Cooling System
Posted: Fri Mar 24, 2023 5:56 pm
by Skippydiesel
The design & implementation of the Rotax engine/Sonex cooling system is possibly the least well understood (too few examples/hrs) part of the whole build.
For myself, current & future Rotax installers, I think it would be very helpful to see photos of cooling system (oil/coolant/barrel) sets ups.
Advice from owners regarding efficiency and ease of installation, would also be useful.
My Sonex has now been flying for about 25 hrs. The concept of an aft coolant radiator, using air exiting from the cowling has proven problematic. After much mucking about the temperatures are just under control but I would like “just” to be converted to well under control. I theorise that the restriction to air flow, by the hot radiator core, is reducing air entry to the cowling, thereby negatively impacting on all other cooling systems - I will be doing a big redesign in the near future.
The radiator will be moved forward (location yet to be decided)- the space it vacates will become an unobstructed air exit vent. This change will result in modifications to cowl shape/design (may be a whole new cowl).
Re: Cooling System
Posted: Mon Mar 27, 2023 9:48 pm
by Skippydiesel
I don’t believe it!
???Not one Rotax 912 UL/S drivers on the Forum have had any problems/solved with their cooling system (oil/coolant)???
Re: Cooling System
Posted: Mon Mar 27, 2023 11:25 pm
by gammaxy
I missed your earlier post, perhaps others missed it too.
I suspect you’re not the only one to have cooling issues. I don’t know how much sense it makes, but I’d try to understand how the RV-12 cooling works and try to set mine up similarly. They’ve obviously got much more time on their installations. I bet we’ve got a bunch of different one-off installations over here.
We used to have a guy who’d talk a lot about the science of liquid cooling and how to size inlets and outlets. I think he’s still on Homebuilt Aircraft, but I haven’t seen him here since Yahoo!.
Re: Cooling System
Posted: Tue Mar 28, 2023 1:19 am
by Skippydiesel
Thanks Chris - I have “browsed” a lot of Rotax 9 installations - lots of ideas BUT I would like to retain the Sonex “look/profile” if possible.
While function is, for me, always ahead of form, I don’t want any unnecessary vents/bumps/protrusions. To this end, it is important to get the location of heat exchangers just right, so as to minimise the number & size of vents (In & out).
My cowl exit vent is (for the time being) fixed in location & size, as is the two inlet “nostrils”.
My coolant & oil radiators will need to be relocated from their present position and with them any added inlet vents.
Do you or any other readers, have any thoughts/advise on the concept of having coolant & oil radiators in air flow series (one behind the other). I ask because on my installation its the oil temperature which is the biggest issue - what if I mounted the oil cooler in front of the coolant radiator (or visa versa)? Could this work?
Re: Cooling System
Posted: Tue Mar 28, 2023 2:44 am
by Kai
That´s how they do it on the composite french sports aircraft Dyn Aero MCR101 Ban Bi (quite a name!): one cooler behind the other. There are quite a few pics of such an aircraft on the web- it is really a ´smiling´cowling. I don´t know which cooler is up front, but I speculate it´s the coolant radiator.
Both coolers are in a common, tightly fitting, very narrow duct under the bottom cowling. That makes both coolers very deep and long, but not very high: quite different from what one normally sees in a 912-installation. Both coolers are out of house specially made for the aircraft manufacturer, and since it folded some years back I speculate it would be quite a task to get hold of new ones should that be required.
The system seems to work well and cools fine as long as the duct is kept free of debris (grass etc). To my knowledge there are no thermostats in the system- I know of owners who have experimented with outlet flaps to restrict airflow during low ambient temperatures.
Re: Cooling System
Posted: Tue Mar 28, 2023 3:22 am
by sonex892.
Sorry no experience with the rotax, only thoughts here.
Your cruise speeds with the constant speed prop are likely to be quite a bit higher than most others 912s with a fixed pitch. So what other guys have done may not be optimum for you anyway.
I dont think blocking the cowl exit with a radiator is a good idea. I imagine the air entering the radiator would be a bit preheated and also restrict airflow. My thoughts on stacking the oil cooler and radiator are that, I would avoid it.
I would try to get cool air to the barrels and cool air to both the radiator and the oil cooler. Maybe a scat tube feed to plennums on rear mounted coolers.??
