Cincinnati Jet Club F-18's project
11-14-2014, 02:01 PM
#179
Joe,
Funny, on my flights with the twin P-80SE's, it was the small main door that would open up on full-throttle passes. The wind keeps the big door closed, but somehow I had enough internal pressure to hold those little ones open. I never figured it out because the engines were fully bypassed and there was no obvious source of air force-feeding into the fuselage.
Funny, on my flights with the twin P-80SE's, it was the small main door that would open up on full-throttle passes. The wind keeps the big door closed, but somehow I had enough internal pressure to hold those little ones open. I never figured it out because the engines were fully bypassed and there was no obvious source of air force-feeding into the fuselage.
11-16-2014, 04:04 AM
#181
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Joe.. Do you have any pictures of the elevator and rudder servo mounts? I thought I read somewhere that you were going to move them back closer to the stabs. I'm on the fence what to do. I could live with Nyrods on the rudders, but not sure if I would be comfortable with Nyrods on the elevators.
11-16-2014, 07:37 AM
#182
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I made plywood mounts and glued and glass them to the side of the fuse a couple inches behind the rear main former for the elevators. The rudder servo mounts are mounted to the top of the fuse about halfway back from the main former. both use aluminum arrow shaft with solid aluminum ends, tapped 4-40 and have a stud coming out for ball links. I did not like the rudder torque rods that came in the kit for the rudders (mine is old polyester kit). I made 5/32 wire torque rods bent as needed them welded small, thin steel section on the ends. tapped 4-40 for easy install of ball links. My rudders are not removable. I have seen guys put the elevator servo at the bottom inside the fuse and reversed the horns on the elevators. I'm not sure you could get the pipe in and out that way.
11-16-2014, 07:29 PM
#183
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Been back and forth on the elevators. Had planned on moving them to the rear about 5in in front of the elevator box. It would require building a structure to hold the servo and getting access and proper alignment seem to be problematic. I watched a guy fly an older yellow version with small rods going back and plastic servo arms. He also had a P200 in it and it didn't have any problems. I am not suggesting or promoting that set up, but it make me think I could make a sturdy long push rod control for the elevators and mount them in the stock location. I have full threaded 8/32 rod slid into a carbon fiber rod and all metal ball links. I got the threaded rod and HD metal ball links from McMaster Carr. I will still have it supported mid span but it will probably not be needed.
I would not use Nyrods anywhere on the airplane. For my rudders, I cut in through the bottom of each vert stab and mounted 8411 servos internally with a small 3in push rod going to the rudder. My rudders are removable, so I have access to the servos when they are off.
I would not use Nyrods anywhere on the airplane. For my rudders, I cut in through the bottom of each vert stab and mounted 8411 servos internally with a small 3in push rod going to the rudder. My rudders are removable, so I have access to the servos when they are off.
11-18-2014, 06:14 AM
#185
Hi,
I don't think the kit calls for use of nyrods. I think the rudders are 4-40 rods moving through nylon sheathing. You would not have any issues whatsoever with those. As far as stabs go, you could put the servo in the nose and not have any issues (regardless of engine size) if you're using a rigid rod. I used the Dave Brown fiberglass pushrods in all of these I've built (two full builds from kits and two ARFs). You would have to have yards and yards of length on those rods to get into any issues with flexing and even then, you'd have to make sure NOT to have any support.
Try to remember that the guy who designed the kit has a PhD in Aero Engineering and knew what he was doing. Also, how many failures related to stab servo placement have you heard about since the plane came out in '88? I'm guessing that number is gonna be somewhere around zero
90% of the mods I've seen on this bird are classic examples of a 'solution in search of a problem', and really only answer the question "Gee my plane is too light, so how can I weigh it down with mods and reinforcements that look cool but have no utility or benefit whatsoever?" I once saw a build where the guy glassed the outer skin of the 2-piece gear doors because he felt the stock ones were too flimsy. He used 6-oz cloth because he wanted his gear doors to "not flap around in the wind." I mentioned to him that when he glued the liners on, they'd become quite a bit more rigid but he wasn't impressed with that. His doors were so heavy that they'd open up in a turn. Another guy I saw added shear webbing the entire length of the inside of the LEX because he felt there was too much room for compression. I mentioned that the bulkheads would take care of that to the extent needed AND that I wasn't aware of all the Hornets falling out of the sky due to LEX compression...
