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Nitro models pusher Bobcat?

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Old 04-05-2007, 07:25 PM
  #1451
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Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: countryshooter

yes I did and I'm learning alot here. but the reason I'm moving things around is when the plane is flying straight and level my elevator is pointing upward meaning nose heavy but yet doing a turn it does a tip stall very easy. and flying inverted lots of down elivator is need for level flight. now its flying much better but still elevator is up alittle and inverted are almost hands off.

While a lot of up trim on the elevator can be an indication of a nose heavy condition, you cannot assume it from this one fact alone. If I remember correctly you said your final CG was 9 5/8". It's not clear if your CG was adjusted after you shimmed up the tail booms or if you were flying there all along. The recommended CG is 10.3" which seems to be fairly close by most reports. 9 5/8" is probably making your plane a little nose heavy which would explain the need for a lot of up elevator trim. After you created negative incidence on the stabilizer by shimming up the tail booms you now have more down force on the tail which in turn lessened the amount of up elevator trim needed for level upright flight. What seems really odd though is your statement that inverted is now almost hands off. With negative stab incidence and a little up elevator trim, inverted should push the nose down pretty hard. Let us know how the next flights go.
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Old 04-06-2007, 07:11 AM
  #1452
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Default RE: Nitro models pusher Bobcat?


Quote:
ORIGINAL: Stick Jammer


Other than the whip possibly being a cosmetic choice, I really don't see the advantage. I'd be interested in reading any hard data that proves a whip antenna gets better reception than a properly installed stock wire. I would think that if this were true the radio manufacturers would supply a whip instead. At any rate, I've never had any range problems whatsoever by using the stock antenna on all of my planes including several that are fully concealed within the airframe.
For the best solution a properly installed stock wire should run outside of the plane completely away from internal wires, carbon fiber or batteries. While the range we get using the stock wire, internally, is generally more than enough the best solution is an external solution. The whip adds to this by placing the antenna not only outside of the plane but up and away from it. Do a search on the jet forum and read the research many of those guys have done. There is a reason you see so many whips on top dollar planes. As for this plane, there probably is no need for a whip. I installed one because an external wire can get into the prop and I want removeable wings and didn't feel like threading the wire each time I reassemble.

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Old 04-06-2007, 11:13 AM
  #1453
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Default RE: Nitro models pusher Bobcat?

okay

at last mine is finished and ready for its test flight

power is from a JEN57 engine spinning a APC 11x7, radio gear is Futaba

havent carried out many mods from the original, although i have used silicone tube to take the exhuast away and stop the air being driven down it

whip aeriel fiited to the front, and i have changed all the standard pushrod linkages with carbon fibre ones

balance is around 10.6" which is where my manual state

here are the pictures

steve
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Old 04-06-2007, 11:28 AM
  #1454
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Default RE: Nitro models pusher Bobcat?

Your wings fit a lot better than mine..I have a 1/4" gap at the trailing edges...need to attach a strap back there to pull it in to the fuse. That yellow silicon exhaust tube is a nice touch.....
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Old 04-06-2007, 01:51 PM
  #1455
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Default RE: Nitro models pusher Bobcat?

yeah, the whole plane went together well, i think i must of been lucky

my wings are also glued in position, so only the tail section comes apart

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Old 04-06-2007, 05:28 PM
  #1456
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Default RE: Nitro models pusher Bobcat?

Original: MMallory

Quote:
For the best solution a properly installed stock wire should run outside of the plane completely away from internal wires, carbon fiber or batteries. While the range we get using the stock wire, internally, is generally more than enough the best solution is an external solution. The whip adds to this by placing the antenna not only outside of the plane but up and away from it. Do a search on the jet forum and read the research many of those guys have done. There is a reason you see so many whips on top dollar planes. As for this plane, there probably is no need for a whip. I installed one because an external wire can get into the prop and I want removeable wings and didn't feel like threading the wire each time I reassemble.
When you say top dollar planes I'm assuming you are referring to turbines. I have yet to see any TOC or expert giant scale aerobatic prop plane with any type of external antenna, whip or stock. I would consider these planes top dollar and they are almost always routed inside the airframe. I don't fly turbines but maybe most of them don't have an adequate internal location for the antenna wire due to all the extra wiring and components which are not typical in a gasser. A lot of them also have a scale metallic finish of one type or another which would most likely cause problems with an internal antenna. A modern day radio system is supposed to have a line of sight range of one mile, which is way beyond where any of us can see the plane. There are enough top notch expert pilots flying with the antenna concealed for me to feel it's perfectly safe as long as it's done correctly.
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Old 04-06-2007, 06:17 PM
  #1457
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Default RE: Nitro models pusher Bobcat?

You can't compare a giant scale aerobatic plane with massive amounts of space to a smaller plane. In these planes the fuse is large enough to mount the two, yes most have two, antenna wires within the plane. Add to this they typically do not fly very far away from the pilot and you don't need the extra range. That is not to say their installation is the "best", it simply works for that application. I've seem many giant scale civilian and warbirds use whips. Mnay pilots unscrew them on the ground and some add a scale feature that screws on the mount for static display.

