Exercise 7 Climbing
Jim Davis
Here’s a whole bunch of interesting stuff about climbing. It’s mainly for instructors, but everyone is welcome to eavesdrop.
Remember from your student pilot days that when you climb, the wings produce less lift than they did in straight and level flight. It’s true – I’m not just saying it to grab your attention.
Imagine you have a special kind of aircraft that has no wings and therefore can’t produce any lift. But it has a hell of a powerful engine driving a vertically-mounted prop. Not only does this aeroplane exist – it’s pretty common – and it’s called a helicopter.
So we know that in straight and level flight a fixed-wing aircraft is supported entirely by the wings. And in vertical flight it is supported entirely by the propeller – the wings give no lift at all. So the steeper the climb the less lift you need from the wings.
To go from level flight to a climb, you need more power (actually it is thrust, but power is fine for our discussion). In fact your ability to climb depends entirely on how much extra power you have – over what you need for level flight.
Different climb speeds
If you look in your aircraft’s POH you will find it gives you two, or sometimes three, different climb speeds.
The slowest is the best angle of climb speed (Vx). So this gives you the greatest angle above the horizontal. You use it if you need to clear obstacles after takeoff. My handbooks, for both the 140 and the 180 Cherokees, say that 74 mph is the speed to use of you have trees to clear after a gross weight takeoff. Any slower or faster than this will give a lower gradient.
Here’s a dramatic clip of a Stinson 108 that didn’t have that extra horsepower needed for a climb. It’s taken from inside the crashing aircraft https://www.youtube.com/watch?v=OVM3RRd1vf0&t=172s
Notice how the pilot gradually eases the nose up in a futile attempt to steepen the angle of climb. This hopelessly gutless aeroplane was expected to climb, with four up, from a density altitude of… wait for it… 9200 ft.
Next we have best rate of climb, or Vy. This is the speed that will get you to altitude in the shortest time. It’s the speed generally used for circuits and landings. Again both my Cherokee handbooks say 85 mph is the best speed for this
Finally, we have cruise climb. This is the speed to use on a cross-country. It gives a good compromise between covering distance and getting you to your cruise altitude. It also gives good engine cooling and decent visibility over the nose. Again both the 140 and the 180 use the same figure – 100 mph.
It is interesting that the extra 30 hp of the 180 makes no difference to climb speeds. Remember we said at the beginning that climb ability depends on the excess power that you have over what you need for level flight.
It is interesting that the 140’s sea-level rate of climb is only 670 ft/min while the 180 gives 750 ft/min despite it being 300 lbs heavier.
Starting your climb
This is not a big deal. First listen out and lookout to make sure it is safe to climb. You don’t want to climb into another aircraft, or into different airspace without clearance.
Then tell ATC, or someone who cares, of your intention to climb. Richen the mixture, either all the way, or at least to a sensibly rich setting and smoothly go to full power while raising the nose into the climb attitude.
If you have a constant speed prop you need to increase to climb rpm and manifold pressure – in that order. And remember to use enough right rudder to keep the ball in the middle. And finally, when the airspeed settles, trim any pressure off the stick and the rudder.
There is a nonsense belief that you ‘save the engine’ if you throttle back a little in the climb. Nothing could be further from the truth. Most carburettor engines have a power-enrichment-jet which only operates at full throttle. Its job is to prevent detonation and keep the engine cool in the climb. If you throttle back, even a little, you cut out this jet and may actually cause engine-damage through detonation and overheating.
With a constant speed prop it’s important to remember the sequence in which to use the power levers during increasing and reducing power.
The thing to remember is that you must avoid being like the old lady in her little Golf, who chugs up a steep hill in top gear. In other words you don’t want full throttle and low revs. There is an easy way to remember this: it is common to talk about revving up an engine, or throttling it back. So if you remember those two phrases then you will get it right. That’s exactly what you do. If you want more power – rev up, in other words increase the revs first (with the pitch lever). And if you want to reduce power you throttle back, meaning you use the throttle first, and then bring the pitch back.
And of course you must always increase and decrease power so smoothly that your pax don’t notice. In fact you should do that with all the controls. My first instructor told me to always fly as if I had my grannie in the back seat with a basket of eggs on her lap.
Maintaining the climb
Okay, so now you are established in the climb, what do you do to maintain it?
Actually you need to be quite wide awake. ATC, or other traffic, should know what you are doing. You have to think about whether you are doing flight-levels or altitudes and have the sub-scale set on 1013 or QNH respectively.
You need to be aware of climbing into controlled airspace. And think about looking after your engine. It’s putting out more power than normal and getting less cooling. So the cowl-flaps should be open, and you must keep an eye on temps and pressures. Do whatever the POH has to say about leaning out in the climb.
Talking of watching temps and pressures. I once lost both engines of an Aztec, climbing out of Port Elizabeth. It was a military flight, and the SAAF had refuelled me with vast quantities of water instead of Avgas. This was after massive floods. I hadn’t spotted the problem during the pre-flight because the drain valves on the Aztec are not directly on the bottoms of the four tanks. They have pipes from the tanks to the actual drains. This means that when you think you are sampling the fuel in the tanks you are actually sampling the fuel in these pipes.
Fortunately I was able to spot approaching trouble by keeping an eye on engine temps and pressures. Both engines displayed the same symptoms. Not a flicker from the fuel flows – but rapidly increasing EGTs and slowly following CHTs.
Of course the engines didn’t enjoy the water so they stopped and surged and banged causing me pangs of mental anguish as we slowly lost height over the sea.
Eventually the gasping engines dragged me to the threshold of 26.
I learned two things that day. First; to understand all the idiosyncrasies of fuel systems, and second; I should take it very seriously if the gauges show even the slightest inching away from normal climb temps and pressures as the airfield gets further and further from your tail feathers.
