Is best rate of climb speed really BEST?

[Dick Mitten]

Two scenarios:

1. We've lifted off and cleared all obstacles. Climb speed is set at 60kts 'cuz that's the machine's best rate of climb speed, and it'll get us up to (safe) altitude fastest. The engine fails. Now the nose'll have to be pointed down to pick up speed, and we'll lose some of that altitude. It'd be nice to have a full 70kts (best autorotational speed) to start the flare...

2. We've lifted off and cleared all obstacles. Climb speed is set at 70kts 'cuz when the engine fails no altitude has to be given up to gain speed.

So, is the best rate of climb speed really the BEST speed to use when climbing?

Thanks in advance for your comments!

[CTD]

What type of aircraft?

[Dick Mitten]

R44, but I think the question applies to any type where the best rate of climb speed is a bunch less than the 'best speed for autorotation'.

[S76Heavy]

I think that "best rate of climb" is just that, and not necessarily the safest, or most prudent speed in any specific flight. It just gives you maximum altitude gain in minimum time.

It's up to you to decide what other factors you need to consider to come up with the best take off profile for a particular flight.
On the S76A+ Vbroc is 75Kts, Vtoss is 65 so we don't have the problem of sacrificing altitude for speed in a single engine failure scenario.

[vorticey]

well the best rate of climb is only that. most hight to distance.
dont forget that if the engine fails and you were doing 70kt's instead of 60, you would'nt have the altitude to play with.

[Devil 49]

Best ROC, like the straight line you draw on your map for route, is a planning tool. Adapt and use what's most advantageous to each situation.
I use max continous power in a cruise climb at 600 fpm and whatever airspeed results. Shorter block times and easier on pax.

[212man]

Quote: "well the best rate of climb is only that. most hight to distance"

This is actually the definition for best angle of climb; best rate is height per unit time.

Also the reference to Vtoss is a little misleading as it refers to multi-engined aircraft where minimum performance guarantees have to be given in the event of a critical power unit failure, that don't necessarily come from Vy.

I am suprised there is such a large difference in speeds, what exactly does 'best autorotational speed' mean? Is it a compromise between minimum rate of descent, flare characteristics and range? Normally min RoD and best RoC speeds are very similar (TAS). Is it a function of pressure error (IAS)?

I suppose that what ever the reason, you are better at higher speed as it gives you more options in the event of engine failure, and is probably more comfortable for the pax and you make better progress en-route.

[HeloTeacher]

A couple things, the 70 knots for the R44 is definitely a speed based on moderation, a mix of reduced rate of descent, good range, and good inertia.

If your forced landing area is short, you won't want that much speed anyway in the flare. Also be aware that the higher the power setting in the climb, the faster you will lose that RRPM in an engine failure situation. I recommend trying a couple autos in the various departure conditions during your company training, it will be a good eye opener.

Myself, it was best rate of climb over hostile terrain, moderate power cruise climb over good terrain once above 300-500 feet, and always a good plan for what speed and direction would be needed if the engine did falter.

Good luck.

[CTD]

For the rotor, the Best Rate of Climb and Minimum Rate of Descent are usually the same (admittedly oversimplified) the highest ratio between power available and power required.

Some aircraft have fuselage or other issues which affect these speeds so they're not the same.

[S76Heavy]

212man, how can the reference of Vtoss be misleading if it is clearly stated that it involves a twin suffering a single engine failure?
I merely stated that the dillemma of having to dive on speed did not apply in that case, so any single pilot would have to make his/her own mind up on how valuable the info is in their particular A/C.

For us the difference between Vy and VminRoD in auto is 1 knot IAS, and that is apparently due to a different fuselage angle causing the pitot tubes to be in a slightly different airstream. I can't fly it to the exact speed anyway with a 5 knot difference between ASI1 and ASI2...

[Nick Lappos]

Dick Mitten,
Your question is rooted in our imprecision of language. The speed is not the Best speed for a climb, it is the speed where you get the best climb. There is a difference. At Vy, your climb rate is maximum, that's all. It may be a really poor speed for climbing (try using 60 knots while making a cruise climb on a busy airway in the North East US!!)

You are exactly right, Vy is not the only climb speed, it is not the best speed to climb at, it is the speed where you climb fastest.

An illustration of how poor Best rate of climb is can be seen when you examine the DC-10 accident in Chicago, where the engine loss created an assymetrical flap situation, and when the crew slowed to Vy, they lost roll control. In simulation trials afterward, the crews that did not arbitrarily slow down the Vy (who needs to with 3,000 feet per minute climb?) survived the situation.

"Best" is in the eye of the beholder!

[Dick Mitten]

Awesome comments, folks! Thanks!!