Improving the cabin heat on a stock 170

russfarris · Post by **russfarris** » Mon Jan 12, 2004 5:39 am

At the risk of flogging this subject to death - I know it has been heavily discussed and I re-read all the posts - I need to do something about the lack of cabin heat in my 52 B.

The stock setup does OK to about 35 OAT or so; not great but livable.
But tonight, with the temp around 25 or so (unusual for South Carolina, I'll admit) I just about froze. I have done a pretty through job of sealing the air leaks, but that cold a temp revealed a few more heat suckers; one at the top of the windshield leading edge left wing and another at the bottom of the pilot side door. During winter ops even around here I close off the sump hole in the nose bowl and tape off the wing root vents. Tonight the oil temp barely got to 140 degrees. Speed tape across the top louvers probably would have helped there.

I'll run some ideas up the flag pole and see what you guys think. First, would double wall SCAT hose from the left shroud to the heater valve possibly reduce some heat loss? (probably not enough to notice, but every little bit...) Has anyone actually tried the three inch valve used on early 150s, as someone suggested? How would you adapt a three inch SCAT hose to the shroud? (short of getting another shroud with the three inch outlets.)

One idea is to install another heat valve on the right side of the firewall and T into the right side system between the carb heat box and shroud. Install another cable to operate - I already have a blank knob on my panel anyway. This of course would require a field approval. I think a non-return flapper would be required; don't the rag wings have a similiar system?

I know some guys have put a 1953 and up heater on their airplane. Tom Buchanan's and Forrest Walton's 52B is setup that way, lucky guys! I even looked into a DC electric heater Aviation Consumer reviewed, but it needs to be wired in to the aircraft electrical system and pulls like 40 AMPS! How about those little DC heaters RV stores sell? They plug into the cigarrette lighter, but I only have a 5 amp breaker there, plus the wiring is a little light.

I'm trying everything I can think of to maximize what I have, but I'm open to ideas. Plumbing off the right side seems to be the easiest solution, it would double the amount of heat going into the cabin (with the carb heat off, anyway.) Changing over to a later model system seems like a lot of work, but if I lived any further north I'd consider it! Thanks, Russ Farris

DensityDog · Post by **DensityDog** » Mon Jan 12, 2004 6:20 am

Russ,
How about a bigger or somehow more efficient scoop that brings more air into the heat muff from the front of the cowl? Seems to me a 3" duct from the muff to the cabin won't do anything if it's not getting more fresh air from the front to start with. Maybe you could experiment with a funnel that sits closer to the back side of the prop? (Be careful!)

Another idea, perhaps off the wall, is try to vent the cold air out of the cabin so more warm air will come in, sort of like in your car, when you want maximum defrost you have to crack a window so the heater fan is not fighting a positive pressure inside the car.

Not sure where you would vent the cabin to a lower pressure area. Out the tailcone somewhere? Out the wingroot?

Max

zero.one.victor · Post by **zero.one.victor** » Mon Jan 12, 2004 6:25 am

I pre-heat the cabin with a small space heater ($20 at Walmart) in my hangar. Once the cabin is warm,the cabin heat can keep it warm,but if it's starting from scratch it's woefully inadequate. For short trips just bombing around,that works great. If you're gonna R.O.N. or even just park for an hour or more,it won't help.
I replaced the stock directional grills for the cabin heat system on my ragwing with expanded metal--that really let a lot more air flow & helped quite a bit.

Eric

4-Shipp · Post by **4-Shipp** » Mon Jan 12, 2004 1:52 pm

Russ, one of the tricks I was shown in Winnipeg was to wrap the scat tubing with fiberglass insulation and secure it with safety wire. They claimed it worked.

Max, at the Mineral Wells fly in last spring, a gentleman had a freshly restored B model that had a small opening (about 12" by 12" if I remember correctly) in the lower protion of the panel that sepparated the baggage compartment from the tail cone. It was covered by a flap of the upholstry materia, sewn across the bottom and velcro'd on the sides and top. When he wanted increased ventilation flow through the cabin he would open this flap as much as he needed. Again, just saw it and don't know much about its effectiveness. I'm sure someone else who was there can provide a name and contact info...I don't remember

Bruce

N1478D · Post by **N1478D** » Mon Jan 12, 2004 3:18 pm

That's Stu from Cleburn in his beautifully restored A that has the clever vent system in the baggage area. Says it really reduces wind noise in the summer time, haven't heard him talk about heating benefits. Will ask him the next time we talk.

N1277D · Post by **N1277D** » Mon Jan 12, 2004 3:31 pm

My 170A has a Y adapter that connects both heat muffs and feeds them into the cabin heat valve. This setup is an improvement, but still is inadequate for below 0 weather.

Post by **Bruce Fenstermacher** » Mon Jan 12, 2004 4:26 pm

Russ you and I are on the same page. I once gathered all the part numbers of the various parts and even wrote a 337 to be submitted but never followed through.

I was going to add the 3" scat and heat muff found on the right of later B models from the front engine baffle to the firewall but use a new 3" valve installed in the firewall under my battery. My 50 A probably has a 52 fuselage (another long story) with the battery on the right. I would then use the Y to connect the left 2" scat to the carb heat then to the standard 2" valve on the left side. I'd have to block one of the sides of the Y.

