|Oct 30, 2012, 06:57 PM|
Fin and rudder
Ray suggested that since the CF spar caps are 36" in length, that rather than cutting them to 32" as per the wing plan, he has left them at 36" and added rib bays extending the span by 8" total with near zero added cost. I have decided to do this. Hey, if a 10' 6" wing is hard to store, an 11' 4" wing shouldn't be that much worse, right? Plus lower wing loading (I swear I try hard to build light. )
I was thinking that that extra wing might take a bit more rudder to push around so I drew up a modification of the Hawk fin-rudder pulling up the aspect ratio and making it a bit taller. This is what I am building. It is glued directly to the fin-core/stab pylon in the fuselage design.
I was just starting the build of the fin-rudder when the big tropical storm Sandy came to town. I was a bit distracted so it's not my most careful work. Sorry. I'll do better.
|Nov 01, 2012, 09:00 PM|
The fin-rudder will be glued directly to the fin core-stab pylon and aligned for vertical once the fuselage is completed. Before then, it will need sanding to bring it to the proper cross-section shape. I'll leave that for later.
|Nov 01, 2012, 09:20 PM|
Once all of the formers were glued in and cured, I attached the second fuselage side taking care to line it up correctly for a straight fuselage. Forward of F5, I glued those formers with thickened epoxy like the other side-former joints before and I clamped the fuselage sides together to cure. After curing for four hours or so, I set the fuselage on its bottom edge along a long strip of 2" wide blue masking tape laid out perfectly straight on the table top with a heavy black line drawn down the center of the tape its full length to be sure the fuselage was straight and true for its full length. Then I carefully drew together the tail sides and checked again for straightness. Once satisfied, I glued formers F6-F8 to the second side and glued the tail portion together.
The fuselage bottom is too long to be cut from a 48" piece of lite ply, so I created a tail extension section that uses a slot and tab method to glue the two bottom pieces into one long bottom piece. This joint is under the solid stab pylon section of the tail so these two things should make that joint strong. This is intentionally made to be too long for the fuselage length, even the 1" extended length option that I am building, and that extra length makes fitting it in place a simpler task. I glued this with Titebond. I learned that laser cutting takes out about 1/32" of dimension for the cut so this joint was too loose as a result. I wedged two thin strips of 1/64" ply in the slot joint so to make a tight fit and then sanded them flush when the glue had set.
Before the fuselage bottom is glued in place with Titebond, I ran the rudder and stab control rods through holes in the formers. I had to drill some new holes rather than using the pre-cut holes in the parts to align them for smooth movement of the rods in their housings. The rods are 1/32" wire in synthetic tubing that can be glued. At the ends of the rods, they are spliced to thicker wire for the parts that exit the housing so they can't deflect sideways when under load. This may have not been necessary but I wanted to be sure the wire was strong enough when outside the housing. The splices were made with heavy heat shrink tubing over a full overlap of the two pieces of wire with CA wicked into the tube after shrinking. Where these splices run inside the tail, I built small balsa channels around the spliced part of the rods so that they could not deflect sideways more than about 1/8". The control rods move smoothly and seem solid without flex when compressed from both ends.
Once that was done and the housings were glued in their holes with Gorilla Glue, I lined up the fuselage on 2" wide blue tape laid out straight on the table top to be sure the fuselage was straight and true.
I turned over the fuselage so it was resting on the top edges and sanded the bottom edge with a sanding block to make sure it was completely flush with all the laminations and former joints.
The tow hook beam was set in place for a dry fit and sanded the bottom of the beam to be flush with the bottom edges of the fuselage sides. When the bottom piece of lite ply is in place it will bond firmly with the bottom of the tow hook beam, the sides and doublers, and the formers under the wing. I hope this will be good and strong.
Epoxy was spread on the bottom and ends of the tow hook beam and in the notch on F4 and slid the beam in place from below. I spread Titebond around all the bottom edge of the fuselage from F1-F5 and placed the bottom 1/8" lite ply laser-cut bottom piece in place. I decided to slide it forward about 1.5" from the designed position to eliminate the tight inward curving section at the nose. With the tail extension of the bottom, there is plenty of extra length to make this possible. This does result in the bottom being inset from the side edges about 1/16" since the bottom taper is shifted forward. I found that the dimensions of the formers needs work in the design and so the bottom was not a perfect fit even before sliding ti forward. Since the bottom is carved and rounded along the side-to-bottom joint, cutting in all the way to some of the spruce longerons, this misalignment will be cut away when the final shaping is done anyway.
The forward-slid bottom piece is seen in the photo below. That extra bottom piece at the nose will be cut off when the nose block is fit and the sides are pulled inward and glued to the nose block and bottom piece at the nose That will come a bit later.
