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Pit
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« on: June 27, 2010, 06:21:48 AM »

OK, everyone. Here we go. I have started this thread for everyone to post their "designs", drawings, trials and tribulations with profile scale or fully built-up catapult launch gliders.

Feel free to post everything, from ideas for that obscure aircraft, drawing up a plan or sketch, building it and teaching it how to fly. All info to the success or lack of, welcome. I see this as a neat, inexpensive way to get people of all ages and gender involved with something that they can more easily relate to (Hey, I saw something like that fly over the house yesterday!). It does not particularly have to be a jet, but should be WWII or later and possibly earmarked for conversion to jet power. "Secret" (ex. Luft 46, Skunk Works, Star Trek/Wars) aircraft that never flew, are fully "eligible". The emphasis is on FUN!

There is a similar thread on SFA on the glider forum "Frustrating Catapult Jets" that was well visited for some time, but has become dormant despite attempts by me to revive it. Lots of good info there, tho.

I'm in the process of chopping wood for the "Scorpion". I won't get much done today - Formula 1 race and the Germany-England soccer match are in the way Grin - but I should have the parts cut by tonight.
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« Reply #1 on: June 28, 2010, 08:15:15 AM »

To get this thread going, I'll run through how I "developed" Roll Eyes the F-89 "Scorpion".

I found a suitable 3-view that was large enough to show panel detail. Some 3-views are SO small that they are useless when blown up to a usable scale, so a bit of judgment is needed as to WHAT you want. I "saved" it to my hard disk, in this case as a jpeg file (tiff of gif might be better as less resolution gets "lost" when enlarging). Importing the file into a graphics editing program lets you then modify the file to your hearts content.

I DON'T recommend MS Paint as it is too limited, but can do in a pinch. I use either TurboCad or Inkscape (highly recommended in that it operates with vector graphics). I imported the file to the "0" level and "traced" over it on level "1". A couple extra levels were added for complicated areas that might (and usually do, like spline and bezier curves) need modification. Once I'm satisfied with what is shown, I'll scale the "drawing" up to the size I want (can be done at the start with the imported file, if the resolution allows) and print a copy. You should have been "saving" your work while drawing Wink.
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« Reply #2 on: June 28, 2010, 08:34:54 AM »

Once I have a "hardcopy" of the plan, I make up cutting templates. Tack-gluing a "copy" directly to the wood is also a good way to make your kit, but I generally make a bunch of each glider, so it's templates for me.

I use all sorts of material for templates, but for these small planes, I have come to prefer cardboard from cereal boxes or the heavier stock from the back of paper tablets. The heavy grade manila folders are also very good. I use permanent gluestick to attach the rough-cut printouts to the card stock, and final trim with a scalpel and scissors. The edges are then sealed and hardened with CA and sanded smooth. Sometimes I'll give the complete template a coat or two of clear "whatever" for added protection.

Pictured are the finished templates for the "Scorpion". I left the tip-tank winglet "raw" for description purposes.
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« Reply #3 on: June 28, 2010, 09:09:18 AM »

One thing I forgot to mention, is to check whatever 3-view you use AND whatever plan you print from a file, is to check for symmetry. Many times, the top view is a slightly different scale than the side view or one side of the wing is "different" than the other.

A printout can come out lopsided, but not immediately noticeable due to many factors - worn feed rollers, platen or "helping" the paper as it emerges from the printer. I caught the guy at the copy shop "helping" an enlargement of mine. He insisted that it didn't matter with the big machines, so we measured the copy and ran another WITHOUT "help". I did NOT have to pay for the second copy.
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« Reply #4 on: June 28, 2010, 10:21:53 AM »

Quote
one side of the wing is "different" than the other.

Pete

The old chuckie build trick is to only cut a template for one half of the wing. Draw a centre line on the wood, cut out one side, flip the template over and cut out the other side - obviously lining up both sides on the centre line. It's the thing to do for tails (stabs) as well. Pas de probleme and easy peasy as they say Cheesy

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« Reply #5 on: June 28, 2010, 02:14:12 PM »

You're right Peter. It's the way I'd usually draw up a plan, but it's been my experience with those fairly new to building from a plan, that trouble pops up with the flip & cut. Since I use the mirror function in my drawing program, I can rest assured that the original drawing is "accurate". The template can be cut either way.

