RE: Bob Cat Copy Falcon 120 Jet
 

Pass?

RE: Bob Cat Copy Falcon 120 Jet
 

Ok Guys, got mine up in the air 2 days ago, flew beatifully.
First, I am powering mine with my own built jet, which is heavier than a comercially available engine ( about 1.25 lbs heavier), so had to go on a diet. My model weighed 15 lbs 2 oz with a full UAT, but empty fuel tank.. Now it weighs 14 lbs 2 oz.

- I am using a carbon spar tube instead of the ally one, saving @ 35 gms. I fitted the tube fully in each wing recess and cut the tube to give me max penetration in each wing. The carbon tube is slightly longer than the ally one now.

- I removed the Dudro tank, which weighs empty, 185gms. I fitted a pop bottle, 2 liters in volume, which is 3.5 inchs square in section. This fits perfectly in the fuse and sits on top of the rear spar, which gives perfect access to the wing attachment bolts that fit from inside the fuselarge. Pop bottle weighs just @ 70 gms complete with all tubes and clunk.

- I fitted 7.4 volt 1320 mah lipo bats for receiver and ECU for the engine. Lipos weigh 65 gms each, old batts were 165 gms and 280 gms respectively. big saving here.

I fitted an Align voltage regulator which is made for Lipos, dropping voltage to 6 volts, and can handle 6 amps. It has a set of LEDs which display actual voltage of the lipo and gives indication of when not to fly, and recharge instead. Brilliant piece of kit. I fitted it directly to the receiver as it has its own switch, but remember, if you are using a 2.4 Ghz radio, then you need to carry the switch harness and the binding plug with you, as the switch harness has the additional 3rd wire built in the charge lead, to acctivate this fuction. At @ 14 pounds in UK it is excellent value. I mounted it inside, on the side of the fuse, and cut a small slot and fited a scoop to direct air over the cooling fins of the I.C. Looks good. Weight was about 30 gms, but worth the extra weight. (remember, if using some types of digital servos, you can not use 6 volts. My JR 821 servo can take 6 volts, others cant).

I am using ally bolts in all wing fittings and machined some ally washers to suit. Saves a reasonable amount of weight.

- I moved the UAT fwd , adjacent the nose gear plastic bay, along with the pump and moved the lipos (mounted on two carbon rods) right fwd as far as possible in the nose. The model only just balances in the c of g mark like this

- I bored out the internal steel pluger in the nose gear spring strut.

- I was worried about the loads imposed on the undercarriage, while taking off from grass. I made inquiries about which Jet-1A gears fitted the plane but have had no response, so in the interim, I fitted some JP oleos to the mains, which I found on a model shop shelf . With the excess spring wire cut off and these fitted, they added just 15 gms to each side, but gave me some kind of shock absordtion, worth the weight.

Right now to the flying, had a hell of a job finding anywhere to fly, that wasted weeks. The field I flew from was mown and grass quite short, but still offered quite a bit of resistance to the wheels. I used the supplied 2.75 inch wheels on the mains and a 2.5 inch wheel on the nose oleo. This trailing link oleo is from a Mick Reeves Reaper kit.
First I had problems starting the well tested and reliable engine. There was a stiff breez and I thought the wind might have been assisting the propane to exit the combustion chamer too easily. We tried putting the gas bottle in our coats (yes it was cold) and this helped.
First attempt led to flame out during the take off roll, as did the second. I started the engine and tried everything to stop the engine, holding the plane vetical and shaking it, all ok.I tried again, this time the plane attain a desent speed on the ground but resisted rotating, then hit some slightly rougher grass and stopped the plane. The nose wheel spring wire was bent. Remove the nose wire, strightened it and off again. This time the model appeared to be slightly faster, but again refused to rotate, then bang, nose wheel sheared off, screws being torn out.
I had seen it mentioned, not to use flaps for take off, and this was with the flaps up.

During the build, I checked the wing uc mounts, the nose uc mounts and the boom attachment points, and all were dry of glue. I had reglued all these joints and luckily the nose had survived, just the screws had torn out, damaging the beach blocks. (please check all these joints, before you fly, they were not safe on mine)
I cut out the damaged areas of beach bearer and inserted new sections of bearers. I then reinforced the bearers by fitting some 90 degree extruded ally angle (from B and Q), to the o Outside face of each bearer, so the other side of ally angle then sat on top of the bearers. I drilled holes in the ally side so glue could squeeze through them and improve the bond. The nose retract unit now sits on the ally angle and screws pick up in the ally first, then carry on through the bearers. This will help when flyng off grass, would have probably have been ok on tarmac.

