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bobcat construction Q

Old 01-21-2002, 09:36 PM
  #1  
Nikita
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Default bobcat construction Q

I am trying to figure out what to do with the nose gear (building the fuse now). I have an XL and a durostrut. I remember seeing somewhere that you had to shorten the strut by 1/2" - is this true? The instructions don't seem to say anything and the cutout for the wheel well that they have on the plans is totally unhelpful (I think it's definitely the wrong size and even the knee is pointed the wrong way). What to do? It seems that the way the wheel is positioned on the plans I would have to cut something off. But there is space in the fuse to leave it the current length...
Hopefully you understand what my problem is and can help. Just a note: some of the scribe lines on the fiberglass are off, can't rely on them much more...
Thanks. Nikita.
Old 01-21-2002, 11:33 PM
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bvmjethead
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Default Bobcat Questions

Sir,

I would e-mail the BVM website directly or call in the morning. There are some mods listed on the website as well, and I'm sure if your questions aren't addressed there BV would be more than happy to answer any question you have.

Scott
Old 01-22-2002, 12:26 AM
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TonyF
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Default Durostrut nose

Sorry to say I'm not sure about the length of the Durostrut. I think the plans show the standard wire gear. If you install the strut and check the length against that on the plans, you should be able to tell if the strut needs to be shortened. Also, the scribe lines on the fuse for the nose gear are only for the wire strut, not the Durostrut. You have to change the openings to accomodate the durostrut.
Old 01-22-2002, 02:02 AM
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Harley Condra
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Default BobCat Duro Strut length

Nikita,
I have a BobCat XL with the mild landing gear upgrade. When I opened the landing gear package, I found that the nose strut had been cut .400 shorter by BVM. The XL uses the Bandit strut, which is 5.95 overall, at full extension.
Measure the overall length of the strut. It should be 5.550 from the top of the tube to the axle center. If it is full length (5.95), cut off .400. When setting the ground angle, the wing should be posative .375 inches. See the fuselage plan for that information.
I have 18 flights on mine, and haven't bounced a landing yet! Now that I've said that, I'm sure to bounce lots of them.
I have been setting my timer for eight minutes, start the timer at light-off, and get in the pattern after the eight minutes counts down. The header is usually more than half full. IT's even better with less fuel in the header. Don't let the UAT run dry!!!! I've been flying it at or around one-half throttle, (RAM 750 PLUS) so its been economical, and loads of fun. It will slow down to a crawl on final.
The knee is the right way..the scissors are on the aft side of the Duro Strut.......
Happy BobCatting!


Harley Condra
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RAM REP
BUY AMERICAN!!!
Old 01-22-2002, 02:47 AM
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Nikita
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Default durostrut

Well, I wish I could understand how to navigate their web-site, after the change many links are not even operational.
Harley's response is what I was looking for. My strut measures about 5.5". According to what you say it's the right length. What has me confused is that when I lay it against the plans it seems a little bit too long (just over 1/4" too long). Same with the scribe lines outside the fuse. But the scribe lines are not too accurate (e.g. wing mounting holes in the back are way off, forward edge of the nose door was not perpendicular to the fuse etc) and the plans are not 100% accurate either (they have the template for the durostrut cutout and the rectangle does not even match the size of the nose door and according to that template the knee is definitely the wrong way!).
So I will trust you, Harley, and go with the current length. The worst that can happen is that I would have to enlarge the wheel well afterwards.
In any case I would like to say that I am not complaining about anything. The instructions seem great for a kit that has been in production for such a short period of time, but for a first-time jet-builder some things seem to be missing. So far I've been able to figure all of it out, since most of the parts just fit so well, but this issue I was not able to resolve myself. But I am enjoying the construction very much, I wouldn't consider my money wasted even if I crash it on the first takeoff!
Nikita.
Old 01-22-2002, 03:21 AM
  #6  
rc4mike
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Default Strut Length

I just measured length of strut on my Bobcat. It's 5.4". Came this way from BV. I just laid the strut on the fuse and cut the opening large enough to fit the wheel. It took a little trial and error, but not too tough. I have 9 flights in the past 2 weeks since I finished it. Only have 15 on my F4 that was finished early last year. Boy I love this bird.

