7 January 2016 Revitalize
Adrian didn't fly the Sportster.
That model must have weighed between 100-200gm and even though it was 21", the wing loading was high and the 1/16" curved foiled balsa wing was probably not up to it because the completed wing could be twisted, so it wasn't ideal. I read recently that 'proper' foils are for low angle of attack high speed and 'curved' foils are for high angle of attack low speed. The other problem I had was the weak landing gear.
Today I noticed that the plan of Walt Mooney is actually for a 16" span. If I were to do it again, I should make the model much lighter and improve upon the landing gear, this time, with wheel pants.
For example:
Keep the model's weight to something under 40gm by using WLToys' F929 939 motor and receiver board. Use a single 2gm servo for the ailerons if 4 channel is desired.
Construct the sides from 2 or 3mm foam sheets. In this case I could use the 2mm yellow foam sheet (or keep it for future models of WWI planes?). The basic structure could be a single sheet rolled into an inverted U-trough as that seems strong enough (Farman Carte is proof) or I could construct it by gluing bottom sheets to the two sides over the plan and have the top carved from 10mm foam sheet.
If I choose to use the 10mm foam sheet for the top, I could make a long magnetic access hatch for the battery and access to the WLToys' receiver board. Previously I had glued two servos to the starboard side of the fuselage, and that resulted in inconvenience with the pin pulled out after a crash and additional weight at the nose. The cowling should just be from 10 mm foam sheet with additional foam packed to the correct level to glue the WLToys' motor.
For the wing, I could still use the curve foil but making it from 2 or 3mm foam sheet. When the whole model is lighter, the twisting should be relatively minor. If ailerons are cut out, they shall be operated by a centrally mounted 2 gm servo. Only a single servo arm will be required. The arm will protrude through to the bottom of the wing. The end of a coil of soft bead wire shall be inserted to the servo hole and bounded to the other end. A fine wire runs through the coil to link the 2 ailerons via underside surface horns. When set, add superglue!
For the wheel spats, they could be cut from the 10mm foam sheet and have the sides from plastic sheet or additional foam sheets, depending on personal whim on how much curvature is desired. The axle can just be a short length of wire that passes through the whole pant and glued at the ends of the wire before painting (marker pen of course!). Instead of using 1/16" balsa for the wheel trousers, which will be inserted into a slit in the spats, the trousers could also be made from 10mm foam together with the wheel pants. That might not look 'scale', but it would be easy to shape it to a nice fairing shape and cut accurately for mounting direct to the underside of the wing. Besides, maybe the late Mr. Mooney simplified the trousers in the interest of lightness? Working wheels may be made from 10mm foam sheet by first having an oversized piece cut out, bushing inserted perpendicularly, held fast on an electric portable drill and turned to shape with sanding blocks and such, and coloured before assembly onto the wheel spats. The landing gear of foam ought to be sufficient to for a 40gm model, alternatively, they could be made removable and knock-off-able by using 3mm magnets (still to come from Banggood) to attach them.
Pull pull for rudder with single servo arm
Pull pull are normally of two pulling strings and two opposing arms of a servo horn.
Here's an idea to use pull pull with single servo arm.
Gee Bee Model D Sportster (Days 1-9) (Retired)
Given Away, 24 May 2014
Given away to Adrian. Let's see if he comes up with anything.
Retire, 3 May 2014
The Gee Bee was flyable on a Turnigy 1811 turning a GWS 5"x3" prop. Repertoire included zooming up followed by a wingover but is apparent that vertical is lacking. The speed had to be kept up because it tip stalls rather easily. I think this was because of the high wing loading and the way I like to fly. I didn't manage to get good rolls and loops and fly at ca 75% throttle. With a 2S 500mah battery I added 5gm of weight at the nose. With a 3S 450mah, the weight was not necessary, but the motor was too hot. The landing gear I made were too weak and they were removed.
Perhaps it is the dihedral, rudder is more effective than ailerons. Or it could be the 1/16" curved balsa wings which could have flexed at speed. Overall, this model was not pleasant to fly and cannot be a "reach-to" plane.
I lost a set screw holding the Turnigy motor, and it didn't like being mounted on a single set screw. I decided I want more power, so I changed the motor with the biggest motor I can fit into the nose, an Emax 22 or 28 something, spinning 7"x4" propeller. This motor was previously used in my version of the red butterfly.
