Set Cruise Power?

[Severe Clear]

When do you set cruise power? Some people say its best to allow the aircraft to accelerate to the fastest speed possible while level before setting cruise power. But does this not prevent the aircraft from accelerating to the fastest speed due to flatter props at higher RPM causing drag?

I’ve seen others set cruise power about 400 feet prior to level off. They say that the aircraft can accelerate quicker by changing the blade angle at a lower RPM causing less drag.

I’ve also seen other people climb 200 feet high then descend to the cruise altitude and set cruise power while descending.

What do you do??

[BTD]

But does this not prevent the aircraft from accelerating to the fastest speed due to flatter props at higher RPM causing drag?

No. The maximum power output of an engine is a function of the max torque and max RPM. If you reduce either one of these without increasing the other you are reducing the power output. For your above explanation to be true the props would have to be turning the engine, as in an engine failure scenario. If that were the case anything with Garrets would start NTSing (negative torque) as if the engine had failed when you were approaching cruise speed.

Also, remember that in most aircraft you are setting the speed of rotation for the prop and not the blade angle. So as you accelerate to cruise speed the blade angle is very likely already changing anyway to make sure you remain at 100% RPM or whatever it is you have selected. It is not a fixed pitch prop.

BTD

[x-wind]

Maybe I miss interpreted... and I did.

Back to the original post. Never flown a turbine or a piston with much "extra" power. But in the pa31 (Navajo) I pull it back after level 10-15 kts before cruise power. I like watching the fuel flow go down and it doesn't take long before it's at cruise speed.

When I was teaching on twins I suggested (because everything is a suggestion ) waiting until cruise speed. It seemed to lead to a more successful level off and altitude control. Not doing so would diverted too much attention to trimming.

[Tim]

I always hold off on bringing the power back until cruise. If you are trying to pitch down to level off and reduce the power immediatly you won't have AS MUCH extra power to keep the a/c level, so you'll have to keep backstick pressure until the airspeed catches up. Obviously the pitch up increases your drag therefore you won't accelerate as quickly. If you try to pitch for the airspeed you won't be able to maintain altitude initially.

my 2 cents

[Rowdy]

In the king airs I'm flyin now.. Level off.. wait about 30 secs to a minute for the speed to increase and when it's close to what we should be indicating.. start the cruise checks (read: reduce rpm). This seems to produce the most seamless transition for me anyways. It's all opinion at the end of the day.

[flying4dollars]

Usually I'll wait for the airspeed to increase until the indicator needle slows down and it becomes pointless burning the extra fuel for a couple mins worth. Then I call for cruise. Especially fighting headwinds.

Somtimes I'll have it pulled back shortly after levelling off to keep the cabin sounds levels to a more comfortable level for the pax.

I've seen some guys pull the props back to 1450 (cruise setting in the 1900) during climb power settings (instead of 1600). Then just pulling the power levers back for cruise to cruise ITT settings.

Don't think there is a set way of doing things, it's all personal preference at the end of the day.

[AuxBatOn]

What about the good old APT/PAT trick? If you climb faster than you cruise (it DOES happen), use PAT (set power before reaching the altitude, drop your nose to catch the altitude and trim the aircraft). That way, you should be on speed as you level off.

If you climb slower than you cruise, use APT. Set the attitude to intercept the altitude, reduce the power once you reach the airspeed and trim the aircraft.

If you climb at the same speed you cruise, Set attitude and power simultaneously and trim the aircraft.

I don't know, they seem to be the most efficient ways of doing things....

Climbing 200 ft then descending? WTF?

[North Shore]

Climbing 200 ft then descending? WTF?

Seems to be an old bush thing.. Climb 200 ish higher and then put the nose down, thus giving you a bit of a downhill run at cruise... before you pull the power/props back.

[AuxBatOn]

Sure, but the fuel/time you loose by climbing the extra 200 ft won't be gained back by accelerating faster.

[Tim]

Not to mention the professional element of it. I wonder what the check pilot would say if you tried the 200' thing on a ride. I agree with auxbaton, the old APT method works.

Just out of curioussity, what a/c climbs at a faster airspeed/mach then it cruises?

[monkeyspankmasterflex]

Climbing 200 ft then descending?

It's like getting on the step on floats. Takes more energy to get there than to maintain it once you're there.

[Jeremy]

Another issue would be when you're pushing gross at high alts while picking up bags of ice. It can be difficult to maintain the min icing speed. I usually wait a good minute or two to get well above this speed. If cruise is set too early the aircraft might not accelerate in cruise. Then your stuck having to descend to maintain min icing speed and also increasing the burn at lower alts.

