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Old Aug 22, 2014, 04:11 PM
Boo
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Joined Dec 2004
162 Posts
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MK retracts question

Hi,

I'm building an Atlanta 60 and the instructions I've seen on the web say to use either MK S60 or SP types. Can anyone tell me what the difference is between the two (Sp vs S60) ?

I've looked around but I cannot find S60 retracts anywhere and the numbering system seems different for the MK retracts I can find at eg Singa Hobby where they have MK 0706 S types vs MK 0704S SP types.

Can anyone tell me which type I need for an Atlanta 60 ? Or is there a cheaper alternative that is a drop in replacement ? I've seen people recommend the Dave Brown retracts but AIUI the nose gear is bulkhead mounted so that's out...

Thanks,

Boo
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Old Aug 24, 2014, 05:15 PM
Kevin S. Gribben
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I have done a couple with spring air.......
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Old Sep 05, 2014, 02:07 AM
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United States, CA, SF
Joined Sep 2001
158 Posts
Boo,

On the MK S vs SP retracts: you can use either the S or SP for the precut rails in the wings of the Atlanta. Both will drop straight in. Golden Gate's instructions recommend S for the mains and SP for the nose.

Here's the difference if you're interested: The SP is the original standard version, the S is the newer "lightweight" (and cheaper) version.

They are actually completely different designs: SP pull to extend, while S pushes to extend. The SPs use an aluminum rail with plastic trunion body, the S uses full plastic body. S is much lower profile, making them suitable for thin wings, SPs are quite a bit taller.

In actual use, the SPs give a more solid lock and allow for some play in the pushrods while still maintaining locking integrity. The aluminum rails design gives it more room to lock/unlock. It also pulls to extend, so the rods are at tension when locked gear down, giving it strongest strength. S on the other hand have very little tolerance for play; slight play in the pushrods and the retract will tend to collapse. It pushes to extend, so locking at gear down is maintained by compression of the rods which tends to be weaker.

The downside of SPs are that even though the rails are aluminum, the plastic trunions and square bushings will wear and break over time. IMO the later Hanno designed OK / EZ Supras (not MKs) give easiest locking/setup and durability. The cheap Hobbico mechanical retracts sold by Tower Hobbies are a direct copy of the EZ Supras, just with less precision and cheaper materials. But they are not a drop in fit for the Atlanta wings which which was cutout for the MKs.

Hope that helps!
Matt
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