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Hawk Spark F5j build log


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Not done any posts for a while as so busy with things sorry. A lot of the time has been spent putting models together for people - yes Flightech now offers a build service £100 inc. frames for wings and £150 inc frames for complete models. And it is proving popular with customers with a fair few models put together for people by me but  I have now enlisted two very trusted and high quality experienced builders to help ease the workload and more importantly improve delivery times on builds.

With a couple of the beautiful new 3.98m Hawk Sparks already sold and out there, this was the first time I was asked to put one together for someone. This time just the wings which suited me fine because the fuselage looks straightforward and a lot easier than the likes of Prestige, Eternity etc but I was keen to see how the unique Hawk factory installed IDS system was to fit out and how it works in practice. With thanks to Keith Fisher however, who has put together a Hawk for himself I can share some installation pics of a completed fuselage to give you an idea..

Okay then we'll start on the fuselage. The Hawk fuselage leaves you very little to do. The rudder comes pre-fitted with a metal horn that engages into an L-bend made in the pushrod. So nothing to do to on the rudder. The elevator comes with a small piano wire horn that engages into a tube already installed for the elevator pushrod so nothing to do on the elevator either. The wiring loom and wing-fuse plugs are already made up and installed at the factory so no wiring loom to do either..




The Hawk comes with a complete accessory pack that looks to have everything you need for the fuselage. There is a carbon servo tray and carbon motor mount included. The tray is CNC cut for 12mm servos and accepts the popular Kingmax CLS2035HHV perfectly.



Installation is nice and straightforward and very familiar and conventional. The only thing Keith notes is good planning of the servo / battery locations is essential to get the recommended CG depending on what motor and battery type you are using. As you can see the fuselage is still relatively slim but has plenty of room for the gear and a nice big canopy to help ease all the bits in and give easy access. You can see Keith has used 12mm Kingmax servos on rudder and elevator.





And so to the wings. As mentioned the Hawk comes with its own unique IDS system pre-installed. It features very nicely molded carbon pushrods terminating in a piano wire L-bend at the servo end. 


They are extremely stiff both vertically and horizontally which is of course great news. Vertically it means the large big flap control surfaces should remain firm and rigid. Horizontally it means the L-bends should never come as they feel like stiff and spring like.

So how to link up that L-bend to the servo?  Two options....

1) Use either normal servorahmen frames or the bearing frames and use conventional servo horns. Keith did this and found the aileron horns needed drilling a bit closer to the hubs to get them under the servo cover. For the flaps Keith chose to use metal control horns and these proved slightly proud of the bottom surface and needed a small blister..




2) Use a Servorahmen IDS system but modify it to accommodate the L-bend rather than the normal servorahmen IDS method. I chose this route. First job is to modify the servo arms. You need to cut the side off nearest the bearing to allow the L-bend to slide into the other side unrestricted. You also need to open up the existing 1mm holes to 1.5mm (I will double check the diameter of the piano wire as I opened up the holes with a reamer not a drill bit). You also need to modify the frames somewhat. First file some width off so they fit width wise into the servo apertures (a few millimetres needed for the recommended CLS0612W/KST X10 mini size) but servos smaller than this shouldn't need any width taking off. Then you need to cut the shelf off all 4 frames and grind off a triangular section on one side to allow it to slide under the Hawk IDS pushrods. Even smaller frames will need this modification. As they say a picture is worth a thousand words..



Whilst we are on the subject of servo horns, the usual length suspects are also used on the Hawk Spark..



So with the necessary horns and frames prepped accordingly, the installation then follows your usual preferred method. One thing I quite liked was the lengths of the Hawk pushrods. To get the frames centrally located with both lug screws easily accessable without resorting to dremelling a semi-circle out of the aperture lip it required the aileron horns to rake back one tooth. This makes the aileron linkage a bit better mechanically and gives a bit of natural differential and more unrestricted up aileron movement. Here is an aileron servo horn at neutral..



Flap horns also needed my preferred horn offset and needed raking a small amount forward towards the spar to get the frames centrally located. Certainly all good so far.

Getting the servos and frames into position seems best done by going in at and angle and getting the bearing side of the frames underneath the IDS pushrods (hence cutting off the shelf part and grinding off the triangular sections). Then lowering into position and sliding into place and linking up the L-bends into servo horns. Again picture worth a thousand words..



