 2023 Posted April 9, 2023 The wall thickness, a few thou extra is not a great issue for heat flow. The extra strength may well be the deciding factor. 130 +MPH rain has a bit of a whack effect. Nev 1
Marty_d Posted April 9, 2023 Author Posted April 9, 2023 Just now, facthunter said: 130 +MPH rain has a bit of a whack effect. Nev Fortunately that's about 50mph faster than I'll be going! 1 2
danny_galaga Posted April 9, 2023 Posted April 9, 2023 I've been having fun taking note of alternative spare parts for my build. I will try and see what brand my radiator is next im at the hangar. Bushcat roughly similar specs to the Savannah. 1
danny_galaga Posted April 9, 2023 Posted April 9, 2023 oh, i can see in the manual it is Setrab, same as the oil coolers. Setrab have agents in australia. I'll see if i can find a part number in the picture, otherwise i will still have to have a physical look. 1
rodgerc Posted April 9, 2023 Posted April 9, 2023 The 912ULS’ oil cooler is on the suction side of the oil pump....Only sees atmospheric pressure. 1 1 2
RFguy Posted April 10, 2023 Posted April 10, 2023 (edited) and note well- there is a strict limit to the pressure drop permitted in the system, (on the suction side)- pretty well dictated by the oil cooler. You'll find oil coolers that are wide in width and short in height (IE long tubes left to right ) will not meet the rotax vaccuum limit requirements. Tall, with lots of short tubes will usually meet the vaccuum limit requirement. SETRAB publish the pressure drop for oil flow at some oil visc spec. Edited April 10, 2023 by RFguy 1
Marty_d Posted April 10, 2023 Author Posted April 10, 2023 Got an oil cooler (standard for Rotax) thanks to the generosity of a forum member who had a spare. 2 1 1
danny_galaga Posted April 29, 2023 Posted April 29, 2023 Just in case you need another and this one is the right size, this is for the Bushcat 1
danny_galaga Posted April 29, 2023 Posted April 29, 2023 Couldn't find one in Australia for prices but here is a us dealer. No idea about this company but it lists the specs https://www.improvedracing.com/setrab-25-row-series-9-oil-cooler.html
skippydiesel Posted April 29, 2023 Posted April 29, 2023 On 10/04/2023 at 6:20 PM, Marty_d said: Got an oil cooler (standard for Rotax) thanks to the generosity of a forum member who had a spare. Need any oil cooler fittings ? - I have some unused Rotax origional. 1
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