[AuxBatOn]

Not to mention the professional element of it. I wonder what the check pilot would say if you tried the 200' thing on a ride. I agree with auxbaton, the old APT method works.

Just out of curioussity, what a/c climbs at a faster airspeed/mach then it cruises?

We do sometimes on short legs. We climb at 0.74 and fly at 0.65/0.7, just so we don't get jammed and rushed.

[KAG]

The climb 200' the descend to gain your TAS is an old bush trick, one that newer more powerful planes don't need to do. It's not a matter of professionalism (or lack there of) it may be what was required/the norm back when DC3's and such were the common machine to fly.

Climb to altitude, attain your speed, then power back to cruise.

[SAR_YQQ]

We do sometimes on short legs. We climb at 0.74 and fly at 0.65/0.7, just so we don't get jammed and rushed.

That seems like a local procedure. Why climb at .74 when you can climb at .50 (or whatever) and get to altitude earlier. What is best rate on the Hawk?

In the mighty BE-90 that I strapped on - we climb out at 150 and cruise around 220 - so we use APT all the time.
Same for the old girl - climb around 130ish, cruise in the 200's.

[AuxBatOn]

We do sometimes on short legs. We climb at 0.74 and fly at 0.65/0.7, just so we don't get jammed and rushed.

That seems like a local procedure. Why climb at .74 when you can climb at .50 (or whatever) and get to altitude earlier. What is best rate on the Hawk?

In the mighty BE-90 that I strapped on - we climb out at 150 and cruise around 220 - so we use APT all the time.
Same for the old girl - climb around 130ish, cruise in the 200's.

That's SOP on the Hawk (and that's the procedure in the MFT). That's our IFR (and VFR for that matter) climb profile for the Hawk. AFAIK, it gives us the best rate. Mind you, we don't fly 0.65/0.70 very often, unless we want to go for range or we don't want to get rushed. A more normal cruise speed would be 0.8.

[KAG]

We do sometimes on short legs. We climb at 0.74 and fly at 0.65/0.7, just so we don't get jammed and rushed.

That seems like a local procedure. Why climb at .74 when you can climb at .50 (or whatever) and get to altitude earlier. What is best rate on the Hawk?

In the mighty BE-90 that I strapped on - we climb out at 150 and cruise around 220 - so we use APT all the time.
Same for the old girl - climb around 130ish, cruise in the 200's.

if your machine can cruise at around .80, and your trying to climb it at .50 your going to find out what it's like to stall a jet. If your lucky you'll only get behind the power curve and have to descend to regain your speed.

[Red Line]

I've seen some guys pull the props back to 1450 (cruise setting in the 1900) during climb power settings (instead of 1600). Then just pulling the power levers back for cruise to cruise ITT settings.

Haha, yep I know what you mean! On our 1900s it seems like we let the rattle of the airstair door determine at what time and how much the props come back during the climb! (Finding the right frequency RPM on different machines is somewhat of an art form!)

break - break

Climbing 200 ft then descending?

It's like getting on the step on floats. Takes more energy to get there than to maintain it once you're there.

Agreed! On a hot summer day at a high FL you can actually observe the difference it makes.

[KenoraPilot]

In the Otter we'd fire it right into cruise about 10 seconds into level flight....but the Otter only does 145kts in cruise anyways. Climb at 100kts.

[goldeneagle]

Not to mention the professional element of it. I wonder what the check pilot would say if you tried the 200' thing on a ride. I agree with auxbaton, the old APT method works.

A check pilot will as you why you climb 200, then descend. If you know why, and can answer the question with something more intelligent than 'sounds good to me', then likely will give you high marks for it, assuming the answer actually gives a reason for why your airplane, at the loads you have, will perform better that way.

It is not an old wives tale, and not an figment of the imagination of the old bush pilot that climbing an extra 200, then descending into cruise will result in a faster cruise, it's simply a case of the aerodynamics of a heavily loaded, and under powered airplane. Older piston planes aka DC3 et al, do not have a lot of excess power at altitude, and at lower cruise speeds, are actually operating behind the power curve. If you level off and set cruise power, the airplane will stabilize at the speed it can attain yet maintaining level flight, and there it stays, just slightly on the back side of the power curve. Climb an extra 200 feet, now use that altitude to descend back to cruise alt, leveling off slightly above cruise speed, and voila, the airplane stabilizes on the front side of the power curve, 15 knots faster than it did by just climbing up and levelling off.

