Why the difference in Vfe?

[nulloranje]

I'm curious why the airspeed limits for my '62 M20C are different from the later models.  From the TCDS, it appears that Vfe is higher by 25 mph.

Was there a structural change to the airframe that allows for this, or was it a paperwork exercise?

[hammdo]

Electric probably. Mine had to have a doubler installed due to cracks - I’m hydraulic flaps. That was probably changed when electrical flaps came out…

-Don

[kortopates]

I recall it being stronger cowling able to better handle the air loads. don't recall details though.

[ArtVandelay]

May have to do with gear doors (strength/design).

[Hank]

@nulloranje, flaps went electric, and they attach to the wing differently. Your hydraulic flaps will damage the stub spar that they are mounted to if you overspeed them many times, but doing so with my electric flaps has other, different unhappy results.

[nulloranje]

1 hour ago, Hank said:

@nulloranje, flaps went electric, and they attach to the wing differently. Your hydraulic flaps will damage the stub spar that they are mounted to if you overspeed them many times, but doing so with my electric flaps has other, different unhappy results.

That's exactly the answer I was looking for.  Thanks @Hank!

[Ragsf15e]

3 hours ago, Hank said:

@nulloranje, flaps went electric, and they attach to the wing differently. Your hydraulic flaps will damage the stub spar that they are mounted to if you overspeed them many times, but doing so with my electric flaps has other, different unhappy results.

I’m not sure that’s correct.  I have a 68 F with hydraulic flaps and it has 125mph Vfe.  I don’t know why it changed, but it doesn’t seem to be hydraulic to electric flaps causing the change.

[carusoam]

1 hour ago, nulloranje said:

That's exactly the answer I was looking for.  Thanks @Hank!

 Hank covered it well…

but there are pics around here… showing exactly where the cracks form in the stub spar….

We can’t typically use electric vs. hydraulic as a gauge… the actuator didn’t change the stub spar physics…

We can check what the physical changes are in the newer birds…

 

Just know the forces grow… squared with speed…

If you have ever lowered or raised gear manually at higher speeds… you can imagine the bending forces of the flaps at higher speeds as well…

Stay within the documented speeds for best results….  

PP thoughts only, not a CFII…

Best regards,

-a-

[nulloranje]

23 minutes ago, carusoam said:

Stay within the documented speeds for best results….  

Not looking to do anything differently.  I've just been curious about the delta.

[carusoam]

39 minutes ago, nulloranje said:

Not looking to do anything differently.  I've just been curious about the delta.

M20s have evolved every year since 1958….

Some of the evolutions are pretty small… others are gigantic… a few serious ones are noted on the ASI…

One remarkable change to the M20J line… was a tube dimension that allowed for greater MGTW…

Some planes got it, while the older ones did not…

MGTW, Vge, Vfe, Vna, and Vne all increased over time….

for the increase in Vfe… expect the stub spar grew in strength… or the hardware for mounting flaps was changed…

 

Many of the updates are available… for a price…

An M20F can be upgraded until it performs similar to the latest M20J that left the factory…

This is great if you have an M20F forever-plane… where the finances no longer have to make sense…

Realistically, it is more economical to change planes… 

There are a few Mooneys flying around on newer wings…

 

If you find that you have spar cracks at the flap mount bolts… there is a proven maintenance procedure to fix them…. That includes a doubler.

 

Keep asking questions!!!

About me… My first Mooney was an M20C… after a decade of ownership, my plane needed some serious updates…

Comparing the costs of upgrades, to the pre-flown market of other Mooneys…. We started looking at M20Js, and came away with a pre-flown M20R…  the economy had them priced the same at the time… (2008) 

PP thoughts only, not a mechanic…

Best regards,

-a-

[47U]

9 hours ago, nulloranje said:

From the TCDS, it appears that Vfe is higher by 25 mph

Without access to the blue line drawings, my speculation is that once Mooney became aware the stub spars were developing cracks at the flap actuator torque tube attachment bracket, they elected to increase the thickness of the stub spar  and gave it a new part number to delineate.  The increased thickness also allowed an increase to the Vfe speed, irrespective to hydraulic or electric flaps.  

Interesting that Mooney didn’t provide for increasing the Vfe on those early airframes after accomplishment of the stub spar beef-up service bulletin.  Perhaps they thought increasing the Vfe would transfer the load to the next weakest point in the structure… regardless, the Vfe on my ‘63 C is still 100 mph.  Which isn’t necessarily a bad thing, I can’t get to Vfe without first extending the landing gear.  Complacency be damned.  I strive to follow the before-landing checklist.

[AIREMATT]

2 hours ago, Ragsf15e said:

I’m not sure that’s correct.  I have a 68 F with hydraulic flaps and it has 125mph Vfe.  I don’t know why it changed, but it doesn’t seem to be hydraulic to electric flaps causing the change.

1968 and later seems to be the increase to 125mph Vfe. My 1967 C has 100mph limit yet.

Maybe they reinforced the spar regardless of flap drive type that year.