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Vx and Vy - almost completely useless?

The original SC was produced for the MDAP between the US and European countries post Korea.
It has a Continental 90 hp engine and while it can be converted to flaps, nearly all were flapless. The flaps became standard with the 135 hp and 150 hp variants. I would need to check, but I think the 105 hp variant (Special) was also mainly flapless.

Oh, that’s interesting. So there are two 90 hp cubs, the one with the J3 wing, but a 90 hp engine, and a flapless Super Cub with the larger span?

It's supposed to be fun.
LFDW

There may well be instructions in the POH to use take off flap in all cases and if there are, there is no reason not to.

It is the case with my plane, the POH sais clearly:

5. Set wing flaps to take-off setting (see flaps indicator).

and in the after take off check

4. Retract wing flaps.

I don’t see much ambiguity here, it sais take off with flaps so that is what is done.

I recall a discussion in the forum for owners and one former test pilot piped up in there and sais that during development it was discovered that the wing flap take off setting would allow for the air cushion below the wing to build up faster and therefore lighten the load on the structure with speed build up. Makes sense to me and is not runway lenght dependent.

On the other hand, the manual states regarding climb out:

An enroute climb speed of 115-120 mph IAS is recommended for improved cooling and good visibility. The speed for maximum rate of climb is approximately 105 mph IAS, The speed for maximum angle of climb is about 80 mph IAS.

Basically that is what John sais. Apart from avoiding an obstacle there is no reason to ever climb at Vx and there is rarely much to be gained from strictly flying Vy either for prolonged climb out. However, Boscomantico points out a VERY valid argument for flying in Europe:

The only thing that one might have to add to the equation (especially in Europe) is noise. The method used will have a big effect on the altitude reached at the airfield boundary and thus an enourmous effect on noise levels. Therefore, in certain conditions, one might consider staying closer to Vy (or, theoretically, even Vx.)

That is one of the things that make a lot of the things John sais (and not only him btw, Bob Kromer sais the same in his Mooney reviews) relative. In Europe, unless you fly from large airports where you actually will reach 1000 ft before the airport boundary even with the reduced regime, climb with IAS beyond Vy will most certainly get you attention from the local anti noise folk. I might add to that one other consideration however. Many airplanes still carry the power reduction instruction in their take off procedure list, usually at “safe height” to reduce to 2500 RPM typically.

What I aim for is to reach the airport boundary at a reasonable height, if possible already in climb configuration, that is clean and climb power. On my homebase that is easy, a normal departure will see us over 1000 ft AGL before passing the fence, in other places not. Noise related however, the power reduction as well as height makes good (well, or at least better) neighbours.

After that initial climb out, I fully agree that a cruise climb is much preferrable to a maximum effort climb which is hardly ever really needed. Johns graphs on distance covered and energy potential in case of engine failure are extremely useful to understand how the different methods work.

A small word however in “defence” of Vr. While it is correct that Vr is something that was not invented at the time our prop planes got their books written and has only limited use, the more interesting factor is what it actually would be were we to use it. I discovered that quite a few schools use some arbitrary figure “for procedure practice”, which is not only wrong but potentially dangerous. So i set about checking what the speed would be for the airplanes I fly.

I fully agree with John and some of the posters here that the use of a designated Vr is neither defined in our POH’s. Nevertheless, some times I see airplanes struggle in the air because the nose gear is “unloaded” fart beyond simple unloading, therefore creating considerable drag through a too high pitch command at too slow speeds, exactly the same thing which caused the accident which is the reason we now have the definition of Vr. I further found that on my first Cessna, “unloading” considerably lengthened the ground run. If however the nose gear was left on the ground and a rotation was initiated at about Vlo, the airplane took to the skies much more readily.

John is quite right when he sais Vr was established with the upcoming jets. Or rather, the need became obvious after one Comet I crashed on take off in Rome, when their crew followed the “unload the nose gear” procedure a bit too enthusiastically until the airplane got into a situation where it did not accelerate at all. A summary can be found here

Vr has a large significance for airliners as well as for multi engine airplanes due to the fact that it is determined in part by the minimum control airspeed (Vmca). Rotation in ME planes should not be commenced before reaching a speed which allows control of yaw in case of an engine failure. Obviously, that has no importance at all for single engine planes. The 2nd factor is that it has to guarantee that with the power available the airplane can reach Vlo which is the lift off speed in a rotated state, so it can’t be too slow. The 3rd factor is V1, which of course has low significance with a single engine plane. So Vr is always somewhere between V1 and Vlo, which in turn is Vs for the configuration x 1.05. The target speed for any take off is V2, which is defined as 1.2 times Vs or 1.1 times Vmca where appropriate. So all we need is Vs.