Next I modified the nose oleo assemly to accept a 2.75 inch wheel.
I then fitted a slightly longer nose spring wire (10mm longer). The distance from the base of the retract mount to the nose wheel axel is now 156 mm, the nose wheel only just fits in its bay. I also fitted a stronger spring in the oleo, as was definately to soft. With the 5 deg down thrust on the engine, it is noticeable how much the nose wheel trys to dig in during the take off roll.
The main wires are as short as poss, just to allow the wheels to just fit in the bays without rubbing.

- Engine- i removed the glow plug, teased the element out a little further, as far as possible and adjusted the propane from 60% to 80% for the start.
I also adjust max rpm from 108,000 rpm to 110,000. At 108,000 I get just under 12.25 lbs. At 110,000, maybe 13 Lbs, will have to measure.

Next flight attempt.. Very strong cross wind at 70 degs across runway

Engine started first time, run up to 110,000 rpm was faltless, engine smooth and sweet.
Aircraft acceleration was possitive and with the nose now a little higher, wing grabbed the air better and she lifted off very quickly indeed. The wind caught the wing and tried to push her over, she settled on the ground then lifted straight off again. I held her down to gain speed, then pulled her up and tucked the gear away. The climb was really impressive and i continued to a higher height than normal, in case the engine stopped, to give me time to think.
She required about 7 clicks elevator trim to fly level, nothing on ailerons. I set the elevator level with the bottom of the stab, maybe as sugested, it needs to be level with the top of the stab. The plane is really gracefull in the air and flew incredibly smoothly in the really windy conditions. Most of the flight was about 1/2 throttle, giving a fair turn of speed. When you drop the nose the plane picks up speed quickly, the ailerons felt really nice and during a slow roll, i fed in full aileron and she rolled round rapidly and very axialy.
I did one tight turn and she went round unbelivably quickly. I had mixed in 40 % expo on the ailerons and the elevator. I have now reduced this to 30 % as i think, during the tight turn, the elevator was fed in gentely then really came in just a little to fast.
Not knowing how much time I had ( i had filled the 2 litre tank with @ 1.8 litres to help it get off the ground), I decided to try the flaps and land. I had mixed in a slight amount of up elevator with the 20mm flap suggested and a little more with 45 deg flap. With gear and flap down, 20mm flap selected, I needed to trim the elevator down around 4 clicks for striaght and level flight. I did not try full flap as the cross wind was so strong, I didnt wont those two barn doors pulling the nose round at the wrong time.
I flew down wind further than normal, selected idle and she flew rock steady all the way down. I kept on some extra speed for the crosswind and she handled it really well. I landed a bit further down than I would have liked, but didnt wont to go around again in case of fuel shortage. After touch down, the right oleo folded up and she came to rest on her right wing tip. No damage done, and I have since tested and cant fault the gear, it locks every time. Strange.
I prepared for another flight, but lost a winding on my starter motor, so the bendix would not throw in, had to canx flying for the day.

All in all, i am over the moon with the plane, it is a really stable platform and handles the strong wind well. It looks stunning in the air and you can just cruise around or open the tap and eat up the sky. Obviously i did not have time to test the stall or inverted, but after the first failed attempts trying to get off the ground i was disillusioned now I am dieing to get her up again, when I return from work in a couple of weeks. I feel a good set of Jet-1a Oleos would really help the pounding on the grass and now I am confident that any extra weight that is added by them, can be carried confidently by the wings. I think the higher nose up attitude helped the take off, but it would be nice to try again in calm conditions to confirm this.After landing there was still some fuel in the tank and the UAT was full, we were running for 9.5 mins, although throtlled back most of the time. (It seemed like 2 minutes ).

Hope this helps, thanx to everyone who has contributed, and Gary, what Jet-1a struts are you using, Boomerang intros?, do they fit straight on, or need modding?.
Tim

RE: Bob Cat Copy Falcon 120 Jet
 

Tim777, where did you get the carbon spar? Details please. Is it an exact fit (diameter wise)?

RE: Bob Cat Copy Falcon 120 Jet
 

Carbon spar was from Als Hobbies in Uk. oo44 (0) 1908313142. website www.alshobbies.co.uk
The tube was 20mm O.D. and I think wall thickness of 1.5mm. Came in @ 1 meter length and was 27 pounds. You only need about half this length.
You can buy carbon tube from kite manufacturers. The carbon tube must be very slightly smaller diameter than the ally as it is a light sliding fit in the spar mounting hole, whereas the ally tube was a tight fit. I pull my spar out now for transportation. When I enquired about the tube, i asked for a boomerang spar tube, as this would have been designed to take the stresses for a similar sized aircraft, but they could not supply one. I rang around and the general concessors, was that any carbon tube would be fine. I have not tested the tube to destruction, and have not pulled high G in flight yet. In fact the saving of 30 or so grams in weight, was not much as I had hoped for, but every bit helps.
Hope that helps, Tim

