|Nov 15, 2013, 01:27 AM|
Comet 19 2X
I came across Steve Smiths 1995 plans for his Comet 19, a free flight model built around the little KP-01 geared electric motor on the Hip Pocket Aeronatics site (http://www.hippocketaeronautics.com) I liked the old timer looks of it and thought it might make a good foamie.
I downloaded the plans and used the pdf reader to scale them up 200%. After a lot of tape and trimming, I had a plan to work from. I seem to have a hard time getting all my pages to line up right as my printer is a bit naughty when printing in poster mode.
I traced out the parts of the model, correcting where needed and created a set of paper templates to transfer to the $tree foam. I made a few small errors, but I will see how things work out.
The wings are similar to the Flite Test foldover construction. I drew up a side view of the airfoil to get the measurements right. I made a mistake when laying out the leading edge line and the wings are slightly cockeyed, but they are out the same amount per panel. This lead to a forward sweep of 1/8" and a slight twist toward the wingtips. I plan to build another wing with the paper stripped from the inner surface.
The spars have the dihedral angle built in and overlap in the center section. When putting the wing together, I taped the center section, unfolded, in place and propped up the wingtips (3") After gluing the center of the spars down with some extra blocking, I folded the top surface over and marked where I needed to cut away material from the wing roots to make the center section fit between. The center section feels sturdy, but it is a little rough due to my relative inexperience with this foam building technique. I come from stick and tissue and I was a bit of a hack at that too!
The tail feathers are fairly standard, but I had to put a bit of dowel between the elevators.
The fuse weighs a little under 6 ounces as shown on the photos. The curved bottom was teased into shape by de-papering the inner surface and lightly kerfing the bit by the nose. Internal arrangement is still to be determined. The ESC at the moment lives in a bay behind the firewall. The original plan had the landing gear sewn on to the forward former, but I will be bending up a band-on wire gear such as Flite Test uses. This will lessen the stress on the fuse, I hope.
9 gram servos will be used. The motor on now is a little 2204 Donkey 1550 KV from Hobby King. 15 amp ESC 8x4.3 prop and a 500Mah battery are the initial electronics. I am guessing that the AUW will be about 12-14 ounces if I am careful. Fuse as shown is 5.6 oz and the wing 3.5 oz. Receiver, LG, pushrods and horns are still to be added. The power combo is good for about 285 grams of thrust, so it may be a bit underpowered. I am new to this stuff, so I will see when it come time to maiden
|Nov 18, 2013, 05:05 PM|
Ready for a test flight (nearly)
Yes, it does indeed look like a Simplex. Only the stab is a little different in the Comet design.
I have just about finished construction. All parts glued on and the controls hooked up. The control rods slide through coffee straws and cross in the middle (yay for servo reverse switches!). To insert the straws, I twiddled a bamboo skewer through the foam at a low angle and the straws just pushed through. Very neat and tidy, just a little Tacky Glue to keep them in place.
The landing gear needs a bit of tweaking yet. The stance is still a little narrow and the mounting is a bit dodgy. I have a screw with a large flange to hold the aft end of the gear in place. This may break. I need to work on my wire bending mojo some more and maybe get larger pliers. The wheels were loose on the wire so I found some aluminum tube to slip over the axles. Tape for wheel collars, very crude
The CG is still a bit aft, as is expected for a design with such a short nose. Weight as shown is 11.2 ounces. About 320 grams. If I build another, I will strip some of the paper off (inside wings, inside after fuse) to reduce weight.
I best guessed the control surfaces. I do know that with a long moment arm, smaller surfaces will work. The elevator will be well within the airstream, but I am a little unsure of the rudder. The bulk of the rudder area is below the wing.
A little sticky lead is needed to balance, and I need a dry calm day to test fly. Since I live in Upstate NY, I may have a long wait!
Here are some more pix
The blood spot on the wing is part of a new DNA based lost model retrieval tracking system.
|Nov 18, 2013, 05:16 PM|
I checked out the Wing Loading calc at http://www.flyingsites.co.uk/downloads/wingloadcalc.htm. I fudged the wing dimensions a little to allow for the rounded tips (36" x 6" instead of 38" x 6.25") The results say that wing loading will be 7.7 OZ per Sq ft. I guess that is not too bad according to their chart:
Glider 10 oz/sq.ft
Trainers 15 oz/sq.ft
Sport Plane 20 oz/sq.ft
Fighters 25 oz/sq.ft
|Nov 23, 2013, 11:18 PM|
A little nose art
I added some tissue paper decals similar to the ones described in this thread: http://www.rcgroups.com/forums/showthread.php?t=1217546
Since I was going to coat the plane with Minwax, I used the stuff to attach the tissue decals. Looks like it will work well. You have time to gently reposition your graphics.
I floated the Minwax on with a brush cut from a bit of old chair foam and dropped the decal on. Once I had dabbed it with a bit of paper towel, I spread another light coat of Minwax. The HP Vivera ink was not effected at all by the finish, but I guess you should test yours before applying to the plane.
Still waiting for a good day to test fly. Show has come and the sun don't shine here in November!
2 minutes extra flight time to those who 'get' why I chose a goldfish!
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