Cabin heat and Rotax Powered Aircraft

[c162pilot]

It is cold here today in New York, 18F and was -16C at altitude. The heater in the SR20 I was a passenger in was struggling to barely keep us warm. It got me thinking, in Rotax powered aircraft, does the cabin heat come from the exhaust shroud like other Lycoming powered aircraft or from the hot water cooling the cylinders like an automobile. In general how good is the cabin heat in a S-LSA?

[CTLSi]

......

[Nomore767]

Stephen,

I believe the 'heat' for the cabin comes from the cylinder coolant. My 912ULS Rotax has some metal duct tape over the oil cooler to improve time to heat up to the magic 122F (so as to exceed 2500rpm) and it works well. In SC lately we've had some cold days too. Yesterday on the ground I got some nice heat and the CHT temps are just inside the lower green band. Once airborne at 4C OAT the cabin heater doesn't put much out because the coolant temp ( CHT) drops into the caution range. Around 10C to 12C more 'normal' SC winter temps the cabin heat is pretty good. I've been pulling full cabin heat on the ground to try and make it toasty before launching into the cooler air above. I can fly about 35-45 mins before I start noticing the chill. My RV-12 has a little draft behind the seats which doesn't help.
You can also put some metal tape over the radiator but it's more difficult to access so as yet I haven't done that. There are some really nice shutter devices available for the Experimental owners but as yet not approved for SLSA. Vans say they're working on one for SLSA.

At the above temps, the CHT is at the top end of the caution range and whilst oil temp is around 208F. At around 12-15C I usually get above the more desirable 212F temp to boil off any condensation in the oil. At this time of year the CHTs are in the top end of caution and as they go down so does the cabin heat.

I flew a P2008 in frigid MN weather this past spring and it had a 'defrost' setting as part of its cabin heat. needless to say it was so cold that neither really worked and the windshield was frozen-fog at the edges. To be fair it was really cold. Did I say it was firkin freezing!?

I figure long-johns at 40F and below and for a more normal 45F-58F SC temp range the cabin heat is 'okay' in the air, great on the ground.

[comperini]

I believe the 'heat' for the cabin comes from the cylinder coolant

It's possible of course, but you can't just make that statement as fact for everyone. My 912 powered plane gets hot air from the shroud around the muffler. I think the most correct answer is that it depends on the plane!

[CTLSi]

......

[dstclair]

Stephen,

Once airborne at 4C OAT the cabin heater doesn't put much out because the coolant temp ( CHT) drops into the caution range. Around 10C to 12C more 'normal' SC winter temps the cabin heat is pretty good. I've been pulling full cabin heat on the ground to try and make it toasty before launching into the cooler air above. I can fly about 35-45 mins before I start noticing the chill. My RV-12 has a little draft behind the seats which doesn't help.

I figure long-johns at 40F and below and for a more normal 45F-58F SC temp range the cabin heat is 'okay' in the air, great on the ground.

My Sting is shrouded off the radiator and does a much better job of heating than the above. I think the coldest OAT at altitude I've flown is 25F (-4c) and the heater was till cranking out warm air. There are several air leaks in my plane (cargo area, flap handle and throttle) that counteract the heater but flying was comfortable in a sweatshirt. Key is plugging the air leaks for me. I would estimate that flying under an overcast in the mid-teens would get cold in my plane for a longer trip.

[drseti]

I believe the 'heat' for the cabin comes from the cylinder coolant.

Strictly speaking, Howard, there is no cylinder coolant. The Rotax jugs are finned and air cooled. It is the cylinder heads that are liquid cooled. That said, I have seen only one Rotax-powered aircraft (the Aerotrek A220) that used coolant liquid for cabin heat, and that was an after-market add-on, for supplemental heat. The primary heat source, even in that plane, was a shroud around the muffler. I haven't had an RV-12 uncowled, so I can't say from first-hand knowledge, but I would be very surprised if it used anything different from the standard muffler/shroud system.

[dstclair]

I believe the 'heat' for the cabin comes from the cylinder coolant.

Strictly speaking, Howard, there is no cylinder coolant. The Rotax jugs are finned and air cooled. It is the cylinder heads that are liquid cooled. That said, I have seen only one Rotax-powered aircraft (the Aerotrek A220) that used coolant liquid for cabin heat, and that was an after-market add-on, for supplemental heat. The primary heat source, even in that plane, was a shroud around the muffler. I haven't had an RV-12 uncowled, so I can't say from first-hand knowledge, but I would be very surprised if it used anything different from the standard muffler/shroud system.

Paul -- The radiator for the Sting is immediately below the muffler but the heater muff itself attaches to the back of the radiator.

