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  1. #1476

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    RE: Nitro models pusher Bobcat?

    Interesting theory but I don't think I'll be tryin' this setup anytime soon, keeping thinks simple is usually better. Maybe it's an option for someone who is having fuel problems but I really doubt this would be the cure for a lean running engine. But who knows?
    The more you fly, the more you buy.

  2. #1477

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    RE: Nitro models pusher Bobcat?

    Well, at least you'll have control all the way to the ground but then again landing with out a nose wheel isn't much fun either!
    The more you fly, the more you buy.

  3. #1478
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    RE: Nitro models pusher Bobcat?

    I've been flying 605BB's on my Sukhoi. They are original, (I bought the plane used) and I guess they are 4-5 years old.

    When I ground looped it last Fall while taxiing back to the pits,(big 'ol gust of crosswind), it popped the rudder and cracked the firewall.

    Anyway, I got all the repairs completed over the winter and have been reconnecting the airborne pack. Guess what? The ground maneouvers last Fall stripped the output gear's teeth real good on the rudder servo,(I use pull-pull wires on an elongated Dubro output arm). I have 605's on the elevator halves, too.

    I ordered replacement gears BUT they are metal. Now my HS-605BB will be an HS-605BBMG, :-). I may just replace the other 2 servo gear trains as well. They are spline gears and appear to be very hardy. I'm quite suprised to read here that folks have so much trouble with them.

    As to the length of pushrod to the elevator. Yeah, well when ya put a ruler to it, the length isn't all that bad at that. I use Central Hobbies CF rods and their titanium ends. You are 100% correct that the $$ are in the ends. However, I happen to have several 2-56 and 4-40 ends and some scrap tubing laying around so I guess my original post is moot.

    That's what I love about RC Universe. Where I usually fear to tread, others have trailblazed, LOL...

    Thanks!

    PM

    Oh...can anyone enlighten me on converting a new set of trike Rom Airs over to pressurized air? Freon 12 is well, extinct. I have questions if you have answers, :-)
    Ah yes, snakes in the cockpit....

  4. #1479

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    RE: Nitro models pusher Bobcat?

    Oh...can anyone enlighten me on converting a new set of trike Rom Airs over to pressurized air? Freon 12 is well, extinct.
    I'm not familiar with these, were they really designed to operate with freon?
    The more you fly, the more you buy.

  5. #1480
    PointMagu's Avatar
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    RE: Nitro models pusher Bobcat?

    Oh yeah...in colder weather they recommended R-22 as a suitable sustitute. Otherwise, R-12 was what they were designed to operate on. Their "O" rings need the heavy oil, 512wgt, to properly seal. The pressure cylinder has the feed tube running midway into it so as to keep the liquid freon from entering the pressure cylinders on the gear. Pretty elaborate but actually quite simple IF freon R-12 wasn't banned and illegal to use since 1995.

    I know others use pressurized air but I am not familiar with the "in's and out's" of that conversion nor the subsequent maintenance requirements.

    I bought these for my Invader but they won't work in a nacelle-mounted configuration, unfortunately.

    I could probably mount 'em in my Bobcat as I've got mine stripped down. The nose gear cylinder is vertical and I'd have to measure the height and allowance within the nose of the fuselage to see if that might be possible. Otherwise, I'm looking to trade 'em away for Robarts or Spring Air's...

    PM
    Ah yes, snakes in the cockpit....

  6. #1481
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    RE: Nitro models pusher Bobcat?

    Pointmagu,
    the hitec 125 works great when incorperated into the elevator..It will provide more than enough pull to get the elevator were you want it when you want it...It's a great solution...The down side is the install.....You must thead the servo wire through the tail boom and it is a tricky process and careful skill is required in cutting the access holes required to allow the wire to be run....I think your selling yourself short if you bought the servo.....There are enough illistrations to give you an idea of what has to be done in this thread.....I can carve the sky with mine and turn on a dime...It's like she's on rails....Mark

  7. #1482

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    RE: Nitro models pusher Bobcat?

    Oh yeah...in colder weather they recommended R-22 as a suitable sustitute. Otherwise, R-12 was what they were designed to operate on. Their "O" rings need the heavy oil, 512wgt, to properly seal. The pressure cylinder has the feed tube running midway into it so as to keep the liquid freon from entering the pressure cylinders on the gear. Pretty elaborate but actually quite simple IF freon R-12 wasn't banned and illegal to use since 1995.
    That's interesting. Not sure why they would have chose refrigerant for pressure. The freon itself has no useable purpose for retracts other than to supply pressure. Also, R-12 or any other refrigerant does not contain any oil, the oil is added to the system separately. The only possible reason I can see for using refrigerant is to get more cycles from the retracts without having to re-pressurize the tank. Once you have the oil in the system that the O-rings require you should be able to simply use air as long as the tank is of sufficient size to get a few cycles. Other than that if you want to use refrigerant, R-134a should do the job as most older cars that used to run on R-12 have been switched to R-134a without even changing the oil. Another down side to using freon is the weight. I don't know how much liquid the tank is designed to hold but it's gonna weigh a lot more than air.
    The more you fly, the more you buy.