As with most everything R/C, use what works for you and have fun. Just because an advantage isn't apparent or necessary for you doesn't mean it won't work for others.
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Old 04-06-2007, 11:29 PM
  #1458
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Default RE: Nitro models pusher Bobcat?

Very well stated. I have found incredible gains in ground range using base loaded whips. They are a must for turbines with all the wiring, EMF, and carbon fibre in the fuse, but certainly not necessary in every plane. In the case of my Bobcat, I had a full length ant inside; some thin CA got underneath it un-noticed and glued it to the servo tray. It broke when I tried to jimmy it loose, fortunately leaving the 4-1/2" I needed to solder a connector for a Deans antenna.... So, it my case, it was a neat and practical solution to a (self inflicted) problem......
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Old 04-07-2007, 08:20 AM
  #1459
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Default RE: Nitro models pusher Bobcat?

Very long thread on this airframe covering well, just about everything but the box art, lol...

I've read about every reply and response as my "in-box" has daily and sometimes, hourly notices of postings, :-)

However, I'm going to be lazy and ask for a summary of several points I still have questions about.

~For 2-stroke 50-61 sized engines:

1) best all-around servos for tail booms if all 4 are used
2) best servo to install if only 1-elevator servo mounted in the stab is used*
3) will the plane fly successfully WITHOUT rudder control at all?
4) are replacement canopies available and if so, from?

*(I bought the Hitec HS-125MG aileron servo but 41oz stall torque appears to be rather light for the elevator this design seems to require.)

I'm at that point where these decisions need be made before I recover the airplane and repaint the fuselage. I stripped the yellow off down to the gelcoat.

The landing gear issue has been resolved in a manner no one else here appears to have used. It will be interesting to see if my idea pans out.

Thanks for any and all feedback...

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Old 04-07-2007, 09:19 AM
  #1460
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Default RE: Nitro models pusher Bobcat?

I can answer questions#3 and 4

Yes...it flies just fine without rudders,..my friend Serge has set his up this way,...just tape the rudders straight with packing tape.
Canopies here...but they have been sold out for months.. http://www.nitroplanes.com/canopies.html
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Old 04-07-2007, 10:48 AM
  #1461
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Default RE: Nitro models pusher Bobcat?

Crashpro,

Thanks for the reply. I had visited Nitro's website a month or so ago. The "sold-out" signs have been there a long time, agreed, (almost as long as the "sold-out" sign on Kangke's website for their SK-50 sport ARF, lol).

I butchered my canopy attempting the "simple" replacement posted by another modeler. Trying to make it clear, I should have reinforced the frame with fiberglass BEFORE I attempted to cut the tinted sections away...The thing is so flimsy, I really made a mess of things. Guess I'll have to carve a foam block to shape, glass it and paint it all silver.

I'm uninterested in performing knife-edge aerobatics with the Bobcat. My Sukhoi and Balsa Nova are unparalleled in that arena. But I do want it to track nicely and be able to do more than cut circles in the sky. Locking the rudders solves a few challenges for me; cost being the principle. I really don't want to invest in servos that would only be used in a single airframe. As mentioned, I already made a bad decision in buying the HS-125 servo. I doubt I'll ever have another application that would require a thin servo such as this.

I'm not opposed to having a thicker servo protruding below the stab as long as I can securely mount it. By not having rudder servos weighing in, I have more flexibility in an elevator servo choice. This is why I was asking about torque and throw amounts.

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Old 04-08-2007, 05:16 PM
  #1462
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Default RE: Nitro models pusher Bobcat?

Quote:
As with most everything R/C, use what works for you and have fun. Just because an advantage isn't apparent or necessary for you doesn't mean it won't work for others.
I most definitely agree. There are certainly some instances where a whip antenna would be a necessary choice. I've been to several major jet rallys as a spectator and never noticed whip antennas on most of the planes but maybe I just didn't look close enough.
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Old 04-08-2007, 05:42 PM
  #1463
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Default RE: Nitro models pusher Bobcat?

Although some have reported flying this plane with a single HS-125 in the stab I have to agree that it would make me a little uncomfortable also. If you aren't going to need rudder servos then a little more weight for elevator isn't a big deal as you said. I would think a single standard BB servo would do the job. The torque ratings would be about the same but a standard servo has a bigger gear train and can handle the load much better than the 125 which is technically a mini servo. Simply enlarge the stock right elevator servo bay to accept a standard servo and you're done. Without rudder servos you could even go with two standards for the elevator without adding much overall weight. Also by using the stock location instead of creating one in the stab you will be helping the CG, not to mention saving yourself some work.
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Old 04-08-2007, 07:32 PM
  #1464
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Default RE: Nitro models pusher Bobcat?

Work is continuing on my Bobcat. Very, very slow but continuing. I have done the mod for the wing bolts and I am still playing with the retract installation on the mains. I am cutting the holes for the wheels to retract into the wing and fuse. Then they will be done and then onto the nose gear.