Here's a photo of my Gee Bee in my motorcycle's carrier box, together with transmitter and field box.
The Gee Bee was compact, the wings will knock off on impact as they were held in placed by a single pair of magnet. The problem with this neat idea was that when the wing pops off, and that was fairly frequent, in fact, regularly on landing, one or two of the aileron servos' plugs will pull out of the receiver, and bends the servo pins.
I had to replace a wing's aileron servo with a Turnigy 1440A from Andy after the Hitec servo turned jittery. Now I have to buy one to return Andy.
With the bigger Emax motor, the increased torque is apparent. When flying, the torque was not unmanageable, even though the 7" prop looks ridiculously large relative to the wing. The 7" prop gave more thrust and can lift the weight of the model and more. Hand launches are ok, the model will zoom (almost) straight and slightly up. Turning is hair-raising if the banking turn was tight (ca 75 degrees), I think it developed aileron reversals and I don't know which direction I should push the rudder. I only know that additional inputs usually result in a stall. My last flight ended up with the motor bashed in, rendering it stuck when it crashed head on to tarmac.
The model was not pleasant to fly, I have tried my best, destroyed a motor and so it should be retired. Seems a waste though, maybe a change to a bi-plane configuration?
Test Flying (Day 9, 18 Jan 2014)
4 test flights in blustery condition were carried out.
On the 1st flight, it was obvious that I needed more right thrust. To compensate, about 32 clicks of right aileron (Hitec Optic 6 Sport), 10 clicks of right rudder were had. I also needed about 12 clicks of up elevator.
The rudder and elevator clicks were subsequently replaced by setting physical trim.
On the 2nd flight, it snapped and the model smacked the ground at around the 1 minute mark. The black GWS propellor was bent.
A new orange GWS 5"x3" propeller was exchanged and flight resumed.
More right clicks of right rudder to reduce the clicks of aileron.
On the 3rd flight, I observed that rolls to the left was much more responsive than to the right.
The aileron and rudder compensation were conclusively too much.
On landing, the undercarriage ripped off the wing as the model trips itself over grass.
On the 4th flight, without the landing gear, it flew better but the motor was markedly louder.
I stopped flying because the wind was way too strong and blustery. It took a long time to crawl its way back upwind and was tossed about in the air.
This model needed more right thrust. It would also be better if I shall use stiffer wire for the landing gear in similar models, because the wheels were twisted out of true too easily. The single pair of magnet wing retention method works. On slightly rough landings, the wing would be twisted out of the wing saddle.
At home, I started to correct the right thrust requirement by trimming the wing mount. This is because the horizontal stabiliser was tilted left, relative to the wing. I think this caused or exacerbated the requirement for right thrust since the horizontal stabiliser was pushing the model to the port side. This is done by sanding away on the starboard side of the wing saddle and filling the gap with hot glue on the port side. The wing and tail is now, more or less aligned.
I then covered the bottom of the fuselage rear of the wing and the port wing saddle, stuck on some vinyl to simulate the cockpit access, hot-glued the landing gear in place, touch up the panther drawing (it proves that fingering the drawing can diminish the drawing even if it was drawn with permanent marker), carve and painted a pilot from blue foam. The pilot's name is Monsieur/Senora Bushelli Brou Zombini. He has bushy eyebrows and a zombie like complexion. On hindsight, I could have used a fine permanent marker sooner, the brows were painted on with a cotton bud. My colour rendition was not good, but it is original and interesting.
I didn't intend to put in right thrust at all since I had corrected the wing tilt. This changed when I noticed that the motor was loose. It was so loose that the motor could bear on the plastic cowling. On removing the cowling, I discovered 1 set screw was missing. This is probably the reason why it was noisier on the 4th flight. Since it was all opened up, it only took loosening of the top and bottom bolts and removal of the port bolt to add in one washer for right thrust. I don't have any set screw in my parts box, the motor will have to be held in placed by that 1 remaining set screw. All bolts secured, the cowl was then taped back to the fuselage.
Well, this model will take to the air again tomorrow. This build log ends.
