Vz Feedback Wanted!

[testwest]

Hi everyone

 

I am presenting the Vz paper to a regional symposium of the Society of Experimental Test Pilots this Friday in San Diego. I would love to hear any feedback from anyone who has adopted this climb profile and uses it on a regular basis. Thanks!

[jetdriven]

Norm, we have used this climb profile exclusively since we bought our plane two years ago. This fact was made apparent when we started doing instrument training and multiple approaches in Houston and we realized we had actually never climbed at Vy (such as a missed approach with another approach next) ever...   It was always 120 KIAS.

 

We didnt call it Vz, however. That term wasn't known then. We called it 120 KIAS and target EGT to cruise altitude.  For that, we always returned 16.5-17.5 NMPG for the block flight and if willing to slow down a bit, 20 NMPG.  Thats 800 NM on 40 gallons from chock to chock.

 

Bonanza guys hate it when I mention that.

 

Come to think of it, Cherokee, Cardinal RG, 210, 182, 172, 152, Piper Arrow, Commander 112/114, Trinidad, Sierra, Cirrus, Navion,  and even Ercoupe, Cub, Luscombe, Taylorcraft, Champ, and Custer Channelwing pilots dont like to hear it either.

[rbridges]

without having to google, what is Vz? Is 120 for the J models?

[bd32322]

Could we have a copy of your paper ? Before or after Friday..

[rbridges]

Hi, Rob. Vz is 112 KIAS for J models and 101 KIAS for C models. So that's 129 MPH IAS for the J.

This is kind of obscure stuff. I'm not sure how much you'd find on Vz specifically via Google.

Jim

 

thanks, but what exactly is Vz?  most economical climb?

[Bob_Belville]

I have been using 120 MPH IAS for climb in my E. Sounds like that's close to Vz for an E?

[rbridges]

I'll give you the run down but it'll have to wait til tonight. I've got an appointment this AM. Really interesting stuff if you are into the minutia of flying efficiently.

Jim

 

thanks.  Every bit helps.  Lord knows I need it.  lol

[jetdriven]

We have actually been using 140 MPH IAS when light and 120-130 MPH IAS when heavy.  I'll remember to change this to 128 all the time.

[carqwik]

Never heard of Vz in 25 years of flying...someone please clue me in!

[KSMooniac]

carqwik, I'd suggest using the search function and find posts by Norman (testwest) on the topic of Vz and flying efficiently...there were some great and long threads in the last 6 months or so.

 

In a nutshell, he wrote a master's thesis on the topic and proposed a new V-speed (Vz) for efficient climbing.  It extends the work of Carson (google Carson's speed) into the climb regime instead of cruise, and adds the great recommendation of the GAMI/APS folks to combine the Target EGT method of leaning a normally aspirated engine in the climb to safely maximize engine efficiency.  He "measured" the results of the Vz profile using CAFE Foundation scoring methods (google them as well...great stuff!). Vz calls for climbing at a higher airspeed than Vy and using the Target EGT leaning method until you cannot maintain 500 FPM in the climb, then you pitch up to maintain 500 FPM (and lower airspeed) until you reach your cruise altitude.  At the end of your climb, you will be farther "downrange" and will have burned less fuel than if you did a POH-style Vy climb, and especially at full-rich mixture.  

[John Pleisse]

Is it not correct that climb rates for Vz and Vy are nearly identical in all J and Pre J, E and F Mooneys? Ca: 750fpm?

[wishboneash]

I have been climbing at 110kts in my J without knowing about Vz. Seems it is close to the 112kts mentioned earlier in the thread. I try to keep the fuel flow around 14-15gph. Temps are a bit lower than target EGT.

[testwest]

So, my use of the term Vz is titled "Best Efficiency of Climb". The cruise speed Vz postulated by Brent Silver never really caught on in the vernacular....and the reason I chose Vz is it is easy to remember   Vx is best angle Vy is best rate Vz is best efficiency. Graphically those ideas could be simply presented in a drawing of an airplane climbing very steep for best angle, a little less steep for best rate and a little less steep again for best efficiency.

 

Vz is 1.32 times the published max gross weight sea level standard day indicated airspeed Vy as shown in the POH. No need to adjust the speed for gross weight, cg or density altitude. All of those variables fall out in one easy-to-remember performance limit, which is 500 feet per minute rate of climb.

 

For the M20J, climb at 115 KIAS, WOT, Target EGT, cowl flaps as needed for CHT less than 380 deg F. When performance drops to 500 fpm climb, transition to constant 500 fpm climb until speed decreases to Vy, then maintain Vy.

[fantom]

For the M20J, climb at 115 KIAS, WOT, Target EGT, cowl flaps as needed for CHT less than 380 deg F. When performance drops to 500 fpm climb, transition to constant 500 fpm climb until speed decreases to Vy, then maintain Vy.

 

You are the man, Norman

[testwest]

Thanks! More to come, I am going to post more a bit later!

[Awful_Charlie]

Vz is 1.32 times the published max gross weight sea level standard day indicated airspeed Vy as shown in the POH. No need to adjust the speed for gross weight, cg or density altitude. All of those variables fall out in one easy-to-remember performance limit, which is 500 feet per minute rate of climb.

 

That means 138KIAS in a Bravo, which is easy at lower levels, but is going to mean full (at in Take Off) power (which is not standard SOP) past somewhere round  I guess 10,000' or so, and that is *not* going to be efficient (25GPH+ vs 18GPH in standard 120KIAS cruise climb)  138KIAS is also way faster than Carson, V_MR and V_LRC.  (V_LRC is from 113KIAS at MTOW to 99KIAS at MTOW-750lbs)  At FL200 max continuous power is only 150KIAS in level flight! 

 

I really think that does need a DA correction

[testwest]

Thanks to JimR for the kind words. The 1.32 (ok, 1.3 is really close enough) multiplied by Vy is the ratio postulated by Carson. This speed is the point at which the product of velocity and miles per gallon is maximized. In math form:

 

Maximize V^1 * MPG = Carson's Speed

 

and there are some interesting other observations with respect to exponent of speed...

 

Maximizing V^0 * MPG = Max Range Speed (and very close to Vy for many airplanes).....Silver discussed this, but the concept really did not catch on for cruise...winds and low SFC at these power settings overwhelm any advantages for most operations.

 

Maximizing V^-1 * MPG = Max Endurance Speed (and very close, sorta, to Vx for many airplanes)

 

Maximizing V^2 * MPG = Max Level Flight Speed at Full Power

 

And finally the CAFE parameter (faster than Carson's) maximizes V^1.3 * MPG.

 

For Awful Charlie, the climb is postulated at the maximum rated power for continuous operations.

[carusoam]

We're going to need to invest in some O2 systems Jim.

Best regards,

-a-

[testwest]

I gave the pitch this afternoon to the Society, and it seemed well received. Thanks to everyone who replied to this topic!

 

I would love to post the thesis to the site here, but my upload barfs after showing a full upload...? Anyone who wants a copy of the whole thesis, just pm me with your email and I will send it out. 12MB and almost 100 pages of "light" reading

[1964-M20E]

When is the movie coming out?

[garytex]

Good stuff and interesting reading, thanks to all who have taken the time to share their experience.

Gary