I will be using a Sport Jett 50 on mine. I am going to use the Turbo Jett in-cowl muffler on it. It may look a little funny but this should blow the exhaust out to the side. Below is a picture of the Turbo Jett. Did anyone notice on page 6 of the instruction booklet, it says the motor can be mounted sideways as well as inverted without affecting the thrust angle.

Also, in the June issue of FLY RC, they talk about a Uniflow 3 fuel line system. This use to be used by the guys flying control line and is being used by the helicopter guys today. I wonder if this will work for the Bobcat to fix some of the problems guys are having when the fuel tank is mounted with the stopper facing forward? Below is a picture of that too.
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Old 04-08-2007, 07:50 PM
  #1465
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Default RE: Nitro models pusher Bobcat?

P 51 Man and H.Dale
Sorry for not getting back to you earlier...easter holidays here in OZ...As per your request here are some pics of nose gear install and engine mount. Hope this helps.
Regards Craig Dyer
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Old 04-08-2007, 07:52 PM
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Default RE: Nitro models pusher Bobcat?

more pics
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Old 04-08-2007, 09:02 PM
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Default RE: Nitro models pusher Bobcat?

.
Quote:
ORIGINAL: thebluemax

Did anyone notice on page 6 of the instruction booklet, it says the motor can be mounted sideways as well as inverted without affecting the thrust angle.
O'm scratchin' ma bald head trying' to figure out how one would side mount or invert an engine on this design????

I'm thinking a Hitec HS-475BB or a 605MG would probably do fine for the elevator. I guess the stab-mount isn't a very good idea with a heavier servo at that. I just didn't like that long-a** pushrod running from the boom(s), lol...

Life is compromise, eh?

Thanks for the input.

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Old 04-08-2007, 09:38 PM
  #1468
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Default RE: Nitro models pusher Bobcat?

That's why I asked. I couldn't figure it out either.
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Old 04-08-2007, 11:35 PM
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Default RE: Nitro models pusher Bobcat?

You'd have to do some serious cutting and figure out how to mount the engine.........
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Old 04-09-2007, 01:53 AM
  #1470
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Default RE: Nitro models pusher Bobcat?

Quote:
ORIGINAL: craigdyer

more pics
I finally ended up putting retracts in mine. I had some spring airs lying around. The front unit was a horisontal mount for I created a simple mount and it retracts backwards. The mains retract forward vs sideways to allow for increased strut height for prop clearance. The first flight was extremely nose heavy (full up trim and still nose down) with my install and the air pocket for the front gear and I ended up doinking the nose in pretty good on landing. I have 2 rcvr batteries that can move back towards the tanks. The repair is finished and I'll post pics of the retract install soon.
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Old 04-09-2007, 05:46 AM
  #1471
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Default RE: Nitro models pusher Bobcat?

4 more flys this easter w/e. 90 deg crosswind. Must say with no rudders its a bit awkward when the model is not straight.
Apart form that it is great and may even be my best/favourite plane
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Old 04-09-2007, 11:47 AM
  #1472
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Default RE: Nitro models pusher Bobcat?

Quote:
Also, in the June issue of FLY RC, they talk about a Uniflow 3 fuel line system. This use to be used by the guys flying control line and is being used by the helicopter guys today. I wonder if this will work for the Bobcat to fix some of the problems guys are having when the fuel tank is mounted with the stopper facing forward? Below is a picture of that too.
I'm a little confused by the theory behind this diagram. Typically a three line system would have the vent line connected to the muffler pressure. If the the second clunk line is attached to the muffler pressure and the vent line is plugged, it will produce bubbles in the fuel. Normally the second clunk line is only used to fill and empty the tank and plugged the rest of the time. I also don't see the need for a three line system on this plane because the fuel and pressure lines are so easily accessible at the engine.
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Old 04-09-2007, 11:59 AM
  #1473
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Default RE: Nitro models pusher Bobcat?

SJ
Maybe this help. I found this link using google. the Fly RC article is pretty much the same.

[link=http://www.fraserker.com/heli/uniflow/how_uniflow_works.htm]Uniflow 3 line system[/link]
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Old 04-09-2007, 12:01 PM
  #1474
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Default RE: Nitro models pusher Bobcat?

Quote:
I'm thinking a Hitec HS-475BB or a 605MG would probably do fine for the elevator. I guess the stab-mount isn't a very good idea with a heavier servo at that. I just didn't like that long-a** pushrod running from the boom(s), lol...
The pushrod is only 6" long, not that big of a deal. Glue a piece of carbon fiber tube over the metal rod if you want a cheap solution. I've done this on other planes and it works great. The end fittings for CF pushrods are the expensive part, the CF tube is cheap. The 475BB should be fine for elevator but watch out for those old 605's. I know several people that had one lock up and lost their plane.
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Old 04-09-2007, 12:07 PM
  #1475
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Default RE: Nitro models pusher Bobcat?

I used a 605 servo, but only on the nosegear. Didn't want to take a chance on a critical surface
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