Flight update 19 Jan 2014: several flights in blustery conditions were had. It had to fly fast, it is prone to stall a wing; not to go below this wing area or increase of wing loading. Motor was running at practically full speed; changing to a smaller prop like the GWS 4.5" might improve, also, this appears close to the limit for this model's weight and loading. I was loaned a 3S 300mah battery, with that plugged in, the motor/prop combination definitely gave more thrust and speed. Installation wise, I added 5gm weight to the battery tray. It was flown without it, but I think that little bit noseweight seems to make flying slightly easier. For this model, I had mounted the two servos for the elevator and rudder too aft. If I had mounted the rudder servo fore of the elevator servo, I wouldn't need the nose weight, and with all servos plugged in, the remaining rudder servo's lead was the shortest. It was only about 2cm remaining. The rudder servo plug came out of the receiver repeatedly after the wing was knocked off on landing. There is not enough contact surface for the hot glued undercarriage. It broke off on the 2nd landing. The 1mm wire wheel axles were definitely too weak, on the 2nd landing, the wheels were twisted and even the end that was inserted to tubes in the wing was kinked. The model climbs much better without the undercarriage.
This model is flyable, but is more difficult to handle.
Design
Walt Mooney's peanut plan is great because it is simple and Model D has captured the 'spirit' of a 1930's sportsplane; low wing, elliptical tip, longish nose, slab sided open cockpit with wind shield, turtledeck and beautiful scallop painting. It is however beyond me to make a 13" RC model, I don't have suitable motor, propeller, esc and batteries to cram into the confined spaces. Also, stick and tissue models are simple to look at but difficult to construct. I would have a daunting time cutting the numerous uprights to the right lengths and angles, and I don't even have a building board.
Using a photocopier, I enlarged Walt Mooney's plan to fit on 2 A3 paper, that turns out to be 165% of the plan, approximately 20" span (20.5" without dihedral), and set about designing my RC model. I lay a piece of tracing paper over the enlarged plan and transfer the key shape of the plane, including the painting patterns and letterings.
Wing (Day 1)
From my tracing paper plan, I transfer the patterns over to A4 paper and from that onto 1/16" balsa sheet by placing carbon paper in between the pattern and the substrate. On hind sight, I could have just traced directly from tracing paper plan to balsa.
The above photograph shows the inverted planform of the wing; the chord lines are the ribs position on the underside.
I chose to have 1/16" curved sheet balsa wing secured with ribs.To add ding-resistance to the wing's leading edge, I added a 1mm x 5mm carbon fibre strip.
To make identical ribs, I made a 2mm ply rib template. I used a pair of shears to cut the ply and then sandpapered to final shape.
I first cut the wing as a rectangular piece, wet it on the upper side to coax the curvature, then cyano'd the ribs to it (the two centre ribs are set with a 1/16" spacer and the bottom chords touches each other). The complete wing is then left to dry on a flat surface.
After the wing has dried, I cut out the tip shape. I cut through the wing at the centre including the 5mm x 1mm carbon fibre strip, and sanded the 1/16" sheet balsa back to the two centre ribs. The two wing halves was then glued the wing to the dihedral. The dihedral was lesser than the peanut plan but a bit more than what I would have liked. I think 1/32" spacer might be good enough. I taped the central joint of the wing with dry wall plastering fibreglass tape, liberally doused with thick cyanoacrylate.
Quite a lot has been achieved for a day. I will cover the wing tomorrow.
Covering (Day 2)
Precovering
I sanded the wing and used fibre filament tape across the chord of the wing/aileron. The hinge will remain even if everything else is crushed.
Scallop
The scalloped pattern was traced on to blue vinyl sticker (making sure I get a handed set) and the vinyl sticker cut out and stuck on the underlying vinyl sticker (I chose gloss white, because I don't like the 'cream' of the original which comes across as yellow-white). Then I added the starboard top letterings (I chose matt black) and the whole vinyl set was trimmed with overlapping leading edge and 90-degrees root chord and stuck on to the upper wing surfaces.
Letterings
To ensure the correct spacing of the letterings, I cut the letterings all except the top and bottom lines. Then I used stationery clear tape over the lettering and only then I cut the top and bottom lines. The stationery tape keeps the letterings in the right position and once affixed, the stationery tape peeled off. I think this is a technique used by vinyl sign writing. Much better than to position the letters individually.
To add interest, I have a set of the lettering applied over the bare balsa underside of the port wing.
Cowling (Day 3)
In a model this size (fuselage width approx. 1.5" and the motor is a turnigy 1811), I don't have sufficient space for a simpler solid balsa or blue foam cowling, so I decided to mould my own cowling.