  8. #1483

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    RE: Nitro models pusher Bobcat?

    While a single HS-125 is obviously doing the job for some on elevator, it is classified as a mini servo. Although 42 oz. of torque is probably enough, considering the small gear train of this servo I would have to wonder how long it will hold up before it might fail. I think Hitec only recommends this servo on gliders and small glow planes under .40 size. As always though, do what makes you comfortable.
    The more you fly, the more you buy.

  9. #1484

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    RE: Nitro models pusher Bobcat?

    To get over any problems that might arrive with small servos I split the elevator Into two halves ,
    No worries then, If one fails then the other will get you down

  10. #1485
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    RE: Nitro models pusher Bobcat?

    While a single HS-125 is obviously doing the job for some on elevator, it is classified as a mini servo. Although 42 oz. of torque is probably enough, considering the small gear train of this servo I would have to wonder how long it will hold up before it might fail. I think Hitec only recommends this servo on gliders and small glow planes under .40 size. As always though, do what makes you comfortable.
    Stick Jammer,

    I have to admit if I was flying a bullet plane that flys at the edge of the envelope say 90 plus that I would agree with you that a stronger servo is in order...
    With that said....I'm flying with the 55AX setup with a 11/7 APC prop....I will never see that kind of blistering speed....On my best day I might get to 90 in a long dive if I'm lucky....
    With that said... Mini servos are what is recommended in the tail of this plane.... The Hitec 125 has all metal gears and does give 42 oz of torque....It might be more as I 'm using a 6v battery....
    Do you still think it might not be the right choice...I do value your thoughts on this set up.....Mark

  11. #1486

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    RE: Nitro models pusher Bobcat?

    I started assembling my Bobcat today and have discovered several of the same small issues that I have read about in this thread. I had to run a tap through one of my threaded inserts in one of the booms, the depth of the front boom mounting holes had to be increased for the bolts to fit, the tail and boom assembly bolt holes do not line up very well and the engine will require spacers to fit. I am not comfortable with holding the stab and booms on with only screws, so I plan to epoxy the wings to the fuselage, the booms to the wing and the stab to the booms. Epoxying these items should make them quite strong and I don't think I will have any strength issues. These are really very minor items that are easily solved. I'm sure that I will enjoy it when done. Can anyone tell me what flight time I could expect using a Tower 75 flying at full throttle on a 16 ounce tank? Or, should I consider trying to stuff a 20 ounce tank in this little bird?

    Best wishes and good safe flying.

    Heli-NuBee (Roger)

  12. #1487
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    RE: Nitro models pusher Bobcat?

    (RE Tower .75) I have never measured it, I rip back and forth and do some loops and rolls and about that time I'm ready to land. It just so happens that I usually have about and ounce of fuel left when I'm done. I'm guessing 5-7 minutes at pretty much full throttle, running a zinger 12x6P. I don't flirt with lean settings though.

    On another note I can tell you for sure now that you do not want a CG greater than 10.3 inches on this plane. It flys really well at 10.25 inches. I tried my own recommendation and went past 10.5 with terrible results. This plane is no fun when it dives for the dirt with a super sensitive elevator.
    If you are flying, life is good.

  13. #1488
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    RE: Nitro models pusher Bobcat?

    I posted some pics of my retract install in my "beater" NP bobcat on the site.
    The next problem I had was too tight pull-pull steering and the nose retract didn't lock out... just a little scrape
    RCMACHINERY.COM

  14. #1489

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    RE: Nitro models pusher Bobcat?

    I agree with AGRA413 about lean settings. Lean settings on a pusher design will most likely result in engine damage. Cooling is a big issue. AGRA413. I can no longer find your video. Is it still posted?

    Best wishes and good safe flying.

    Heli-NuBee (Roger)

  15. #1490
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    RE: Nitro models pusher Bobcat?

    It appears the RCU video portion of the website has been completely reworked, it is still on google though.

    My Bobcat Video on google

    My Bobcat video on the new RCU videos
    If you are flying, life is good.

  16. #1491

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    RE: Nitro models pusher Bobcat?

