4
$\begingroup$

Cessna 172N’s POH has Vx = 59 Knots.

Let’s assume you need to climb from 1000 msl on traffic pattern just after you finished turning cross-wind and are clocking 85 Knots, to 2000 as fast as possible, say to clear the noise restriction zone.

Is it better to let the plane get to some 100 Knots then pull back and climb or just start the climb right away?

As an example practicing full speed stall maneuver I have noticed I climb at a rate of 1500 feet/min while on Vy my rate is never more than 650 feet/min.

$\endgroup$
  • 5
    $\begingroup$ If you want to climb fast you should be climbing at Vy (maximum rate of climb), if you want to climb at the best angle, you climb at Vx (maximum climb angle). Vx is usually used for obstacle avoidance. Since if I remember right, Vy is about 85, you should climb immediately. $\endgroup$ – Ron Beyer Sep 13 '16 at 20:23
  • 4
    $\begingroup$ Obviously, a non-sustainable climb can exceed the maximum climb rate that you can sustain. By immediately pulling up an decelerating to Vy, you'll still get the maximum non-sustainable climb as you drop to Vy, and then you'll get the maximum sustainable climb. How can you do any better? $\endgroup$ – David Schwartz Sep 14 '16 at 4:00
  • 4
    $\begingroup$ What's better ? Shorter in time ? Distance travelled ? Fuel consumption ? Safety ? Confort ? $\endgroup$ – Antzi Sep 14 '16 at 4:42
9
$\begingroup$

Aircraft drag scales with the power of speed. This by itself should make clear that deviating from the point of optimum performance will always incur higher losses which cannot be made up for later.

Quadratic curve and linear interpolation

Let P₁ and P₂ be polar points away from the optimum point $\text{P}_{opt}$ along a quadratic drag polar. No matter how you interpolate between the two points (red line), you will never look as good as when staying at the optimum point all the time.

OK, it seems that even this description is not obvious enough for some people. Dear down voters, I am now typing this especially slowly so even you can follow: No, going fast first and then pulling up will not help. It is better to stay at the speed for the best climb angle all the time.

$\endgroup$
  • $\begingroup$ I would +1 your answer again if I could. $\endgroup$ – acpilot Sep 14 '16 at 15:54
  • $\begingroup$ I dont know if we are talking about the samething? I have had encounters with cowboy GA flyers who have just appeared from nowhere over the ridge of Santa Suzana near Van nuys airpot. I have learnd to keep calm and continue level flight or even descend a bit to let the wind rush over my wings then pull up fast and climb over traffic to avoid potential collision. You wouldnt have sluggish controls and get immediate positive control authority. This will lift you 300-400 feet really fast. Howevr for sustained climb to your flight altitude you want to follow the POH. My question was not that. $\endgroup$ – kamran Sep 14 '16 at 16:37
  • 3
    $\begingroup$ @kamran - another pilot keeping visual seperation from you is not expecting you to do any of that and may require HIM to take evasive action to avoid YOU (and label you a "cowboy pilot")! Right of way rules are already well defined in 91.113. Non-standard evasive maneuvering is a matter of last resort only. A slight turn off course is by far the preferred option. You may want to review collision avoidance guidance in AIM 8-1-8, specifically 8-1-8(c)(d)(e). $\endgroup$ – acpilot Sep 14 '16 at 17:35
  • $\begingroup$ @acpilot, The prime rule of aviation is not to crash! Santa Susana pass, Magic Mountain pass, New Hall pass and a few more in my area are natural bottlenecks of a congested VFR traffic to one of the busiest airports in the world, Van Nuys. We have had three fatal crashes over just last few month. I certainly hope somebody learns from my real life experience and avoids a disaster! $\endgroup$ – kamran Sep 14 '16 at 19:42
  • 3
    $\begingroup$ @kamran: Your question asks for the fastest method to climb from 1000 ft to 2000 ft. If the clock starts ticking at the point you decide to change altitude, the time to accelerate must be included. Then your Cowboy-style popup takes longer (and everyone around you by surprise, I might add). Allow me to not follow your recommendation. $\endgroup$ – Peter Kämpf Sep 15 '16 at 6:34
8
$\begingroup$

Ron nailed it. (See comment on OP.)

It depends on what you’re trying to achieve.

Climbing “fast” in terms of maximum vertical speed = Vy (best rate)

If the noise sensitive zone is immediately surrounding the airport, you want to use Vy to put altitude under you as quickly as possible.

Climbing “fast” in terms of maximum feet per nautical mile = Vx (best angle)

If the noise sensitive area is a few miles away, you may want to use Vx to get to altitude before overflying the zone.

I gather from the question that the noise sensitive area is right next to the airport. If that’s the case then Vy is likely your best option.

While accelerating to 100 and then pulling up feels satisfying, just pitching for and holding Vy (or Vx) is more effective. Peter’s answer explains why this is.

In any case, watch your oil temps (or cylinder head temperatures if you have a CHT gauge) and prioritize keeping the engine cool over noise abatement. While being a good neighbor is important, taking care of the engine and flying safely is even more important.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.