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Author Topic: CATAJETS: Design and Development  (Read 40225 times)
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Sky9pilot
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« Reply #500 on: March 15, 2016, 12:52:02 PM »

isismk2... your jets look fantastic.  I've really gotta build some more catajet!!!
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« Reply #501 on: March 15, 2016, 01:09:45 PM »

Thanks but the building could be better...just built a 14" span Gloster Meteor in the "Yellow Peril" color scheme and am still thinking about that X-32 and a F-16 in prototype colors...you can't have too many Cats because they don't last long enough
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Sky9pilot
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« Reply #502 on: March 15, 2016, 04:50:44 PM »

Thanks but the building could be better...just built a 14" span Gloster Meteor in the "Yellow Peril" color scheme and am still thinking about that X-32 and a F-16 in prototype colors...you can't have too many Cats because they don't last long enough

You are so right.  They do get abused because they are so much fun to fly.  My fetchermites (grandsons) love em and sometimes in retrieval get too rambuncious in racing each other to the planes, and you can imagine what happens then!!! Shocked Grin Wink Cool  Just give the opportunity to make some new one to fly!
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« Reply #503 on: March 15, 2016, 10:15:53 PM »

Yup...I enjoy building, even the dreaded cutting out of ribs...boring and tedious...but once done, everything else is a breeze...
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kittyfritters
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« Reply #504 on: August 28, 2016, 02:54:34 PM »

Finally made the time to upload the plans for my B-52 cat glider.   Waiting for administrative approval.
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« Reply #505 on: August 29, 2016, 12:21:47 AM »

Good lord, that's the first update I've received from here for over a year Shocked Shocked
Cool BUFF Kittyfritters Smiley Smiley
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« Reply #506 on: April 19, 2017, 04:27:14 PM »

Excuse thread necromancy!

As a complete novice I've just built two catajets. First, the West Wings kit of the Eurofighter Typhoon.

http://img.photobucket.com/albums/v108/Coopdevil/IMG_1399x_zpsb7jh6tkn.jpg

This is supposedly suitable as a chuck glider but...

http://img.photobucket.com/albums/v108/Coopdevil/IMG_1392x_zpslxmu8n0i.jpg

...it flies like a brick. Square section wing, no dihedral on the delta. The canard has anhedral but there's not much surface area there. So I've added a hook with an eye to catajet-ing it. Not tested as a catapult glider yet as I'm waiting for some proper rubber to arrive - at the moment the only catapult I have is from one of those toy Air Hogs foam glider things.

(I've made the hook by supergluing a bent pin into the wood with the pinhead clipped off. Will this be adequate? As a novice I've genuinely no idea.)

Also built up the Sabre Dog catajet from the plans in the May 1953 issue of Aero Modeller. A quick Sharpie pen job was supposed to be copying a Pakistan Air Force aircraft but then afterwards I belatedly realised that it was totally the wrong type of Sabre. Should the glider actually work I'll probably repaint it in a proper F-86D scheme.

http://img.photobucket.com/albums/v108/Coopdevil/IMG_1400x_zpsetikscgh.jpg

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CATAJETS: Design and Development
CATAJETS: Design and Development
CATAJETS: Design and Development
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MKelly
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« Reply #507 on: April 19, 2017, 05:12:14 PM »

Hah!  I was just looking through this thread earlier this week.  Sand an airfoil in that Eurofighter's wing, canard and fin and it'll probably fly a lot better.  I learned that with some WWII sheet WestWings gliders - it really made an amazing difference.  If the small canard won't give you enough lift for a good glide you can also bend the trailing edge of the wing up a little.

The pin will probably work for a very light catapult - if it bends you can glue a wedge of balsa in front of it for reinforcement.

I've been working on a Supermarine Scimitar for catajet - see pics.  Camping with the cub scouts this weekend, so I probably won't get it finished and flying until next week. 

Two weeks ago a gentleman got a 57-second flight from a profile B-57 jetcat at the Gainesville Spring Warmup FAC meet!

Your Sabre-Dog looks like it should fly well.