Here are the major parts cut for my preferred building method. Results in a fairly lightweight, bombproof fuselage. The only real "heads up" is that both outer layers HAVE to be cut accurately! One CAN use a single piece of 1/8th and glue the fin/stab assembly afterward (definitely lighter), but the unit WON'T be as strong, however alignment is easier. Tapering the outer fuse laminations from the wing TE to the tailcone will reduce weight in the rear, requiring less noseweight.
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« Reply #6 on: June 28, 2010, 04:00:35 PM »

Pete,

With the discovery a number of months ago of the Jetex designs for jets, I wondered if the designs might be adapted to Catapult Launch. I haven't done work on trying one out, but maybe this winter...

I'd think that if you scaled one of the designs properly, built light where you could, and used the rubber strip / heavy thread catapult method, they might put in some interesting flights. Unfortunately, most jets are not that generous on wing area, so the glides will suffer, but there are a few exceptions, and if you could get the others to glide even a little bit, it might be a rewarding effort.

Justin
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« Reply #7 on: June 28, 2010, 06:05:17 PM »

I'll pipe in with some wisdom from Paul Grabskie, who has flown a BUNCH of JetCats.

Don't put the nose weight all the way forward. Go about halfway to the nose. It requires some more weight but cuts down on the inertial moment, which helps recovery.
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« Reply #8 on: June 28, 2010, 07:15:30 PM »

I've looked at the stuff on Jetex.org. They've got some really nice plans and they shouldn't pose any problems whatsoever to convert. I choose my subjects based on wingspan/area. There are a number of good to great subjects out there which I simply "like" and I've chosen 8-10" spans for convenience. These are NOT intended to be world beaters, but the OKHA easily does 30 seconds or better and my F9F Cougar is getting better each outing with a flat plate 1/16" wing. Both are pretty close to scale.

The tip about the nose weight is a good one, probably the reason one of my attempts was so inconsistent. The F-89 has a VERY long (and pointy) nose almost requiring a more rearward ballast placement. I like to embed the ballast completely, using just enough clay for fine trimming.

If anyone else has a catajet in the hanger, this is the place to bring it (back) into the spotlight. Tell us what it is, how it flys (or won't), post pics - yadda yadda. There's just too much fun to be had with these puppies.

I've gotten the fuselage glued up and the major sanding done. The stab is simply resting on the doublers (triplers?) going up to the stab. These "fin base doublers" my not be necessary (they're sanded to almost nothing), but it's something I wanted to try. Tailplane is tapered to .025". The whole thing as shown is only 3.69 grams. The wing blank (2.5mm/.098") weighs 3.41grams and should finish out around 2.2gm or lighter (based on another wing of similar size/raw weight). I don't think I posted the span: 8.5 inches.
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« Reply #9 on: June 28, 2010, 07:29:09 PM »

Hi All,
Here are my templates for my Mig 15 this jet is great if done light.... I have gotten a consistent 35 seconds out of this designs and many lift assist flights of over a minute.

Next I present my Hawker hunter plan.... this works as a cat jet (reduce the decalage to near zero-zero) and is great as a rapier jet (it took the best flight award at open scale).

Last... a prototype Mig 17.... I have not built one of these yet but I suspect it will go as well or better than my Mig 15.

enjoy.
B
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« Reply #10 on: June 28, 2010, 07:51:52 PM »

Glad you've jumped in Bernard! It's your doing that's gotten me into this "mess" Grin.

What were, if any, trim quirks with the swept planform? I've gotten the Cougar to do almost everything well but near the end of the flight envelope, it suddenly pitches up and stalls -very small stability margin I'm thinking, coupled with a bodacious amount of side/fin area? I washed the tips out some more which required more nose ballast and that helped a lot, but the condition was still there - just not as severe. A bit more schnoz weight got it "almost" perfect, but a sand grain more or less was too much.