A mould was first cut from 1" blue foam. The following photograph shows the circle the size of the spinner that I will use.
And the rough mould was then sanded. I traced the outline onto 2mm ply and make a well rounded slightly oversized cutout. This ply template is where the PVC is afixed during moulding.
Left to right: The first attempt was stretched too thin. It broke at one side. The second attempt was not fixed sufficiently, the moulded part is the thickest but has too many folds and wrinkles. The third attempt is the one at the right. I didn't manage to plunge all the way because the PVC has cooled, nonetheless the usable depth is 5/8", it is usable on the model. With this dimension, I can now proceed to build the fuselage.
On the second attempt at plunge moulding, the heat damaged the mould and charred the ply. The photograph is of my third attempt. With the moulded piece over the blue foam mould and inside the ply template, cut off line was traced around the cowlingand the centre point of the motor opening dotted.
Here's an attempt at covering the cowl with a single piece of vinyl. No reason to try it next time, too many wrinkles.
A photograph of the complete cowl with openings cut/sanded.
Tools and Equipment: Toaster oven at approximately 175 degrees celsius. Stationery staplers to pin the PVC onto the template. Ikea's cordless drill with a small drill bit and rotary sanding bit. NT cutter. Permanent marker. Ruler
Material: Blue foam for male mould; 2mm ply for template; 0.4mm PVC from Jethobby for moulding material.
Total time taken was 3 hours. This is my first successful moulding, perhaps I ought to do the wheel pants with this technique later.
Fuselage (Day 4)
From the side view of the tracing paper plan, I marked out the fuselage sides and fin/rudder onto 1/16" balsa sheetwood. To make a straight fuselage, I used a top sheet, the sides are glued on the top sheet and joined at the rear, hence the centreline on the bottom side of the top sheet. The following photograph shows a 1/4" square balsa strip (to be cyano'd on to bottom side of the top sheet), the 4" wide 1/16" balsa sheet with the pattern of fuselage sides and vertical stabiliser transferred.
The motor (not-shown) is mounted on 2mm ply and 1/4" balsa firewall. The motor assembly is to be epoxied to the two sides with approximately 2 degrees downthrust and perhaps 1 degree of right thrust. I have the wing at approximately 2 degrees incidence with the tail at 0 degree. The plastic cowl is 5/8" deep, the front face of the firewall is closer to 7/8", so I had to set back the markings accordingly.
I made three mistake when drawing up the patterns and the whole fuselage didn't line up as intended. For one, the top piece was marked off wrongly, so the stiffener position were off. This is not serious but the second mistake was with the two fuselage sides, I didn't cyano'd them in their right position, so when the wing was offered to it, I noticed the wing was skewed. The only solution was to break off the two sides from the top sheet and do it again. The third mistake was I had used the rib template to mark out the wing seat. I didn't want to make another template just for the wing seat and thought it won't make much difference. Well, my approximation of the rib template as I guided it to the sides were a bit off, resulting in a gap of approximately 1/32" and 1 cm wide when the wing was matched to the fuselage. I leave it as it is.
Then it was to epoxy the firewall, checking with the plastic cowl and discovered it might be a bit short and undersized. I will not be able to have the cowl lap the fuselage sides. However, it could be taped on flush, so it is still ok.
Then I glued on the top side two 1/16" top formers, one at the instrument panel, and the other at the backrest position. Position marked by comparing the fuselage assembly with the tracing paper plan. These were secured with gussets, I didn't want the top formers to snap when I put on the top sheeting.
I used a single piece of 1/32" balsa sheet (approximately 2" wide) for the entire top sheeting. A straight cut was introduced just behind the back rest position, the two parallel sides cyan'd on, the two tails overlapped each other and the sides. The excess was trimmed and this is where I did yet another mistake. A bit too much pressure was applied to the top sheeting and there is this "starved-horse" look in between the formers. There was also some locations where it will be sanded to nothing. My workaround is to ignore it if I can, use vinyl pieces if I can, and fill in the area with balsa if all else fails.
Some off-cuts of the 1/32" was rolled up and a 1/16" headrest former cyano'd together, then the fin position was cut out and the whole headrest fairing trimmed and positioned on to the rear turtledeck.
