Rotax Parts Supply Problems

[skippydiesel]

1 hour ago, danny_galaga said:

And if you get it wrong, and the engine blows up,  there will be max suck alright 😄

 

On a serious note, the Bushcat has its two oil coolers in different positions- one below the propeller, and one above. Perhaps if you used the same coolers you could have them in different positions too, thus potentially reducing the impact of poor cooling when taxiing? One could be in the cowl, one could be say under the wing a la Spitfire.

Hence my preference  to go with the Rotax Extra Large Oil Radiator (Cooler) - minimising the rick of making a poor after market choice. If my serch for the Rotax product fails I will certainly go down the after market rout - Setrab have some promising products.

 

Thanks for the Bushcat suggestion but no. Wherever I can, I apply the KISS principal - having long hoses additional oil coolers, many extra connections, is the stuff of my nightmares🙃

 

 

Edited June 19, 2023 by skippydiesel

[skippydiesel]

3 minutes ago, facthunter said:

Flow is ONE thing. It's proportional to pressure difference . Operating at below ambient pressure is something else requiring other considerations structurally.   Nev

Please expand Nev

[RFguy]

Nev's talking about the oil cooler to operation under tension conditions instead of pressure being a mechanical consideration

Like whether a hose is designed to resist pressure or suction and not suck and and damage itself etc etc.

Coolers may be stressed for only pressure and not tension  (due to a design assumption).

The Setrab people said "good either way" for their product when I asked. since Dry Sump and suction is a regular thing in other industry.

[danny_galaga]

2 hours ago, RFguy said:

Nev's talking about the oil cooler to operation under tension conditions instead of pressure being a mechanical consideration

Like whether a hose is designed to resist pressure or suction and not suck and and damage itself etc etc.

Coolers may be stressed for only pressure and not tension  (due to a design assumption).

The Setrab people said "good either way" for their product when I asked. since Dry Sump and suction is a regular thing in other industry.

Probably why Bushcat have gone with them. By all reports they work well. My plane is number 231. Had it quite a while so they might be up to say 300 or so aircraft. Even if mine was the first with those coolers , there's say 70 odd flying with them. You can trust that series of setrab coolers are suitable 🙂

Edited June 19, 2023 by danny_galaga

[IBob]

It'll be interesting to see where you arrive at with both resizing and repositioning of the cooler, Skippy.
The Savannah has the cooler at the pointy end with it's own air intake and a pronounced lip under the rear cowl to reduce exit air pressure.
I can't tell you the size of the cooler (I can measure it when next at the hangar, if you wish), and obviously we don't have your elevated temperatures here in Nuzeelun. But in winter I'm flying with about 2/3 of the cooler blanked off, in summer 1/3, and it still takes a sustained climb to hit the recommended 100'C mark.

[skippydiesel]

59 minutes ago, IBob said:

It'll be interesting to see where you arrive at with both resizing and repositioning of the cooler, Skippy.
The Savannah has the cooler at the pointy end with it's own air intake and a pronounced lip under the rear cowl to reduce exit air pressure.
I can't tell you the size of the cooler (I can measure it when next at the hangar, if you wish), and obviously we don't have your elevated temperatures here in Nuzeelun. But in winter I'm flying with about 2/3 of the cooler blanked off, in summer 1/3, and it still takes a sustained climb to hit the recommended 100'C mark.

Veeeery neat! I am  impressed.

 

Intersted to see a relatively wide (to height) oil cooler - did you read the earlier advise suggesting  short cross tubes for reduced flow resistance? - comment!

 

I will be intersted to get the part/model number and or dimensions.

 

It will be at least a month or two, for all the changes to be completed  - the modifications to the cowling, to accommodate the new heat exchanger locators, are likely to be the most demanding (for me).

 

One of the (many) oil temperature "fixes" I tried was to install a pilot operated electric cowl flap - will keep this feature, at least until I know that both high & low temperatures are satisfactory.

[IBob]

Skippy, I'll take some measurements when next in.
I cannot take any credit for the choice or the installation: I just followed the instructions and equipment that came with the kit (which included both the coolers) plus the excellent build pics supplied by the Oz agent at the time, Reg Brost.

Points of difference between my aircraft and yours would have to include that my fixed pitch prop is set up for the usual compromise between takeoff and cruise. I typically cruise at 5000RPM and 85kts. And while the Savannah will go quicker, as a draggy aircraft with a fat wing, it doesn't really want to.
All of which is to say that your engine is almost certainly working much harder than mine in cruise and so producing more heat.

