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Vx and Vy - almost completely useless?

Emir wrote:

I would avoid any advice from the person who gave such crap as general advice.

Absolutely!

EGTK Oxford

Airborne_Again wrote:

on a maximum performance takeoff you have to make a positive rotation.

Thank you shall keep this in mind and get around to understanding it in more depth.

Emir wrote:

I would avoid any advice from the person who gave such crap as general advice.

I still a nube so thank you for the warning. It seems to work for certain types of aircraft as mentioned by many here and my limited experience, but certainly NOT a general rule – noted!

Germany

In theory the concept of positive rotation is a swept wing Performance Class A concept. The average GA puddle jumper with positive wing incidence has a lift off speed. I can think of a few types where a positive rotation instead of flying off, may, and has on occasion led to grief e.g. Pitts Special, Twin Com (laminar wing, left ground effect, wing dropped, cartwheeled but fortunately no fatalities).

The Super Cub is much more tolerant.

Oxford (EGTK), United Kingdom

acquilinus wrote:

It seems to work for certain types of aircraft as mentioned by many here and my limited experience, but certainly NOT a general rule – noted!

Many things work but it doesn’t mean that they can be crafted into rules. E.g. you can open door on C150 and use it as rudder but nobody will consider this as standard procedure

LDZA LDVA, Croatia

Emir wrote:

E.g. you can open door on C150 and use it as rudder but nobody will consider this as standard procedure

Funny that you mention it. Few weeks ago I was having a conversation with Beech Bonanza pilot who told me of his troubles with open door rudder effect and difficulties while doing a touch down to get it closed properly!
Germany

acquilinus wrote:

a conversation with Beech Bonanza pilot who told me of his troubles with open door rudder effect and difficulties while doing a touch down to get it closed properly!

I had a Beech Bonanza A36 for about 10 years and the door came open about 6 times during this period, including once in IMC ….. never had a problem, just landed and closed the door.

Maybe it was due to the training …. the instructor would get in and not lock the door just to teach me a lesson

I’ve compared the handbook and the checklist for the plane I learned to fly on, a 115hp tailwheel Robin DR.221, to see the difference between what the manufacturer said in the 1960s and what the instructors say now. The aircraft has been in the club 40 years, but the checklist was renewed about a year ago.

Vr is 90-100 km/h in the POH, and 100 km/h on the checklist. This is followed by level flight to accelerate to 110 km/h before climbing out of ground effect. Generally the checklist rounds up speeds compared to the POH, assumedly for safety.

Vx is approx. 115 km/h in the handbook, and not mentioned in the checklist. Instead, there’s ‘initial climb’ at 130 km/h, and ‘normal climb’ at 145 km/h which is the same as best glide at maximum weight.

The only mention of a ‘positive takeoff’ is with a crosswind, to stay on the runway longer at faster speed before rotating.

My memory is that Vx was only used on a short-field take-off or to clear an obstacle, and higher speeds were used in normal use. I was told off a few times for taking off too early and being in the almost-stall in ground effect: stay on the ground until definitely flying. This wasn’t taught on the nosewheel aircraft, which would take off with gentle back pressure on the stick. The larger-engined planes didn’t need to accelerate in ground effect.

Vx and Vy don’t really figure in my normal flying, and are only used if needed, e.g. clearing obstacles or climbing over cloud. Vr doesn’t figure at all: I do it by feel. Admittedly I don’t fly anything much above 1000kg MTOM.

EGHO-LFQF-KCLW, United Kingdom

I guess that if we were to condense this six page discussion into one rather long sentence it might boil down to:

Should we practice, as often as we can, techniques which wring maximum performance from our small aircraft (like autorotative landings or short field/obstacle take-offs) or should we, like the airline pilots of which William Langeweische wrote in Fly By Wire, “spend year after year deep inside the flight envelope, within the narrow range of maneuver that delivers smooth and safe rides to the passengers”?

Glenswinton, SW Scotland, United Kingdom

There is a great article in the last US AOPA magazine by Barry Schiff, making the point that if you get an engine failure during a Vx climb, it is very likely to kill you, because at that point you basically have no options left.

Administrator
Shoreham EGKA, United Kingdom

It’s easy to test at 4kft agl how much you have to move stick and height loss if you introduce 5 seconds delay with engine idle at Vx (I dropped wing followed by 1/4 spin in one of the attempts)

With the ground at 100ft agl bellow, there is NFW I would push the nose that fast & low, it’s game over !

In gliding winch cable breaks ee teach prompt push on stick sometimes from 45deg pitch up to -45deg pitch down on a high cable, bellow 200ft agl, we do instructor “demo only”, the student does not have to demonstrate the maneouvre just watch what the instructor does…

Last Edited by Ibra at 22 May 08:16
Paris/Essex, France/UK, United Kingdom
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