If you are flying an airplane with lots of excess power at level cruise, it's a total non issue. If you have dragged a heavily loaded piston engine up to significant altitude, in an airframe that struggles to maintain level at those alts, then by climbing up a bit, and 'diving' into cruise, the airplane can stabilize on the front side of the power curve, and it'll go a little faster. The old farts call this 'cruising on the step'. If you are cruising at 140 on a 4 hour leg, then an extra 10 knots in cruise will make a huge and significant difference in your fuel burn for the trip.

If you are flying a kingair at fl250, the technique probably sounds silly, and likely is silly. But, if you have a single otter, with a full load of fishermen and all thier beer, nice warm day and you really struggled to roll the second float out of the water without putting the first back in, then, a small dive back to level after the climb is likely going to give you a few extra knots in level cruise. Again, likely not a huge difference if it's only a 30 mile leg to/from the camp, but, if you level off with the gps saying 200 miles to the next gas stop, yah, 5 to 10 knots, gonna make a big difference in the 'feel comfortable' factor, especially if there is a bit of a breeze pushing on the nose.

If you really want to understand the concept in detail, read up on how the center of pressure moves with angle of attack on an airfoil, both the wing and the tail feathers, and how this affects induced drag. Then read up about operating an airplane at altitudes where there's only a small delta between the front and back side of the power curve, a flight regime commonly called 'coffin corner' in the early days of jets. Then read the old bush stories of otter drivers that grew up to be 707 drivers, and how they claimed they could save a ton of fuel by cruising the 707 'on the step' over the pole to europe. Then do the detailed math on how much fuel could be saved by coaxing one of those old jets to the front side of the power curve, and you will discover, they were wrong, they didn't save a ton, they saved 2 tons....

For those with a real interest in the subject, here's todays homework assignment. Come back and tell us why you would load your airplane either at forward or aft cg limits, to reduce fuel consumption. Assume your cruise will be up near service cieling, operating within 10 knots of the power curve limits (right dead center in the middle of coffin corner), and you are cruising for maximum range, overwater delivery flight. Would you load the a/c forward, or aft, and why ? What techniques would be best for setting optimum cruise conditions ?

[ahramin]

Why would you climb on the back side of the power curve? Why slow down both your forward speed and vertical climb speed?

[Airtids]

Climbing 200 ft then descending? WTF?

I believe it's called flying "on the step". I've tried it, but never been able to convince myself of it's veracity, but if Goldeneagle says it's so, I'm tempted to believe him.

Now, I don't know how it would work for me when I'm zipping around in the RVSM airspace. Seems controllers get cranky about 200' deviations...

[teacher]

If I'm not mistaken the down force (to keep the nose up) on the tail is less with an aft C of G therefore a more neutral elevator position and less drag equaling better speed and or efficient flying. You might need ( I think) a higher angle of attack as well with a nose heavy airplane leading to increased induced drag.

[goldeneagle]

Why would you climb on the back side of the power curve? Why slow down both your forward speed and vertical climb speed?

Cuz you are slowly clawing your way to altitude, 300fpm or less, and there is a tendancy at times to 'pull back' a bit, try increast the rate of climb. It's counter intuitive to most pilots to push the nose down to increase climb rate. Mix in a little turbulence, an old underpowered piston airplane with no autopilot, clawing it's way up to near the service ceiling, and, arriving at cruise altitude on the back side of the power curve, instead of the front side, pretty easy to do. If you are at a weight/altitude combination where the front and back side are only separated by 10 or 20 knots, it's really easy to end up on the back side unintentionally.

Again, only applies in very specific circumstance, not really relavent with most airplanes today. Much more relavent in the days of hand bombing around the edges of coffin corner, after a 2 or 3 stage step climb to altitude.

[sarg]

[/quote]

It is not an old wives tale, and not an figment of the imagination of the old bush pilot that climbing an extra 200, then descending into cruise will result in a faster cruise, it's simply a case of the aerodynamics of a heavily loaded, and under powered airplane. Older piston planes aka DC3 et al, do not have a lot of excess power at altitude, and at lower cruise speeds, are actually operating behind the power curve. If you level off and set cruise power, the airplane will stabilize at the speed it can attain yet maintaining level flight, and there it stays, just slightly on the back side of the power curve. Climb an extra 200 feet, now use that altitude to descend back to cruise alt, leveling off slightly above cruise speed, and voila, the airplane stabilizes on the front side of the power curve, 15 knots faster than it did by just climbing up and levelling off.

[/quote]

The only problem with this is you need smooth air or you end up wallowing thru the air again after getting hit by the turbulence.