[facthunter]

The main problem I've encountered with the Rotax 912  would be cured by having an adjustable cowl flap. Moving packing (foam) in and out is hard to do in flight. On some longish flights the ambient temp changes a lot. It would also permit quicker warm ups on frosty mornings. Nev

[IBob]

Nev, someone in the S Island here is now manufacturing a louvre setup.
Initially for the Sav, I think, but no doubt adaptable for other configurations. A mate who flies a lot more and often higher than I do recently sent me pics, and it looked like a really nicely designed and engineered thing.

[IBob]

A little light relief (and a whole lot of thread drift).
This remains one of my favourite Monty Python sketches of all time. And the phrase that sticks in my head (and could be applied to all things, aviation included) is at 03:15.

 

[Blueadventures]

Also consider mounting a second oil cooler in front of the coolant radiator.  Some installation run a R912ULS with such a setup with success.

[skippydiesel]

42 minutes ago, Blueadventures said:

Also consider mounting a second oil cooler in front of the coolant radiator.  Some installation run a R912ULS with such a setup with success.

Thanks! Will consider pretty much all suggestions however my policy (made to be broken) is to take small incremental (hopefully minimal cost) steps - a second oil cooler adds complexity & weight, so will be way down the list of potential fixes

[walrus]

A standard sized cooler, Rotax or setrab should be fine provided you are not doing anything unusual.

 

Your Airmaster comes set at about 5700 for takeoff and 5500 for climb.

[skippydiesel]

1 hour ago, walrus said:

A standard sized cooler, Rotax or setrab should be fine provided you are not doing anything unusual.

 

Your Airmaster comes set at about 5700 for takeoff and 5500 for climb.

Thanks Walrus - I only use TO Mode to get to circuit height. From then  to altitude or stooging, Climb Mode which in my set up is max 5450 rpm. To be honest I have never taken much notice of TO Mode rpm but if its in line with the other settings it would be max 5750 rpm. 

[skippydiesel]

Thanks Walrus - I only use TO Mode to get to circuit height. From then  to altitude or stooging, Climb Mode, which in my set up is max 5450 rpm. To be honest I have never taken much notice of TO Mode rpm but if its in line with the other settings it would be max 5750 rpm. 

 

As for heat exchanger sizes - From (faulty) memory Rotax only offer one size in coolant Radiators and four sizes in Oil Coolers. Therefor there is a single standard in Radiators but not in Oil Coolers. Further, I assume because there are  4  Oil Coolers to choose from, this reflects, more complex/variable cooling environments. My aircraft is fitted with the standard Radiator and the Large Oil Cooler (next size up is the Extra Large)

 

My coolant cooling is well under control in the air (90-95C) - way to hot on the ground (120C) -  Radiator is not receiving sufficient air flow, on the ground, to keep the coolant temperature below 100C - must improve Radiator air flow on ground - relocate Radiator from aft/ventral location to forward location. This will also improve exit air flow and assist in overall cooling.

 

My oil cooling is fine on the ground, 80C, (low engine power) but steadily climbs when in the air. If I stay in prop Climb Mode I can keep the temp from rising above 104C. As soon as I switch to Cruise Mode the temp goes up and can reach 120C. At this point I start a shallow decent, at low rpm, which brings the temp back down below 100C.

 

Various air flow adjustments have been tried, to improve the oil temperature with some success - it now takes much longer for the  temperature to rise and with great care (not much fun) can be kept to 112C in Cruise

 

My challenge is to design/select a system that will deliver on ground coolant temps below 100C and Cruise oil temps that will stay in the range 90-95C in the air, no matter the ambient temperature or demand on the engine eg extended climb on a hot day.

 

In general- I would much rather be dealing with an overcooling situation (easy fix) than an overheating problem.

 

At this stage;

I haven't purchased a larger oil cooler - but hope to very soon. 

Just finished setting up my temporary aircraft workshop and will start, today, on the relocation of heat exchangers, to be followed by remodelling of the cowling (ugh!) to accommodate the changes 

[BrendAn]

5 minutes ago, skippydiesel said:

Thanks Walrus - I only use TO Mode to get to circuit height. From then  to altitude or stooging, Climb Mode, which in my set up is max 5450 rpm. To be honest I have never taken much notice of TO Mode rpm but if its in line with the other settings it would be max 5750 rpm. 