I'm trying boundary layer fences next (the full size needed them to cure low speed problems). Hopefully tomorrow (today).
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« Reply #11 on: June 29, 2010, 01:22:15 AM »

I got the wing airfoil sanded, dihedral set, slot cut in the fuse, and the first sealing coat on & sanded. AUW is 7.25 grams with the CG at 50%. Worked OK for the still warm (indoor thermals?) bed test. This one will get some color with the basic F-89 red and silver finish, so the finished weight will be pushing the 8 gram mark.

I used the same airfoil that I put to my OKHA and Reichenberg gliders so I'm confident that it'll fly reasonably well.
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« Reply #12 on: June 29, 2010, 08:01:06 PM »

Trim Quirks: Not really they all seem to go pretty well as long as you have ample washout in the wing (swept planforms need more washout apparently).

B
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« Reply #13 on: June 30, 2010, 02:18:57 AM »

Pete, when you say airfoil, do you mean that you are specifically sanding a particular shape of airfoil? I just give the ones I have a high point at about 30% and make it look 'airfoilish'. Maybe I am doing something inferior? I also only use 2mm wood to make my wings.

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« Reply #14 on: June 30, 2010, 04:34:25 AM »

Thanks Pete! This looks like a fun project for rainy summer days. I am not so familiar with CLG, so I have some basic questions: What do you use for Nose Weight on these small jets? And do you have instructions for a catapult? What rubber, length etc.
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« Reply #15 on: June 30, 2010, 07:22:58 AM »

Pete, when you say airfoil, do you mean that you are specifically sanding a particular shape of airfoil? I just give the ones I have a high point at about 30% and make it look 'airfoilish'. Maybe I am doing something inferior? I also only use 2mm wood to make my wings.

These jobbies, being primarily "fun "models and relatively quick to build (unless u use my laminated fuz method - then 10 minutes more is required Grin), is the reason I didn't specify any particular airfoil. So anything that "works", will work. Natch', if you plan on the jet catapult comp, then you'll want to use the "competition" 'foil.

I use the "flat slope" from a 25-30% high-point to TE 'foil with a phillips entry (or upsweep) to a point 0.5-0.6mm up on the LE (2.5mm wing thickness). The LE to HP curve is an ellipse TLAR shape that is done with a small flat sanding bar (lazy way) or with a shaped bar (finicky way).

I also like to use 2mm wood for these jet models, but 2.5 (0,098425197") is all I have at the moment. The suggested 3/32" (0.09375") is less than 2.5mm so the choice is yours.
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« Reply #16 on: June 30, 2010, 08:17:19 AM »

Thanks Pete! This looks like a fun project for rainy summer days. I am not so familiar with CLG, so I have some basic questions: What do you use for Nose Weight on these small jets? And do you have instructions for a catapult? What rubber, length etc.

Hi Arne,

For nose weight, I have (still) some sheet roofing lead that I got before it was placed on the "verboten" list. It's 1.5mm thick, and I use a 6mm paper punch to knock out consistent 0.37gm "disks". These are then embedded into a hole punched into the wood wherever it's needed with a 6mm o.d. sharpened brass tube, glued in with CA and then the cavity leveled with spackle (filler) if needed.

For a catapult, I use a hardwood dowel of at least 6mm (10mm is IMO better) with a loop of rubber between 150 and 240mm attached to the end. I use 1/8th Tan 1 for sport flying, 1/8 and 3/16 FAI Black for "serious" flying but HAVE used 160 x 6 BROWN rubber bands from the hobby shop or office supply store (hard to find now in my area Sad).
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« Reply #17 on: July 01, 2010, 01:09:16 AM »

Pete,

Thanks for this thread... I've already gotten insight into why a couple of my planes wouldn't fly today when I took my bunch out to the park. My Ohka's are not performing fairly well...no where the time you get but very satisfying and fun for myself and the Grandsons.

Any insights on the tail-less Me 163A 15inch wingspan. Just tumbles... added weight to the nose still no satisfying glide. Will look at washout on the wing tips.

Working on a couple of new clg's for the future... Will have to try BG's birds as well. These things are a real treat and just take a short time to construct.

Regards
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Tom
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« Reply #18 on: July 01, 2010, 02:09:24 AM »

Tom,

On a tailless design 'tumbling' invariably means that the CG is too far back.. add more noseweight. Tailless models need a CG further forward the normal planes.