I would try to not reinvent the wheel and look to other designs for ideas. Designs that successfully use a 912, designs that have a 130 to 140kt cruise in a tight cowl.
If you can make a cowling from scratch you would be able to make fibreglass plennums for your coolers and barrels, you can then hopefully place the coolers where they fit.
Re: Cooling System
Posted: Tue Mar 28, 2023 6:46 am
by Skippydiesel
Kai wrote:That´s how they do it on the composite french sports aircraft Dyn Aero MCR101 Ban Bi (quite a name!): one cooler behind the other. There are quite a few pics of such an aircraft on the web- it is really a ´smiling´cowling. I don´t know which cooler is up front, but I speculate it´s the coolant radiator.
Both coolers are in a common, tightly fitting, very narrow duct under the bottom cowling. That makes both coolers very deep and long, but not very high: quite different from what one normally sees in a 912-installation. Both coolers are out of house specially made for the aircraft manufacturer, and since it folded some years back I speculate it would be quite a task to get hold of new ones should that be required.
The system seems to work well and cools fine as long as the duct is kept free of debris (grass etc). To my knowledge there are no thermostats in the system- I know of owners who have experimented with outlet flaps to restrict airflow during low ambient temperatures.
Amazing engine installation - definitely some tangential thinking went into that design. Unfortunately I must work within the Sonex airframe/engine alignment . I agree with the likelihood that the oil cooler comes second in a series installation - oil taking longer to absorbed/give up heat.
Re: Cooling System
Posted: Tue Mar 28, 2023 6:56 am
by Skippydiesel
sonex892. wrote:Sorry no experience with the rotax, only thoughts here.
Your cruise speeds with the constant speed prop are likely to be quite a bit higher than most others 912s with a fixed pitch. So what other guys have done may not be optimum for you anyway.
I dont think blocking the cowl exit with a radiator is a good idea. I imagine the air entering the radiator would be a bit preheated and also restrict airflow. My thoughts on stacking the oil cooler and radiator are that, I would avoid it.
I would try to get cool air to the barrels and cool air to both the radiator and the oil cooler. Maybe a scat tube feed to plennums on rear mounted coolers.??I would try to not reinvent the wheel and look to other designs for ideas. Designs that successfully use a 912, designs that have a 130 to 140kt cruise in a tight cowl.
If you can make a cowling from scratch you would be able to make fibreglass plennums for your coolers and barrels, you can then hopefully place the coolers where they fit.
As is, I seem to be able to get to around 147 Knots TAS @ 6500 ft - probably get similar with a ground adjust optimised for high speed cruise but then TO/Climb would be anaemic.
“I dont think blocking the cowl exit with a radiator is a good idea” - well it turns out you are correct but that was the card I was dealt & the install was so neat/clever, that I thought I would give it a go.
“make fibreglass plennums for your coolers and barrels, you can then hopefully place the coolers where they fit.” - not sure what you are saying here - oil/coolant cooler locator comes (in my mind) before cowling design
Re: Cooling System
Posted: Tue Mar 28, 2023 7:04 am
by Skippydiesel
I am quite impressed by some of the Zenith 912 installations - the engine location & general lay out seems to be similar to the Sonex
Re: Cooling System
Posted: Tue Mar 28, 2023 5:11 pm
by Kai
Just to field something more to mull over:
When Edge tested out his original EFI setup, it was done on his Sonex Legacy (#037). This engine had a turbo, an aftercoolder, and a CS prop. See pic below (never mind the non standard windshield and canopy). Incidentally, this airplane originally had a VW Aeroconversions engine under its universal Sonex cowling, so this was the starting point for the conversion.
The fairly large coolant radiator that the 912 requires, was a bother to position under the existing original cowling- there was just not enough space with all that other hardware. The bright idea then came up to have two identical radiators manufactured, with a total grid identical to that of the standard radiator. It would then be fairly easy two find space for these two rads behind the existing cooling air intakes. Incidentally, these rads were then hooked up in series and installed with selv made brackets on the front of the gear housing, just behind the prop flange. The pic should give some idea of the setup.
The intake side of the cowling had to be slightly doctored, but this work was minor. To the best of my knowledge, there have been no cooling issues.