 

As for heat exchanger sizes - From (faulty) memory Rotax only offer one size in coolant Radiators and four sizes in Oil Coolers. Therefor there is a single standard in Radiators but not in Oil Coolers. Further, I assume because there are  4  Oil Coolers to choose from, this reflects, more complex/variable cooling environments. My aircraft is fitted with the standard Radiator and the Large Oil Cooler (next size up is the Extra Large)

 

My coolant cooling is well under control in the air (90-95C) - way to hot on the ground (120C) -  Radiator is not receiving sufficient air flow, on the ground, to keep the coolant temperature below 100C - must improve Radiator air flow on ground - relocate Radiator from aft/ventral location to forward location. This will also improve exit air flow and assist in overall cooling.

 

My oil cooling is fine on the ground, 80C, (low engine power) but steadily climbs when in the air. If I stay in prop Climb Mode I can keep the temp from rising above 104C. As soon as I switch to Cruise Mode the temp goes up and can reach 120C. At this point I start a shallow decent, at low rpm, which brings the temp back down below 100C.

 

Various air flow adjustments have been tried, to improve the oil temperature with some success - it now takes much longer for the  temperature to rise and with great care (not much fun) can be kept to 112C in Cruise

 

My challenge is to design/select a system that will deliver on ground coolant temps below 100C and Cruise oil temps that will stay in the range 90-95C in the air, no matter the ambient temperature or demand on the engine eg extended climb on a hot day.

 

In general- I would much rather be dealing with an overcooling situation (easy fix) than an overheating problem.

 

At this stage;

I haven't purchased a larger oil cooler - but hope to very soon. 

Just finished setting up my temporary aircraft workshop and will start, today, on the relocation of heat exchangers, to be followed by remodelling of the cowling (ugh!) to accommodate the changes 

Skippy I have a friend with a sonex 912 which he built. I think he has built more than one.  He never mentions anything about cooling problems and he flies it a lot.

[danny_galaga]

1 hour ago, skippydiesel said:

Thanks Walrus - I only use TO Mode to get to circuit height. From then  to altitude or stooging, Climb Mode, which in my set up is max 5450 rpm. To be honest I have never taken much notice of TO Mode rpm but if its in line with the other settings it would be max 5750 rpm. 

 

As for heat exchanger sizes - From (faulty) memory Rotax only offer one size in coolant Radiators and four sizes in Oil Coolers. Therefor there is a single standard in Radiators but not in Oil Coolers. Further, I assume because there are  4  Oil Coolers to choose from, this reflects, more complex/variable cooling environments. My aircraft is fitted with the standard Radiator and the Large Oil Cooler (next size up is the Extra Large)

 

My coolant cooling is well under control in the air (90-95C) - way to hot on the ground (120C) -  Radiator is not receiving sufficient air flow, on the ground, to keep the coolant temperature below 100C - must improve Radiator air flow on ground - relocate Radiator from aft/ventral location to forward location. This will also improve exit air flow and assist in overall cooling.

 

My oil cooling is fine on the ground, 80C, (low engine power) but steadily climbs when in the air. If I stay in prop Climb Mode I can keep the temp from rising above 104C. As soon as I switch to Cruise Mode the temp goes up and can reach 120C. At this point I start a shallow decent, at low rpm, which brings the temp back down below 100C.

 

Various air flow adjustments have been tried, to improve the oil temperature with some success - it now takes much longer for the  temperature to rise and with great care (not much fun) can be kept to 112C in Cruise

 

My challenge is to design/select a system that will deliver on ground coolant temps below 100C and Cruise oil temps that will stay in the range 90-95C in the air, no matter the ambient temperature or demand on the engine eg extended climb on a hot day.

 

In general- I would much rather be dealing with an overcooling situation (easy fix) than an overheating problem.

 

At this stage;

I haven't purchased a larger oil cooler - but hope to very soon. 

Just finished setting up my temporary aircraft workshop and will start, today, on the relocation of heat exchangers, to be followed by remodelling of the cowling (ugh!) to accommodate the changes 

One other thing to consider is airflow direction is not always as straight forward as you might think. Is it worth experimenting with the angle the cooler is facing in regards to airflow? For instance, pointing it downward a few degrees more than it is.

 

An example of how surprising air flow directions can be- when they put a model of a Junkers JU 52 in a modern wind tunnel, apparently almost NONE of the corrugations were in line with actual airflow! Of course the plane didn't know that, and so it flew 😄

 

 

[skippydiesel]

1 hour ago, BrendAn said:

Skippy I have a friend with a sonex 912 which he built. I think he has built more than one.  He never mentions anything about cooling problems and he flies it a lot.

It sees to me that almost all Sonex / Rotax 912 ULS have / had cooling issues to start with - even the fairly recent factory one.  Your friend may be particularly gifted/lucky in this area or has learnt from earlier builds and has designed his cooling system accordingly. 

