Recips-Cyl Hd Temp/Mixture, etc.

[atpcliff]

Hi!

Only about 100 of my 1650 is recip, and it was long ago.

I would appreciate some help on the finer points of recips: How to manage Cylinder Head Temps, details on mixture use, etc.

One specific question: Would there ever be a WX condition where you would WANT to use Carb Heat on TO? Can you get carb heat on TO?

I am mostly flying C-182s, and apparently they get carb ice pretty easily.

I would like to hear about how to safely and efficiently manage a recip engine.

Cliff
GB,WI

PS-For example, I read about the Cirrus, especially the smaller one, overheating rather easily. Why, and what do you do about it?

Thanks a bunch 4 all the responses

 

[Buschpilot]

Can't speak too much of single engine carb heat/cyl head temps, I'm way out of currency on that, but to add something to this, a DE once told me that the only time you would use carb heat on takeoff is when you are in Ice Fog.

Now, I don't think you'd really want to take off if you were in ice fog.

 

[avbug]

During ground icing conditions, rare occasions exist when it is appropriate to use carburetor heat during the takeoff phase. These situations are best reserved for lower compression engines, and in all cases, should be done only in conjunction with a carb air temperature gage. In most cases when carb heat is being used for takeoff, special leaning proceedures should be used to compensate for the increased richness that comes with application of carb heat. Also, in most cases, a reduced power takeoff may be preferable with carb heat applied (depending on circumstances).

Some larger radial older airplanes regularly use carb heat for takeoff in colder climes, and also humid climes, but use anti detonation fluid (ADI) with it.

Rather than type an enitre treatise on how to operate a piston engine, it would be better to answer specific questions, or touch on specific points. Throw some out, and we can start from there.

 

[Wiggums]

Lycoming's Key Reprints have quite a bit of information. Is the C-182 you're flying Lycoming or Continental?

 

[172driver]

Never taken off with carb ht but have had carb ice on the ground numerous times during taxi. Remember...it doesn't have to be freezing to get carb ice. Cool, moist wx will do it every time. I always use carb ht at low power settings regardless of the wx....usually approach and landing. Keeps me from forgetting to apply it when I really need it.

CHT on Lycomings should be kept in the upper 2/3 of the green range.

 

[tarp]

C-182.

Carb Heat:

1- Carb Heat robs the engine of power by providing heated less dense air rather than colder more dense air. Which do you want for takeoff. Other folk have jumped all over this.

2-Carb heat should be used in the advent of carb icing or as a preventative on base and final legs. Read the POH! Carb icing is usualy detected by a slow decrease in RPM/MP. (The actual mental trigger is that you seem to keep having to bump the throttle up to maintain whatever numbers you are keeping. Most of us don't get this picture until we try to "bump" it up one more time and we find that we are at the "stops". At that point, you've pretty much confirmed you are fighting carb ice.)

Cyl Head Temps, the C-182 and cowl flaps:

The C-182 is pretty sensitive to airflow changes. That big ol' Continental just makes that CHT run all over the place. As someone suggested, you would want to target the CHT in the top half of the green range without getting to the orange/red line. The management of this is controlled by your rate of climb/descent and those not quite good enough cowl flaps.

Make sure on takeoff that your cowl flaps are open. You should constantly run a "Charlie-GUMPSS" checklist whenever the airplane changes pitch angle. Charlie-GUMPSS is Cowl flaps, gas, undercarriage, mixtures, props, seat belts, switches. So on takeoff your flow as turning onto the runway is cowl flaps open, fuel on both, green light (if retract), mixture full forward (now if you leaned for taxi), seat belts, windows, lights on.

A PS is here - the Continental loads up on lead fouling if you taxi around with mixture rich. Lean, even at sea level, on the ground and make sure those cowl flaps are open when taxiing.

On climb out, even with the cowl flaps open, the C-182 can show some pretty dramatic CHT temps. Set in your mind to scan the CHT every 500ft while climbing. If you are trending toward the red line, lower the nose! The difference between a 1000fpm climb rate and a 500fpm climb rate in this airplane will change the CHT a long way. If you can keep that needle right about 3/4 deflection, you are doing an excellent job.

As you reach altitude and level off (pitch change) run your C-GUMPSS again. You'll need to close the cowl flaps pretty quickly because the airflow at cruise is so much greater in this airplane and you'll go from red hot to cool pretty fast. (Unless low altitude on a hot summer day).

On descents, and as you make the power and PITCH change, C-GUMPSS and close the cowl flaps. Keep them closed until you land or go-around. However, once you land or go-around, the first move with your hand when you have a free second is to open those cowl flaps again. This engine is the hot and cold leader!

