1967 vs 1968 - Max Flaps Speed Increased 20 MPH - what's different?

[furledd]

Here's one that might take a little research or history - or maybe there's a thread already on this i have not found?

 

Can a 1967 M20F be updated to allow for white arc being extended from 105 MPH CAS to 125 MPH CAS?

 

I see in 1968 for the M20F that the limitations were changed - this could come in handy at times when trying to get the speed down entering a pattern

 

Anyone know what was changed to allow this? Control rods, flap structure, hinges - spar in wing? Whos got a good Mooney engineer contact?

 

I saw this thread below but it didn't address WHY the allowed speed was increased in 1968 (manual printed in mid 1967 for 1968 models) 

 

http://mooneyspace.com/topic/8669-maximum-flap-speed-what-does-really-mean/?hl=%2Bmaximum+%2Bflaps+%2Bspeed

 

 

 

[Mooneymite]

I am no expert, but wasn't this associated with the change from hydraulic to electric flaps?

 

The electric flaps are braced against a fuselage bulkhead and don't brace on the aft spar.  I believe that the aft spar was the reason for the lower speed limitation on the hydraulic flap Mooneys.  My 74 C with electric flaps has the 125 kt limitation.

 

So, if the flaps on the 67 are braced against the aft spar, it would not be structurally prudent to go with the higher air loads of the 125 limit.

[furledd]

That's a good guess, but the 1968 Owners manual describes the manual flaps operation showing the hydraulic lever and flaps release handle, just like on the 1967 model, so that isnt the reason.

 

But you are right on one thing, in 1968 electric gear became optional, manual gear was standard,  just not any electric flaps yet...

[EDNR-Cruiser]

Hmm... - the POH of my '67 M20F (which actually flew in 1966 for the first time) already describes (optional) electric gear and it seems as if mine left Kerrville equipped with the electric gear in November 1966.

[Marauder]

I am no expert, but wasn't this associated with the change from hydraulic to electric flaps?

The electric flaps are braced against a fuselage bulkhead and don't brace on the aft spar. I believe that the aft spar was the reason for the lower speed limitation on the hydraulic flap Mooneys. My 74 C with electric flaps has the 125 kt limitation.

So, if the flaps on the 67 are braced against the aft spar, it would not be structurally prudent to go with the higher air loads of the 125 limit.

Interesting. My VFe is 109 KIAS. Wonder what changed between 1974 and 1975. My electric great has a 104 KIAS VLe/VLo.

[Mooneymite]

No clue, unless there was a difference in the way the flap drive is braced.

 

My 74 C electric gear has a 120 gear speed/125 electric flap speed.

 

As a matter of operation, I try not to operate either near the max, but that's what the POH says and that's how the IAS indicator is marked.

 

Of course a C that is as fast and efficient as mine   really needs those higher speeds to fit in with the slower Mooneys.  

[Marauder]

No clue.

My 74 C electric gear has a 120 gear speed/125 electric flap speed.

As a matter of operation, I try not to operate either near the max, but that's what the POH says and that's how the IAS indicator is marked.

Of course a C that is as fast and efficient as mine really needs those higher speeds to fit in with the slower Mooneys.

My POH is written in both knots and mph. I think the numbers you are writing are MPH. They match mine in knots.

[Marauder]

I know why they used MPH in the older models but it leads to a lot of confusion especially if you are flying in the system. One of the reasons I had all my gauges including the Aspens converted to knots.

[Mooneymite]

My POH is written in both knots and mph. I think the numbers you are writing are MPH. They match mine in knots.

 

Correct.

 

My POH references MPH, but my AS indicator displays both.

 

I'm used to always using KTS, so MPH seems strange in the aviaiton world.

[furledd]

This thread somehow got going down the road of landing gear discussion?

 

LOL we digress...

 

Regarding the max flaps speed question,

 

I brought up both PDF's of the Owners manuals for 1967 and 1968 M20F and made sure speeds and units were apples to apples

 

It shows 

 

Max flaps operating speed =

105 MPH CAS (1967)

125 MPH CAS (1968)

 

See pdf snagits attached 

 

All other significant speeds are identical between the 2 years.

[Mooneymite]

And I think the answer may revolve around the issue of how the flap actuator (be it electric, or hydraulic) is braced on a particular model.  I can tell you for sure my 125 mph flap actuator is not braced on the aft (stub) spar.  My neighbor's Mooney with hydraulic flaps had the lower flap speed limitation and that actuator pushed against that aft spar.

 

The cracking of the aft stub spar is (I believe) at least partially due to over-speeding the flaps on those models where the actuator is braced on the aft spar since this doesn't seem to affect the electric flap models.