Re: Cooling System
Posted: Tue Mar 28, 2023 5:48 pm
by Murray Parr
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I placed the oil cooler in between the engine mount tubes and also had room to attach the oil canister.
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The 3" scat is almost direct to the cooler, I will most likely build a NACA duct for this in the future
Re: Cooling System
Posted: Tue Mar 28, 2023 6:05 pm
by Murray Parr
Same deal with the radiator, not really much room anywhere else
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I built a fresh air duct attached to the cowl, attached piano hinged air deflectors sealed up against the cowl and radiator
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This arrangement was a blend of 2 other peoples designs and they might chime in here, Brett and Gary B they both told me it is sufficient in the air but don’t dawdle too long taxiing around. I haven’t flight tested it yet but it does seem to get hot rather quickly on the ground stationary while doing full power tests. Interestingly, it cools great without the cowl on and not so great with either full cowl or just the bottom cowl. This tells me that the fresh air duct is a bit too close to the center of the prop so I might add a naca duct inside the fresh air duct and scat tube it directly at the radiator.
Re: Cooling System
Posted: Tue Mar 28, 2023 6:11 pm
by Murray Parr
Just to add to my above posts, I am not a fan of placing coolers in series or ducting the hot cowl air through them. Contrary to common belief, these systems are air cooled, a lot of folks believe the coolant is doing the cooling but it is the air flowing through the cooling fins that removes the heat from the coolant or oil.
Re: Cooling System
Posted: Tue Mar 28, 2023 6:25 pm
by Skippydiesel
Here is another install that has similarities with the Sonex cowl/engine;
http://www.stoneylake.org/pipcom/912cooling.htm
Re: Cooling System
Posted: Tue Mar 28, 2023 6:30 pm
by Skippydiesel
Kai wrote:Just to field something more to mull over:
When Edge tested out his original EFI setup, it was done on his Sonex Legacy (#037). This engine had a turbo, an aftercoolder, and a CS prop. See pic below (never mind the non standard windshield and canopy). Incidentally, this airplane originally had a VW Aeroconversions engine under its universal Sonex cowling, so this was the starting point for the conversion.
The fairly large coolant radiator that the 912 requires, was a bother to position under the existing original cowling- there was just not enough space with all that other hardware. The bright idea then came up to have two identical radiators manufactured, with a total grid identical to that of the standard radiator. It would then be fairly easy two find space for these two rads behind the existing cooling air intakes. Incidentally, these rads were then hooked up in series and installed with selv made brackets on the front of the gear housing, just behind the prop flange. The pic should give some idea of the setup.
The intake side of the cowling had to be slightly doctored, but this work was minor. To the best of my knowledge, there have been no cooling issues.
Hi Kai,
Yeah! this is very similar to the Europa installation. The twin radiators lend themselves to a small cowl frontal area. The down side is a small increase in weight and a large increase in connections/failure points. I could still adopt this concept.
There is/was a Sonex, on the Airmaster web site, that has the twin coolant radiator concept (Owner Thomas Hauklien of Edge Performance) https://www.propellor.com/
Cant quite make out for sure where they have placed the oil cooler - can you enlighten me?
Re: Cooling System
Posted: Tue Mar 28, 2023 6:45 pm
by Skippydiesel
This arrangement was a blend of 2 other peoples designs and they might chime in here, Brett and Gary B they both told me it is sufficient in the air but don’t dawdle too long taxiing around. I haven’t flight tested it yet but it does seem to get hot rather quickly on the ground stationary while doing full power tests. Interestingly, it cools great without the cowl on and not so great with either full cowl or just the bottom cowl. This tells me that the fresh air duct is a bit too close to the center of the prop so I might add a naca duct inside the fresh air duct and scat tube it directly at the radiator.[/quote]
Hi Murray,
Great work!
Ref your oil cooler; It looks to be regular LyCon style, quite diffrent from the Rotax offering.
The one I have in the Sonex is probably 1/2 as big again, as the one I had in my Zephyr. The Zephyr one, located on the firewall, down near the air exit, without ducting/shroud of any kind, overcooled in winter, just about right in summer (95C in cruise) - My Sonex one is struggling to keep cruise temperatures below 110C and it has a dedicated air in/out circuit - something is wrong!