RE: Bob Cat Copy Falcon 120 Jet
 

Found the Align voltage regulator on their website, just for info,

http://www.align.com.tw/html/en/asse...b6x_en.htm#top

RE: Bob Cat Copy Falcon 120 Jet
 

tim777,
Thanks for posting all of that great info, as well as everyone else that has posted here. It really helps guys like myself who is building their first turbine.
I installed a set of Behotech C-36 spring air retracts and oleo struts from Altecare.com. The 158mm struts are perfect for the mains and 150mm for the nose. The strait nose strut would require reshaping the wheel opening so I plan on exchanging it for an off set strut. These retracts drop in prefectly for this plane, like they were made for it.
I originally tried the Behotech C-21 retracts. They are good for up to a 15lb airplane and are smaller and lighter than .40 size mechanical retracts. However, the mounting rails are too wide in the Falcon for these retracts without modifications.

I'm interested in the 2L Bottle you used for a fuel tank. How did you fabricate a stopper for bottle?

Thanks,
Cody

RE: Bob Cat Copy Falcon 120 Jet
 

Hi Cody, I just used the original bottle top. I usd a threded nipple which I screwed into a slightly undersized hole, that i drilled in the center of the cap. I wrapped the threads of the nipple in PTFE tape, screwed it into the plastic cap and fitted a rubber washer and secured it with a nut on the inside. I screwed the bottle top on after wrapping the threads with PTFE tape. I fitted a breather pipe in the top of the bottle, same procedure, drilled undersized hole, screwed in a nipple after wrapping threads in PTFE and fitted a nut. No Washer on this one though. Pumped up the bottle a few psi and tested in bowl of water.
You can get threaded nipples from alshobbies.co.uk or try mickreevesmodels.co.uk.
I am interested in your oleos, would you happen to have any pics you could post with them installed. What sort of weight are they.
Just for info, my plastic moulded nose wheel well was smashed when the nose gear detached. I resecured all the damaged bits, with sellotape, on the outside surfaces to reform the correct shape, just so I could fly the plane. This is stronger than you might think. I remade the half tube section were the leg folds into, with ally self adhesive tape (speed tape). Really quick repair, that works well. Some models I have seen, dont even have any kind of fairings, just a large gapeing hole and dont seem to have problems.
By the way, this is my first turbine model as well. Where are based?
rgds Tim

RE: Bob Cat Copy Falcon 120 Jet
 

how about a pic of the coke bottle gas tank?

RE: Bob Cat Copy Falcon 120 Jet
 

I was told, rumour has it that "POP BOTTLES" for use in turbine aircraft are more prone to splitting on impact. Therefore ending up in a ball of flames.
Is the correct? I'm sure all you modellers out there have your own thoughts on this?[:-]

Regards

BiGToP

RE: Bob Cat Copy Falcon 120 Jet
 

Mine's starting to look more like a plane now. Looking nice with the Saito 1.80 in the back. I hope it provides good motivational force w/a 16x10 3 bladed prop. I'm going to use the Robart 710 retracts with the 6xx struts.

One of the blind nuts for the horizontal stabilizer was installed too deeply inside, and thus the supplied hardware is too short. I have to order a new one.

And, one of my nylon wing bolts stripped while I was tightening it inside the fuselage. And trust me, I didn't supply excessive torque. It is just crappy nylon.

The indentation marked on the side of the fuselage where the wing bolt holes need to be drilled was off by enough to make it not work correctly. Mark your own holes after aligning the wing with the two aluminum joiner rods so you don't have to fill and drill a second hole.

Pretty average ARF quality, I'm getting what I paid for, and I'm happy.

The third picture shows my other current time sink-- rebuilding my 1987 Porsche 911 Carrera motor. I was just going to freshen the top end, but projects do tend to snowball. I'm starting complete reassembly this week.

-- Preston

RE: Bob Cat Copy Falcon 120 Jet
 

Weird man. MY Falcon 120 does not have any of the above problems with bolts and alignment All servos are mounted with pushrods installed. I'll be replacing the metric hold downs with 1/4-20 for sure. Just waiting on the SpringAir retracts to complete the "build". haven't decided on a turbine yet altho the Wren MK3 kit looks like it would be a lot of fun the do. I was with Gary when he maidened his last Monday. I'm sure the 14 pounds of thrust the Wren has will be plenty. We actually discussed a Wren 44 Gold would fly it fine too! I'm using a 2l Ocean Spray Cran-apple juice bottle for a fuel tank.

Dave

RE: Bob Cat Copy Falcon 120 Jet
 

Tim,
Thanks for the info about the 2L soda bottle tank. Please post a pic if you have one. Here are a couple of pics of the C-36 retract instal.