From a 'How to' document:

The cabin heater muff attaches to the radiator and covers part of the back side of the
radiator. An air hose connects the heater muff to the heater airbox diverter attached to the
firewall

[drseti]

Interesting design, Dave. Very different from the AeroTrek mod I described, in which warm coolant is actually run through the firewall, inside to a heat exchanger in the cabin. This underscores the fact that each airframe manufacturer can have its own heater design (or, sadly, none at all...)

[BrianL99]

It is cold here today in New York, 18F and was -16C at altitude. The heater in the SR20 I was a passenger in was struggling to barely keep us warm. It got me thinking, in Rotax powered aircraft, does the cabin heat come from the exhaust shroud like other Lycoming powered aircraft or from the hot water cooling the cylinders like an automobile. In general how good is the cabin heat in a S-LSA?

I owned an SR20 for 3 years and regularly flew in single digit (F) temps, with never a problem other than too much heat.

[Nomore767]

Paul,

I was being a bit too simplistic. Yes, only the cylinder heads are cooled with liquid coolant. Comperini, sorry I'm talking about my airplane not all Rotax powered LSAs.

On the RV-12 ambient ram air enters through the opening in the front of the cowl, and is ducted past the oil cooler along the left side to the coolant radiator. A flap type door controlled by the cabin heat control determines whether the air coming off the back of the radiator is dumped out, or forced through the perforations in the firewall near the pilot's feet.

In cold weather the heat will be insufficient unless the cooling air flow effect is reduced, thereby raising the temperature of the cylinders and thus the coolant. Some inventive folks have designed cockpit controlled doors to modulate the air flow but this isn't an option on the SLSA, although Vans are apparently working on it as a future option.

However, this option brings the CHT temps up nicely into the green range, and gives you improved cabin heat. Quite a lot of heated air can pass through the radiator into the cabin when the door is fully open. However, the amount of heat provided is proportional to how hot the radiator is ( the temperature of the coolant.) On a COLD day, the amount of heat transfered from the radiator to the cabin heat air may not be sufficient to ensure a toasty cabin. As I stated earlier I've raised oil temps by partially covering the oil cooler with metal duct tape. I haven't done this with the coolant radiator and hence I see lower temps, at the bottom of the normal green band into the top of the lower caution range. Usually it's flipping back and forth caution to green by only a degree or two. On the ground, without the higher cold airflow, the coolant temps are higher and the cabin heat is excellent. Airborne the coolant temp is reduced and so it's less effective. I'm going to see about improving this.

On the RV-12 cabin heat is related to coolant radiator heat not the exhaust system.

Like heaters in the cars in the old days- you don't get much "heat" until the engine gets really warmed up.

[Jack Tyler]

"I figure long-johns at 40F and below..."

Howard's comment reminded me of AOPA's current on-line video seminar on dealing with the consequences of an off-airport 'landing'. One of their guidelines: "Dress for the terrain and weather conditions you will be flying over rather than your departure or destination.” I know this takes us a little far field from cabin heat output but, given the recent winter blasts many of us have been seeing, it's worth noting.

BTW that written + video article is here: http://www.aopa.org/News-and-Video/All- ... e-prepared
Posting it was prompted in part by the 7 year old daughter who survived a recent plane crash and, with everyone else killed, managed to get herself to a residential area and rescue. Both the incident and the AOPA article are good reminders of our responsibilities as PIC when we carry passengers, at any time of year.

OK...back to our regularly scheduled program. Thankfully, our Grumman has no 'leaks' and abundant heat, even in wintertime temps.

[rgstubbsjr]

I've flown the Tecnam P-92 in -15° F conditions with no problem. Colder than that and the cabin heat can't keep up. At -25° F (in the plane) the touch screens fail, and the electronics stop working. On the plus side, other than to say "Get me home, NOW!" my wife also stopped talking.

[dstclair]

Paul,

I was being a bit too simplistic. Yes, only the cylinder heads are cooled with liquid coolant. Comperini, sorry I'm talking about my airplane not all Rotax powered LSAs.

On the RV-12 ambient ram air enters through the opening in the front of the cowl, and is ducted past the oil cooler along the left side to the coolant radiator. A flap type door controlled by the cabin heat control determines whether the air coming off the back of the radiator is dumped out, or forced through the perforations in the firewall near the pilot's feet.

In cold weather the heat will be insufficient unless the cooling air flow effect is reduced, thereby raising the temperature of the cylinders and thus the coolant. Some inventive folks have designed cockpit controlled doors to modulate the air flow but this isn't an option on the SLSA, although Vans are apparently working on it as a future option.