The mods that actually help: Gear plate reinforcement, steering arm modification, beefing up of the two main bulkheads (particularly for twin-engine setups or with older generation kits), plywood 'capture' of the spar receivers. I love Joe's rudder mod. I'm doing a similar mod, but placing the servo such that the arm is level with the very bottom of the fin. I'll use a ball link to deal with the geometry of the hinge-line and a smaller servo. I figure given the size of the rudder and the speed potential of the plane, the servos used on 400mph glider control surfaces should be adequate. With the arm at the base of the fin and the horn mounted to the base of the rudder, the linkages will be nearly invisible and you won't have that fugly servo plate in the middle of the fin like on most ARF F-18's.
Joe, superb build. Really motivating me to get mine moving again now that I'm on the mend (health-wise).
I don't think the kit calls for use of nyrods. I think the rudders are 4-40 rods moving through nylon sheathing. You would not have any issues whatsoever with those. As far as stabs go, you could put the servo in the nose and not have any issues (regardless of engine size) if you're using a rigid rod. I used the Dave Brown fiberglass pushrods in all of these I've built (two full builds from kits and two ARFs). You would have to have yards and yards of length on those rods to get into any issues with flexing and even then, you'd have to make sure NOT to have any support.
Try to remember that the guy who designed the kit has a PhD in Aero Engineering and knew what he was doing. Also, how many failures related to stab servo placement have you heard about since the plane came out in '88? I'm guessing that number is gonna be somewhere around zero
90% of the mods I've seen on this bird are classic examples of a 'solution in search of a problem', and really only answer the question "Gee my plane is too light, so how can I weigh it down with mods and reinforcements that look cool but have no utility or benefit whatsoever?" I once saw a build where the guy glassed the outer skin of the 2-piece gear doors because he felt the stock ones were too flimsy. He used 6-oz cloth because he wanted his gear doors to "not flap around in the wind." I mentioned to him that when he glued the liners on, they'd become quite a bit more rigid but he wasn't impressed with that. His doors were so heavy that they'd open up in a turn. Another guy I saw added shear webbing the entire length of the inside of the LEX because he felt there was too much room for compression. I mentioned that the bulkheads would take care of that to the extent needed AND that I wasn't aware of all the Hornets falling out of the sky due to LEX compression...The mods that actually help: Gear plate reinforcement, steering arm modification, beefing up of the two main bulkheads (particularly for twin-engine setups or with older generation kits), plywood 'capture' of the spar receivers. I love Joe's rudder mod. I'm doing a similar mod, but placing the servo such that the arm is level with the very bottom of the fin. I'll use a ball link to deal with the geometry of the hinge-line and a smaller servo. I figure given the size of the rudder and the speed potential of the plane, the servos used on 400mph glider control surfaces should be adequate. With the arm at the base of the fin and the horn mounted to the base of the rudder, the linkages will be nearly invisible and you won't have that fugly servo plate in the middle of the fin like on most ARF F-18's.
Joe, superb build. Really motivating me to get mine moving again now that I'm on the mend (health-wise).
11-18-2014, 11:52 AM
#187
11-18-2014, 11:59 AM
#188
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Joe... I don't want to intrude on your thread, but just wanted to thank all for the insight on the elevator servo location. I decided to move my servos back to the aft rudder bulkhead with a 4-40 rod/CF tube for stiffness. Works really awesome and a very stiff linkage.
More details here on the build thread
http://www.rccanada.ca/rccforum/show...203169&page=16
And a quick video....
https://www.youtube.com/watch?v=_ylQi1fdYrY
More details here on the build thread
http://www.rccanada.ca/rccforum/show...203169&page=16
And a quick video....
https://www.youtube.com/watch?v=_ylQi1fdYrY
11-18-2014, 01:58 PM
#189
Tbrum,
Wow that's a lot of torque! May I humbly suggest you maybe add another vertical sub-former to the aft side of your servo mount? If you pushed real hard on the outside of the skin where your mount is, could you get it to make any cracking noise? Also, now that your servo is in an area that's hotter than the stock location, are you going to cover it with anything or are you feeling good about the heat back there being ok for the servo?