Mike J
Old 01-22-2002, 03:40 AM
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Nikita
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Default nose axle

All right, I am going with what I have.
A follow-up: should I cut off a part of the axle? As I understand there is only a plastic washer between the strut and the wheel, and then there is another plastic washer on the other side followed by the E-clamp. Now that leaves quite a bit of axle, about 3/8" sticking out the other side of the strut - just get rid of it?
Thanks again.
Old 01-22-2002, 05:42 AM
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Harley Condra
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Default BobCat axle length

Nikita,
The axle length is longer than what you need in theis jet because the axle is used for other BVM Jet Wheels that have a thicker hub.
Simply cut off what isn't needed on the other side. You have the right idea for the length adjustment. Use a plastic washer/spacer on both sides of the wheel, install the E-clip, tighten the 5-40 set screw, and cut the excess off with a moto-tool. Don't forget to lube the bearing before you fly it. Make it flush with the lower unit casting. You don't want or need the excess.
The inaccuracy in the scribe lines is because the fuselage is marked for both types of struts; the wire gear, and the Duro Strut. The plans, being made of paper, are subject to dimensional chages because of temperature and humidity. When you "scale" a plan, you will be slightly inacurate. Do what Mike J did. Cut the opening for the strut and tire after the frames are installed and the adhesive has cured. . Trim the glass away carefully, for a perfect fit. Give the strut and wheel about 3/32 clearance all around.
While you are waiting for the adhesives to cure, download Tony Frackowiak's BobCat flight trimming article from the BVM website. There is a tremendous amount of knowledge to be gleaned from his article. He is a master trimmer.
Keep after it...you'lle have a great airplane. Buy lots of fuel...you're going to need it.

Harley Condra
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RAM REP
Buy American!!!!!
Old 01-22-2002, 01:32 PM
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DavidR
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Default bobcat construction Q

Amen to the Bobcat being a great flying airplane. I built one for a frined and had it in primer for Superman, where we proceeded to log close to 40 flights on it. We flew a total of 52 flights on the airplane before I finally just had to force myself to strip it down and paint it. Both of the Bobcat's (XL's) that I have built were very early kits and I had to cut off the duro strut. One of the other guys I fly with just got his and the strut was already cut to length......well he now has a short strut if anyone needs one.
Old 01-27-2002, 04:49 AM
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Nikita
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Default another question

Now that I am almost done with the wings and will work or putting the wing the the fuse together, I face the following question: how do all the wires and tubes get from the fuse into the wing? Is there supposed to be some hole in the top of the wing to run all the stuff through? Can't seem to find anything in the instructions about that (or any kind of general rigging instructions for that matter).
Thanks again. Nikita.
Old 01-27-2002, 05:19 AM
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TonyF
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Default Holes in Wings

I believe the plans do show cutting a couple of holes in the top sheeting for routing fuel lines and servo leads. Anyway, that is how you do it.

I'd recommend that you go to BVM's website and download the BobCat trimming article I wrote. I give all the control throws and set-ups I use in the article. Also, I'm working to get the TX set-up I use available for download using the JR Datasafe.
Old 02-02-2002, 05:05 PM
  #12  
Nikita
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Default soldering the struts

Ok, I am trying to get the strut soldered into this brass adaptor. Using silver solder. I can't get both pieces heated up enough for the SS to melt! I thought I needed a more powerful iron, so I got a 75wt one, it's still not enough. I've been trying for at least 5 minutes straight and it still won't do anything. How do you guys do it? I am starting to think that I should probably just use JB Weld and be done with it....
Nikita.
Old 02-02-2002, 05:38 PM
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F9F Texan
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Default bobcat construction Q

Silver solder requires a torch(flame) and the proper flux to work properly.

The higher the silver content, the higher the temp required and
the stronger the joint will be.

If the material is clean, the proper flux is used and enough heat is applied, silver solder is a joy to work with.

Johnny
Old 02-02-2002, 05:58 PM
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Nikita
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Default bobcat construction Q

A heat torch? What kind of? I thought that this can be done with an iron. And it worked on smaller items before. I have the Great Planes SS, which came with the flux. But with this adaptor-strut thing I guess the pieces are too big for my iron to get them hot enough.
Nikita.
Old 02-03-2002, 12:03 AM
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rcjetflyr
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Default Soldering struts

I finally had to use a torch, (propane bottle with torch head) to get mine done. I usually use a gun but i couldnt get the brass and strut hot enough but with the torch just took a few minutes and i had both done, i was using staybrite ss.

