nigels real world ramblings 6 , weight and balance

[britfrog 180]

Many of us simmers , especially with airliners, do effectively do a mediocre weight and balance , if only to get the fmc to work properly.

However in smaller a/c it is more important as many of the smaller a/c have little power to spare. but how many of us bother?

 

Virtually every small aircraft produced cannot carry full fuel plus a full compliment of seats , there are some exceptions but they prove the rule,

Take the latest cherokee 180 from A2A if you look in the fuel tank you will see a tab you should not fill the tank above that tab if carrying 4 people, a simple security aid.

However cessna's dont have such an easy solution. On these a/c you are supposed to use the POH which has graphs where you can add the weight and position of the passengers and fuel and baggage and that will indicate if you are have a forward c of G or if you are in the envelope. some planes like the cessna 207 are way outside the envelope with just a pilot and low fuel , but it makes no odds, likewise you can fly them 1000 lbs over max gross weight as long as the c of g is in the right place, it will just take a much longer runway to get unstuck.

Even the humble c150 has issues!

when I was a check pilot at Popham for the aircraft that Joe Public could hire, i was befriended by a rather solid (heavy and muscular) Norwegian who wanted to hire the 150 to see the region. so without further ado i arranged for him to conduct a preflight check whilst I watched from the cabin as he went around the a/c with POH in hand.

When he had finished I let him stew a bit (instructors are like that ) and then went out to make sure all was ok and strapped myself in. "right lets go then" I said and in he hopped , "we shall go and show you the circuit"  (we had neighbours to avoid flying over) so he fired it up taxiied to the hold ran up the engine correctly checked the t's and p's lined up and off we went

No Problem (if you cant fly a 150 you should not be allowed near an a/c , they are simplicity personified)

the first circut was a little ragged but to be expected as i pointed out the houses to avoid , we called downwind , final and arrived quite well over the threshold after the weird dog leg approach to Popham (to avoid flying over the petrol station) wheels touch down, flaps up to the first click and full power , and away we went again this time letting him choose the route.

This time he lined up on the runway correctly landed, pulled up the flaps , opened the throttle  and away we went,

well sort of !

Popham has 900 meters , so plenty for a 150 but that hedge at the end was getting mighty close, yet we hadnt left the terra firma! 

weird I thought ! the big feller was sitting there stoney faced ! oh well I will wait a second or two more------ when he pulled back on the column and we took off with not a lot between us and the hedge and the stall warning was squawking away like a duck being strangled, slowly

Strange I thought!   as people who know Popham there are 3 rather large oak trees a few hundred yards beyond the threshold, and they were not getting lower but staying in the middle of the screen!!!

Houston I thought, we have a problem here! and by now i could see where, in what tree, we were going to end up.

"whats up? " I asked --- "I dunno it wont climb" he retorted  , well i could see that half an hour ago, but why? it had taken off well before why not now?

 

As the oak trees loomed up I started to grasp at straws and pulled his very large hand off the throttle to ensure that indeed he had given it full throttle , and the reason for our trouble became evident!!

 he had not pushed in the carb heat knob!!  and from my side I could not see that because he had wrists like tree trunks and they completely hid the carb heat .

well as soon as i pushed that home with a flourish and a "i have control" we climbed away with no problem and i let him take control to carry out the rest of the circuit and landing. when we parked up the poor fellow was sooo apologetic he virtually grovelled all the way to the cabin, where I signed his log book as fit to fly.

I knew he would never make that mistake again!!  we had both learnt something!

but why did the a/c not climb?

the tanks were full and our combined weight put the poor 150 over max gross where the poor little donk at the front with reduced power due to the carb being fed hot air could not produce enough power to climb.

And yes it was my fault as pilot in charge to ensure the weight and balance was correct, still we survived and we both learnt about flying from that !

it just shows you cannot ever be complacent about flying in any aircraft especially a mundane little 150

[allardjd 1,853]

GA Rule: Fill the seats; fill the tanks; fly - pick any two.

...and yep, for sure, Carb Heat makes a hefty difference in power output, but so does carb ice. I was taught that the three things you do after touching the runway on a T & G are flaps, carb heat and throttle. I guess he learned that too, but almost the hard way.

John

[brett 2,315]

I was under the impression that carb heat is used according to the aircrafts owner manual on takeoff and landings. A touch for cold mornings starts and certain weather conditions will also dictate when it should be used during flight. This includes using CH when retarding the throttle on descent, especially into clouds.  

 

This makes me think that there is no general rule for it's use and the when and where should be a part of reading the manual for the aircraft you are flying. Learning how weather creates icing and knowing when and if the air you are flying in would be conductive to icing goes right along with it.