Levelling off in the circuit
Strangely, levelling off elsewhere can call for different techniques – we will come to that shortly.
So if you are just climbing to circuit height, you must know what the altimeter will read when you get there and exactly what to do. Sadly, many instructors are too damn lazy to insist that you get this levelling off procedure right – and it’s not that easy.
Let’s say you have been climbing your Cherokee at 85 mph, and you know that on downwind you will get say 105 mph at 2300 revs. Here’s what happens to pilots who have not been taught properly. When they get to circuit height they throttle back to 2300 revs as they lower the nose into the level flight attitude.
Of course the airspeed gradually increases and the revs go with it. The next thing they know, they are outside the flap limiting speed and the revs have crept up to 2450. So then they throttle back to 2300. But this won’t be enough to sustain level flight, because by the time the airspeed has settled the revs will have decreased to 2150.
All this is accompanied by pointless trimming which further stuffs up the whole downwind leg.
Why does this happen? It’s generally because of the horrendous multiple-instructor problem. If my own student was to spend much of the downwind leg battling with the airspeed-altitude-revs-trim-problem, I would take her out of the circuit and teach her to level off properly.
The downwind leg is a seriously busy time for a low hour student. Not only must she fly accurately, she has to do the pre-landing checks, orientate herself with the runway, listen and look for other traffic and make her downwind call. And she has to listen to the well-meaning instructor’s debrief on what went wrong with the last landing and how to correct it on the next one.
If she is someone else’s pupe, who I will possibly never see again, I may be tempted to concentrate on getting in more practice landings than on fixing the levelling off problem.
This is how to level off at circuit height. Lower the nose to the level flight attitude. Wait for the airspeed to increase to 105 mph, and then throttle back to 2300 rpm, using just enough left rudder to keep the ball in the middle, and finally trim. Then everything will stay where you put it.
Levelling Off On A Nav Flight.
This needs a bit of planning because you have to work out what indicated airspeed to expect for your altitude and your choice of power setting. And once you have that, you need to get it to coincide with slightly less revs than the POH specifies for that power, because when you lean out the revs will increase a bit. It takes some juggling and practice before you get it right for your particular aircraft.
Vertical navigation
Vertical navigation, or V-nav, as it has become known, has largely been the domain of the airline guys. They have been using it ever since they got pressurised hulls and could fly above the weather and seek out jet streams.
However it’s become more important to us bottom feeders as these mushroom-shaped chunks of airspace get in our way. We have to plan not to climb into one by mistake. Also Met has learned to forecast upper winds with reasonable accuracy, so we can look for our own baby versions of jetstreams.
Actually sometimes they are not so baby. I had just collected my brand-new 180 Cherokee, ZS-KHW, from Johannesburg and was flying it home to my base in George. Those were the days of NDB letdowns.
George weather was like the inside of a cow, but no problem, I was in recent practice with instrument flying, and my shiny new aeroplane had all the dials I needed – even a DME.
Rassie, in the tower told me that the surface wind was calm. Wonderful, I got myself over the Golf Golf NDB at 8000’ and turned outbound for two minutes and then turned inbound. In zero wind I should have been back over the beacon again in another two minutes. Would you like to guess how long it took me to get back to the NDB? It turned out to be 21 unbelievably long minutes. My DME told me I was battling an 80 knot westerly, and Met knew nothing about it.
Sorry, a long story to explain why V-nav wasn’t such an issue then – the upper winds in our ten to twelve thousand feet of operational airspace were largely unknown, so vertical planning didn’t happen much – it was more of a suck-it-and-see enterprise.
Here’s what V-nav is about: in the same way that normal nav takes you from A to B via a pre-planned route, so V-nav will take you there via a particular vertical route. You might first need to climb steeply to checkpoint 1, in order to clear the mountains, and then level off until you get to checkpoint 2 so you stay below a lump of airspace. You could then plan a cruise climb to checkpoint 3 to get the best tailwind. Finally you may want to start a 300 fpm descent to destination. This will help compensate for the speed you lost in the climb – and to stop your pax’s ears from popping.
So V-nav is a plan – the same as normal nav. And you need to make sure your aircraft is capable of following the plan. It must have a certain ability to climb at various altitudes, and it might need oxygen, or pressurization, or two engines, or de-icing equipment.
And don’t forget about altimeter settings for flight levels and altitudes.
So your climb, like most things in aviation, needs to be planned, and achievable.
External effects
Let’s see how wind, weight and altitude affect the climb.
I had all three against me when, as a young charter pilot, I took off from Middleburg in a 260 hp Cherokee Six on a hot day, with a 15 kt tailwind, and four bulky German tourists – together with their bulky German luggage. I cannot say this is the stupidest thing I have ever done – but it’s right up there with a dozen other pea-brained attempts at suicide. We came within millimetres of mingling with a church steeple and were only saved by an Ernest Gann trick of using full flaps to hoik us over this pinnacle of rectitude.
Why take off downwind you may ask. Well, because into wind involved uphill in the lee of a hill that was producing downdraughts and turbulence. And why take off at all? Because I was a mission-driven idiot – I had to get these tourists back to catch their flight to Europe. It seemed like a life and death matter. The truth is that I hadn’t earned my Live Cowards’ Club (LCC) membership by then.
Briefly, then, a headwind increases your angle of climb – unless it takes you into the lee of a hill or mountain. Increased weight flattens your angle of climb. It also reduces your rate of climb and lowers your ceiling.
And altitude, actually density altitude, which is a combination of altitude and temperature, does the same as increasing your weight.
It is a good idea not to have them all working against you at the same time – it’s high on the list of things that kill unwary pilots.
Next time we will look at descents, and the most graceful or all manoeuvres – sideslips.