If we were to fly a take off according to airliner procedures, we’d rotate at Vr, lift off at Vlo and aim for V2 initially and V2+10 shortly afterwards. How much difference is there really to the procedure outlined in our books? Not that much actually. Also, due to the fairly low speeds, the different speeds are very close together.

Stall Speed with take off flaps can be found in the POH. During rotation, wings are level for obvious reasons but once we unstick, we have to expect some minor bank angles. So in my example I read that the stall speed applicable for my plane is 64 mph for wings level and 67 mph for 20° bank. Vlo by definition would therefore be between 67 and 70 mph which. V2 in this definition would be 80 mph, which, incidently, is identical to Vx.

The spread between those speeds, particularly Vr and Vlo is fairly negligable, so an appropriate rotation speed for this configuration would probably bee about 68 mph. With this speed, a dosed pitch up input of maybe 1-2 degrees will similarily rotate and unstick the airplane fairly quickly. Acceleration to V2/Vy is likely to happen during the first seconds of flight, while acceleration to Vy can take some more time depending on the pitch aimed for immediately after unstick. What I found VERY interesting in that regard is the “red area” John defines. To avoid that certainly has merit.

My aircraft needs an almost immediate release of the back pressure (an effect described in the POH) in order not to pitch up too quickly, yet it does need a clear rotation and will not fly off by itself. After unstick, the plane will accelerate through Vx in the first few feet of climb, where gear retraction should be done as forces will grow after Vx and make it more difficult. Once the gear is up, acceleration is rapid so power reduction usually happens shortly after that and the flaps need to go up actually before reaching Vy which is outside the white arc. By that time, 1000 ft is usually passed. Vy incidently is at the same time V L/D, the optimum glide speed. Cruise climb will allow a speed loss of 10-15 mph before Vl/d is reached, a nice safety aspect.

So what about using Vr? Again, it is not in the POH and therefore using a self defined Vr is not really appropriate. However, it does not hurt to actually calculate Vlo at some stage and put it in one of these drawers in the back of your head and if it’s only verifying what you know already. And, no two types are the same. While some take rather dramatic attitudes at Vy, others won’t have more than 2-3° more pitch than during cruise climb. So it comes down to “know thy aircraft” while keeping John’s graphs and explanations in mind.

Thanks for sharing.

Last Edited by Mooney_Driver at 23 Mar 10:44
LSZH(work) LSZF (GA base), Switzerland

Of course the pilot flies the plane, but FEEL will tell you when the aircraft wants to fly as long as, as I said “The trim set somewhere near correct”

This is very much dependent on the type aircraft. The Bonanza will happily roll along with the nose wheel on the ground at 100 Kts with the trim set for takeoff unless the pilot inputs significant back pressure. Every pilot has words that annoy them, John D. is hung up on the word “rotate”, I am not. (My pet peeve is calling runway 2 “zero two”, I will call it that when they paint the zero on the runway). One can hold substantial back pressure on the yoke and the nose will lift off near its normal takeoff speed, but with normal technique, the controls will naturally come aft with trim setting so as to lighten the nose gear load but still require a positive pilot input 3 or 4 knots prior to lift off speed in order to lift off near the POH lift off speed. I call that a rotate. So do some of the Cessna manuals. Failure to apply the “rotate”, the Bonanza with the trim set for takeoff will continue to accelerate on the ground well past the desired lift off speed. The takeoff trim is roughly the setting needed for the initial climb out. Setting the trim further aft can be a handful, especially if it is not anticipated as the pilot will have to use significant force to keep the nose from coming up into a stall attitude.