Cheers,

Mike
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FLYACE1946
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« Reply #508 on: April 19, 2017, 05:29:46 PM »

That sure is a sweet looking jet cat Mike.
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ZK-AUD
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« Reply #509 on: April 19, 2017, 06:12:22 PM »

Mike, I've never taken these things particularly seriously but that's a very nice piece of balsa bashing.  Your example makes me wonder why they need to be profile at all.  I'm guessing that some weight is desirable for penetration / inertia etc so why would a fully carved fuselage not be a nice thing to do?  By the way are you a Cub leader? I'm a Scout leader over here.
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« Reply #510 on: April 19, 2017, 06:16:53 PM »

Hey, just thought of something - why not spring load that hook to retract flush while we're at it?!  These could be quite serious scale models....
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OZPAF
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« Reply #511 on: April 19, 2017, 07:03:42 PM »

I'm impressed by your Scimitar as well Mike - nice work. 

Quote
...it flies like a brick. Square section wing, no dihedral on the delta
I agree with mike - sand an airfoil into the canard and wing. Keep the airfoil fairly sharp at the LE with a very small nose radius, about a 20-25% local chord high point and straight taper to the TE which only needs to be around 0.8mm thick.

These small models need thin airfoils with fairly sharp LE's.

The CG on these cat gliders will probably need to be a fair way back towards the tail.

I have done a depron cat version of the Sabre and it flew well.

Kiwi Mike - I work with a local Air League Squadron and they are an aviation minded equivalent of the Scouts. Small world.

Happy Flying

John
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FAAMAN
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« Reply #512 on: April 19, 2017, 09:11:13 PM »

Well it's only been nine or so months since the last post Shocked and I've been purely building scale non-flying models I was pleasently surprised at this sudden spurt of posts Grin

Coops we gotta have 'novices' in the hobby or it will die Shocked Shocked Welcome aboard!!! Grin Grin
That Typhoon's not a bad start from a kit it just needs some serious work. Firstly sand in a rounded leading edge to the wing till you get a nice airfoil shape to the leading edge, sand the trailing edge down from the top surface only to get a fine trailing edge. The canards should be sanded with a rounded symmetrical leading edge and carefully thinned trailing edge. Round the leading edge of the vertical stab symmetrically and thin the trailing edge. These actions will remove form drag and smooth the airflow considerably. Next gently slice the underside of the wing trailing edge outboard flaperons and gently bend them up to approx +1mm and glue them to hold the position, gently bend the wing tips down at the leading edge to create some washout (twist). This delays the onset of tip stall and pitch up into a full stall. Round off all the flat sheet edges (except for any forward facing intakes and aft facing exhausts) as it makes the balsa a bit more resilient to damage (it also removes weight Roll Eyes.

Great F-86"Dog", don't forget a bit of washout (negative twist from root to wing tip) to stave off tip stall and smooth all edges as I said above. Don't touch the chin intake it's meant to be 'flat'. I look forward to you posting test flight results Wink Cool

MKelly, 57 seconds!!! Shocked That's amazing!! Shocked Cool You got a pic of the model?
Your Scimitar (love the choice of subject) is a very ambitious and beautiful piece of work Cool Cool I just hope those beautifully formed intakes don't act like a set of heavy deployed speed brakes and create huge drag. They may steal initial speed off the catapult and shorten your flight considerably. Also as the nose comes up as it slows the intakes may speed the model into a stalled condition due to trapped air in those intakes. Reason I'm mentioning this is I tried 3D intakes etc on a CATAJET Buccaneer (12" wingspan) only to fail for the above reasons, and after a long and involved conversation with an mate who's forgotten more about aerodynamics than I know that was the conclusion. In the real aircraft there are engines in there providing thrust, and when they stop working they become pure drag hence the 'flying brick' monika for jets with a flame out. The ducts are responsible for the same thing, wouldn't have thought it but. . . hey who am I to argue Huh I actually hope I'm wrong and your Scimitar will fly, and well at that as it really is beautifully done Cool Cool Just remember weight and drag are the enemy Angry

