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Author Topic: CATAJETS: Design and Development  (Read 65151 times)
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FAAMAN
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« Reply #125 on: September 25, 2010, 09:32:48 AM »

Just spotted a B-52 Catajet in Yahoo Groups "Free Flight Cook-Ups" (FFCU). It's by member 'kittyfritters' and the two pics are posted in Photo Albums - Howards Hanger. It flew a 16 second competition flight from a FAC regulation catapult which is an 8" loop of 1/4" flat tan rubber.

I think it looks great, does anyone know if he is a member of this forum? It would be nice to get some first hand info and some more pics.
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« Reply #126 on: September 25, 2010, 11:40:22 AM »

I don't think that Howard is a member here. He IS planning to post the plan on the Yahoo site as soon as he gets some bugs worked out. I have some contact with him, and as soon as I get more info, I'll post it here.
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« Reply #127 on: September 25, 2010, 02:30:41 PM »

What size sheet balsa is the fuselage and wings cut from; lets say for a 12" ws bird?

Thanks,
Curtis
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« Reply #128 on: September 25, 2010, 04:37:34 PM »

You can get by with 1/8th. I prefer to laminate 2 x 1/16th to a central core of 1/32nd with the rear third of the center core following the fin sweep. This is for catagliders up to about 10" span. I also add doublers to the front if nose weight looks to be needed (note: the Suchoy [show us your collect...] came out VERY nose heavy).

For 12-18 inchers, I think 3/16 is a good bet.
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« Reply #129 on: September 25, 2010, 06:29:01 PM »

OK, thanks, I appreciate the info. I'm thinking of joining in with something.

Curtis
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« Reply #130 on: September 25, 2010, 06:38:35 PM »

From the "Show us your collection ........ " thread I thought I'd add this quote from a post I did there to get the swing wing discussion on this thread:

"Tom, I think you'd find that the Grumman F-10 Jaguar would be a difficult and frustrating subject to fly with swing wings because the distance between the pivot points is very small, causing some large CofG movement probs, all the early swing wing aircraft had this prob 'till the engineers worked out that if they put the pivots further apart it reduced the CofG movement to manageable level. Just look at the planview distance between the pivots of the F-111, F-14, Tornado, Sukhoi Su-17, Su-22, Su-24, MIG-23/27, Tupelov Tu-22 Blinder and Tu-22M Backfire. The distance between these pivots are greatly exaggerated on some of the Russian aircraft, but it also further limits the CofG move."

If you look at the planview of the F-10, you'll see that to swing it's wings (increase the wing sweep) it has to change the actual position of the pivot point forward from the initial pivot position in the swept forward position (pivot point fully aft). The idea of putting the pivots out on 'gloves' or root extensions was to allow fixed pivots for the wings of modern swing-wing aircraft thus clearing up many of the probs, some serious, that these earlier swing-wings had.

Can't remember who asked, but this link will take you to an online Centre of Gravity calaulator ;
http://adamone.rchomepage.com/cg_calc.htm

Keep flying all !! Grin Grin
Neil
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« Reply #131 on: September 26, 2010, 07:20:51 PM »

Pit and Curtis...looked up the B-52 on the yahoo site. looks nice. One of the things that always facinated me with the real B-52's that flew around my home in Sacramento, CA...they climbed out nose low. I don't know if it was the large swept wing and the horizontal stab incidence or what but it was always kinda wierd to see them climb out with the tail higher than the nose.

Neil...thanks for the cg link... Grin

Tom
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« Reply #132 on: September 26, 2010, 08:24:31 PM »

Tom, I got stationed at half a dozen bases with BUFFS. You're right about the odd way they climbed out. They also had a real odd way they landed in crosswinds, as they could end up with their tail and nose canted way off from the axis of the runway. The landing gear was designed to handle those crosswinds. I was communications support for those crews for probably 12 years. Will be interesting to see what a CataBUFF will look like.

Caley
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« Reply #133 on: September 27, 2010, 06:10:18 PM »

I've noticed in a lot of posted pictures not much wing dihedral (as best as I can see); how are the CATAJETS performing with the wings built this way?

