Can anyone explain to me why one needs VSI>0 or Vz>0 before pulling the gear up? on after takeoff or on low go around? why the simple look out of the window that you have left the ground on safe height and adequate ASI indication is not sufficient? or the SOP intended for people flying LVP hardcore stuff in 50m visibility and 10cm cloud based or fog, then it would make sense
I guess with all position error involved in static ports from config & ground effect and VSI lag that would not make the vertical speed instrument a very reliable one, what happens if altimeter/vertical are not working? or statics are clogged? you are underpowered to deliver climb or accelerate in ground effect with the gear down, would one really hang it on prop to see Vz>0 before pulling Gear Up?
I understand risks of hitting ground again with gear up but that comes specifically from gear down drag and early pull to achieve Vz >0 at slow speeds? that surely would never be the case if one keeps Vz=0 and gear up until they hit VNE…
Just a guess… this SOP callout stems from the airlines and these are predominantly IFR, so the check values are derived from instruments as well.
One operator mandated double digit increasing radar altimeter reading as „positive rate“.
I assume that is a clear indicator that you DO have excess power to climb, an objective one.
I don’t mind how you determine “positive rate”, I just want you thinking about it, and not retracting the gear at seemingly the first time the weight is off the wheels. There are very few circumstances where there is a desperate need to have the wheels up right away, so pause, confirm the airplane is actually climbing, then retract. This is particularly important for night and instrument departures, where the visual cues may be less. Some airplanes lose a little climb when the gear is selected up (Cessna 310 and 337, for example) as gear doors open to admit the retracting gear, and add drag while the gear is in transit.
It’s not about focusing on the VSI to confirm positive rate before reaching for the round knob, it’s about thinking about what you’re doing, and not rushing it.
In my case, I sometimes like to accelerate in ground effect at 2ft height before climbing out. A couple of times I barely touched the runway after t/o which was a non-event…because the gear was down.
For our type this criteria it is not very meaningful anyway as a climb above 50ft obstacle clearance height is required before gear retraction . Furthermore, I like to reduce power after t/o typically 400ft AGL before retracting the gear to preserve gear door integrity. Both items are type-specific (*), the latter of my own construction after all of the Cessna 210’s I sampled over the years had cracked main gear doors. After our doors were repaired and using these procedures as well as deliberately low gear-op speeds we have never had an issue with gear doors again.
Pre-1979 Cessna 210’s had fully enclosing main gear doors, which are sequenced open before gear retraction and extension. Typical max gear-op speed in such configuration is 140KIAS, but I normally use 115KIAS. Gear-extended speed limit is same as Vne.
Make sense that it is not about VSI reading of Vz>0, it’s more about knowing what you are doing, also interesting to know that gear retraction creates temporary drag while in transit
If one is picky on vario use at least one needs a “total energy vario” in case of slowing down after rotation, getting hit by gusts or to exaggerate a bit: make sure one is actually climbing off the ground rather than mean sea level an uphill runway takeoff, at least the radio altimeter gets one xxft agl>0…
For excess power when one is underpowered, it’s all about removing drag: clean flap/gear config & level acceleration to low drag speeds, I had the impression gears go into the wells ASAP irrespective of the vario: this is the case for high density takeoff in SEP, you will have to accelerate in ground effect to very high Vx=Vy values, this may need gear up and sometimes literally there is no way to get Vz>0 before that without 3000m runway, the same for MEP with engine failure after Vr rotation or low go-around on one engine with landing flaps & gear down, there is no “vario check”, you have 20ms to clean the drag mess or it’s the ground or Vmca !
On Mooney, the gear is not draggy and one can climb with it to 12kft (got it stuck once) or even don’t notice it’s down (I have been there ), on Arrow one surely needs the gear up
Some airplanes lose a little climb when the gear is selected up (Cessna 310 and 337, for example)
Not only these ones, all Cessna RGs lose some climb during the retract procedure. Reason being that the wheels turn into the slipstream, thus acting as air brakes for a few seconds. It’s normally not noticeable, but if you’re heavy, hot and high….
The VSI on most light aircraft is not an “IVSI” with an instantaneous reading as the airliners have. I think it’s a bit of a useless indicator because of the large lag in its needle movement.
When I depart from some runways that are not that level, the VSI is still indicating a descent when I’m clearly climbing. The altimeter is a better indicator (together with looking out obviously).
Primarily I think it has to do with being in a stabilized climb before getting the gear up.