    I have to admit if I was flying a bullet plane that flys at the edge of the envelope say 90 plus that I would agree with you that a stronger servo is in order...
    With that said....I'm flying with the 55AX setup with a 11/7 APC prop....I will never see that kind of blistering speed....On my best day I might get to 90 in a long dive if I'm lucky....
    With that said... Mini servos are what is recommended in the tail of this plane.... The Hitec 125 has all metal gears and does give 42 oz of torque....It might be more as I 'm using a 6v battery....
    Do you still think it might not be the right choice...I do value your thoughts on this set up.....Mark
    I have the same engine/prop on mine which by most reports actually seems to be one of the best choices for this plane as far as performance and speed. You are correct that the design of this plane is for mini servos in the tail but it is setup for two of them on elevator, not one. According to Hitec's specs you should get 49 oz. of torque from the HS-125 using a five cell pack, but you will get twice that amount using two HS-85's and 134 oz. using two HS-225's. I agree that the elevator on this plane isn't that big, it's not a 3-D plane, and the amount of throw at high speed is minimal. You may very well be fine as long as you check that 125 after each flight to make sure it's OK. That's typically something that should be done on all surfaces before each flight anyway.
    The more you fly, the more you buy.

  17. #1492

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    RE: Nitro models pusher Bobcat?

    Original: Heli-NuBee

    I am not comfortable with holding the stab and booms on with only screws, so I plan to epoxy the wings to the fuselage, the booms to the wing and the stab to the booms. Epoxying these items should make them quite strong and I don't think I will have any strength issues.
    Permanent attachment of the tail booms to the wings will make it extremely difficult ever re-wire or replace any of the tail servo leads and also to repair or replace a tail boom should the need arise. Just harden the bolt holes in the wings with thin CA and ream them out with the correct size drill bits when the glue is fully hardened. Reinforce the mounting points in the booms and replace the supplied nylon bolts with 4MM steel bolts and washers. Use a drop of Blue Locktite on the bolts and you're good to go.
    The more you fly, the more you buy.

  18. #1493
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    RE: Nitro models pusher Bobcat?

    Stick Jammer,

    Thanks for your input....Could you please be kind enough to tell me how you set up your fuel tank. Did you use the stock tank?
    Do you have it facing forward? I'm using a sullivan 16oz with the tank plug facing forward....Do you run you OS 55 AX pretty rich?
    Have you had any problems with this motor? Mine will heat up very quick and stall out if not set to run very rich.....What speeds do you think you might be getting?
    I look forward to your reply.....Mark

  19. #1494

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    RE: Nitro models pusher Bobcat?

    gofastz,

    I haven't been able to fly mine yet, the weather here has not been very cooperative yet. The little bit of warm weather we had a couple weeks ago was coupled with 40 MPH winds and everything is pretty soggy from a long sloppy winter and spring rains. The last few days have been 30's and low 40's for high's with 20's at night and last night we got about 3 inches of snow. [:@] I have the stock fuel tank in mine with the stopper facing forward. As soon as we get some decent weather on a weekend I'll get her in the air and let ya know.
    The more you fly, the more you buy.

  20. #1495

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    RE: Nitro models pusher Bobcat?

    FLIGHT REPORT

    Hey guys i have a few things i would like 2 add as i have about 8 flights on mine now.

    First flight had problems getting motor started cut my finger was frustrated and shouldnt have flown went to take off the plane jumped off the ground i panicked went into a tipstall spiraled 2 the ground broke fuse 3 inches foward of wing busted the nose gear and bulkhead horizontal boom ripped out along with the right vertical stab pulled through I was CRUSHED !! oh and canopy

    Ok enough of the bad lets get 2 the good i bought some fiberglass mat and resin and went 2 work i had 2 glue the nosegear bulkhead back together and servo tray i ended up putting 2 layers on side walls and 3 on bottom of fiberglass matt very easy 2 work with i had never used it before i ended up glassing in the bulkheads wich mad the nosegear much stronger than it was before i glued and epoxyed eveything else back together had 2 make a conopy out of a plastic windsheild washer fluid bottle and spraypainted it black still waiting on NP 2 get those in stock they are saying anyday

    OK time for second attempt i take off down the dragstrip [2600ft of paved runway just outside my backdoor] get good groundspeed and take off this time i flew out and gained some speed before making my turn it flew great but didnt know what 2 expect on landing i made my turn 2 come in and i decided i was 2 far away and wanted 2 land closer so i powered up 2 make another approach and it ran out of gas i was up 2 long im guessing my flight times are about 8 minutes well i landed it very rough had 2 land it about 500 feey away from me and had a little more damage pulled the left wing bolt out and loosened the allen set screw on nosegear SOB !!

    2 flights 2 crashes busted the 5 minute epoxy out ran back 2 the hanger forsome more tools

    Did I mention that my buddy Rob J was there with his bobcat and everything for him was going ok!!!