Thank you,
Curtis
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« Reply #134 on: September 27, 2010, 07:05:16 PM »

Poorly. As though needed more dihedral. Wink
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« Reply #135 on: September 27, 2010, 08:06:20 PM »

Tom, I got stationed at half a dozen bases with BUFFS. You're right about the odd way they climbed out. They also had a real odd way they landed in crosswinds, as they could end up with their tail and nose canted way off from the axis of the runway. The landing gear was designed to handle those crosswinds. I was communications support for those crews for probably 12 years. Will be interesting to see what a CataBUFF will look like.

Yeh, I saw one land at Mather AFB when they were stationed there and With the bicycle landing gear I couldn't believe the angle of the aircraft as it landed...the nose was at least 45 degrees off center line of the runway...but as soon as it touched down it squared up with the centerline. Really something to see. Shocked Grin Cool

I'm curious as to how the CataBuff would fly....a buddy who flew them told me the wingtip of the real ones flexed upwards approximately 18 feet. He had some really neat Red Flag stories to tell.

Tom
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« Reply #136 on: September 27, 2010, 08:39:59 PM »

Tom, I was stationed at Mather from 1983-1990 when they closed the unit down. Sad I've never seen the tips flex up that far, but I guess they could if they are fully loaded with conventional ordinance. They could carry a lot of that stuff. I heard some really good stories also. One wasn't so pleasant for one crew who strayed inside Dreamland and were met and carted away by special agents upon landing. After that none would ever mention anything about that flight. I still wish I was up in the Sacramento area. Loved the area. Just say one of your creations over on the CATAPROP thread. Real nice.

Caley
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« Reply #137 on: September 28, 2010, 09:23:18 PM »

Caley,

Sacto is a nice area...we live there from 1977 to 1988. Did a lot of photographing the birds there and at McClellan and up at Yuba City/Marysville, Beale AFB. Got some nice pics of the real birds, SR-71s, U2C's and U2R's, B-52's at Mather and a whole bunch of types at McClellan...A10's, F-111's, F-106's, F-105's, C-130's, C-135's, F-105's and some British birds as well. Loved all the activity.

Yeah, I got a Cataprop on the other thread... my fetchermites have already claimed it as well... got some pics there.

Regards,
Tom
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« Reply #138 on: September 29, 2010, 08:24:36 PM »

Been doing some research through my library and around the web (SFA, S&T, HPA etc) the past week or so looking for some answers in regards to our "launch loop", transition probs, stability and glide flight-path.

So firstly, the "launch loop" is caused by the "excessive speed" required at launch (causing huge lift coupled with the models inability to correct it's set trim for gliding) to get our models to a decent altitude therefore giving us longer glides. In all the references I've checked, including Hip Pocket, it seems that the tailplane (enlarged @ least 25% over scale) should be at 0deg with the wing root at no more than +0.8deg incidence with the appropriate amount of washout for your model. This washout should be started at -5mm root to tip as a starting point. Also, the amount of weight we use for trimming CofG to get a nice smooth glide across the yard is not enough. It seems that at least another 1/2 again as much weight is needed set approx 1/4 - 1/2 way back from nose weights before the CofG. This gets a little messy when a model with a short nose is created and the positions for the weights get a little close or even overlap (more a prob with single engine Prop driven designs).

The probs with transition after launch come down to a number of factors, including speed, inertia, wind direction & strength and obviously model design/trim/weight. From what I've read (in some cases reread 'cause I'd forgotten Embarrassed) it seems we also need a little more dihedral than we've been using (scale models do not have enough for inherent stability in free flying). This modification coupled to the previous ones' mentioned above smooths the transition point.
I came across a thread in "Hand Launched Gliders" here on HPA that tightened the angle of incidence to +0.5deg (! Shocked), there was also a very good idea to sand an airfoil into the vertical stabiliser so it "lifts" opposite to the direction of flight thus turning without deflecting the rudder and causing form drag.