And once you do all this using your chosen method to bond the frames in Hey Presto..!  One pair of aileron servos in very neatly and with plenty of servo movement needed to get the required control surface movements so as to minimise slop and maximise power and resolution.



Flap servo installation notes to follow shortly.......




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Right flaps. Nothing different or special here. With IDS you are able to get enough up travel and plenty enough down travel for braking and keep the horn under the servo cover. 

It has occured to me I have been talking about the unique Hawk IDS system and not taken any pics of the control surface end so here you go..



As you can see it is a specially made carbon molding. It is about 1.5mm thick and of particular note 8mm width so hence the tight springiness of the L-bend. I would think this is done on purpose as everything i am coming across on the Hawk features a high level of attention to detail.

With regards to the frames you need to modify them exactly as per aileron ones if you use standard size 10mm aileron servos. There will be more depth to play with but there is no advantage in tweaking accordingly. 

As mentioned the flap horn has to rake towards the spar to get the correct neutral which is the correct way of doing things and again proof of the right way to do it direct from the factory. Here is a pic of the flap set at neutral and the angle of the control horn set in its bearing frame ready to slide in the servo. Slide in a servo to an IDS horn i hear?!?!  Read later and see how it is done...




Frame bonded in place and ready to install the servo. You can see in the above pic the length of the supplied Hawk pushrod arm and the required forward angle of the servorahmen servo horn to make the flap neutral. This is perfect. You can also see the frame has been left the whole length to cater for the longer Kingmax CLS0911W / KST X10 servo size servo. This is recomended for all but lighter air builds given the size of the flaps.

And with a similar installation process to the ailerons it's job done. The shorter 50mm servo leads of the Kingmax wing servos make for an easy and neat installation.



Any other useful hints and tips? Well hopefully yes...

1)  Fitting of tight Servorahmen IDS horns onto servo gears.

For Kingmax we use the same as the KST IDS mounts as they have the same diameter and tooth count. The frames fit the servo perfectly but are a tight fit on the servo horns (they are also a tight fit on the KST gears but to a slightly lesser extent). So here's a trick....use heat!  I must have passed on this on to dozens and dozens of people but don't think have ever documentated anything. 

Servorahmen stuff is made from an injection molded carbon plastic. Because of this it is light and extremely rigid which is perfect.  It has also been designed to be tight fit on the servo output gear as any advantage gained by an IDS system can be lost with needless slop. So to overcome this it is purposely a tight fit be it KST or Kingmax

So the trick is to heat the horns up before fitment. You can really heat them up quite a lot as they are pretty resistant to normal amounts of heat but what they will do is expand that tiny bit and also become a more pliable and then you will find they will notch in much better and with a bit of twist and wiggle whilst hot they will locate and push on perfectly. Once done they will then forever go on and off easily like a normal servo horn. No need for heat.

What you will also find using this technique is that the servo gears will have located much better in the horn. They will notch in and push on very positively and this will prevent any stripped IDS horns in use. Any stripping of the IDS horn in normal use can generally be put down to a horn that has been poorly located on the output gear (kind of inbetween teeth) and then forced hard into position. This can mush up the splines in the IDS horns and cause them to strip if given enough provocation.

It does take some messing about with and practice to hone the technique but you can have a play with the unused IDS horns left on the sprue. Definitely try to heat the horn rather than the servo! The more heat the better as far as the horn is concerned but do try and avoid too much heat getting to the servo.


2) Getting perfectly matched flap servo neutrals (geometrically) so the pushrods are an identical length


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  • 3 weeks later...
On 13/12/2021 at 11:21, MikevE said:

I love these kinds of detailed build logs. So useful for people building the same model.

Thanks Mike. I try and build and fly all models i sell before sale so I can pass on any helpful info to pilots or weed out any poor models or accessories which I have done. For F5j i do most of this testing  but  if I can't I put it out to very trusted pilots who I know will do it for me.

For f3f and slope models it is exactly the same principle  but with less top end competition experience on my part with these sort of models I have been working with established and notable names to help refine lay-ups etc to make sure the models available for sale are spot on and perfect for the job.




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  • 3 months later...
  • 2 weeks later...

Hawkes NOW IN STOCK if you are looking for a new model in time for this coming season 🙂

Price has gone up to £1700 (from £1650) due to increased production costs but remember all Hawkes come with with IDS already factory fitted and a very high quality set of wing and tail bags.




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