My reasoning for this mod is that I'd be using all approved parts and I'd be providing the same amount of heated air for carb heat as the original setup. Doing this I thought an approval would be easiar to obtain.

The end result would be a full 3" more warm air entering the cabin with an additional 2" worth when the carb head is not applied.

zero.one.victor · Post by **zero.one.victor** » Tue Jan 13, 2004 1:31 am

The Q2/1997 issue of The 170 News has an interesting article written by member C.K.Gackstetter about a cabin heat mod he installed in his IO-360 powered B model. He added a blower off a Volkswagon heater at the heater valve (firewall) for forced-air heating! He doesn't mention it in the article but the photo's look like he had another smaller blower mounted on the inside of the firewall adjacent to the heater outlet,possibly for a forced-air defroster?
He also sewed up a sort of curtain arrangement that goes from ceiling to floor just aft of the front seats,so that he can heat just the front seat area.
Velvet could probably supply you with copies of the article.

Eric

blueldr · Post by **blueldr** » Tue Jan 13, 2004 5:30 am

BUY a Parka and Bunny Boots!

Dave Clark · Post by **Dave Clark** » Tue Jan 13, 2004 3:11 pm

In the Avcon STC instructions the early cabin heat valve is modified to accept the larger heater hose. (3"?) Basically they give you a new flange to rivet on after you open the valve housing plate to get the larger hole. The valve drills off the firewall pretty easy and it gave me a chance to rework the innards to get it to seal better.

I thought a bit about all that air and no more area for dumping the air when the valve is closed (which keeps the muffler temperature down) but then I figured that is accomplished by the carb heat dump as it's only one shroud on the Lycoming. On the stock setup it wouldn't matter either because you'll get the designed dump for the muffler if left unchanged.

I do get better heat in the cabin with the Lycoming but the distribution of it sucks on the early system. Fortunately I rarely need cabin heat and when I do I have more than enough. Next I need to reseal the doors and windows, a project slated for this Winter but a house restoration is getting in the way. Oh well she's happy, and when she's happy I'm happy.

David Laseter · Post by **David Laseter** » Tue Jan 13, 2004 11:39 pm

What size Bunny Boots do you you need?

Post by **GAHorn** » Wed Jan 14, 2004 9:03 pm

DensityDog wrote:Russ,
How about a bigger or somehow more efficient scoop that brings more air into the heat muff from the front of the cowl? Seems to me a 3" duct from the muff to the cabin won't do anything if it's not getting more fresh air from the front to start with. Maybe you could experiment with a funnel that sits closer to the back side of the prop? (Be careful!)

Another idea, perhaps off the wall, is try to vent the cold air out of the cabin so more warm air will come in, sort of like in your car, when you want maximum defrost you have to crack a window so the heater fan is not fighting a positive pressure inside the car.

Not sure where you would vent the cabin to a lower pressure area. Out the tailcone somewhere? Out the wingroot?

Max

The bulkhead at sta. 108 (PN 0512121) is the aft bulkhead of the cabin. It has four 2-2-3/4" lightening holes at it's upper roofline curves which provide more than adequate exhaust ventilation for the cabin. The is no cabin "positive pressure" those bulkhead openings won't relieve. (In fact, most airplane's hat shelves have no rear wall to them except the headliner material, and there's a huge hole several square feet worth, thru which to exhaust cabin air.) Therefore I do not believe exhaust ventilation is necessary or desireable.
Good door seal, wing-root seals (especially at the windshield vent areas) will be a good start to improving cabin heat. Double-walled scat tubing is also a good idea, but you'd be surprised at how many systems have mud-dauber/mouse nests etc. blocking them.
Increasing inlet air volume might help, but too much may prove counterproductive. The air has to go thru the muffs slow enough to absorb heat.

Dave Clark · Post by **Dave Clark** » Thu Jan 15, 2004 12:42 am

George

So when I soundproofed over the vent holes in the aft fuse former did I do a bad?

I do have the Javelin scoop on the bottom forward fuse that sucks air forward and out under the floorboards.

blueldr · Post by **blueldr** » Thu Jan 15, 2004 5:02 am

Cessna had an answer for the lack of adequate heat in winter.
They had a optional South Wind or Janitrol combustion heater located in a hole in the floor beneath the rear seat. Mine was fed fuel from a tee fitting in the left wing fuel line under the floor. Exhaust went overboard through a hole in the belly skin. Mine was removed when I bought the airplane. The previous owner gave me his parka and bunny boots!

DensityDog · Post by **DensityDog** » Thu Jan 15, 2004 8:24 am

True, the 108 bulkhead has holes, but they don't go to the outside of the aircraft to a known low pressure area (unless the assumption is that the holes way back in the tailcone for the rudder cables, elevator rod, and gaps around the stabilzer mount area, are in a lower pressure area).

I guess instead of "positive pressure", I should have said relative pressure between the cabin interior and the heater outlet into the cabin. My guess is that there is not much pressure left of the incoming heated air, once it has passed through the restrictive hoses and heat muff. As a comparison, we certainly get plenty of air from our wing root vents, more than I have felt from a 170 heater.

Maybe someone with a manometer can take their 170 up and take some actual measurements around the cabin for us some day.

Max

The International Cessna 170 Association

Improving the cabin heat on a stock 170

Improving the cabin heat on a stock 170

Cabin Heat