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-   -   Bob Cat Copy Falcon 120 Jet (http://www.rcuniverse.com/forum/rc-jets-120/5913492-bob-cat-copy-falcon-120-jet.html)

Ed 07-20-2008 10:53 PM

RE: Bob Cat Copy Falcon 120 Jet
 

Quote:

ORIGINAL: joeflyer


In Booms/ In Wings/ In Fuse
Rudders/ (2) 12"/ (2) 18"/ (1) 12" Y
Elevator/ (2) 24"/ (2) 18"/ (1) 12" Y one elevator servo is reversed
Ailerons/ -/ (2) 12"/ (2) 18"
Flaps/ -/ (2) 6"/ (2) 18"
Steering/ -/ -/ (1) 12"

This allows me to have connections at each interface (boom/wing and wing/fuse).

Joe
Excellent Joe, excellent ! Just what I needed. Yes, I will take additional measurements at the joints, and modify if needed, but this is a great start.

Regarding Tumblers structural failure, what might be the strongest one part glue to drip down thru the root rib, and hit the wing tube & rib assembly joints ?
Gorilla glue ? Polyurethane ? or what ?

Thanks gyz, great thread !

... zak


sweetpea01 07-20-2008 11:02 PM

RE: Bob Cat Copy Falcon 120 Jet
 
Poly probably good. It will expand to the spots it doesn't dribble to.

erazz 07-21-2008 12:29 AM

RE: Bob Cat Copy Falcon 120 Jet
 
Well It's a cheap airplane. We all know that! I fully expect to trash mine sooner or later. That's part of the appeal for me. I really don't care all that much if I crash it.

OTOH it's a great trainer. Flies slowly and has a low w/l.

aquaskiman 07-21-2008 10:02 AM

RE: Bob Cat Copy Falcon 120 Jet
 
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I tore a gear out in a stiff cross wind mishap; any gear would have ripped out in my case. I had added glue to the gear mounts. I also re did the fuselage formers and glued with hysol glue.
When I cut the sheeting back I found that the sheer webbing on the main spar has the grain running the wrong way. I have about 50 flights on mine but have been pretty gentle with it. I have another kit and I will be cutting the wings up on that one to make it stronger by putting the sheer webbing the right way and re gluing all the ribs.
George

GreenAcre 07-21-2008 10:03 AM

RE: Bob Cat Copy Falcon 120 Jet
 
Now I am questioning putting a Modellbau T-750 on mine! (24lbs thrust) [sm=confused.gif] I have Gorilla glue everywhere in the wings/retract area and will NOW get a carbon wing tube. Maby I will just save up for a Velox...

TUMBLER 07-21-2008 10:06 AM

RE: Bob Cat Copy Falcon 120 Jet
 
I am looking at a Velox myself.

Quote:

ORIGINAL: GreenAcre

Now I am questioning putting a Modellbau T-750 on mine! (24lbs thrust) [sm=confused.gif] I have Gorilla glue everywhere in the wings/retract area and will NOW get a carbon wing tube. Maby I will just save up for a Velox...

TUMBLER 07-21-2008 10:10 AM

RE: Bob Cat Copy Falcon 120 Jet
 
Yeah, looking at the wing, it was built ok for a glow plane and don't see why anyone would have a problem with a glow engine, but it was not built for a turbine and needs some beefing up beyond what you can get to from the outside. Had I had it to do over again, I'd strip the bottom and add wood and carbon and make sure it is done right. A few extra nights could have saved it.

Tumbler


Quote:

ORIGINAL: aquaskiman

I tore a gear out in a stiff cross wind mishap; any gear would have ripped out in my case. I had added glue to the gear mounts. I also re did the fuselage formers and glued with hysol glue.
When I cut the sheeting back I found that the sheer webbing on the main spar has the grain running the wrong way. I have about 50 flights on mine but have been pretty gentle with it. I have another kit and I will be cutting the wings up on that one to make it stronger by putting the sheer webbing the right way and re gluing all the ribs.
George


Jack28 07-21-2008 11:53 AM

RE: Bob Cat Copy Falcon 120 Jet
 
Hi Guys, Just an insight on Tumbler's wing failure, I was spotting for him when it happened, The whole flight was at 1/2 throttle, when the wing failed it was only flying at maybe 40- 50 mph. The flight was very smooth , no High G manuevers and no burners. I can vouch for Brian in his flying/building ability, he is an expert pilot with alot of experience. You have to remember that this is a chinese copy ,and never designed to be a turbine aircraft. Due to its low cost it attracts alot of guys that want to get into turbines cheaply, I believe it can be flown successfully with a light engine (12-14 lbs) as long as the wing spar area is reinforced. I think the failure was the wing tube itself, I would definetely insert a hardwood dowel into the wing tube with Gorilla glue, this will increase the yeild strength of the tube, I would also look at the joints where the wing tube ends and extend this area out further on the wing. Take a good look at your wings and flex them at the wing tips, they have alot of flex in them ,not a good thing for a 160 mph jet. Jack.