Jack
Old 02-03-2002, 12:06 AM
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TonyF
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Default Propane torch

You need a propane torch available at any hardware store. Also, I would pick up a package of Stay-Brite silver solder. I'm not familiar with Great Planes SS, but I know Stay-Brite works well. Use just enough heat to make sure the solder flows well, And clean all the parts well with thinner or acetone prior to assembly. Unless you have a mongo one, a soldering iron will never get those parts hot enough.
Old 02-03-2002, 12:18 AM
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Harley Condra
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Default Silver soldering

Slip on down to the Home Depot or your favorite hardware store, and buy a Bernz-O-Matic propane torch. If you intend to use Stay Brite or Great Planes (Stay Brite) you will need it. Clean both surfaces to be joined with acetone or laquer thinner, add the liquid flux, heat 'er up, and add the solder. The solder will follow the flux.
If all fails, read the Stay Brite instructions. Use this method for all control system solder joints. Soft lead solder just doesn't cut it for our valuable toys.

Harley Condra
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RAM REP
Buy American!!!!!!
Old 02-03-2002, 04:35 AM
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Nikita
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Default a gyro

I am still thinking whether I do or do not need a gyro. Don't want to spend a fortune. Now somebody is offering a new JR G460T gyro for $105. Is this something I should be interested in for the Bobcat? I think the manual specifies a 450, is there a difference?
Old 02-03-2002, 05:41 AM
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TonyF
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Default Use the gyro

Do install the gyro. The 450 gyro has been discontinued. The 460 is the new sport Tail-Lock gyro from JR and will work fine in the BobCat. When you install it just set it to Rate mode. You do not want the Tail-lock feature.

There may be other gyro's suitable for the BobCat rudders, but you do want one with controllable gain. You do not need much gyro sensitivity when the gear are up, just when the gear are down. A better description is available in my BobCat Trimming article on BVM's website.
Old 02-08-2002, 04:55 AM
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Nikita
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Default Y-harness PCM?

The manual suggests using Y-harness PCM for rudders, elevators on the Bobcat. What is that? What's so special about this Y-harness?
I will be using JR digital servos, futaba receiver and I think I will stay with PPM. And who sells this type of harness anyway?
Thanks again. Nikita.
Old 02-08-2002, 06:22 AM
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TonyF
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Default Typo

It must be a typo, just use a regular Y-harness. I only Y'd the rudders and I used separate channels for the elevators.

I would highly encourage you to use a PCM system. With PPM a stray signal could shut-off your turbine.
Old 02-08-2002, 07:48 AM
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Default bobcat construction Q

Dont know about the Duro-Strut nose leg but the scribed lines on the fuselage for the wire strut are very inaccurate
Old 02-08-2002, 12:26 PM
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Silver182
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Default JR Gold Y Harness is Amplified (for a reason!)

If the distance from the receiver to the servo location's is more than 24 inches, and your using a JR receiver, it is recommended you use their amplified Y harness. You stated that your using a Futaba receiver, "if that is true the more expensive "amplified Y harness" is not necessary.

Another option (even more expensive than the amplified Y harness) would be to use the New JR match box for the elevators on your Bob Cat. With the Match Box you then can trim each servo for perfect throws. The one thing I am not sure of about the match box is whether the signal is amplified through the Match Box? I know it has the remote battery option needed for some of the big birds, so I would assume the Match Box also amplifies the signal from the receiver, (the reason for the amplified Y harness)!

If you stick with the Futaba receiver and a Futaba Y harness or make your own Y harness you shouldn't need all or any of the above. Of course the trimming of the elevator surfaces is going to have to be done manually!
Lee H. DeMary
AMA 36099
PS: I also would recommend a PCM receiver as Tony mentions ------using two channels for the elevator also eliminates the need for the Match Box and or the Amplified Y harness ------ a great way to go if you have enough channels ------- I hope the new 12 channel radios get out on the market soon!! We need them!!
Old 02-08-2002, 01:53 PM
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TonyF
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Default bobcat construction Q

I am using 36" long or longer leads with my JR equipment without amplified Y's with no problems. This is the case in all three of my jets, MiG 15, Bandit and BobCat. IMO the amplified Y's are not necessary. In fact I'm using the Futaba Y's in my models. In my BobCat the leads for the elevator and rudder servos are 24" long out of the wing, then another 18" long in the booms for a total of 42". Again, no problems.

I have just recently received some of the JR Matchbox's. I installed one on the elevators of my BobCat. It is exceptionally easy to set-up. I've got 6 flights on it so far, and it has worked perfectly. It installs right next to the RX and then the extension leads go to the elevator servos. IMO this device is easier to use then programming the TX.
Old 02-08-2002, 02:31 PM
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Gordon Mc
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Default Re: Y-harness PCM?

Originally posted by Nikita
The manual suggests using Y-harness PCM for rudders, elevators on the Bobcat. What is that?
It's a typo. (Confirmed by David Shulman at BVM). Just use a regular Y harness.

Gordon

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