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Bob Cat Copy Falcon 120 Jet

Old 03-07-2010, 07:02 PM
  #3276
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Default RE: Bob Cat Copy Falcon 120 Jet

I have an intermitten issue with my Falcon and I was wondering if anyone else has experienced the same thing. I have 2 of these airframes, the first one was flown about 50 flights and is now in the attic. The plane is so inexpensive that i decided to get another and do some improvements and lighten it a bit. The current one , with the issues has 70-80 flts now.
What I experience is a violent pitch down on downwind after the flaps are deployed. It is not consistant and it has occured 5 or 6 times in 70-80 flights. My older airframe never did this. I thought maybe I had too much travel in the flaps yet i had much less than some others in this thread. I reduced the flaps movment and I thought the problem was solved but 20 or 30 flights later, it happend again with only about 20 degrees of flaps. Once the situation is corrected, it doesnt happen again but recovery is "sporty" to say the least. It has never happend on base or final. I am always slowed and at idle when I deploy the flaps, but I'm thinking it is speed or attitude related and im guessing its a very fine line where it occurs. I really dont want to reduce the flap travel any further. I have slowed the flap speed to 3.75 seconds and taken the small down elevator/flap mix out. I havent flown it this way yet.
Anyone have any ideas or experienced something similar?


Thanks,
Cody
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Old 03-08-2010, 03:10 AM
  #3277
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Default RE: Bob Cat Copy Falcon 120 Jet

Cody

I will have a go at diagnosing it:

I think this is speed related as it happens on the downwind leg, and the variables will be the wind blowing at the time, turbulance over trees or even from buildings on the upwind side, by only deploying the flaps at 20 degs or so you increase the lift of the wing, but also increase the drag and turbulance behind the wing significantly, with the decrease of downforce from the tail (now not having fast moving air under it from the turbine) a pitch down will happen if all these variables occasion together, the most significant being the speed of airflow over the tail and the turbulance from the flaps.

The main reason for the excess downthrust needed on this particular airfame is IMO the speed of the airflow under the tailplane causing a negative pressure and hence revearse lift and a nose up pitch on increasing speed, if the turbine is at tickover and the flaps deployed, it would be easy to stall the tail which would give the syptems you describe.

Ready to repel boarders.

Mike
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Old 03-08-2010, 04:02 AM
  #3278
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Default RE: Bob Cat Copy Falcon 120 Jet

Might be simple radio glitch or lock out. Are you using 2.4 set up. Put model in the down wind postion and stand in the same place. Get helper to check the model while operating flaps 40 times. Try turnng the TX off and see what your failsafe settings are, maybe the elevator kicks down a tad.
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Old 03-08-2010, 04:07 AM
  #3279
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Default RE: Bob Cat Copy Falcon 120 Jet

Tim

I always think that everyone is on 2.4Ghz these days, therefore I don't think about glitching anymore. Strange how in such a short space of time 2.4Ghz has changed our perspective of the radio link to our toys.

Mike
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Old 03-08-2010, 04:51 AM
  #3280
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Default RE: Bob Cat Copy Falcon 120 Jet

Mike, a really good flyer at our field, a few weeks ago, lost his large model, quite close to him. When He checked the wreckage, we did a radio function and there was nothing wrong at all. He was on 2.4 g, had the standard set up , 1 rx and 1 satelite aerial. He will now add a couple more aerials. I have the basic spektrum with standard rx and 1 satelite aerial as well. I was consious flying model in the area he just crashed in, i had no probs. We are 99.9 % bullet proof, I think, but there is always a risk any time a model takes to the air. IT could be just a bad blackout area, at the guys club site, where he has noticed this problem. The engine, he said was at idle, so wouldnt notice any change there. An Odd one though. Cheers tim
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Old 03-08-2010, 06:54 AM
  #3281
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Default RE: Bob Cat Copy Falcon 120 Jet

Tim

I fly in an area that has always been known for it bad interferance on PPM, the Graupner IFS (US XPS system) did not work at all, locked out in four places in one flight, Spektrum in my large petrol models has suffered from intermitent lock outs and various other malidies, loosing link on switch on, servo glitching on fully charged batteries, co-axial popping off the aerial connection inside the module (lost that one) etc: I now use Futaba FASST and have for the past year and a bit without any problems of any kind.

Spektrum is now only used in my electrics and foamies and seems to be rock solid in them, go figure?