    Ok 3rd flight back up i go shortened my flight times and started working on landings i was having a little problem getting turned 2 line up straight but came in safe had 2 more flights that day evrything ok

    Flights 4 through 8 were awsome by now the plane had been crashed twice still in pretty good shape but looking at it its still fine

    Anyway takeoffs are straight and landing is very stable as well it is an awsome and fast plane no radar but guessing 90+

    Setup is 46 fx 10x7 prop
    CG 10.5

    I think arg is right on no farther back than that as ROBS isat 11 and his lands like a dolphin at seaworld his bounced bad a couple of times like ive seen in a few videos in this forum

    So my tips would be allthough by neccesity i had 2 reinforce the sidewalls and nosegear on plane it seemed 2 help on ground travel as the nosegear bulkhead is very flimmsy

    Notch the set screw on nosegear between the 2 planes we had 2 jetblues and nocked em loose a couple times

    Also just 2 stirr the pot a little i have a WHIP antenna ROB had 1 and did away with i have had no problems

    I love the plane baddest thing ive flown

    I will have more later THX for everyones help on this forum

    Thx again

    Jason Becker

  21. #1496

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    RE: Nitro models pusher Bobcat?

    Another side note i agree with S.J. had i epoxyed the tail booms 2 begin with it would have made my repairs alot harder, because they werent epoxyed they broke off in 1 peice

    And i think 2 servos in the tail boom is a good idea in case something happens 2 one of then i had a pushrod come loose on 1 elevator servo noticed it on the ground just before taking off for my 6th flight so it appears i landed it with 1 just my 2 cents

    Thx

    Jason Becker

  22. #1497

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    RE: Nitro models pusher Bobcat?

    AGR413, I would appreciate your opinion on the nylon bolts used to mount the booms. I note that you used these as indicated in your review. Has this method of mounting worked out OK for you?

    Best wishes and good safe flying.

    Heli-NuBee (Roger)

  23. #1498
    AGR413's Avatar
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    RE: Nitro models pusher Bobcat?

    I need to update that review......while I was getting ready to go fly one day I checked the tightness of the wing bolts and one of the front ones just turned and turned. I ended up drilling out the front mounts right up to the upper sheeting and installing dowel rod with a generous amount of epoxy. I then very carefully, from the top side, re-drilled the bolt holes and changed to stainless steel hardware. To get the replacement front bolts right I purchased shorter bolts about the same length as the height of the wing and then measured several times to figure out how long to make the dowel plugs. I used stainless bolts on the back also but used washers on the surface of the bottom of the wing.

    I never had a problem with the nylon bolts breaking or anything, the problem was with the mount point. The irritating thing is I initially had to ream out the front mount points a little bit so the nylon bolts could reach the blind nuts in the booms. I guess this contributed to the mount points failing. If a person was planning on pushing this airframe and wanted to do it right I would drill out the front mount points right up to the sheeting and replace it with hardwood dowel rod, and use stainless hardware. I have not resorted to through bolting through the booms.

    AN IMPORTANT NOTE: I don't know about anbody else but I scarred up the bottom of the wing tips the very first time I tried to take off. It took me awhile to figure this one out. Because of imperfections on the runway or whatever, every now and then the plane would veer off and scrap a wing tip, it ended up being that the stock control rod for the nose gear was flexing enough to allow the nose wheel to turn enough sideways that it would catch and cause the wing to dip into the asphalt. The fix is easy, cut a piece of dowel rod shorter than the conrol rod and cut a straight groove in it from one end to the other, then tape the dowel rod on to the control rod with electrical tape. Once I made this mod the problem went away completely.

    This planes tailheavy CG behaviour is to dive for the ground like an earthworm in the Arizona sun when the power is pulled off for landing.

    Oh and BTW I changed to the Pitts muffler for the Tower .75 and it totally took care of the going rich problem however, the engine does not produce the same amount of power with the pitts muffler. I don't mind the trade off the plane is still very fast (for me) and the engine is rock solid now.

    Oh and BTW..again, I don't recommend using epoxy on the wing or the booms, think you will regret it later. The 1/4 inch wing bolts have proved more than adequate. There was a small gap between the wing and fuse at the back after I installed the bolts but I used two strips of clear packing tape and pressed the wings to the fuse when I put it on, it works great. Somewhere...I think in this thread I posted a detailed description on how I intalled the wing bolts.

    I hope some or all of this helps.
    If you are flying, life is good.

  24. #1499
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    RE: Nitro models pusher Bobcat?

    oops I hit quote instead of edit..disregard.
    If you are flying, life is good.

  25. #1500
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    RE: Nitro models pusher Bobcat?

    Received my yellow bobcat today. I was very glad to see the anti-glare area in front of the canopy was grey... not green!
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    Andy Steere
    http://astro.umsystem.edu/andy/rc/


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