TUMBLER 07-21-2008 01:33 PM

RE: Bob Cat Copy Falcon 120 Jet
 
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Just so you guys know I am not totally against Falcon's, I have 2 Falcon .25's. I freak'n love it! I have eletrified it and modified the wing for retracts because it comes with fixed gear only. It was clocked in the video at 139mph and 122mph in an inverted pass. I put waaay more G's on this little thing the bigger one ever saw and she took it well. So the design I think is good, but as they scaled it up, they did not strengthen it accordingly.

In fact, Nitroplanes had my video on their site to advertise the plane.

http://www.rcgroups.com/forums/showt...84#post8490044

Tumbler

tim777jet 07-21-2008 05:35 PM

RE: Bob Cat Copy Falcon 120 Jet
 
Ref the guy fitting a 24 lb turbine in this aircraft, I really think you should consider what you are doing. 24lb thrust in a aircraft designed to have an AUW of around 12 lbs!
I spent around 10 years designing and finally achieving a working jet engine. I left it lying around for about 3 years in my garage, collecting dust, then decided to get it flying.
I was going to design my own aircraft, but saw this plane advertised for around 180 pounds in UK. I could not buy the materials to build a plane like this for that money, so bought it thinking I could use maybe just the wings or a few other parts, but was so suprised at what you get for your money, beautiful lines and in general, a really beautifull design, so decided to convert it and keep it as it was.
My model owes me nothing, I have had enormous pleasure from it, and learnt a lot, but if you need a model with a 2 to 1 power to weight ratio, then I think you should be looking at the high end of the market manufacturers. This model will take off fully laidened with fuel, from grass with around 12 lbs of thrust, a real credit to the model, 13 to 14 lbs is great.
As aquaskiman has indicated, he found his wing shear webbing with the grain the wrong way round, hard to belive in 2008 that this can happen, worth a check on all our models.

Fly safe Tim

Gandalv 07-22-2008 12:51 AM

RE: Bob Cat Copy Falcon 120 Jet
 

Quote:

ORIGINAL: TUMBLER

...........but it was not built for a turbine and needs some beefing up beyond what you can get to from the outside. Had I had it to do over again, I'd strip the bottom and add wood and carbon and make sure it is done right. A few extra nights could have saved it.

Tumbler

Tumbler, could you explain a little more on where you wood beef up the wood and carbon fiber etc ? I am about to start the build on my Falcon and are considering to do some "drastic" changes to the wing after reading this last pages in the tread.

That said, there must be several hundreds on hundreds flight with the Falcon without failing, but still, think I going to ripp the bottom of the wing.

Regards from Gandalv

TURBINATOR 07-22-2008 08:19 AM

RE: Bob Cat Copy Falcon 120 Jet
 
It is amazing to me what a single crash has done to this thread. We have one person warning the sky is falling and everyone is gun shy about putting this plane in the air now. The actual cause of the crash is purely speculation. Maybe it was poorly built at the factory, assembled incorrectly, damaged from previous gear failure, etc, etc. The fact is all airplanes are doomed. It is just a matter of when and where it will happen. Every time you leave the ground, it may be your last flight on the airframe. I don't care how many precautions you take, there is always going to be a weak link somewhere. We just had two catastrophic failures of some aerobatic planes at our field from reputable companies and we have no idea how it happened at such low airspeeds. Things happen, but it should not make us all paranoid about this airplane. I have over 50 flights on mine with a P-60 and I pretty much fly wide open the whole flight. Stay within the low end of the turbine thrusts numbers and everything should hold up. I feel for your loss Tumbler and am glad you have alerted us to potential problems to address. However, I hope we can get back to talking about everyone else's successes and keep these rare incidences from putting a damper on things.

Jeff

TUMBLER 07-22-2008 08:45 AM

RE: Bob Cat Copy Falcon 120 Jet
 

Quote:

ORIGINAL: Gandalv

Gandalv,

First off, it seems several people have had problems with the gear ripping out. This is because the wood is typical low grade light ply. Common to tons of ARF's so nothing out of the ordinary, but again we are trying to fly the plane beyond what it was intended for so some exrtra strength would be nice. Adding ply doublers to the existing ribs would really help. The wing tube does not extend all the way to the gear and would be nice if you could get a tube 6" longer so it would go to the next rib in each wing. Now, what my buddies and I really noticed was the flex of the wing outside of the wing tube. This is where the wing seemed weakest. Hold your wing by the boom area and try to flex the wing tip and you will see what I mean. I would try to get some carbon spars tied into the wing tube/gear area or at least add some shear webbing. I would also add some balsa or ply in the area between the wing skin and the phenolic tube.