Mike
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Old 03-08-2010, 09:36 AM
  #3282
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Default RE: Bob Cat Copy Falcon 120 Jet

Mike,
The scenerio you desribed makes sense, but what I dont get is, why do i expeiencr it with this airframe and not the other and I have read no other similar cases from the dozens of falcon fliers her? I'm wondering is the stab incidence on this particular airframe could be just a bit off ?
Tim, I wondered if I had some sort of intermitten glitch , possibly with the ele correction with flaps downs, I eliminated that mix and rebound, I will fly again soon I hope and see if that helped, problem is, it is so intermitten. I am on 2.4 but you brought up a good point, geographicaly, it seems to happen in the same area but i do have elevator control during the event.
I think I might try to simulate the speed and various attitudes at high altitude and see if I cant zero in on the paramaters that induce the violent pitch change.
Thanks for you input guys,

Cody
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Old 03-08-2010, 10:39 AM
  #3283
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Default RE: Bob Cat Copy Falcon 120 Jet

Cody - I tend to think the problem is more electrical related. If you're using just one receiver battery make sure it's fully charged before each flight. Also you might just try a different type of new battery. Something like a 2 cell A123 battery, regulated or unregulated. Also check your failsafe settings and make sure all surfaces , including flaps, go to a neutral setting. The extra load on the servos when the flaps are actuated may be causing a voltage drop that is causing the receiver to lock out for just an instant when the battery isn't fully charged.
Just my thoughts.
Galen


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Old 03-08-2010, 10:52 AM
  #3284
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Default RE: Bob Cat Copy Falcon 120 Jet

Galen that a good point. I will make it a point to note my battery voltage if this problem re-occurs. I did reset my failsafe and rebind yesterday.
I am using 2 2600mah Li ion 2 cell packs thru a regulator. The flap servos are Hitec 5245 so they shouldnt draw a big load

Cody
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Old 03-08-2010, 02:40 PM
  #3285
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Default RE: Bob Cat Copy Falcon 120 Jet

Galen, very good point about the servo drain. As mentioned on the forum before, it is best to set the servo arm, so it is nearly inline with the control rod, when full flap is selected. This takes the electrical load off the servo and places the mechanical load to the servo meachanism and arm directly.

Just a point, that I would like to bring up ref batteries. I fly with one RX battery. A lot of folks fly religiously with two and the associated expensive spliters etc required for redundency, which is great. I have read lots of reports on how all these systems function so well. I have never read, how these people are fitting a second battery to the Transmitter, ever.
Are all these set ups only there, because modellers have set up their controls incorrectly and the servos are stalling out, draining their batteries, or are they saying there is not enough battery capacity to run their setup. If so, simply fit a larger battery.
I flew for years with just a 1320ma Lipo powering my Falcon, with 9 servos, couple of air operated valves and the ECU. I could fly for 6 , Seven minute flights without recharging no problem. I fly now, with a 2200ma pack, only because of the freezing cold temps i fly in, I have been worried about the cold reducing bat performance.
I use a Lipo voltage monitor (in fact 2). The first is built into the voltage regulator, a series of LEDs for the Receiver pack. The second for the ECU, has one LED and audible horn, which sounds if the battery voltage drops below a predetermined level. This I only fitted after leaving my ECU switched on for a day after flying and had to dispose of the battery. Now it is a reminder horn. When the strater kicks in after a days flying, it can occasionally beep on intial power drain a then remains off, so good check to ensure it does work.

Only reason I can see for fitting a second back up battery for RX is if the Voltage reg fails

Stands back for a verbal tounge lashing, cheers tim
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Old 03-08-2010, 04:07 PM
  #3286
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Default RE: Bob Cat Copy Falcon 120 Jet

Cody,
I suspect you have the flap servos Y'd from the flap channel on the receiver with one of the Hitec's reversed with a programmer. As Tim says a stalled servo or one that is working extra hard, can cause funny things to happen. If you have your servo arms set so the arm is 90deg to the flap hinge line when full down there would be no strain on the servo motor, but anywhere in-between the strain will be on the motor. I lost a Bobcat because a small servo on the retract valve went bad and caused a heavy drain on the receiver battery. The elevator servo went to full down and pan caked it into the runway. Fortunately your elevator servo recovers before it causes a crash. Whether you have one or two batteries you're usually limited by the switch or other small connections. If you haven't done so, be sure to check all connections even swapping out the Y.

Galen
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Old 03-08-2010, 04:08 PM
  #3287
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Default RE: Bob Cat Copy Falcon 120 Jet

Tim

Do you have a voltage monitor and horn on your Tx?

I don't use voltage regulators, just A123's via a Fromeco Kodiak switch straight into the Rx, the switch reads how many Mah has been used during all your flights until you re-set it.