If once the tumbling stops the model just wants to 'lawn dart' then you need to bend the elevons (the control surfaces on the wing TE) upward. On a swept wing like the Me163 washout also works well but the elevons should do the trick on their own.

Bear in mind that on a flying wing a 'normal' flat bottom airfoil does not work very well.. Best to sand in some 'upsweep' at the TE to give a reflexed airfoil effect, also an airfoil with a well forward high point is best for tailless planes. If the airfoil is already carved then you might be able to steam some reflex in.. but movable elevons give a similar effect anyway.

Steve
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« Reply #19 on: July 01, 2010, 08:47:45 AM »

I'm currently working on plans for DH100 Vampire (22.5 cm span), Yak 15 and A10 Thunderbolt (both 19 cm span)! If only work didn't keep getting in the way!
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« Reply #20 on: July 01, 2010, 08:56:35 PM »

Steve,

Thanks for the input.... will cut out the elevons and add some wire from twist ties and set some upsweep to them. Also some more nose weight to see if we can get the Me 163 into the air.

Regards,
Tom
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« Reply #21 on: July 03, 2010, 07:24:13 AM »

The F-89 is pretty much finished. I decided to pretty this one up a bit with one of the well recognized polished alu and red schemes. Haven't done any lettering or national markings yet - I'll wait till I see if she catalaunches. I think I have some decals that will fit - I have to draw the line as far as hand lettering goes.

With the "paint" (silver floral spray and an Edding marker) and my Techno-pens, I was able to approximate the chosen scheme. Backyard glides needed a bit more nose ballast, so now the beastie is at a nice FAT 9.3 grams - but, seems to have a fair glide.

I WAS planning to take it to the field this morning along with the Phantom Flash, but I didn't think I'd have time. I needed to get at least one GOOD flight with the PF for the cookup (got two before the wind got too strong Smiley). I'll go out again this evening after the Germany/Argentina World Cup match (if the beer level stays below eye level Grin).
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« Reply #22 on: July 03, 2010, 07:35:01 PM »

Pete,

The Scorpion looks great. Glad to hear she's gliding so well. Haven't had a chance to get back to the park and will be out of town for about a week so no building or flying for a while. Started working on a Douglas D-558-1 Skystreak based on the old Comet plan. I am also working on a Grumman EA6B will keep you posted.

Regards,
Tom
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« Reply #23 on: July 04, 2010, 11:53:53 AM »

Thanks Tom.

I was going to run to the field earlier and decided to give the Scorp another toss in the backyard. Wasn't a good idea Sad. I recently "share" the yard with a sandbox, a massive wood-framed swing and a "hollywood" swing. The toss went clear across the yard, smack into the swing's main upright, taking off one of the pods, tailplane and popping the wing loose in the slot (and a nice dent on the leading edge). The high weight, resulting in a higher speed and energy really showed it's "bad" side.

One BIG caution must be made clear! Those big wing pods (or ANY form of tip tanks) MUST be absolutely square to the centerline, otherwise the aircraft will never trim out. This also means that, even with the pods parallel to the wing CL, the WING has to be perfectly centered an square. An easy alternative is to leave the pods/tanks off. In the case of the Scorpion, which has flown without the pods and is pictorially documented, it simply doesn't "look" right. The same applies to the F9F Panther. For this reason, I can't recommend a model with tip tanks (profile) as a first catajet.
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« Reply #24 on: July 04, 2010, 07:11:09 PM »

I got to the patch late this evening just in time for the wind to die almost completely. I wanted to get two more flights with the P. Flash, but a repair failed, nixing those tries. The F-89 turned out to be a mixed bag.

The GOOD: It flys.

The NOT so good: A bit too much incidence, a severe rolling tendency to the right, the way I mounted the stab is NOT strong enough - the ONLY part that broke.

I was able to get the roll at least under control to where it only completed one rev, leveling to a fast but flat left turn, then breaking right. The right panel somehow Roll Eyes ended up heavier than the left. A bit of ballast on the left reduced the right roll and the glide is now in the correct direction (almost). Another stab break (four in all) and impending darkness made me switch models.

The Scorpion shows definite promise. A few minor changes and I'll have the plan ready for posting.
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