ZK-AUD, CATAJETS and CATAPROPS need to be mostly profile as that's the whole idea of the designs. Simple sheet balsa flying models launched by catapult that with a bit of gentle tweaking can be made to really preform in the glide. Weight and drag are the enemy with these models and you do not want to go 'too far' overboard with "correct 3D" details or operating bits as it's all weight and ultimately drag. You can obviously finish your models however you wish at the scale size of your choice just do not add too much weight and remember to test fly when you finish to see if there has been any changes to your models' flight characteristics. Just remember that the proportions in side elevation and plan view used in your model must be very close if not exactly the same as the actual aircraft you are modelling as a CATAJET. There are modellers out there that have to catapult launch their "Stick and Tissue" Rapier rocket motor powered models as a glider due to the unavailability of the rocket motors to power their models. They obviously must be careful with their models as it is easy to crush structure when pulling back for the cat launch but one thing that holds true, they must be light.

OZPAF, great advice on sanding wing shape Wink CofG is approx 1/3 the chord from the leading edge depending on the CofG rules of your chosen wing plan form and the actual balance point of your model (you want it to be slightly nose down for a CATAJET or CATAPROP when balanced on it's CofG). If you put the CofG back too far you risk having a model that does the 20G death loop off the catapult ending in a "sudden unplanned air/ground interface" that usually damages or destoys your model and sometimes injuring yourself also. I've never used depron so i cannot comment on it's flying characteristics.

Cheers all and happy flying Grin Grin
Neil Cool Cool
 
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MKelly
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« Reply #513 on: April 20, 2017, 09:07:04 AM »

Thanks all, the Scimitar has been a fun build.

Mike, I am a Tiger (7-year-old) den leader.  Fun stuff - never having been in scouts before I'm learning just as much as the cubs.

John, rather than scouts I was in Civil Air Patrol as a young teenager, sounds like a similar organization to your Air League.  I had a lot of fun and that time did a lot to set up my subsequent career in the Air Force.  When my kids gets older I may get back into that if they show interest in it.

Neil,  thanks for the thoughts on the Scimitar.  The nacelles are 1/4" sheet - enough to give the impression of depth but hopefully not so big as to completely spoil performance.  The intakes are carved fairly shallow, again just deep enough to give the look. I'll watch out for the stall characteristics you warn of.  Might be interesting to make another without the nacelles and compare performance.  Weight is not too bad, just over seven grams before any decoration.  Balance is pretty close already so I don't anticipate adding much noseweight, should be able to keep the finished model under 10 grams.  The stab is adjustable so that I can play with balance and decalage to see what gives the best flights.

Unfortunately I didn't get any pics of the B-57.  It was a simple sheet model, profile fuselage and nacelles, looked like about 10" span.  There were two at the meet, both flew well although one had some trouble transitioning from very impressive launches into a good glide.  The 57-second flight was in windy conditions.  Pilot got a great launch and each turn from upwind to downwind recovered most of the launch altitude keeping the model in the air for an impressive time and distance.

Cheers,

Mike
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« Reply #514 on: April 20, 2017, 11:39:49 AM »

Pit, a most compelling subject....Mike, have you tried turning the scouts on to a simple cat jet? Guys are always talking about drawing the young kids into the hobby, and few succeed. Marcelo is one, but he is stupendously atypical.  I bet a simple and well behaving cat jet presentation will hook a few... Keep it simple, and no "Kelly masterpieces"  Just saying. Great subject Pit!
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« Reply #515 on: April 20, 2017, 01:14:30 PM »

Thanks for the advice re airfoil profile chaps, I'm going to practise on a few 1/8" pieces of sheet first before hitting the completed Eurofighter model.

Beautiful work there Mike, gorgeous stuff!

On the subject of profile vs full fuselage - the thing that has attracted me to catajets in the first place is that I know I can put together a profile model from conception to completion in a short enough period of time to not get bored with the project. And I tend to be a real butterfly when it comes to subject models (I had this problem when I raced slotcars too) so being able to find a cool looking 1:1 prototype and know it won't be six months, and more importantly another 200 lovely looking cool aeroplanes that I discover in the interim, before it's finished is a huge plus to me.