Simple, straight forward and less things to go wrong.

Mike
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Old 03-08-2010, 04:19 PM
  #3288
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Default RE: Bob Cat Copy Falcon 120 Jet


Quote:
ORIGINAL: Grodus

Mike,
The scenerio you desribed makes sense, but what I dont get is, why do i expeiencr it with this airframe and not the other and I have read no other similar cases from the dozens of falcon fliers her? I'm wondering is the stab incidence on this particular airframe could be just a bit off ?

I think I might try to simulate the speed and various attitudes at high altitude and see if I cant zero in on the paramaters that induce the violent pitch change.
Thanks for you input guys,

Cody
Cody

I think you are on the right track, a small amount of incidence difference would make each airframe behave differently, as the booms are attached to the top of the wing a small discrepancy in the wing tube or incidence pins on the wing to fus joint would throw out the longitudinal diahedral.

Does the airframe dip its nose straight down or is there a turn to one side or the other, if its straight then to be a flap induced flight change would mean that both Flap servo's are behaving the same to cause the elevator to give un uncommanded control deflection, which I think is highly unlikley, but who knows, I am still in favor of the tail stalling through the excess turbulance from the part deployed flap at a very low airspeed on the downwind leg.

What batteries do you fly with? sorry if you have posted this already, but my age allows me to ask more than once.

Mike
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Old 03-08-2010, 04:25 PM
  #3289
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Default RE: Bob Cat Copy Falcon 120 Jet

Tim,

You're opening up a can of worms. This topic has been discussed many times in numerous threads on various forums.

The reason most guys use dual battery packs is for redundancy. If a battery pack, switch, or regulator fails they don't want it to cost them a plane. Most guys have their favorite battery set-up and swear by it.

I have been flying RC for 16 years. I don't use regulators and never have had a switch or battery pack fail in flight. The most common type of battery pack failure is a shorted cell therefore I use only 5 cell nicad packs. If a cell shorts out the pack still has enough voltage to power the radio and servos. I cycle my packs about once a month and replace them if they fall below 70% of rated capacity or when they are three years old, whichever is sooner. I use only good quality heavy duty switches with dual contacts.

I have dual battery packs in only one of my planes and that's because I needed the nose weight. If you decide you need dual packs you don't need to waste your money on any of the available battery backer electronics. Just plug the second pack into a spare receiver channel (or use a Y).

The best RC battery advise comes from Red Scholefield. See http://www.hangtimes.com/id33.html

Joe
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Old 03-08-2010, 04:34 PM
  #3290
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Default RE: Bob Cat Copy Falcon 120 Jet


Nice couverage joeflyer ..
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Old 03-08-2010, 04:37 PM
  #3291
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Default RE: Bob Cat Copy Falcon 120 Jet

Cody

Just a thought, have you tried as much flap as you can get and controlling the decent and speed with the turbine?

I use 85 degs of flap to act as an airbrake, its deployed fast and in two stages, stage one 45deg flap on the downwind leg whilst slowing down, stage two 85degs on the base leg and control the height and speed with the throttle, turn onto finals and start to lower the throttle still further to bring the wheels onto the numbers at mimimum forward velocity. Both stages of flap have a down elevator mix on them.

Mike
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Old 03-08-2010, 05:26 PM
  #3292
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Default RE: Bob Cat Copy Falcon 120 Jet

I am using 2 2600mah li-ion packs. As far as the reason for using 2, first off, i needed the weight and in the case of a battery shorting out like Joe mentioned, i would rather have a spare batt that lead to help balance.
I used an amp meter when setting up this plane as i always do. I even went as far a using a leaf blower on the flaps to simulate an air load and monitored the flap servo amp draw. Before i started reducing the flap travel to eliminate the problem, I had the servos set to 180 degrees of travel so that I had zero load with no flaps and full flaps, it was mechanically locked flaps up and full flaps.
Best I can remember, the pitch change is not occuring during flap deployment, it occurs after the flaps are set. And at the risk of sounding really confusing, the event does not look like the result of a simple down elevator command, its is more like a inverted cobra manuver. I really think it is some sort airflow problem on the stab caused by the flaps that only occurs in a very fine parameter of conditions.

Cody
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Old 03-10-2010, 02:23 AM
  #3293
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Default RE: Bob Cat Copy Falcon 120 Jet

Hi,

Is this airplane polyester or epoxy glass? Anyone know for sure? Sure smells like polyester....
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Old 03-10-2010, 05:37 AM
  #3294
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Default RE: Bob Cat Copy Falcon 120 Jet

Difficult to tell once set, but I agree it does smell like a polyester, but then it all accords what has been used as a catalist as its normally that which gives off an odor, I don't think its worth worring about though as Hysol seem to bond extreamly well to it, I have not tried any other glues to see what reaction I could get, so not much use rearly.