I placed bricks on this forward section of the bottom and let the glue cure for about two hours. Once cured, I then lined up the fuselage on the blue tape and lined up the rest of the bottom in place from F5 to the rudder post after smearing a layer of Titebond on the side bottom edges and former bottoms. I weighed it all down with bricks, triple checked it for straightness, and let the glue dry overnight.
|Nov 01, 2012, 09:35 PM|
The nose block and canopy carving will be the last parts of the fuselage top to make. Before then, I edge-glued several cross-grain pieces of 1/4" balsa to make the top of the tail of the fuselage from F5 to the fin. The 1/4" top was cut to be slightly over sized by about 1/4" along both sides so it could be cut to flush after glued in place. This 1/4" top stops a bit short of the section where the TE of the wing is located near F5 so that a fairing from 1/4" balsa can be made and fit in place once the wing is complete.
I had intended to add a 0.040 CF 1/4" strip from F5 to the fin to add stiffness to the thin tail section, but when testing the stiffness before adding the top, I was pretty satisfied that the CF stiffeners on the sides of the tail were doing a sufficient job so I left the top CF strip off to save any weight I could on this long tail. I let the edge-glued piece dry overnight.
Since the Yardbird fuselage has the wing sit and bolt onto the top of the fuselage, that section of the fuselage is relatively flat and supported across the top with inset laser-cut 1/8" ply top pieces that have holes laser-cut from them for access to the spaces in the fuselage below the wing for spoiler servo connection, ballast, etc. These pieces also strengthen the fuselage torsionally through the wing mount area creating a stiff box under the wing connected to the sides, bottom, and tow hook beam. In the updated design this section of the fuselage sides are actually slightly curved downward to match the bottom of the airfoil shape without causing the LE to rise as much off the top line of the fuselage. Since the full-flying stab decalage can be adjusted to rotate the angle of attack of the wing without much additional drag, I chose to build this prototype with a flat section at the wing mount area of the fuselage rather than trying to make an accurate cut in both fuselage sides free-hand.
When gluing the top in place on the tail portion, I made sure to address any torsional misalignment in the tail section by checking the vertical alignment of the fin core/stab pylon. Luckily, there was none that I could see or measure so the Titebond was smeared on the top edge and formers and the 1/4" top piece was placed and weighed down with bricks to dry.
Once the glue was dry, I used a hobby knife to slice the slightly oversized 1/4" top to within about an 1/16" overhang of the sides and then used a sanding block to sand the top flush against the sides. All of the sides, top and bottom will receive a good carving and sanding later to achieve the rounded cross section for the tail of the fuselage.
Once dry, I removed the fuselage from the table and gave it a good bend and twist to see if the design, which is quite narrow for a long section of the tail, was going to be laterally and torsionally stiff enough. I was happy that it seemed quite strong in all directions. This may change once the carving and sanding to round are complete on the tail, but I have a feeling that it will retain its strength through that reduction. Since the slender long tail is a feature of the design, I was happy that the strength seemed to be there as well as the nice look. We'll see when it is launched and flown if I am correct. Once rounded, it will have the proportions not too far from those of pod and boom tails.
|Nov 02, 2012, 10:04 PM|
United States, FL, Shalimar
Joined Jan 2009
She might not be an "approved" fiberglass fuselage in the end, but the plug from which the mould is being constructed is. FYI, mould should be done by the end of this month.
|Nov 02, 2012, 10:46 PM|
hi there from Toledo
Excellent!! Good work and keep us apprised.
ps: Wingloada: Equally excellent work on the woodie fuselage. ciao -rjf
|Nov 02, 2012, 11:16 PM|
Original Concept Drawing
OK... The "original" concept drawing on the Houston Hawks website is NOT the original concept drawing. There was a member of our club at the time that kind of went overboard in trying to finish a Hawk first, and I'm not talking about AJ... This guy was all push... but he was a nice guy, and a friend. I allowed his drawing to remain to keep from hurting his feelings. I wish they would remove it now because of this misunderstanding. The Condor fuselage, along with several others that fall within an acceptable range of moments, are all "approved" fuselages... To be honest, I like the Sapphire fuselage better than the Condor, because it has a longer nose moment and a roomier cockpit area. That allows the radio to be installed further forward, resulting in less added nose weight... and a lighter model. The green one I sold to a fellow up north was the lightest, and best flying Hawk I had ever built... and used a Sapphire fuselage.
That's the real story about fuselages. If I could have come up with the Sapphire molds, I'd have made myself several with cf aft of the spar and Kevlar nose sections, and nose cones.
Rich... Looks great, please keep us posted!