This is not by any means a comprehensive fix for our Catajet probs, nor is it the be all to end all on the subject. Any constructive input from those far more experienced and knowledgeable is more than welcome, and if I've got it wrong, I gave it a good try. Best way is to trial what I've found on test articles and test, test, test! Grin

Regards all, keep flying!!
Neil
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« Reply #139 on: September 30, 2010, 07:25:21 AM »

Another thing to try (it actually works for some subjects - HAS been used for comp. C/HLG) is to sand in an airfoil into the stab (Neelmeyer or Clark-Y style) and mount it INVERTED at 0/0 decalage. Supposedly has a teeninesy bit less drag, but the airfoil has to be "just right" to lift just the right amount of "down" lift. I've tried it successfully, but prefer the neg. incidence route - less work.
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« Reply #140 on: September 30, 2010, 09:53:56 PM »

Poorly. As though needed more dihedral. Wink

Which models are you referring to? The Catajets that I have built have sufficient dihedral or polyhedral for a stable recovery after launch and roll out at the top and then proceed in a large 45 to 50 foot circle in a fairly flat glide.

I've found that the angle of launch has a lot to do with the effect of the full power launch. I have found that more balast has helped with dealing with the, as Neil says 10+G Loop. My F-94C has been the most successful of my designs so far with a nice high launch and glide that produces a consistent 19 second flight and a nice walk all the way across the park where I fly. If I tweaked for more performance I'd probably lose it where I fly. Still lots of fun and almost everyone who sees it stops to watch it fly across the park. The dihedral on most of my birds is 15mm under the wingtips and on the LearFan its 22mm with the V-Tail. Still sorting that one out. I don't know if this is appropriate but I use the same rule as for the rubber powered planes. I try to keep the tips above the trust line of the fuselage.

I've been doing most of my engineering on the TLAR style. So most is guestimation. I'm careful with the decalage of the wing and stab. I usually start with +1 degree on the wing and negative 1 degree on the stab. I leave room on the vertical stab to adjust the horizontal stab and use shims to get the glide I'm looking far. I try to get it just below the stall at the end of the glide. Then add a bit more ballast for the catapult launch. I usually try to add turn at the base of the vertical stab/rudder by tweaking the balsa with my fingers. Shocked Roll Eyes must be careful not to crack the balsa.

Regards,
Tom
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« Reply #141 on: October 01, 2010, 06:16:09 PM »

Got the Catajets out this morning to do some flying...remarkable how the slightest warp in the structure affects the flight pattern. The FH-1 Phantom flys fast... needs to be larger which won't be a problem as the last flight (number 5 or 6) she caught a gust of wind on the launch which rolled her inverted... did her best to pull out but lawn darted and wound up in four pieces. Will rebuild larger. Was really flying pretty good but hadn't gotten to transition into the gliding circle. She would roll out on top start a large left turn and then straighten out and glide straight till she landed.

The F94C put in two good flight but the fetchermites wanted to do the new ones so we progressed to the Mig 15. This was a surprisingly good flyer. almost no ballast and she would rocket up on launch. When she rolled out she leveled off and flew straight ahead across the park. Still working on getting a shallow turn introduced. But she glides really well.

Natter was the showoff today... three really good flights very high and all the way across the park...forgot to time her but got a shot of her at altitude...

Lear Fan is still very fast...needs enlarging as well. Wind came up too soon and the fetchermites decided to run the bases at the ball park so we packed it in after the NoCal P40C caught a gust and did a wingover into the ground and then tried to relaunch...did a nice ground loop and destroyed itself on the rubber motor and prop beating into the ground. Roll Eyes Shocked Grin Wink

Will try again...
Tom
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« Reply #142 on: October 01, 2010, 06:52:45 PM »

Tom, Some great stuff. I always get a smile when you get your fetchermites in the photos. They just look like they're having so much fun, and I'm sure you're having fun watching them.

Caley
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« Reply #143 on: October 07, 2010, 01:13:09 AM »

Tom, Some great stuff. I always get a smile when you get your fetchermites in the photos. They just look like they're having so much fun, and I'm sure you're having fun watching them.