Perhaps mine was an isolated incident and will never happen to anyone else, which hopefully is the case. Maybe I got one of the newest ones and they had a bad batch of wood or glue....who knows. I do know that if I was about to test fly a plane worth $3-$4,000 and saw this happen to someone who just bought the same plane I did, I would want to take extra precautions. These threads are not only about sharing the good, but also the bad, so things like this don't happen to others if they can be prevented.

Anyway, I am moving on, so good luck to all you guys. Hopefully I am the only one with this problem.

Tumbler




Quote:

ORIGINAL: TUMBLER

...........but it was not built for a turbine and needs some beefing up beyond what you can get to from the outside. Had I had it to do over again, I'd strip the bottom and add wood and carbon and make sure it is done right. A few extra nights could have saved it.

Tumbler

Tumbler, could you explain a little more on where you wood beef up the wood and carbon fiber etc ? I am about to start the build on my Falcon and are considering to do some "drastic" changes to the wing after reading this last pages in the tread.

That said, there must be several hundreds on hundreds flight with the Falcon without failing, but still, think I going to ripp the bottom of the wing.

Regards from Gandalv

airspeed917 07-22-2008 03:06 PM

RE: Bob Cat Copy Falcon 120 Jet
 
1 Attachment(s)
After reading what happend to Tumbler I thought I would look into beefing up the with wings so I did a little exploratory surgery and one thing lead to another and I ended up stripping the whole wing of its covering.. I took off the sheeting on the underside of the wing from the flap servo pocket all the way to the root.. My shear webing was OK, (Vertical) One thing that was a little surprising was the wing tube socket was not phenolic, it was a rolled up piece of heavy paper, from what I can see it was a set of instructions to another plane,,, I plan on glassing over it... I used gorrila glue on all the joints, and I plan on adding some more shear webbing,, and most of all I'm going reinforce the whole retract area... as you will see in the pictures the retract rail are not supported very well. I know it might be a bit much to do what I'm doing, but if a little extra effort can save a $2500 Turbine, I'll do it.
By the way guys the aluminum wing tube is 20mm x 508mm I found a carbon wing tube from from Aero-Works that they sell for their 120 Yak it is 20mm x 654mm which is perfect so for those of you who want to extend the tube into the retract area this tube gives you about 3 inches extra on each side. That's what I'm going to do.
That gorilla glue is crazy stuff,, it foams up and expands like crazy,, but it sure holds well its cures very hard,, I'm just glad you wont see it once the wing is covered... I post updates on the build

tim777jet 07-22-2008 03:37 PM

RE: Bob Cat Copy Falcon 120 Jet
 
Nice one Airspeed. One thing that Tumbler mentioned was that his wing was flexing from the boom to the tip. After a couple of hard landings on the grass, I have physically tried manipulating my wings by hand and mine have always been rock solid. By thw ay guys, can we get this sort of Gorilla foaming glue in the UK or France, is it under a different name.

sweetpea01 07-22-2008 04:14 PM

RE: Bob Cat Copy Falcon 120 Jet
 
1 Attachment(s)
Its also Poly glue.....

Lots of places sell it......even Amazon

[link=http://images.google.com/imgres?imgurl=http://ecx.images-amazon.com/images/I/41SE9R169XL._SL500_AA280_.jpg&imgrefurl=http://www.amazon.com/Elmers-Ultimate-Polyurethane-16-Ounces-P9413/dp/B000BQW5LA&h=280&w=280&sz=9&hl=en&start=7&tbnid=58 lEgrfFCsgfRM:&tbnh=114&tbnw=114&prev=/images%3Fq%3DUltimate%2BGlue%2BPolyurethane%26gbv% 3D2%26hl%3Den%26sa%3DG]Poly Glue Link[/link]


Speny 07-22-2008 04:38 PM

RE: Bob Cat Copy Falcon 120 Jet
 
tim777jet

since you spend a lot of time at your pc - get some off ebay andsave your petrol - its the gorrillas b****ks

spen

tim777jet 07-22-2008 04:47 PM

RE: Bob Cat Copy Falcon 120 Jet
 
Ill stop monkeying around and get some, cheers tim

GreenAcre 07-22-2008 07:21 PM

RE: Bob Cat Copy Falcon 120 Jet
 
That what I did EXACTLY to my wings! Gorilla glue is nice...:D Hopefully my T-750 will NOT be to heavy