Re: Cooling System
Posted: Tue Mar 28, 2023 8:27 pm
by Murray Parr
Hi Murray,
Great work!
Ref your oil cooler; It looks to be regular LyCon style, quite diffrent from the Rotax offering.
The one I have in the Sonex is probably 1/2 as big again, as the one I had in my Zephyr. The Zephyr one, located on the firewall, down near the air exit, without ducting/shroud of any kind, overcooled in winter, just about right in summer (95C in cruise) - My Sonex one is struggling to keep cruise temperatures below 110C and it has a dedicated air in/out circuit - something is wrong![/quote]
My oil cooler came with a VW engine I used to have, maybe it will be too small but so far it cools well on the ground, probably needs longer run times to get the oil temp high though.
For your cooler, maybe confirm the temp quage is accurate first. I wouldn’t be too worried about 110c though
Re: Cooling System
Posted: Tue Mar 28, 2023 11:16 pm
by Skippydiesel
Hi Murray,
The 110C can only be maintained with constant care/attention and in cool air - I had to return to base the other day when encountering 30C at 4500 ft - oil temp went up to 120C before I reduced power and slowly descended back for a landing.
My oil/coolant/head cruise temperature goal, is to have consistent sub 100C (Australian summer, although a rarely fly above 30C ambient) . In climb, I am comfortable with temps up to/not above 120C.
I would very much prefer to have an over cooling situation in winter, that needs to be managed by temporarily reducing heat exchanger/air flow efficiency, than a system that wont allow worry free summer operations.
Re: Cooling System
Posted: Wed Mar 29, 2023 3:26 am
by Kai
Skippydiesel wrote:Hi Kai,
Yeah! this is very similar to the Europa installation. The twin radiators lend themselves to a small cowl frontal area. The down side is a small increase in weight and a large increase in connections/failure points. I could still adopt this concept.
There is/was a Sonex, on the Airmaster web site, that has the twin coolant radiator concept (Owner Thomas Hauklien of Edge Performance) https://www.propellor.com/
Cant quite make out for sure where they have placed the oil cooler - can you enlighten me?
Consider yourself enlightened: look closely at the oil tank in the picture- next to it you see a vertical squarish object. That is the cooling air collector/hood for the automotive oil cooler, fed with 2 in scat hoses (not in the pic). Also in view are the (capped) blue AN type elbow connectors for the lubeoil in and out of the cooler. Personally I am not in favour of using automotive style coolers in aircraft installations: their cooling grids are often too dense for the much higer airspeed encountered here. However, I must admit, that very often they seem to work quite well.
Re: Cooling System
Posted: Wed Mar 29, 2023 7:51 am
by Skippydiesel
So does anyone know of a reputable supplier ???
Re: Cooling System
Posted: Wed Mar 29, 2023 9:52 am
by Kai
I had my twin radiator setup especially made in the Check Republic- ordred them through Edge Performance: we´re practically neighbours. Maybe a little too far away for you :-). The oil cooler is the largest $$$$$$€€€€€€€ Rotax 912-series type. It overcools in summer- in winter it takes my poor luboil straight to the north pole. For the time being I solve this with different sizes of seasonal inlets in front of my cooler, but it is only bordertline satisfactory, and there must be an oil thermostat in my future- I just need to find some free, unoccupied space under the bonnet 
Re: Cooling System
Posted: Wed Mar 29, 2023 8:51 pm
by Skippydiesel
[quote=“Kai”]I had my twin radiator setup especially made in the Check Republic- ordred them through Edge Performance:
I thought Edge/Thomas Hauklien was in Norway - I have emailed him about the double radiator installation in his Sonex
The oil cooler is the largest $$$$$$€€€€€€€ Rotax 912-series type.
As is mine - I am beginning to wonder if mine has some sort of internal restriction, it should do better than 110C.
there must be an oil thermostat in my future-
I have an unused (never had oil through it) one - happy to exchange it for a nice pair of radiators 
Re: Cooling System
Posted: Thu Mar 30, 2023 2:20 am
by Kai
Skippydiesel wrote:
Kai wrote:I had my twin radiator setup especially made in the Check Republic- ordred them through Edge Performance:
I thought Edge/Thomas Hauklien was in Norway - I have emailed him about the double radiator installation in his Sonex
The oil cooler is the largest $$$$$$€€€€€€€ Rotax 912-series type.
