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Restoring a Hobby King Slow Stick

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Simon Chaddock21/08/2015 23:03:09
5715 forum posts
3034 photos

I recently acquired a HK Slow Stick that had seen better days.

Actually the foam bits (wings and tail feathers) were in surprisingly good condition as was the CF fuselage 'stick' but the same could not be said for much of the rest.

The combined U/C and front wing mount was broken.

UC & Wing mount

And the motor mount was rather bent!

Motor mount bent

And only half a 10x4.7 prop.

The electrics were just as bad. Neither the ESC or the rx worked and the rudder servo behaved erratically but on the plus side the other 3 servos and the motor did work.

I am quite impressed by the quality of the foam flying surfaces. The wing has a fairly thin slightly under cambered section with carbon rod reinforcment.

The fin and tail are also a 'proper' symmetrical section, reinforced and quite thin.

The main undercarriage is very stout, 1/8" piano wire, which probably explains why its mounting broke!

Having said all that much of it other features seem to me to be specifically designed to create drag and add weight! wink 2

However before 'improving' anything my intention is to restore it to its 'original' condition and to fly it enough to get a good Idea of how it performs.

The HK site does have a downloadable set of instructions so the restoration can begin.

First the motor mount is carefully bent back.

Motor mount unbent

Seems to be ok but it is probably a bit weaker. This is not the original motor mount which is plastic but, surprise surprise, is out of stock!

Interesting the original GWS slow stick (for which motor mounts are readily available) however it uses a 10x10mm stick where as the HK version is 11x11!

The front wing mount was repaired with CF tow and epoxy.

CF tow and epoxy That is the easy 'mechanical' repairs but what about those electronics?

John Olsen 122/08/2015 02:51:34
446 forum posts
23 photos

I have one of these. It flies quite well although it prefers really calm conditions. Would be fun indoors in a large enough hall. I don't think the electronics would be that critical so you should be able to find something cheap that will do.

Mine has been known to drop the undercarriage out in flight, but it flew fine without it. It just relies on the spring of the wire gripping in the slot. I found that I could only easily get a slightly bigger battery than specified, but that worked out fine since the battery is well forward to get the right CoG lead needed.


GONZO22/08/2015 09:51:53
1371 forum posts
14 photos

Got the original GWS item now up rated with brushless power, infact too much power. Take off is with zero roll and it will climb vertical OOS. But, has a very great reluctance to turn right even with a significant amount of right thrust applied by the crude method of bending the front of the aluminium fuselage. Not touched it for ages, perhaps I'll give it a look.

Simon Chaddock22/08/2015 18:07:54
5715 forum posts
3034 photos

To my surprise the ESC, radio and the errant servo did eventually work. The problem was moisture under the shrink wrap of the ESC and radio. Once it was removed and blown dry with a hair dryer they worked fine.

The same treatment on the disassembled the servo cured that as well.

A new prop and a 2200mAh 2s battery for its maiden.

A bit nose heavy - no bad thing for a maiden - but perfectly controllable.

The biggest issue is the rather high drag airframe and the fine pitch prop. Plenty of low speed thrust but huge 'windmill drag' when power off but just cruising slowly about its fine!

Simon Chaddock28/08/2015 22:36:15
5715 forum posts
3034 photos

Now comes the "lets see if we can make it better" bit.

The moulded hinges really are pretty stiff. This gives an idea of the problem.

An aileron with a modest 30 degrees static deflection.

Stiff hinge 1

But it takes a substantial force on the push rod to achieve it

Stiff hinge 2

150 g lump of lead!

And that's before any aerodynamic load is added.

Whilst this is not beyond the capability of a 9g servo it is putting an unnecessary load on the gears and linkage. It also increases the current draw.

On the other hand with a simple top tape hinge the aileron deflects to 75 degrees just under it own weight! wink 2

Free hinge

The elevator and rudder are similar but the hinge is moulded on the centre line so little Barbi hinges will be used instead.

Barbi hinge

With truly free moving surfaces I am happy to use tiny 3.7g micro servos. Indeed I have used them on heavier and faster flying planes than the Slow Stick!

Edited By Simon Chaddock on 28/08/2015 22:38:32

GONZO29/08/2015 09:02:11
1371 forum posts
14 photos

WOW! A box wood 'Crown Stationary Office' ruler with imperial measurements and twelfths of an inch. Now that must be a collectors itemwink

Simon Chaddock29/08/2015 11:01:57
5715 forum posts
3034 photos


Yes very imperial!

Twelfths and Sixteenths on the front with tenths and metric firmly relegated to the back! wink 2

Simon Chaddock05/09/2015 22:09:44
5715 forum posts
3034 photos

The elevator and rudder now using the Barbi hinnges and 3.7g micro servos buried in the fin and tailplane.

The long heavy steel push rods and guides are no longer required. Overall this change alone has saved just over 40g and reduced the drag as well.
Simon Chaddock06/09/2015 20:15:28
5715 forum posts
3034 photos

To make use of the now low(er) drag airframe the prop was changed from 10x4.7 to a 9x6. The loss in static thrust from this is more than compensated for by the 2oz reduction in the all up weight with the result there is no loss in take off performance.

On the other hand the coarser pitch means its 'penetration' speed is significantly improved and with the ESC brake 'on' it is actually capable of a glide loop. Something that was completely beyond its capabilities in its original specification.

However all was not perfect. It required no less than 5 'up' elevator clicks to maintain level flight. For some reason the radio lost contact (I had flown it much further away previously) and it went to 'fail safe'. This of course did not include the 5 up elevator clicks so the ground intervened before the connection was regained (Spekky is notoriously slow!) wink 2

The motor was pushed back on the stick, although it was not bent.

Motor pushed back

The prop broken of course!

As the wing slewed round on its mounts the rubber bands damaged the trailing edge.


Rather more serious was the substantial impact stripped the gears on the elevator and one aileron servo.sad

Whilst waiting for replacements I started to improve the streamlining of the motor/ESC/battery 'lump'.

A new lighter motor mount placed the motor directly in line with the stick.

New mount

The battery and ESC are only a couple of mm wider than the motor although the battery is quite a bit deeper.

Motor front

Requiring a simple Depron fairing.

Battery/ESC fairing

The motor/battery/ESC fairing complete.

Motor fairing complete

It is supposed to be fairly calm tomorrow! wink 2

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