Aussie1 07-22-2008 07:51 PM

RE: Bob Cat Copy Falcon 120 Jet
 
1 Attachment(s)
G'day all! I'm new to this forum and like many, have found it to be a valuable and informative aid to building my Falcon120. The kit that I have is one of the latest and the manufacturer has tried to address some earlier quality problems by using harder and better quality wood and more glue where it is needed. As I will be using my trusty PST600 turbine, I have gone over the whole airframe and beefed up all of the high load and stress areas, particularly the undercarriage mounts and main spar supports. I also wicked a full 2-ounce bottle of thin cyano throughout the whole structure. This alone seemed to make a huge difference to the overall rigidity and strength of the airframe. I shortened the mains legs by 20mm and this gives 1.5 degree positive stance when sitting on a flat surface. Talking to others here in Australia that have the model, this makes for a very short and smooth take off run, and by default places less stress on the undercarriage. I was a little concerned about putting too much fuel forward of the CG, and after some hunting in the supermarket found a Coles brand distilled 2L water bottle that was short and wide. With the rear formers removed and the bottle pushed in hard against the rear of the fibreglass fuselarge, the centre of the bottle is right over the CG. The full UAT is forward of this, but this should normally only be considered in static balance calculations. The Aus MAAA reguires 3 different methods to stop the turbine, and I have the manual fuel shutoff valve, the Aux3 to the engine fadec, shutting off the fuel solenoid, but my problem is that I am running out of channels to do the third, which is the RX directly shutting of power to the fuel pump. My radio is a JR3810 with a 2.4 gig module. If anybody has any suggestions, I would love to hear it! So far my projected dry weight will be 12.5 Ibs and the PST at 14Ibs should be ideal. Just back to the fuel tank, once you have it in the final position, warm it with a heat gun and it will conform nicely to the fuselarge shape. Also I was finding it hard to buy a decent felt clunk for the tank, so tried the local lawnmower shop. For $12, you can buy a Honda brusscutter clunk, which looks like it was made for our purpose! My job takes me away alot so time permitting I hope to have the first flight in about 4-5 weeks, so I can't wait!

Ed 07-22-2008 11:13 PM

RE: Bob Cat Copy Falcon 120 Jet
 
Nice informative post with good pictures Aussie. I'm in the very early stages of assembling mine, so keep the good stuff coming. ;) Glad to see that you didn't use those wimpy little control horns. I used the same type here, Sullivan giant scale.

... zak

SJN 07-23-2008 01:26 PM

RE: Bob Cat Copy Falcon 120 Jet
 
1 Attachment(s)
Fired uo the engine last night, to see if all was ok, and see how hot the tail would get.

Well, I could hold my hand under the stabilizer with out any problems at both idle and full throttle. The air at my servo links was only luke warm.
Anyway, I hae replaced the plastic control horn, and glued in a glass horn, just to be safe. Im 90% certin that the plastic horn would have been ok.........but who knows ;)

I also made a high tech heat shield for the tail when starting. Just a bent sheet of alu. Works great :)



One thing that annoyes me, is that it takes ages to assemble the plane. And its best if someone helps out, holding, or connecting the servo plugs in the wings booms.
My car is small, so everthing has to be taken apart for transport. [:@]

I hope in the future, they make a falcon with a molded in mid wing section, like the Formost-Bommerang, so at least the plane can sit on all 3 gears while assembling the plane.
The falcon looks so much better than the others....;)

tim777jet 07-23-2008 01:45 PM

RE: Bob Cat Copy Falcon 120 Jet
 
Sonnich, tie a piece of locking wire and red streamer to you tailplane protector, might seem silly, but when everyone is asking you a million questions whilst trying to start a reluctant engine with freezing cold hands and a thousand and one things on your mind, you might just forget it is on there.
I leave the booms on the wings, just slacken the bolts 1/2turn when in storage, this saves a great deal of time.
I stack the wings on top of eachother with a piece of bubble wrap bettween. I can get the whole model in and all fuel, tools boxes and starting equipment, plus a fold up deckchair in my 2 plus 2 Mitsubishi GTO (3000) sports car with me and two adults. Not bad at all eh, cheers Tim

SJN 07-23-2008 02:07 PM

RE: Bob Cat Copy Falcon 120 Jet
 
1 Attachment(s)
Yea, good idea......it only has to happen once, and disaster strikes ;)


Ive sent hundreds of 737 NG and Classics off, with these NWS bypass pins a few years back
Better put the streamer to good use again :D




tim777jet 07-23-2008 04:23 PM

RE: Bob Cat Copy Falcon 120 Jet
 
I think we are in the profession, as long as it is not a GLP, !!!!


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