Mike
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Old 03-12-2010, 09:40 AM
  #3295
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Default RE: Bob Cat Copy Falcon 120 Jet

Quote:
ORIGINAL: BaldEagel

Difficult to tell once set, but I agree it does smell like a polyester, but then it all accords what has been used as a catalist as its normally that which gives off an odor, I don't think its worth worring about though as Hysol seem to bond extreamly well to it, I have not tried any other glues to see what reaction I could get, so not much use rearly.

Mike
Nitroplanes... think cheap.... think polyester! Hysol sticks to it fine though, as Mike said.

Stab issue/tip:
I noticed that when I assembled my booms to the stab and bolted the assembly to the wings, there was a bit of left-right sway in the fins at the stab joint, even with the single stab mounting screw on each side well tightened. Also, tightening the screw deformed the fin wood inward quite a bit. Both of these findings are due to the fact that the flat surface of the stab edge does not mate perfectly with the inside of the fin. The fix I used for this was to carefully tape waxed paper to the ends of the stab, overlapping it an inch on the sides of the stab and apply a generous amount of AeroPoxy to the stab ends. Then coat the stab mounting screws in silicone grease and tighten everything up in flight position on the wings. Tighten the stab screws until they just start to deform the fin, then back off a touch. Let it cure overnight and then disassemble. I had to repeat this once because the gap at the bottom of the stab wasn't completely filled the first time, but this greatly strengthens things and eliminates the flexing. Even if you replace the small single screw with two larger screws you might want to consider this if your stab and fin don't mate flush.


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Old 03-12-2010, 10:17 AM
  #3296
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Default RE: Bob Cat Copy Falcon 120 Jet

Here is what I did to tighten the stab mounting without the crushing of wood. With the pilot hole drilled, I carefully used a forstner bit to drill a bigger hole for a hard point. I drilled down to the bit of hard ply that was there and scraped out the balsa in the center. To make a hard plug for the center, I cut a ply disk just a bit larger than needed, and used the Dremel with a sanding block to make it a perfect fit. Using a little epoxy finished the job.
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Old 03-12-2010, 11:37 AM
  #3297
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Default RE: Bob Cat Copy Falcon 120 Jet

I just glued the stab to the booms. It's not a large assy. It still fits in my car great and though I feared hangar rash it's not a problem so far.
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Old 03-12-2010, 11:49 AM
  #3298
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Default RE: Bob Cat Copy Falcon 120 Jet


Quote:
ORIGINAL: erazz

I just glued the stab to the booms. It's not a large assy. It still fits in my car great and though I feared hangar rash it's not a problem so far.
Yep, that's sure one way to go. I thought about doing that and I suspect that I'll end up leaving these parts together most of the time as well, but I wanted the option of breaking it down if I really had to.
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Old 03-12-2010, 12:35 PM
  #3299
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Default RE: Bob Cat Copy Falcon 120 Jet

Hello, everybody!

I finally finished my Falcon last week. It took me some good months to finish it.

It´s my first jet and I think it was the best choice, although it was not easy to build it.

It has a K80E, what is more than enough power for this plane. I flew half throtle stick all the time, less on dives (iddle) and long verticals (full).

For who wants to see how it flies with a K80E, here goes the maiden video. It´s the third flight of the first day she flew. It´s without brakes, but after the maiden I decided to add brakes:


http://www.youtube.com/watch?v=67VHRPnAy-s



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Old 03-12-2010, 06:13 PM
  #3300
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Default RE: Bob Cat Copy Falcon 120 Jet

Quote:
ORIGINAL: rivarella

Hello, everybody!

I finally finished my Falcon last week. It took me some good months to finish it.

It´s my first jet and I think it was the best choice, although it was not easy to build it.

It has a K80E, what is more than enough power for this plane. I flew half throtle stick all the time, less on dives (iddle) and long verticals (full).

For who wants to see how it flies with a K80E, here goes the maiden video. It´s the third flight of the first day she flew. It´s without brakes, but after the maiden I decided to add brakes:


http://www.youtube.com/watch?v=67VHRPnAy-s
Congrats mate,

Looks realy good, and as you said, doesn't seem short of power, but it does sound like you need more down thrust to fix the climbing/diving issues

thanks

dave
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