Mixture and leaning:

No different from any other plane other than the tendancy to plug fouling on the ground. If you have an EGT gauge, pull on the mixture (i.e. lean) until "peak" EGT and then enrichen by 25 degrees. This is just about perfect.

If you don't have an EGT, do the old pull it back until you get roughness then add about a quarter inch back in on the mixture control. If you monitor the MP while you are doing this. Set the airplane in cruise at something square like 23 over 23 or 22 over 22. Pull the mixture until you feel the roughness and see a RPM drop. Push the mixture back in until the number on the MP is reset.

Other:

The C-182 is one of the few airplanes where the manufacturer invites you to run the engine "over square". That is you can load this continental by asking the prop to turn slightly faster than the engine RPM. Use the POH.

The neat thing about this flexibility is that you can do some real smooth flying in the 182 without a lot of throttle jockeying. For example, if you have a simple 1000 altitude change to make - you can twist in a turn of prop and the airplane will climb using the higher RPM as a pseudo climb prop. Want to descend, twist out a little prop and the added drag will give you a nice 400 fpm descent. Very cool!

 

[tarp]

Typo:

"slightly faster than the engine RPM"

should have been

"slightly faster than the engine MP".

Yes, after all that discussion I do know that the crank is connected to the prop!

Tarp

 

[Speedtree]

One reason carb ice happens at lower throttle/rpm settings is because the throttle body is almost completely closed. When you are at takeoff rpm the throttle is pretty much parallel to the airflow so not much surface area for ice to grab onto. I wouldn't worry about carb ice on takeoff and if it ever would happen in my opinion it would be obvious and you could abort.

The other danger mentioned previously with normal carb ice is the slow detection. By the time the throttle is that far forward and you have confirmed carb ice it may be too late and you may not have enough warm air to melt the ice.

 

[FlyinBrian]

I used carb heat on takeoff once. I did it in a c-152 on a hot summer day in phoenix off of a fairly short field. (Stellar) The reason I did it? When I pulled on the carb heat turning downwind, the cable snapped, and a good three inches of cable came out of the instrument panel with the carb heat knob. I landed, taxied back, and did a short field takeoff. I don't think I'd want to do it again. I didn't reach TPA before I got back to Chandler (CHD and Stellar are about 6 mi apart.) When I got back, I pulled the rest of the cable through the firewall and handed it to the chief mechanic on the way in and told him I thought the carb heat was "kinda acting funny." Those of you who know the mechanic I'm talking about can imagine his reaction.

 

[atpcliff]

Hi!

Thanks a ton for the responses.

Question on shock-cooling.

I was told on descents it is possible to over-cool the engine. I read about closing the cowl flaps on descent.

If I am descending and the engine is getting to cool (how do I know?), what do I do as far as power settings/descent rates, etc. How do I manage my descent to keep the engine in a proper CHT range.

Cliff
GB,WI

PS-The C-182 is comparable to the Dakota (Piper-235). My dad has a '68 235, which doesn't have cowl flaps-apparently it is a different engine than the C-182. Why doesn't it have cowl flaps? I didn't realize that different makes of recips w/ the same horsepower would vary in design this much.

PPS-Once again, thanx a lot 4 all the help!!!

 

[tarp]

Cliff:

Shock cooling must be the subject of the month on this board. There have been lots of posts (including some of mine) that deal with this.

With the C-182, just work on keeping the CHT in the green and take steps (via the cowl flaps) to provide the proper air flow across the cylinders at the proper time. In the descent, if the CHT starts dipping too low, reduce the rate of descent by holding the nose up. Think "Commercial" pilot. Smooth going up, smooth going down. A nice 500fpm each way on high performance engines is a good way to increase their life span.

C-182 vs. the Dakota - Well first thank Mr. Lopresti. He designed the Commanche series while he worked for Piper. The engineers consulted him again for the Cherokee series. What he did was create an air gap at the rear of the cowling that was exactly the same size as the air intakes at the front. Then by using the baffling (those sheet metal pieces with the pieces of rubber attached) he forced the airstream up over the cylinders and out the rear of the cowl. The shape of the air inlets is not compromised by a climb (unless overly steep) or a descent (again if not overly steep). Basically, the Cherokee series has a consistent airflow and therefore the engine never really gets super hot or cold. In the higher performance series, Piper also added an oil cooler to help keep the engine running cool. Finally, and I don't want to start a flame war on the board - but the O-540- A series Lycoming in the Dakota is slightly less fickle than the Continentals in the C-182. This is basically because Lycoming came along later and with 20-20 hindsight, saw that by increasing the size and density of the sylinder cooling fins, the engine would stay cooler and more stable.

Good luck with all.