 

Most of the successful (eventually) ones are using a side mounted Radiator with large NACA inlet and side outlet (pretty ugly in my eyes).

 

My Sonex is a little unusual in that it has a;

• Firewall/bottom Radiator that is sealed ie is dependent on cowling air flow - it actually works, but only once airborne. This is about to be changed.
• Constant speed prop (CS) - most aircraft will be flying with a fixed pitch which is likely to unloaded the engine when in cruise while mine maintains/increases the load.

[skippydiesel]

26 minutes ago, danny_galaga said:

One other thing to consider is airflow direction is not always as straight forward as you might think. Is it worth experimenting with the angle the cooler is facing in regards to airflow? For instance, pointing it downward a few degrees more than it is.

 

An example of how surprising air flow directions can be- when they put a model of a Junkers JU 52 in a modern wind tunnel, apparently almost NONE of the corrugations were in line with actual airflow! Of course the plane didn't know that, and so it flew 😄

 

 

200%  agree!!! Air flow/cooling is , for those without a wind tunnel and all sorts of sensors, a dark art.

[BrendAn]

3 hours ago, skippydiesel said:

It sees to me that almost all Sonex / Rotax 912 ULS have / had cooling issues to start with - even the fairly recent factory one.  Your friend may be particularly gifted/lucky in this area or has learnt from earlier builds and has designed his cooling system accordingly. 

 

Most of the successful (eventually) ones are using a side mounted Radiator with large NACA inlet and side outlet (pretty ugly in my eyes).

 

My Sonex is a little unusual in that it has a;

• Firewall/bottom Radiator that is sealed ie is dependent on cowling air flow - it actually works, but only once airborne. This is about to be changed.
• Constant speed prop (CS) - most aircraft will be flying with a fixed pitch which is likely to unloaded the engine when in cruise while mine maintains/increases the load.

the mates has a fixed prop.

[rodgerc]

Note the radiator is to be installed below the oil pump. 

[Thruster88]

5 hours ago, skippydiesel said:

It sees to me that almost all Sonex / Rotax 912 ULS have / had cooling issues to start with -

 

My Sonex is a little unusual in that it has,

• Constant speed prop (CS) - most aircraft will be flying with a fixed pitch which is likely to unloaded the engine when in cruise while mine maintains/increases the load.

You are not thinking this correctly. The only thing that matters is percentage of power. Two identical aircraft one with fixed pitch the other with a constant speed flying at the same climb or cruise speed at 75% power will be burning the same amount of fuel and loading the cooling system the same. Only difference will be the rpm on the constant speed may be lower, or it could be the same, the pilot has that control. 

 

The rpm of the prop will not effect cooling air flow, only air speed matters,  if both aircraft are at 75% power airspeed and therefore the cooling will be the same.

[facthunter]

In reference to the Fat and short or thin and long heat exchangers I'd go for the ones with the longer tanks as there'd be more of the higher temps exposed in the core.  Nev

[facthunter]

Aircraft that have higher airspeeds have less cooling problems with a motor like a Jabiru so where the cooling is critical the same effect wil be seen with any  motor.   Nev

[skippydiesel]

22 minutes ago, Thruster88 said:

You are not thinking this correctly. The only thing that matters is percentage of power. Two identical aircraft one with fixed pitch the other with a constant speed flying at the same climb or cruise speed at 75% power will be burning the same amount of fuel and loading the cooling system the same. Only difference will be the rpm on the constant speed may be lower, or it could be the same, the pilot has that control. 

 

The rpm of the prop will not effect cooling air flow, only air speed matters,  if both aircraft are at 75% power airspeed and therefore the cooling will be the same.

I agree that if both engines are actually delivering the same (75% )power the fuel consumption/burn/ heat generated,would be the same - but this is not what happens in my real life experience.

 

My last aircraft had a ground adjustable/fixed pitch prop. Pitch set according to Rotax recommend 5200rpm STATIC. Cruise at 100 Kn indicated, 5200 rpm resulted in a whole of sortie fuel consumption, a little over 12 L/hr. 

Infrequent beach run (see level) 5500 rpm, 120 Kn indicated, fuel consumption around 17L/hr. My interpretation of low fuel consumption - prop not loading engine.

 

When a dial in Cruise Mode on my current aircraft, rpm drops, aircraft accelerates, prop adjusts to maintain rpm, engine remains loaded at all times. Sure you could pitch a ground adjust to perform in a similar way (at Cruise) but you would be slow to leave the ground and climb out and you would  very likely be overloading the engine in TO/Climb out.