Obstacle departure configuration.

[bradp]

This came up on the Facebook group.  
 

I can’t recall and I’m sure we’ve discussed this previously, but why does the POH have the gear position “down” for an obstacle departure with the reference to 115MPH? I remember that there is a drag penalty during gear transit, but you’d think a retraction in ground effect would have a performance advantage over the gear hanging out…? 

 

POH cut and paste… :

ElectricFuelBoostmmp-ONatstartof takeoff roll.
Power - FULL TEHROTTLE AND 2700 RPM- Aircraft Attitude - WFT NOSE WHEEL AT
71MPH(62 KTS.) IAS.
Climb Speed - 76 MPH (66 KT'S. ) IAS until clear ~f obstacle, then accelerate to 105 to
                Cs 100'mS.)IAS.
landing Gear - RETRACT IN CLIMB AFTER
115 MPH (91.
  LE.
Flaps - RETRACT AFTER CLEARING
    CLEARING OBSTAG:
   &%ring OBSTACLE.
Electric Fuel Boost Pump - OFF, 

 

[carusoam]

The performance numbers are in line with the configuration…

Mooney assumes that the ordinary Mooney pilot is not a super human test pilot…

So… The procedure is easy enough to follow that any Mooney pilot can do it… and get the known performance….

 

There could be other circumstances that occur when stowing the gear… like all of the gear doors opening more into the wind prior to stowing…

 

Now…  under some circumstances…. Stowing the gear rapidly in ground effect may make sense…. Prior to climbing out…

 

Looking at it openly, the least risky way to achieve the performance numbers found in the POH… requires following the steps outlined in the POH…

 

Looking back on my manual gear days… I wanted to be above the ground before pulling and pushing on the Jbar….   There is plenty of accidental stabilizing forces given to the yoke some times while paying attention to the Jbar… anything that causes unwanted changes in attitude during the performance T/O is not going to be wanted…

Too much complexity added to the important procedure of performance T/Os….  

More complexity… equals a bigger chance of not getting the desired performance…

Just remember you may have found an improvement that YOU can use… Make sure you collect WAAS data to demonstrate your theory is correct…. Not too hard to do, just to know before you go…

 

PP thoughts only, not a CFI…

Best regards,

-a-

[carusoam]

Covering that part first…

115kias to retract gear?

If I have reached 115kias… I have already run out of useable runway…

Does sound like an extraneous data point thrown in…. 

Stand by for a good Mooney CFII to stop in…

Best regards,

-a-

[Mooney Dog]

2 hours ago, bradp said:

POH cut and paste…

Which POH?

The one for my M20E says for Vx climbs, full power gears and flaps up, 94MPH. For all take off retract the gear as soon as the airplane is airborne and under good control. 

[carusoam]

2 minutes ago, Mooney Dog said:

Which POH?

The one for my M20E says for Vx climbs, full power gears and flaps up, 94MPH. For all take off retract the gear as soon as the airplane is airborne and under good control. 

Brad is cruising around in a ‘77 M20J… 

Best regards,

-a-

[Mooney Dog]

3 minutes ago, carusoam said:

Brad is crushing around in a ‘77 M20J… 

Best regards,

-a-

Oh yeah, it does say that under our names...

 

Well going off that and the 1978 J POH I find, It says retract in climb after clearing obstacle. I dont think it means literally going to 105-115 to bring the gear up, just getting over that 50ft mark, which is going to happen rather fast anyways. 

Edited September 21, 2021 by Mooney Dog