SkyWriter
Chartered Club #970
Skymasters R/C Club Newsletter
- January 2000
See Skymasters on the Web at www.geocities.com/~skymasters
The "Super" Slow-Poke
as built and flown by Terry Overton(Over 50 Sloe Poke kits were handed out at our Christmas Party. Terry Overton has already put one together and provided the following for the benefit of those building one. Thanks Terry! Ed.)
The Great Planes SLOWPOKE goes together pretty easily with only one or two minor glitches in the instructions which I have listed. I really don't know why Great Planes put this kit out in 3-channel form without ailerons since with modern radios and lightweight servos ailerons can be added with very little weight penalty. The improvement in control response and much increased range of aerobatic potential which the addition of ailerons provide is well worth while.
I decided to build my first version of the SlowPoke pretty much as per plans with the addition of ailerons and a few minor modifications to the structure. (The ailerons measure 22.25 sq.ins each to comply with the 45 sq.ins. rule) I used Bob Smith's CA glues for all joints. The front end was coated with epoxy for fuel proofing.
Construction Notes
Going through the manual here are the notes I made on the way:-
Page 8 - build the rudder You need to cut a notch in the L.E. for the elevator joiner. I added another piece of 3/16 X 3/8 balsa behind the rudder L.E. to provide reinforcement at the notch.
Page 10 - Before assembling the wing, drill or punch holes for the aileron servo leads. I used a mini servo in each wing and installed plastic tubes to feed the servo leads to the center of the wing.
Page 12 (a minor point) I prefer to drill the landing gear blocks at this stage before adding the sheeting. Follow the instructions and you run the risk of drilling through the top sheeting.
Page 15 item 26 position of wing tip. The front edge of the die-cut wing tip should not be further back than the rear face of the sub leading edge, otherwise when you sand the leading edge to profile you will end up with a hole in the leading edge! (guess how I found that out)
item 27 - Tip Braces I replaced the 1/8" braces supplied with Ό" , the 1/8 just looked too flimsy. I also added some balsa fillers to the front of the die cut tips to blend the transition between the tip and the L.E.
Page 17 - Item 2 fuselage doublers. In my kit the doublers did not match the fuse sides well and needed trimming. It is important that they match where the formers slot into the fuse sides.
Page 18 item 12 Servo tray check cut-outs for actual servos to be used, it is easier to do it now before installing the tray. I did not like the arrangement shown on the plan and so I cut away the ply between the rudder and elevator servo slots to form one wide slot which accepted all three servos.
Item 16 Before drilling holes on the punch marks check for the correct location against the actual servos to be used. I used Hitec 425 servos and the holes were too near the servo tray for correct alignment of the pushrods.
Item 17 The photo labels are incorrect former F4B is actually F3 and former F5 is shown the wrong way round.
Item 19 I added 2 cross braces from 3/16" square to the fuse bottom to stiffen the 1/16" balsa.
Item 20 In my kit, the former F1 was narrower than shown on the plans, but I used it as it was anyway.
Item 21 CHECK the size of the slot in F2 for the wing 'dowel' and trim as necessary for a neat fit before installing F2.
Page 19 item 3. A personal choice this, but with such a short fuselage the method of wing alignment shown does not work too well. I used a rafter square along the center line of the fuse and the wing spar.
My Modifications
Wing Center Section
I sheeted the whole center section (i.e. between dihedral breaks) from the Leading Edge to the MAIN spar. This produces a very rigid structure by creating a "D" tube with the spar webbing.
Dihedral breaks
I epoxied 2 oz. fiber glass tapes at the joints, since they would be stressed more than the original with the installation of ailerons.
Stabilizer Incidence
The plan has the stab set parallel to the flat bottom of the wing. This in effect gives the wing with a flat bottom airfoil positive incidence. This may be OK for a lower powered version, (.10 to .15), but for a .25 powered model I felt would produce some undesirable effects. I therefore increased the incidence of the stab by packing up the leading edge by 3mm (1/8" in Stone Age measurements) When measured with a Robart incidence meter I then had both wing and stab at +2 degrees. This should improve pitch stability and allow greater forward speed for better penetration and controlability in windy conditions.
Ailerons
I decided to angle the hinge line both for appearance and to maximise the control effect by placing as much of the allowed aileron area as possible towards the wing tip.
After completing the wing construction as per plan, I marked out the ailerons and adjusted the hinge line to get a total area of just under 45 sq. ins. Of course I could have generated a sophisticated computer math program to calculate this but instead I traced the wing tip outline onto squared paper and then counted the number of squares within the proposed aileron outline! (Yes, Darryl, I have the copies!)
I then marked lines on the wing tip trailing edge 7mm in front of and behind the hinge line, and cut right through the T.E. on these lines. Next, strips of 6mm balsa (actually Ό") sheet were glued to the trailing edge of the wing tip and the front of the ailerons. The L.E. of the ailerons were bevelled above and below the hinge line which was set 2 mm below the top surface.
