 of an AOA as well! Thanks for saving me the trouble.
Does your AOA adjust for different flap positions? I have read that some do and some don’t.
It doesn’t adjust for different flap settings, but in practice it makes little difference. Mine is the Alpha Systems analog “mechanical” model. When I calibrated it, I adjusted it with flaps up so that the needle was at the red/yellow mark and the airspeed was at the slowest in which I could maintain full control, per the instructions. That results in a stall when the needle is about in the middle of the red segment. Then I flew it with different flap settings, and there was no noticeable difference–there was full control at the red/yellow mark and the stall occurred in about the middle of the red segment. Other airplanes might be different, of course.
It depends on the design. Business jet aircraft ususally have flap compensation designed into the AOA System. The Alpha System AOA systmem installed on GA aircraft does not have flap compensation.
I have installed a Alpha System AoA 7 year ago on my 182 and clibrated the unit for 1.3 Vso flaps up. At flaps 30 the reference is 1.35 Vso and that is close enough. I fly in and out of a 1,800 long sod field that is not flat. My landings are significantly more consistent with the AoA System that includes audio call outs.
Pingback: Have you thought about Vref? | High Altitude Flying Club
Mac,
Good article.
I would take care with the concept that flying above Vref is safe.
Many pilots take this for true and include a lot of additives due to wind, gust, extra margin to stall, etc.
I would say that it is acceptable during the approach phase, but at short final the extra speed should be bled and speed should be reduced down to Vref when crossing 50 ft over the runway threshold.
This is the only way to make sure that the performance predicted in the manual will be accomplished. As you told, every knot matters, specially for low drag/high ground effect airplanes.
On the other side, flying below Vref may not be that bad in some cases, because manufacturers must demonstrate satisfactory flight characteristics landing at Vref – 5 kias in order to comply with landing performance requirements (23.75 and 25.125).
I do not know of this being an issue for Part 23 airplanes, but for Part 25 may be, because those big planes use 1-g stall speed as a reference, thus their Vref is 1.23 times stall speed instead of 1.3.
Your finish brings the most important messages for me:
1 – flying a specific speed brings precision and safety to approach and landing;
2 – have a plan and specific target for everything to do in an airplane.
Thanks,
Ramiro
Was taught to use VREF of 1.3 VSO and adjust for partial flap or other conditions 40+ years ago. It still works well.
The number that is more important to me is that the value of my Comanche decreases in inverse proportion to the price of 100LL. Double the price equals half the value.
Vref (1.3 Vs0) is what I was taught and what I teach for the short final approach speed for a “normal” landing. However, for a short field I teach 1.2 Vs0 on short final.
Here are some numbers for a 172S, in the 30 degree flaps landing configuration.
Vs0 is 40 KIAS. That’s pretty accurate based on the last time I went up and flew at Minimum Controllable Airspeed. Stall warning horn blaring, airplane buffeting, but not QUITE stalled yet.
Vref(normal) would then be 52 KIAS
Vref(shortfield) would be 48 KIAS.
Cessna’s AFM calls for 65 KIAS on final for a normal landing and 61 KIAS on final for a short field landing – both higher than Vref.
So what I normally see is 65 KIAS at the start of the final leg, slowing to 55-60 over the numbers. I don’t want to see less than 55 until the landing surface is underneath the wheels, unless I’m flying with a very proficient pilot who I can trust to lower the nose a little and add a lot of power if the airplane gets mushy.
Interestingly, in the DA40, Vs0 is 49 and final approach is 65, which is a lot closer to the 1.3 Vs0 we’d expect.
I believe it’s due to the fact that speed will drop off very quickly in a Cessna with an increase in angle of attack, and not so quickly in the Diamond. Mooneys are similar to the Diamonds in that if you’re too fast you WILL float forever, so they have you come down at 1.3 Vs0 in those airplanes.
Tim,
Remember to teach the manufactor recommended first or in its absence 1.3 Vso. The PTS is quite clear on this.
Dan
DPE
Mac needs some practice with Full Flaps and gusty weather! Next thing he will be telling us is that Downwind Turns are dangerious…
ALL Approaches should be at a “Vref”, in all aircraft!
It need not be a coldly calculated Vref but a fixed number should be used, never the less or an accepted slop attitude creeps in.
This only lead to decaying proficiency.
(bet you never expected that flap comment to draw such attention)
As a CFI for 43 yrs and flyer to coming up on 50 yrs, plus 3 decades running an aircraft business, typed in six jets, I found this quite interesting. Basically good article.
Skyguy, one of the first commenters needs some serious flying lessons and lots of ground school if he is to continue flying. I agree with Jim Hardin when he says Mac needs lessons landing full flaps in high crosswinds. I have landed full flaps in EVERY aircraft I have ever flown since I’ve been flying (24,000+ hrs worth) and have never had a problem. But I’m also an OLD stick and rudder guy, not many of us left.
Any rate Mac, good article, good topic. Some very good responses too, I might add.
Most informative.
Richard Smith, ATP, CFII, MEI
Hi,
Remember that the 1.3 Vso calculations for Vref should use CAS, not IAS. So if you’re looking for precision, you need to know the Vso in CAS, do the multiply and then convert back to IAS. It’s not a huge difference, but if you want to be precise, that’s the way to calculate it.
Craig
An interesting article leading to important discussions. Thank you, Mac.
On my STOL ICP Savannah (aerodynamically similar to the Zenith CH-750,) with the help of my instructor, I used trial-and-error to establish the best short-final IAS as 55 mph. This value is a far cry from the nominal 1.3Vso = 39 mph and even 1.3Vs = 45.5 mph. If I begin the flare much slower than 55 mph, an excessive sink rate ensues which causes an ugly thump. If I begin it at a much faster speed I can expect long balooning.
As to full flaps for landing, there’s no way I can routinely do that. The Savannah has mechanically operated full-span flaperons and I just don’t have enough muscle force to deflect the flaps to their full 36-deg. position at a speed higher than 40 mph. This option I reserve for emergencies only. (I’ve never yet met the runway that really asks for it.)
I’m going to jump in and defend Skyguy a little, here.
First, on whether “V speeds” are “important” for low-speed aircraft. It’s easy to forget that intuitions and lessons learned in one type of aircraft may be completely wrong in another. For slow airplanes, approach speeds should routinely be much higher than 1.3x Vso (for example). Why? Because ordinary everyday winds have shear that can approach or exceed 0.3 x Vso, while, for a slow-flying airplane, the typical American paved runway is effectively infinitely long. For a slow airplane the risk of overshooting on most runways is likely minimal even at speeds of 1.5x Vso, while the risk of stalling – or at least arriving on the ground with a very high sink rate – is substantial in normal conditions at 1.3x Vso. While jet jockeys, and pilots of turboprops, twins, and even Bonanzas and Cirruses may need to really limit the speed on approach, most of the time the pilot of a slow-flying aircraft will want to “drive it in”, all the way to the flare. Of course, many jet jockeys, etc., who pride themselves on their advanced skills, will try to fly slow airplanes this way, and the LSA statistics bear witness to the results: they bend more LSAs than student pilots do.
Second, on the comment that if the nose is below the horizon, you’re not going to stall. Sure, it’s true that you can stall an airplane in any attitude, but in actual practice, if you’re on a wings-level approach in a nose-low attitude, you’re not likely to stall inadvertently. I picked up this point from Tom Knauff, the