Caley,
They are a kick to watch. Especially as they hurry back to re-launch. I know one of them is going to fall on the model one of these days but that's half the fun. It is fun seeing them get excited when the planes take off and fly across the park. The noise they make as they chase them is priceless. Grin Grin Grin

Tom
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« Reply #144 on: October 09, 2010, 08:32:21 AM »

Here's the latest on my HP.115. A new wing was built as the original looked more like a potato chip than a wing ..... enormous warp! Angry Assembly went ok but I had to make a second canopy blank as the first didn't work very well, got a good canopy to use from the second attempt.
 
The pilot and ejector seat were drawn by myself. The part of the ejection seat visible above the cockpit coaming was copied from a pic I found taken from squarely (well, close) beside the real HP.115 at the Fleet Air Arm Museum at Yeovelton England. The pilot and seat are made from layers of paper glued over some thin balsa (0.5mm) to give the details some "3D relief" and then painted with Humbrol enamels. Cool

The landing gear has been created with a paperclip (nosegear) and .3mm piano wire (mains) bent as per plan. I couldn't really leave them off as they are fixed on the full size beast and it wouldn't look right without them. So I'm using the oleo of the nose gear carefully bent as the catapult hook with a plastic kit wheel drilled and glued to the "hook", the main wheels are balsa with paper oleo pants.

I have to work on the flying control surfaces as both are warped Roll Eyes (more warping .... hmmm ..... may reflect on me Huh) one bent up along the grain and the other has a steeply warped down trailing edge. Angry

My phones' camera is at it again, washing out the colour but at least you'll get the idea.

Cheers all, gentle winds,
Neil
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« Reply #145 on: October 09, 2010, 07:26:34 PM »

Neil,

Can't believe the detail you put in the cockpit of the catajet.  Shocked Shocked Grin kewl Grin

Did it understand that you plunge for the canopy? Slick Idea. "I like it!" as the Rocketeer said sitting on the edge of the pond after his first flight! Grin Wink

Keep me informed on the trimming ...I'm pondering an F102 and F106.

Tom
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« Reply #146 on: October 09, 2010, 07:41:26 PM »

Tom, I built my own vacuum former a few years ago and I'm still learning how to do it well. Smiley I'll supply a pic of my first attempt canopy blank being used.

I'm glad you like the cockpit, it just adds something when it flies past and you glimpse a "pilot". Cool

Have fun and fly high!! Grin

Neil
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« Reply #147 on: October 11, 2010, 06:02:21 AM »

Tom, I built my own vacuum former a few years ago and I'm still learning how to do it well. Smiley I'll supply a pic of my first attempt canopy blank being used.

I'm glad you like the cockpit, it just adds something when it flies past and you glimpse a "pilot". Cool

Have fun and fly high!! Grin

Neil... your vacuform looks great. Very professional looking. I made one for the Koutney Cookup and it works well. I think yours is much bigger than mine. Mine is approximately 8 inch square.

I'll have to try a canopy on my next catajet. Does open up a lot of options.

Keepem flying,
Tom
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« Reply #148 on: October 11, 2010, 05:31:36 PM »

Everyone's neato CATAJets have finally tipped me to take the plunge. But I really don't know how things will go, as I am terrible at trimming these CAT Gliders, or HLG's. I thought I was beginning to see the light on how it was done, but have discovered that much of what I've done was blind luck, and l cannot figure out how I made one fly. LOL!!!!

Anyway, I am going to try a Heinkel He176. I saw one of these airplanes at a RC swap meet I attended this past Saturday. The gentleman took a three view and scratch built an EDF scale model that is just a work of art. He was waiting for the swap meet to finish so he could maiden it. I didn't get to stick around, as my friend was driving us around and he needed to move on to other chores.

I'm not even sure this is a candidate, but I will build it anyway, and try to do the scale markings as well as I can. If it will glide straight ahead with a gentle toss, I'll feel that as a victory.

Caley
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« Reply #149 on: October 12, 2010, 08:20:50 AM »

That ought to work ok as a catajet Smiley. Just project the wing LE and TE to the fuz centerline to maintain the span. The stab looks close to 25% as is, but u could increase it a bit and the fin/rudder looks a bit small.

What size are u going for?

I've come to the conclusion that catajets UNDER 10" wingspan do NOT work too well. They CAN be made to fly decently, but require a huge amount of work. Most of my stuff has "grown" to 10-12", which has made trimming much easier.
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