As is mine - I am beginning to wonder if mine has some sort of internal restriction, it should do better than 110C.
there must be an oil thermostat in my future-
I have an unused (never had oil through it) one - happy to exchange it for a nice pair of radiators
Correct: Thomas is in Norway- so am I.
Getting hold of an oil thermostat is not my issue here- Edge has stacks in stock. Finding some space for it where it does not require rearrangement of the whole instrallation, is.
I enclose a pic of my predicament as it looked during the final stages of installation, just to gain some symphaty for my ordeal to come
Re: Cooling System
Posted: Fri Mar 31, 2023 3:35 am
by Skippydiesel
Hi Kai,
Do you have contact details for the Czech builders of your radiators?
AND
Photos of your cowling showing air in/out?
Re: Cooling System
Posted: Fri Mar 31, 2023 8:06 am
by Kai
Skippydiesel wrote:Hi Kai,
Do you have contact details for the Czech builders of your radiators?
AND
Photos of your cowling showing air in/out?
Rads were ordered through Edge- I don´t know the name of the manufacturer. But getting these things from Edge seems a bit over the top for you- with a thriving competition car industry like you have Down Under it should be fairly easy to get hold of something here?
Cooling air IN openings are per standard Sonex cowling details, slightly enlarged to accomodate the rads.
Cooling air OUT openings are also per Sonex standard. In addition SIDE openings have been incorporated according to drawings I got from Sonex Tech.
BUT: in order to accomodate the fairly hefty Rotax turbo muffler, the cowling as such had to be made slightly fuller towards the front, making the Sonex cowling fairly useless- and since I hate composite work even more than the dentist, I built my new one with sheet 1mm Al7075T6.
A pic will give you an idea of the end result, which is coming close to 100 hrs in the air.
Re: Cooling System
Posted: Fri Mar 31, 2023 6:39 pm
by Skippydiesel
Veeeery Sonex nice Kai,
“thriving competition car industry like you have Down Under” - you would think so. I have written (e mail) to no less than eight custom radiator makers. So far, I have had a flat refusal on the grounds of not being insured for aviation work (???) - another said they did not have to materials/tools for such small radiators (but did recommenced another provider) - I live in hope, that one or more of the remaining half dozen may be willing to quote on the job.
Re: Cooling System
Posted: Fri Mar 31, 2023 7:52 pm
by daleandee
Skippydiesel wrote:So far, I have had a flat refusal on the grounds of not being insured for aviation work (???) -
Many moons ago I owned a Quad City Challenger 11 CWS that used a Gates PowerGrip GT2 belt for the redrive. When you ordered one or went in to pick it up you never said what it was for. Many used the term “airboat” for the same reason you mention.
On my Sonex I wanted the fiberglass spinner to be chromed. I found a few companies that could do it but all said “absolutely not” if it’s part of an aircraft.
Re: Cooling System
Posted: Fri Mar 31, 2023 10:04 pm
by Skippydiesel
Problemo! -
The few installations I have seen with the double/forward coolant radiators, have been aftermarket fuel injected 912 variants - mechanical fuel pump is redundant/deleted.
I will not be removing my fuel pump any time soon - this pretty much makes what I saw as being quite a straightforward installation way more complicated on the right side of the gearbox. - Such is life & homebuilt aircraft!
Re: Cooling System
Posted: Fri Mar 31, 2023 10:06 pm
by Skippydiesel
daleandee wrote:
Skippydiesel wrote:So far, I have had a flat refusal on the grounds of not being insured for aviation work (???) -
Many moons ago I owned a Quad City Challenger 11 CWS that used a Gates PowerGrip GT2 belt for the redrive. When you ordered one or went in to pick it up you never said what it was for. Many used the term “airboat” for the same reason you mention.
On my Sonex I wanted the fiberglass spinner to be chromed. I found a few companies that could do it but all said “absolutely not” if it’s part of an aircraft.
When talking to non aviation service providers, I never volunteer the purpose of my enquiry - if asked outright (as happened) I give a truthful answer.
Re: Cooling System
Posted: Fri Mar 31, 2023 11:59 pm
by 13brv3
“Off road vehicle” is a truthful answer
Rusty