KUZA, United States

My pet peeve is calling runway 2 “zero two”, I will call it that when they paint the zero on the runway

I believe that is ICAO standard and the zero is painted on the runway outside the US. This reminds me of a discussion I had with a CFI in the US, he objected to my calling the airport “KPAO” instead of “PAO”. He said that “K” just means “airport” and I shouldn’t use it. Of course the registration of the airplane is the N-number

I guess if I flew outside of the US, I would have to amend my pet peeve. There are a fair number of differences between ICAO and US, although I am not at all convinced all are a good idea and many have the not invented here aspect to them.

KUZA, United States

There are a fair number of differences between ICAO and US

and this is touching upon my pet peeve: some US’ans thinking (and acting like!) the US is not an ICAO member, or bound by ICAO recommendations. Of course all of that has come historically, and the FAA does seem to make some efforts now to align with ICAO, but there’s a long way to go both in the text book and in some people’s mind.

A gentle yet correct wording would be “the FAA has been very slow in fully implementing certain ICAO recommendations”.

[[very much off-topic, of course, but I think the original subjected has been dealt with to common satisfaction. Thanks for the lessons learned!]]

Last Edited by at 23 Mar 14:57
EBZH Kiewit, Belgium

ICAO recommendations are not law in the US or any other country, and for them to be treated as law in the US (specifically) would be illegal.

The US initiated the formation of ICAO and since then it has certainly served a significant purpose in promoting freedom to fly worldwide. However, because the US typically leads in reducing pointless GA aviation regulation, as with medical requirements currently, I think I’ll continue to be happy that FAA regulations are the law in the US. UN organizations such as ICAO are no particular friend of ours, or mine.

I think the US can, will and should continue to lead in aviation regulation and if ICAO chooses to learn from US regulatory leadership for the continued benefit of individual freedom to aviate internationally, so much the better. The ICAO may even be able to contribute occasionally as with lettered (A-G) airspace classifications in the 90s, which were implented in the US pretty much as ICAO defined – unlike in other places, where quasi-ATC still controls VFR traffic in Classes E and below

Re flapless Super Cubs, a friend has an obscure variant supplied to the US Civil Air Patrol. If I have this right, it was supplied with 135 HP and no flaps, There were a seemingly endless number of Cub variants.

Last Edited by Silvaire at 23 Mar 16:25

and this is touching upon my pet peeve: some US’ans thinking (and acting like!) the US is not an ICAO member, or bound by ICAO recommendations. Of course all of that has come historically, and the FAA does seem to make some efforts now to align with ICAO, but there’s a long way to go both in the text book and in some people’s mind.

That pet peeve works both ways. For example the US adopted the ICAO convention that dropped the usage of TDZE on its approach charts in favor of THRE. Then I pointed out to the FAA that 91.175 specifically specifies TDZE when using the approach lights as the only visual cue. Whoops, the FAA now has to redo over 4000 approaches. In the mean time they published a Safety Alert with the TDZE values for all the existing approaches that had it removed. THRE is not an operational altitude as one never lands on the threshold, Asiana excepted. There are many more examples, but that is for another thread.

KUZA, United States

Pissing contest going on?

ICAO never issued any laws, but the states that signed the membership agreed to enforce the standards and recommended practices as law or notify ICAO of any exceptions such that other states may be informed. The whole point of this organization is to ensure that we all fly more or less the same across the globe, and that we as consumers may expect aircraft, airlines, airports, crews and operations to be similar and safe wherever we are.
Surely that’s a good intention?

A few years ago a Russian cargo plane collided with a European carrier and killed all aboard. This was due to different common practice, Meters vs Feet and the non-standard Russian reaction to an RA from the TCAS vs ATC instructions.
Another accident involving a SAAB 340 with Russian crew occurred when the flying pilot reverted to his old experience with Russian ADI indication and flew the aircraft into the ground. These examples clearly show how different standards cause problems in aviation.

So, if ICAO in it’s unsexy partnership with the ill-favored UN is not a good platform for common grounds, what is? If the US in fact “initiated” the ICAO, why the animosity?

ESSB, Stockholm Bromma

ICAO is a necessary evil, much like any organization that attempts universal oversight of any activity: over time creeping consolidation of power becomes an issue, and needs be firmly limited. Here is the story on how the ICAO was founded.

Link

Last Edited by Silvaire at 23 Mar 16:49
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