 

No clue what other issues may be involved.

 

Someone who works on the various models and knows the various iterations of flap actuators/attach points could give us a more definitive answer, but it is probably more than just a paperwork change to the flap speeds.

 

Where is Don Maxwell when you need him!?

[treebobboy]

My 68G is manual flaps and manual gear.  Speed for lowering flaps is 125 according to my book.

[furledd]

Interesting info Treebobboy

 

So in 1968 something definitely changed as you can lower manual flaps at 125 MPH in more than 1 model Mooney, not just the M20F. 

[furledd]

Checked my 1967 ASI and indeed, it's confirming 105 MPH as max flaps speed (Attached)

 

Seems to eliminate a book misprint as the reason for the difference

 

So, the mystery of what changed to allow a 20 MPH increase on Manual Flaps in 1968 remains unsolved, and if whatever changed can be applied to the older models as an update.

 

[StinkBug]

Just looked through some photos and it appears that the ASI on my 68C also shows 125 for the white arc.

 

 

[Tmack1]

i have a 68 F model flaps are hydraulic and flap speed is 125mph electric gear converted by mooney in 69 gear speed 120 as far as i have dug into it electric flaps were not avalible till later models

[bonal]

Perhaps one might consider a different approach to the question and see if the difference is a result of different supplies of airspeed indicators and there really is no difference in the flaps but in which indicator happend to get installed in the airplane. Seems like the flaps are either manualor electric but some are 125 or 105 or 100 and there seems to be inconsistency to the type of operations. I have however seen lots of different style of indicators.

[1964-M20E]

My 67F shows 105mph and my former 64E showed 100mph. I have learned to manage my energy and sped to work within the POH.

[mooniac15u]

The service bulletin for the rear spar center splice (SB20-217) looks like it includes 1968 models of C, F, and G based upon the listed serial numbers.

[garysuperpilot]

My 67 F model has electric gear and hydraulic flaps. POH call for 120 on gear extension and 105 mph for flaps. I always drop gear first and by the time its down I slow pretty quickly and can put in the flaps almost immediately anyway.

[Andy95W]

The service bulletin for the rear spar center splice (SB20-217) looks like it includes 1968 models of C, F, and G based upon the listed serial numbers.

I found the same thing. Also, the Type Certificate Data Sheet shows all 1968 models with 125 mph flap speeds. Weird.

Somebody should ask Bill Wheat if he remembers what, if anything, changed.

[N601RX]

I believe I've heard that there was some differences in the hinges and possibly the attach points.  If someone has a later model parts manual they could check the pn of these and see.

[furledd]

On the 105 vs 100 mph difference - I was told once when i had my ASI overhauled there was a face screening mistake on some indicators in the past on that. That may be the 105 vs 100 difference.

 

But the actual changes that allowed for flap deployment at 125 vs 105 starting in 1968 vs 1967 it seems for both manual and electric flaps must be tied to a change somewhere in the wing?  I know the twisted wing was in 1967 and it was eliminated in 1968 as i recall - could they have beefed up some parts at the same time?

 

Whos calling Don Maxwell on this??  

[Andy95W]

I know the twisted wing was in 1967 and it was eliminated in 1968 as i recall - could they have beefed up some parts at the same time?

Hmm... That's an interesting point. It wasn't just the F model, but ALL the models were bumped up to 125 mph- they must've learned something from that twist wing and applied it to the standard wing, and given the F model that.

[furledd]

Well, I emailed Russell at SWTA for his opinion, here what i got - i think Member Mooneymite was the closest on track for this answer:

(At least 1 member says electric flaps was an option before 1969 just apparently not a FACTORY installed option) 

 

Electric flaps were not available until the 1969 models. Mooney did have a kit (p/n: 940001-501 & -503) that allowed the installation of electric flaps to be installed on 1962-1968 models. This kit was not produced until the mid 1970's.

The higher flap speed was mostly due to the heaver rear spar center splice that came installed on the 1969 and later model Mooney's. The 1968 and earlier M20's had problems with the rear spar cracking where the flap torque tube attached to it (See Mooney Service Bulletin M20-217). This cracking problem was caused by flap extension at excessive speeds, and from stepping on the flap when getting on or off the wing. Lowering the flaps at a higher than recommended speed will cause cracking of the rear spar center splice which is EXPENSIVE to repair / replace.
 

Heres the SB link
http://www.mooney.com/wp-content/uploads/2014/03/sbm20-2171.pdf

 

Next question is , once you do this SB, does the reinforcement let you lower the flaps at a higher speed i wonder?

Doesnt say so in the SB so guessing not.