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MKelly
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« Reply #516 on: April 20, 2017, 02:00:58 PM »

Crabby,

Yes!  We had a glider night last fall for the full pack - the boys had a great time putting together and flying simple sheet gliders, including some simple distance and looping contests.  We also had a remote control night last month featuring helicopters for the boys to fly (as well as ground vehicles to drive) and demonstration of indoor RC aircraft.  My son has continued to fly the gliders and is getting started on a Guillows built-up profile rubber model (will be his second one).

Mike
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ZK-AUD
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« Reply #517 on: April 20, 2017, 04:29:57 PM »

Pit, a most compelling subject....Mike, have you tried turning the scouts on to a simple cat jet? Guys are always talking about drawing the young kids into the hobby, and few succeed. Marcelo is one, but he is stupendously atypical.  I bet a simple and well behaving cat jet presentation will hook a few... Keep it simple, and no "Kelly masterpieces"  Just saying. Great subject Pit!

We have an air-minded troop with many of the families and leaders having strong aviation connections, and with me being involved it will be no surprise that we include an aeromodelling activity in the programme every year!  Usually we go with something called the Airsail Mantis which is a stick and sheet rubber model.  I get Avetek to laser cut them for me and select the wood myself so that we get really good flights of up to a minute in the local school hall.  Previously I had the kids cutting them out but it took too many nights to get them built and flown.  Over the last 10 years I have done over 500 Mantii with Cubs Scouts and school groups.  I also did Hangar Rats with a group of the more intelligent Scouts last year.   Oh we also did Tiny Bees one year - the little Mark Bees rubber all sheet biplane that appeared in Aeromodeller back in the 90's.  Cat jets are a good idea that we could have a go at this year - I have a couple of interesting plans in the cupboard - an F14 that came out in Aeromodeller and a an F111 with swinging wings that came out in Popular Mechanics in the 60's
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FLYACE1946
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« Reply #518 on: April 20, 2017, 06:24:39 PM »

What about the delta wing on a Skyray ? How much sanding is possible on a wing that is 1/32 sheet balsa to begin with. A few months ago I had a lot of fun with an A4 with no sanding needed and the only reason I went to a bigger jet cat was to be able to keep it in sight. The more balsa broke off the wing trailing edge allowed better flying. Don't know what happened to that plan.
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FAAMAN
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« Reply #519 on: April 20, 2017, 07:06:02 PM »

Hey Flyace, I've an A-4 "E" I think CATAJET plan 10" (?) wingspan somewhere around. If I find it do you want me to post it!
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MKelly
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« Reply #520 on: April 20, 2017, 09:11:51 PM »

Allen,  minimal sanding on the Skyray wing - just round the leading edge and maybe a slight bevel on the trailing edge.  The slot in the fuselage will form the airfoil and reflex the trailing edge.  I don't think I did much sanding at all on the small one I built as a teenager.

Mike
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FLYACE1946
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« Reply #521 on: April 20, 2017, 11:20:30 PM »

Hey Flyace, I've an A-4 "E" I think CATAJET plan 10" (?) wingspan somewhere around. If I find it do you want me to post it!
Sure would like to see that one. Please do post it.

Thanks
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FLYACE1946
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« Reply #522 on: April 20, 2017, 11:22:17 PM »

Allen,  minimal sanding on the Skyray wing - just round the leading edge and maybe a slight bevel on the trailing edge.  The slot in the fuselage will form the airfoil and reflex the trailing edge.  I don't think I did much sanding at all on the small one I built as a teenager.

Mike
Thanks for the advice Mike. Getting mine cut out Friday morning. Nice shade of blue overall except the windshield.
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« Reply #523 on: April 21, 2017, 12:10:43 AM »

Bill Dean did an excellent Skyray in his book...it has a reflex wing and is a fabulous cat jet. I made a dozen of them for my wife's day care one year and they had a blast till one of 'em got hit in the forehead... Cry Grin but these little people were getting major air with 'em!
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« Reply #524 on: April 21, 2017, 10:34:27 AM »

Crabby,

That's the one Allen is building.  Here's it's larger cousin, Bill Dean's 10.5" span Jetex Skyray converted for jet cat. Fun flyer, very fast, but not really competitive - don't think I've ever gotten more than about 12-15 seconds out of it.  The smaller one may do better.

Cheers,

Mike
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