!/4" servo rails were installed between the first 2 ribs of the wing tips to suit my mini servos, and 1/16" sheeting with slots for the servos added to that bay. The servos are installed up-right in the wing and just drop through the slot onto the rails. The bottom sheeting of the aileron was cut out and the Ό" L.E. rebated to accept a 1/8" birch ply horn mounting plate. Goldberg ½ A horns were used with 3/8" #2 screws into the ply plate.
The servo arms were angled about 30 deg forward (with the servo and aileron at neutral) to provide about 50% differential between up and down aileron movement. Because the wing tip section is very thin at the trailing edge tip I used CA hinges. (I normally prefer the pin type)
The Slowpoke was covered with 21st (will it be called 22nd next week?) Century fabric as I had enough left over from previous models. Although it is not as easy to work with as my favourite iron-on, Ultra-coat, I do like the finished effect.
Just one point if you use this material, you have to work more slowly and allow time for the heat to penetrate through the fabric to ensure good adhesion. Do not use a higher iron temperature than specified or you will damage the painted surface.
Power
I used the OS 25 LA with the stock muffler, straight out of the box. Tank is a 6 oz. Dubro which fits nicely in the available space. Prop is a 10 X 4 APC and after the first flights I feel that is a good choice. I would of course have preferred a 4-stroke, but at $40 the OS25 was too good a deal to turn down!
C of G location.
My plane weighed in at 3# 12 oz dry with a standard 600 mAh battery (located as far forward as possible, under the tank), standard Rx, 2 standard BB servos and 3 mini servos (Kyosho, now obsolete but about 0.8 oz each)
The C of G came out about 3/4" behind the plan location. However, it seemed to me that the location given on the plan was too far forward, at least for an experienced pilot, so I compromised and installed a Heavy Hub for the prop nut, Which moved the C of G about 3/8" forward, but still about 3/8" behind the plan location.
Control surface settings
As usual I ignored any advise given in the manual and set elevator and rudder deflections to my normal sport settings with lots of movement. (I set my rate controls to 50% just in case) I suspected that elevator control might be a bit on the sensitive side with that very short coupling, so I also dialled in 20% exponential.
Flight Performance
First flight was at the "Crazy Snow-fly" event on Dec 31.
The tank was filled with YS 20/20 fuel and the 25 started easily for the first time. The needle was tweeked, idle point adjusted on the transmitter (JR 1083) and the SlowPoke carried out to the runway.
Take off was easy, the 25 has plenty of power for this plane, in fact she will go vertical from level flight for quite a while!
I found I was having to hold the nose up so some up trim was dialled in and then I was able to try a few basic aerobatics.
Roll rate was reasonable and response to all controls was good. The model was surprizingly fast at full throttle but could be slowed down to a walking pace at low throttle. At idle and full up elevator, the plane refused to stall, with the tail waggling up and downas the plane descends slowly almost hovering in the light breeze.
Full control was available at speed without ailerons, just steering it around on rudder. In mode one you have to do it all just with the left thumb. I am extremely right handed so my rudder only circuits were not very precise! When slowed right down, I found myself steering with co-ordinated rudder and aileron which gave positive control down to stall speed, which is really slow!
Knife edge or side slip required full oposite aileron and just a dab of rudder, which was to be expected with that amount of dihedral.
Inverted flight was a surprise, the SlowPoke required very little down elevator to maintain level inverted. A spectator asked if it would do an inverted loop, so I did one, from straight and level inverted, easy!
An avalanche was also possible and almost a Lomcevak! Spins were fairly slow with instant recovery as soon as the controls were neutralised. Climbing flat spins however will be left to the "Pink Lady" (MorrisTop Cap)!
The next day, Jan 1 2000, I replaced the heavy hub with a Dubro Spinner nut which looked neat in anodised blue to match the engine and covering (almost). This moved the Cof G back again. The two flights I had this day were OK, with perhaps a slight increase in aerobatic potential with no adverse effects, although the gusty wind made fair comparison difficult. The stall was still almost non-existent and on ocassion the plane appeared to be flying backwards in the wind. The gusty wind with a lot of turbulence near the ground made each landing tricky, although rivalling Matt's helicopter landings for vertical descent. The roll out after touch down into wind was measurable in millimeters!
Conclusions
The SlowPoke turned out to be a much better flyer than I had expected!
The OS25 LA performed flawlessly right out of the box with lots of power and a good reliable idle.
I would strongly recommend anyone building a SlowPoke to install ailerons.
The C of G position shown on the plan is too far forward unless all you want to do is chug sedately around the sky in calm weather! Maybe that is what the Slowpoke was intended to do, but believe me, it is capable of much more!
I think that if it can be built to around 3#, which is possible if the heavy wood in the kit is replaced with selected light balsa, light weight radio gear and a light weight covering is used, the SlowPoke could really perform like a fun-fly with unlimited pure vertical on the 25 LA, while still retaining the super slow stable flight for those balmy summer evenings!
The SlowPoke is definitely a light wind craft, anything stronger than a gentle breeze will exercize the pilot's skill as it really gets tossed around by turbulence on the landing approach.
(Terry is continuing to experiment with CG. More to come later Ed.)