However, this option brings the CHT temps up nicely into the green range, and gives you improved cabin heat. Quite a lot of heated air can pass through the radiator into the cabin when the door is fully open. However, the amount of heat provided is proportional to how hot the radiator is ( the temperature of the coolant.) On a COLD day, the amount of heat transfered from the radiator to the cabin heat air may not be sufficient to ensure a toasty cabin. As I stated earlier I've raised oil temps by partially covering the oil cooler with metal duct tape. I haven't done this with the coolant radiator and hence I see lower temps, at the bottom of the normal green band into the top of the lower caution range. Usually it's flipping back and forth caution to green by only a degree or two. On the ground, without the higher cold airflow, the coolant temps are higher and the cabin heat is excellent. Airborne the coolant temp is reduced and so it's less effective. I'm going to see about improving this.

On the RV-12 cabin heat is related to coolant radiator heat not the exhaust system.

Like heaters in the cars in the old days- you don't get much "heat" until the engine gets really warmed up.

Revisiting the thread.

Sounds like the RV-12 and Sting series have a similar heating design although the ducting of air within the cowl is much different. Anyway, I went up this morning which was fairly cool for us Dallasites. Around 45F on the ground and 37F at 3000'. High, thin clouds pretty much neutralized heating from the sun.

Oil temp was 195F and hottest CHT was 176F. As mentioned above, I do have cold air flowing in around the flap handle and throttle but I was plenty warm wearing a long-sleeve shirt with the heater approximately 1/4 engaged. YMMV.

[Nomore767]

Paul,

I was being a bit too simplistic. Yes, only the cylinder heads are cooled with liquid coolant. Comperini, sorry I'm talking about my airplane not all Rotax powered LSAs.

On the RV-12 ambient ram air enters through the opening in the front of the cowl, and is ducted past the oil cooler along the left side to the coolant radiator. A flap type door controlled by the cabin heat control determines whether the air coming off the back of the radiator is dumped out, or forced through the perforations in the firewall near the pilot's feet.

In cold weather the heat will be insufficient unless the cooling air flow effect is reduced, thereby raising the temperature of the cylinders and thus the coolant. Some inventive folks have designed cockpit controlled doors to modulate the air flow but this isn't an option on the SLSA, although Vans are apparently working on it as a future option.

However, this option brings the CHT temps up nicely into the green range, and gives you improved cabin heat. Quite a lot of heated air can pass through the radiator into the cabin when the door is fully open. However, the amount of heat provided is proportional to how hot the radiator is ( the temperature of the coolant.) On a COLD day, the amount of heat transfered from the radiator to the cabin heat air may not be sufficient to ensure a toasty cabin. As I stated earlier I've raised oil temps by partially covering the oil cooler with metal duct tape. I haven't done this with the coolant radiator and hence I see lower temps, at the bottom of the normal green band into the top of the lower caution range. Usually it's flipping back and forth caution to green by only a degree or two. On the ground, without the higher cold airflow, the coolant temps are higher and the cabin heat is excellent. Airborne the coolant temp is reduced and so it's less effective. I'm going to see about improving this.

On the RV-12 cabin heat is related to coolant radiator heat not the exhaust system.

Like heaters in the cars in the old days- you don't get much "heat" until the engine gets really warmed up.

Revisiting the thread.

Sounds like the RV-12 and Sting series have a similar heating design although the ducting of air within the cowl is much different. Anyway, I went up this morning which was fairly cool for us Dallasites. Around 45F on the ground and 37F at 3000'. High, thin clouds pretty much neutralized heating from the sun.

Oil temp was 195F and hottest CHT was 176F. As mentioned above, I do have cold air flowing in around the flap handle and throttle but I was plenty warm wearing a long-sleeve shirt with the heater approximately 1/4 engaged. YMMV.

Rotax have an S/B out whereby they differentiate CHT from coolant temp. CHTs, the actual temp of the cylinder head are hotter than the coolant.
On my RV-12 my temps seem to be opposite yours. The other day, a 45F day on the ground, with a 3" wide band of metal tape across the oil cooler, I got oil temps around 220F and CHTs (actually coolant temps) of about 150F. The latter are right on the lower green band upper part of the lower caution range.
Usually when the coolant temp is this low there is little heat. Experimenting with the width of metal tape, I've improved cabin heat by raising coolant temp as a function of increasing oil temp.ie. the engine is running hotter with higher oi temps and thus higher coolant temps where the cabin heat comes from.
The other day with temps nearly 62F the oil temps were getting high and so a narrower band of tape is needed. It's a question of finding the sweet spot for the right size of tape in the winter months. Fortunately not so bad as other states.
One point to mention is that a couple of Rotax guys have said it's good to get the oil temp above the magic 212F at least once per day to 'boil off' condensation which can cause damage over time.