This photograph shows the wings, the fuselage, the headrest fairing, the tail feathers dry assembled. I used a single pair of magnet (about 1/2" discs) to mount the wings and fuselage. This is a new mounting technique I am trying. It seems strong enough, but the wings may twist slightly on the vertical-axis. Later on, a short piece of 1/16" square balsa strip ought to solve it.
Undercarriage (Day 5)
This took a couple of hours, working slow to get better accuracy and free-wheeling. The balsa piece is one of the undercarriage fairing. The fairing was made longer to cater to the dihedral of the wing. The rightmost line is where the wheel pants are to be located. The white vinyl will be stuck on to this line.
I used my Guardian surgery tape to mark out the lengths of the 1mm wire. Removing the surgery tape was a hassle. I used a round nose plier to form the z-bend and discovered the control of bending can effect in a bigger or smaller z, especially obvious when looking closely. Other bends are with square jaw pliers.
One of the 30 mm wheels (purchased from Jethobby) was off centred by about 2mm and binding points can be at the side walls of the wheels. I bent the end of the axle to retain the wheel, putting in two wires temporary while I bend with my thumbs to give the wheels some clearance.
The partly completed undercarriage assembly did not spin freely. I sanded the side wall where it dragged the wire, improving it as much as I can and then I sprayed on some WD40 to lubricate the axles and hubs. Under its own weight, each wheel can turn when dragged along a flat surface, and spins, just for a split second, after flicking it.
Covering, Markings, Assembly (Day 6)
The fuselage's top was covered in one piece with V-cuts so the sticker film can conform to the compound curvature. The sides were then covered, leaving the bottom bare.
The cockpit pattern was traced on the covered top with ball point pen and the opening cut out. Black sticker was used to finish up the cockpit floor, back rest and instrument panel. Andy gave me a short length of flexible plastic tubing of around 4mm O.D. A section of it was used as cockpit coaming.
The headrest fairing was covered and glued in place, including the headrest itself. The vertical tail was covered and I used a permanent marker to draw up the 'Gee Bee' and 'NC11043' on the tail. The horizontal and vertical stabilisers was then glued, followed by the windscreen, which was a rolled up piece of PVC.
From the internet, the panther's logo was imitated and drawn onto the model.
The cowling was attached with tape, the wheel fairings glued to underside of the wings.
The PVC windscreen was then glued on.
Rudder and Elevator Controls (Day 7)
I want the geometry plane of the servos to be the same as the control surfaces, and port is the good side of the model.
The elevator's servo was mounted on a cut out and the rudder's mounted vertically with the servo horn sticking out through a slot on the fuselage.
At this point, the CG looks ok. I am tempted to do some test flies (who can stop at one?) after the servos for the ailerons are installed. If it flies well enough, I can proceed with the finishing phase of covering the bottom and completing the decoration and detailing. Perhaps the wheel pants, rigging wires, wing struts, louvred cowling can be done then; there is no point to do more if the model doesn't fly well enough to start with.
Ailerons Control (Day 8)
2 nos. of HS 35 servos were installed for ailerons control. I used BSI's Insta-Flex, perhaps hot glue would be better. The maximum throws are about right.
The transmitter and receiver was switched on and I set up the amount of throw for all control servos, and did some minor adjustment, such as trimming the V-cut of the elevator in order that it does not limit the full rudder travel intended and heat bending the control horn of the elevator because it was interfering with the control horn of the rudder.
I also noticed that the downthrust seems excessive. At higher throttle, there is a marked down-pitching. This might be a good thing, with the wing-tail decalage of 2 degrees, it would mean the model will fly fast instead of zooming up, but only test flights will tell, and I will have my leadweight ready in my flight box so that they may be temporary taped to the nose to trim the centre-gravity of the model, after the first flight.
The GWS push-on spinner flew off the motor at continuous high throttle, it has since been replaced with the prop-saver that came with the motor. And finally I would probably install a ply plate to secure the battery in the nose with velcro strap before this weekend.
I constructed the lines of one wing tip panel and then I folded the paper so the other wing would be similarly cut by the scissors. The top skin was then curled.
Here's a collection of photos of the first Bebe, the F-PEPF, from the internet. I like the tractor paint remark, because I have a piece of 2mm foam sheet which is something like that. Maybe it is possible for F-PAAT to be in tractor orange as well?