Cody

RE: Bob Cat Copy Falcon 120 Jet
 

Hi Cody, sorry cant post pic of bottle, as i am working away from home for couple of weeks. Ref coke bottles, check out stores that sell jet aircraft accessories, you will find coke bottle style tanks for sale and also coke bottle screw on caps, with threaded nipple attachments, designed specifically for jet planes. In the early days, it was quite common to see hospital plasma bags used as tanks, but these seem to have fallen by the wayside, not sure if it is due to spliting in a crash or air locks in the fuel system. When you think about it, more R&D goes into the packaging of items we buy everyday than you think. Try dropping a full bottle of coke on a concrete floor and see if it splits. try pumping it up to 80 psi and see if splits (kids dont try this at home). I have seen some kits that use coke bottles pressurized, to supply brake systems. I am sure that a Dubro 50 oz tank is probably stronger than a coke bottle and probably a home made carbon fiber tank is stronger still, but as long as purpose made Jet aircraft kits are being supplied with coke style bottles as standard, I dont see why I cant use one.
I changed tanks to save @ 100 gms in weight, now see how little glue your wings and all your important wing mounting points and U/C mounting points, havnt got, in an attempt to save maybe 3 grams of weight and then decide what is riskier, have a tank that might split at 1 g less loading than a Dubro, or having your booms tear off the wings in interest of saving 3 grms in weight.
On the subject of safety, the retract kit that came with the kit (at an extra 69 pounds), has no info whatsoever on any pressure limit that the air tank can handle. In 2007 I find this hard to belive. I can only guess that 80 psi should be ok, maybe it can take 100 psi, maybe even 120 psi, then it will probably explode and take your head off. I still can not belive there is nothing in the instructions relating to this, but legally, there should be a safe working pressure stamped on permenantly to the bottle and really there should be press relief valve. The air hose I used, has this info stamped on.
So please make up your own mind, Tim

RE: Bob Cat Copy Falcon 120 Jet
 

Cody, forgot to say, what a neat install you made of your U/C, superb.

RE: Bob Cat Copy Falcon 120 Jet
 

Thanx for the info on the "Pop Bottle" as you so rightly say " more R&D goes into "Pop Bottles" maybe than Dubro tanks and the like?
On the air tank that I got from A1 models it said on the bottom "no more than 12psi" I think it must be a misprint, I think a zero had been left off! I put 100lb psi in it and it's fine.;)


BiGToP

RE: Bob Cat Copy Falcon 120 Jet
 

Hi big top
iam having trouble getting flagged up on rc groups so iam replying to you note hear.
I can see no problem with a visit too us, too check over and test fly your faalcon give us a nod when your ready and ill try to arrange it.
Regards Wingart

RE: Bob Cat Copy Falcon 120 Jet
 

Thanx Wingart

BiGToP

RE: Bob Cat Copy Falcon 120 Jet
 

:DHello Bigplumbs!!! Excellent video, Thanks for that... When you mounted the 54 on your jet you mentioned that you used the provided mounting blocks, do you find the factory angle to be proper for the Jet??? Is the engine slightly exhaust end up or slightly down??? The Jet looks like it loves to fly whatever angle you have... OK standing-by for the Info...
Thank You very much again for the Great Video...
Mojo

RE: Bob Cat Copy Falcon 120 Jet
 

I'm not Bigplumbs but I can answer the question about the angle on the mounting blocks.
It's 5deg of down thrust (slightly down) I just rubbed the blocks down to 5deg on the tail end at the bottom of the block thus leaving the top of the block with it's covering intact!


BiGToP

p.s.

See here for build thread:
http://www.rcgroups.com/forums/showthread.php?t=718236

RE: Bob Cat Copy Falcon 120 Jet
 

RE: Bob Cat Copy Falcon 120 Jet
 

Guys,

which elevator servo would you recommend for the falcon with 6-7kg turbine use ?

RE: Bob Cat Copy Falcon 120 Jet
 

I think guys are using hs-225mg
not sure

RE: Bob Cat Copy Falcon 120 Jet
 

Guys,

if installing one servo inside the elevator stab middle, which servo would you recommend thats small enough and powerful enough ?

RE: Bob Cat Copy Falcon 120 Jet
 

Hi Big Top
Hows the Falcon coming on ,by the look of your photos you must nearly be ready for the big one.
A group of us are flying Raydon on Wednesday this week if thats any good to you.
Keep in touch regards Wingart.

RE: Bob Cat Copy Falcon 120 Jet
 

Hi Wingart,

Plugged my FADEC in to see if everything was still ok and guess what................... Nothing! Then I got the GSU displaying "RC SIGNAL LOST" So I made sure that all the batteries were charged up and checked again in the morning and then NOTHING AT ALL!!!
So I spoke to Wren and they said to send it to them and they'll check it out to see whats wrong. A new one will be around £110.
So I won't be there Wednesday unfortunately [&o]

Regards
BiGToP