 

I always felt that using CH when it wasn't needed made the engine run rougher and lose power, unless this is just an FSX thing. Set me straight fellas.

 

  

[britfrog 180]

Brett carb heat use varies from region to region, ie Florida with its humid atmosphere will be more suseptible than say minnisota. Carb ice mostly forms when the throttle is reduced and the intake is slower allowing the reduced air pressure in the inlet tract to permit the formation of ice.

In Europe it is part of your downwind check , so as you turn onto base leg descending,with reduced power the carb heat should be out. in Europe again , if you are using a dirt runway it is normal practice to push in the carb heat when you are on short final so that you can have full power to perform an overshoot or touch and go. The reason why you push it in is because the hot air does not pass through an air filter so it is possible (but extremely unlikely)  to suck something nasty into the engine that might cause damage, that might have been kicked up from the front wheel.

 

However it is possible to have carb ice at any point of the flight envelope when all the parameters get to the right level, it is just more dangerous and more prevalent at the arrival stage.

 

as for using carb heat when warming up an engine, well i have never heard of that before

 

the increasing use of mogas due to the shortage of proper avgas has been accompanied by a large increase in carb ice events, this had been predicted by the powers to be which is why tthey tend to look at mogas with a long eye, this is beecause mogas is not produced with the same quality control of avgas, and in recent years it has been polluted more and more with other non petroleum products which can affect an engine flying at altitude which cars dont do.

[brett 2,315]

Thanks for those extra tidbit's Nigel.

[allardjd 1,853]

I was taught (midwest flying) to always use carb heat when reducing power, i.e. throttle plate somewhat closed, but to NEVER use it at high power settings because of the risk of inducing detonation in the engine due to high cylinder head temperatures. I'm having a hard time conceiving of how ice can form downstream of a wide-open throttle plate at any temperature or relative humidity. In the real world I don't think I'd ever put carb heat on at full power, particularly if I was the one responsible for the cost of engine repairs.

The adiabatic effect of the air expanding into the lower pressure region past the throttle plate causes a temperature drop, but it requires a pretty good delta p to amount to much. The further the throttle plate is closed the greater the temperature drop. Unless the air is pretty dry, there will always be some condensation forming in the inlet manifold just past the throttle plate. If the inlet temperature is within about 10 degrees F of freezing, it's possible for ice to form downstream of the throttle plate. The further closed the throttle plate, the lower the manifold pressure and the greater the temperature drop.

John

[Quickmarch 488]

I tend to go with the POH. All engines are not created equal and handling of carb heat is specific to each model. The notations, above are good general practices. After all, a bit of carb heat never hurt an engine. Carb heat when trying to get 100% out of the engine is a bad thing. Engine icing indications differ depending on the aircraft (especially those fitted with CV props and MF pressure gauges). In general, a bit of rough running in close dewpoint/temp conditions is a pretty good indicator of carb ice. Unfortunately it takes a lot more time and hot air to melt ice than it takes to prevent it, so it is a good idea to keep an eye out for conditions that lead to carb ice.

 

If you get a chance, look at the POH for the Beaver (R985 - Radial). The POH states "When Carb heat is used during approach, select COLD late on final. This is to ensure that full power is available in case of a baulked landing."

 

The Beaver has a gauge on the panel that reads out carb mixture temperature. The POH recommends that temperature in the inlet should be maintained at 40 to 45 degrees F at all times. This requires quite a bit of attention be paid to the carb heat lever (which is about the size of a Piper flap lever ). The POH then goes on to remark that operation above 45F will result in decreased engine power.

[brett 2,315]

Want more reading, simplified info here and a bit more detail from flight trainers here. An interesting topic Nigel, one worth investigating in-depth. I am sticking with my original RTM thinking but it is still a good idea to have an overall understanding on when and if icing will appear during flight. 

 

  

[britfrog 180]

I was coming back from the beer festival in Germany one year and ATC vectored me smack bang into an embedded CB at 8,000 feet and as if I did not have enough to do screaming at ATC to vector me out of that mess (he said it wasnt painting on his radar the liar) all of a sudden the engine cut, and it got kinda quiet and spooky . After what seemed an eternity with carb heat pulled out the engine came back to life with a big backfire and rough running, but it kept going after that.

 

Carb icing like meteorology is an inexact science, if you had 10 pilots in a room each would deal with it differently, when it strikes you dont have time to read a manual , just time to make an automatic reaction which is engrained from day 1, some pilots never experience it, but we all practice the drill , just in case