Fix for HK Slick 360 Wing Rock

[Steve_B]

Well someone had to be the first to post in the Hobbyking manufacturer forumopcorn:

Anyway i know there are a few people here who have the Hobbyking 51" Slick 360. Colour scheme aside (lets not go there) it's a decent enough model IMHO but it's somewhat let down by bad wing rock in upright harrier. I did a bit of head scratching and figured the cause was the leading edge shape and/or the area of the vertical stab/rudder. After some modification and flight testing I found that re-shaping the LE didn't make much, if any, difference but adding area to the rudder made a remarkable improvement to stability in harrier. For testing I just stuck lumps of foam on the rudder but I'd drawn up a plan for a new rudder that hopefully strikes a good compromise between adding adequate area and not looking too stupid.

I've attached the plan and parts sheet. the parts are intended to print and stick (using low tack spray adhesive) to balsa sheets. After cutting out the parts the paper can be removed. This works well I've used the same method on many scratch builds back in the day.

View attachment Slick 360 Rudder Plan.pdf

View attachment Slick 360 Rudder Parts.pdf

I've not yet built one myself so if anyone beats me to the build please let me know how it goes together and if you find any problems.

Steve

 

[gyro]

Well someone had to be the first to post in the Hobbyking manufacturer forumopcorn:

Anyway i know there are a few people here who have the Hobbyking 51" Slick 360. Colour scheme aside (lets not go there) it's a decent enough model IMHO but it's somewhat let down by bad wing rock in upright harrier. I did a bit of head scratching and figured the cause was the leading edge shape and/or the area of the vertical stab/rudder. After some modification and flight testing I found that re-shaping the LE didn't make much, if any, difference but adding area to the rudder made a remarkable improvement to stability in harrier. For testing I just stuck lumps of foam on the rudder but I'd drawn up a plan for a new rudder that hopefully strikes a good compromise between adding adequate area and not looking too stupid.

I've attached the plan and parts sheet. the parts are intended to print and stick (using low tack spray adhesive) to balsa sheets. After cutting out the parts the paper can be removed. This works well I've used the same method on many scratch builds back in the day.
View attachment 2750 View attachment 2751

I've not yet built one myself so if anyone beats me to the build please let me know how it goes together and if you find any problems.

Steve

Steve, as you know, I had this plane for a little while so I could compare and contrast it to some of the better manufacturers out there. I agree that the biggest issue was the instability in harrier, but I also found that it would stall asymetrically, for some reason. From my experience, the plane actually wasn't too bad for precision flying, but I can't recommend it for 3D. That said, it'd be cool if the work and effort you've put in during your spare time solved the problems with no downsides.
Funny that a RC hobbyist can fix a design flaw that a manufacturer didn't have the patience or desire to fix pre-production.

Now, how you do fix the cheap hardware that comes with the plane?

 

[Steve_B]

Cheap hardware (specifically pushrods) were fixed during the build by dropping straight in the trash where they belonged. I substituted with ball links on threaded solder adapters epoxied into carbon rods.. they have held up great.

I had a nasty wing drop a couple of times, which caused a crash once as you may recall. I think it's probably all associated with the wing rock. With the bigger rudder it's been fine, so far at least.

 

[njswede]

Now, how you do fix the cheap hardware that comes with the plane?

Well, the biggest problem was the flimsy pushrods and I fixed that by sliding a thin CF tube over them and securing it with CA. Very rigid and nice!

 

[Steve_B]

I got the new rudder built and installed. here are the 'bones' prior to covering with the original rudder for comparison:


And here it is covered and installed ready for flight testing.. i actually saved 4g whoo hoo


Flight testing tomorrow.

 

[gyro]

I'm really anxious to hear the flight report today! Awesome job on the design and build!

 

[Steve_B]

Flight tested today and i'm delighted

The big rudder works exactly as intended and has calmed down the wing rock/drop no end. It will still rock a bit if you provoke it but I've yet to find a plane that wont. No matter how hard I tried with my ham fists it's wouldn't drop a wing. Basically it's now as good as anything else I've got in my hanger for harrier'ing with the possible exception of the EF Edge, but there isn't much in it. I even managed a few tail touches and the rudder stood up ok.

It doesn't seem to have had any adverse effect on any other aspect of flight though my pop tops were sucking today but that's more than likely just me, not the plane because they were equally bad with my other models

Video uploading now...

Steve

 

[Steve_B]

here's the video.. bear in mind my 3D sucks
[video=youtube;7V0sSuufrlQ]http://www.youtube.com/watch?v=7V0sSuufrlQ[/video]

 

[njswede]

Wow! Quite a difference! I have to ask the question on everyone's mind: How does it compare to the AJ? Obviously, it seems easier to just buy the AJ, but your work is really interesting nonetheless!

 

[Steve_B]

Wow! Quite a difference! I have to ask the question on everyone's mind: How does it compare to the AJ? Obviously, it seems easier to just buy the AJ, but your work is really interesting nonetheless!

NJ,
Unfortunately I cracked the carbon landing gear on my AJ Slick so it's in the hanger waiting for the spare to arrive (one of the problems buying a plane that's not stocked in the UK). So I haven't had the opportunity to fly them both back to back in the same conditions. Also when I have flown the AJ I've been unlucky with weather, it's always been blustery. That said I've formed a few impressions and I've got to say that at my skill level, now the HK Slick has the wing rock fixed then there really is very little in it. The HK version is a few ounces lighter but the AJ has a little more wing area, they fly like they are very close in terms of speed and 'floatiness' the HK maybe feeling just a tiny shade lighter in flight but that is probably build spec dependant.
The HK version has noticeably more KE coupling than the AJ, but once that's mixed out at the Tx then if anything I think the HK is a little more forgiving in KE, I've never had it snap out of KE like the AJ will do if provoked.
With the new rudder I don't think there is much in upright harrier stability, in fact I'm now more confident with the HK version but that's probably just because I've flown it more and I'm much less concerned about crashing it.
They both do stick banging manoeuvres great. They both have very powerful control authority in all axis. Precision also seems pretty close at my skill level, both are excellent though I think the AJ may have the edge on precision if I was good enough to exploit it.

I really like both models but bear in mind that my HK Slick is now quite heavily modified. it's got:

• Shortened motor box to open up motor choice
• Fuselage stiffened with four full length carbon rod longerons
• Rear servo mounting stiffened
• Re-profiled leading edge on wing (to try to stop wing rock/drop)
• Bigger rudder

The rudder is the mod that has far and away the biggest impact on flight. 'Out of the box' there is no doubt that the AJ is a lot better post stall.

It's a shame that HK didn't do a bit more flight testing to sort out the little bugs (and provide better pushrods). They could have had a genuine top notch 3D model on their hands.

Steve