For the rest of you, I am still doing the woody fuselage... starting just as soon as my yard is in and my MANCAVE is completed... probably around December...
Darth Befuddled Grass Plopper...
Edit: My yard is... 1 acre... and... I'm OLD... please continue to be patient...
|Nov 03, 2012, 09:59 AM|
In this thread I found a comment that the stab can be built to 1.3 oz. I'm having trouble finding other target weights to build to. If anyone has ideas I'm trying to fill in this table:
fuselage+fin/rudder empty but finished/covered =
radio gear including rudder and stab servos =
Rx battery =
nose weight =
stab = 1.3 oz
wing including servo(s) for spoilers =
wing joiner rod =
AUW ready to fly =
Thanks to all.
ps best of luck darth sod plopper of the mancave
|Nov 04, 2012, 09:32 AM|
Nose block and canopy
The nose block rough shape is cut from 2x3x6 basswood using a coping saw or other saw able to cut easy curves. It's glued in place with the sides and bottom overlapping an approximately 1/2" inset of the block into the nose of the fuselage. I used Titebond for this and clamped it for six hours.
The canopy/hatch is made from a 2x2x12 block of balsa. The rough shape was transferred from the plan and the block was cut to that shape using a saw. I spot glued it in place so that I can shape it to flush and then to the full curving final shape and then it will be cut free from the spot glue points and carved out inside for a hollow shape over F2-F3.
|Nov 06, 2012, 03:43 PM|
Can anyone tell me what their Houston Hawk glass fuselage weighs all up ready to fly with radio gear installed and fin-rudder (not stab)? I'm trying to get a feel for the ball park to hit with the wooden designs.
|Nov 10, 2012, 12:04 PM|
I spent some time today carving, planing, and sanding the fuselage to its rough rounded shape. The spruce longerons are a nice dark red color compared to the pale lite ply so when the corners are rounded its easy to see how far into the spruce the rounding has gone. This made it possible to get an almost circlular cross section from F5 to the tail, as planned.
Since the bottom is reinforced with hard balsa 3/8" tri stock from F5 forward, the bottom corners can be rounded well past the edges of the lite ply. The balsa block canopy/hatch is easily carved and sanded to the curving shape to round the nose nicely.
All of this work is done first with light cuts made with a carving blade, then with a shaping plane, then with coarse sand paper. In each case the shaping is done in long lengthwise facets first gradually cutting the rough shape then planing, then sanding.
The next step will be to use finer and finer sand paper to arrive at the final contour and finish.
At this stage the bare fuselage with fin core and push-rods weighs 10.4 oz. without the full fin/rudder in place.
The nose section from F5 forward will be wrapped in 1.5 oz. +- 45º bias fiber glass applied with Minwax Polycrylic. Given the weight so far and the target weights that AJ provided, I think I will also glass the tail in 0.7 oz FG with Polycrylic as well for insurance. The strength to weight gain is probably worth it. Any opinions on that?
|Nov 10, 2012, 12:19 PM|
Here is a photo with the wing adapter in place. The fairings at the leading and trailing edges still need to be made. The adapter is not finished. The joiner rod still needs to be bent to the dihedral angle. I think I have found a place where I can do this now. Perhaps next week the adapter will be complete.
|Nov 10, 2012, 03:33 PM|
Weights so far
Weights so far [updated 11-16-12 after completion of fuselage, fin, rudder, and stab]:
Fuselage empty with pushrods but without FG wrap = 10.40 oz.
Wing adapter without joiner rod = 1.5 oz.
1/2" x 12" 6061 T6 aluminum joiner rod = 3.75 oz.
Fin-rudder (uncovered) = 0.75 oz.
Total fuselage with the rough-framed fin-rudder, wing adapter and joiner rod in place = 17.20 oz.
Stab with axle and actuator pins (uncovered) = 1.82 oz.
Finished Fuselage with 1.5 oz. glass wrap and 3 coats Polycrylic finish with fin, rudder, stab, wing adapter, and joiner rod = 18.6 oz.
Estimated weights for radio gear:
2000 mAh Enloop Rx battery = 3.6 oz.
Charge jack = 0.5 oz.
Rudder, and Elevator servos and wiring = 2.0 oz.
Receiver = 1 oz.
Total for radio gear = 7.1 oz.
Total estimated with fuselage and radio gear = 25.7 oz.
Possible nose weight needed = 1-4 oz.
Estimated fuselage and covered tail ready to fly = 27 - 30 oz.
If the wing with spoiler servos comes in around 26 oz. then the plane will have an AUW of approximately 54 oz. with a wing loading of around 6.2 oz. / ft^2 (wing span extended by 8" to 134").
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