Wow that's a lot of torque! May I humbly suggest you maybe add another vertical sub-former to the aft side of your servo mount? If you pushed real hard on the outside of the skin where your mount is, could you get it to make any cracking noise? Also, now that your servo is in an area that's hotter than the stock location, are you going to cover it with anything or are you feeling good about the heat back there being ok for the servo?
11-18-2014, 02:18 PM
#190
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Great idea for the added member that you suggest. I also plan on lapping some CF cloth from the servo boxes onto the fuse sides but with the bulkhead right there it is already really stiff
I'm not worried about the heat, since this is no different than other jets with the servos back in that area (Scorpion, Mig29 w/ TV, F16, F14, etc). If it's too hot for a servo I have bigger issues, LOL!
I'm not worried about the heat, since this is no different than other jets with the servos back in that area (Scorpion, Mig29 w/ TV, F16, F14, etc). If it's too hot for a servo I have bigger issues, LOL!
11-18-2014, 08:16 PM
#192
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speaking of heat, I test ran my KT180 in the plane a couple weeks ago. Just bolted the motor in, everything else was outside the plane. I'm using a Tam pipe. I just had to hear it run, the sound is amazing. I checked all areas of the fuselage, not even warm! Tams pipes are the best.
11-19-2014, 05:01 AM
#193
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Joe... I don't want to intrude on your thread, but just wanted to thank all for the insight on the elevator servo location. I decided to move my servos back to the aft rudder bulkhead with a 4-40 rod/CF tube for stiffness. Works really awesome and a very stiff linkage.
More details here on the build thread
http://www.rccanada.ca/rccforum/show...203169&page=16
I like it! The geometry looks good.
I would agree regarding another vertical former.
I may just change mine to look like yours.
And a quick video....
https://www.youtube.com/watch?v=_ylQi1fdYrY
More details here on the build thread
http://www.rccanada.ca/rccforum/show...203169&page=16
I like it! The geometry looks good.
I would agree regarding another vertical former.
I may just change mine to look like yours.
And a quick video....
https://www.youtube.com/watch?v=_ylQi1fdYrY
I like it! The geometry looks good.
I would agree regarding another vertical former.
I may just change mine to look like yours.
11-19-2014, 05:06 AM
#195
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speaking of heat, I test ran my KT180 in the plane a couple weeks ago. Just bolted the motor in, everything else was outside the plane. I'm using a Tam pipe. I just had to hear it run, the sound is amazing. I checked all areas of the fuselage, not even warm! Tams pipes are the best.
Some people hate the sound of a bifurcated pipe but I like it.
11-19-2014, 05:07 AM
#196
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I am still working on the F-18s but just not taking pictures. I am doing a bunch of dirty body work..... seems, holes and intake area. It is definitely not the fun part.
11-19-2014, 08:52 AM
#197
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Not looking forward to that stage of things, Joe!!!
I got the gear structure in last night and just need to finish up tweaking of the main gear orientation tonight. Also hope to start on the nose gear tonight. I'm going to shamelessly steal your direct drive servo set-up on the nose wheel Joe. That's a simple and effective set-up. I also need to study the removable formers for access to the twin tanks.
Cheers
Trevor
I got the gear structure in last night and just need to finish up tweaking of the main gear orientation tonight. Also hope to start on the nose gear tonight. I'm going to shamelessly steal your direct drive servo set-up on the nose wheel Joe. That's a simple and effective set-up. I also need to study the removable formers for access to the twin tanks.
Cheers
Trevor
11-19-2014, 10:32 AM
#198
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The steering mod is a good one. I wish I could take the credit but Joe Dirr, whom owns one of the three, designed it. He is a quality engineer at a crane company and I told him the pull-pull stuff has got to go....hate it. He came up with a design that was fairly simple and worked well. It will need to be tested under load, but I don't think it will have any problems.
11-19-2014, 03:07 PM
#199
Hi,
I love pull-pull steering, but in this case, the arms are WAY too flimsy. When retracted, the strut doesn't bring the arms closer, thereby giving slack. Sean Reit made me a beefier arm that was below the grunion and the lines went slack when retracted. Where's the post or pic with your mod? Love to see.
I love pull-pull steering, but in this case, the arms are WAY too flimsy. When retracted, the strut doesn't bring the arms closer, thereby giving slack. Sean Reit made me a beefier arm that was below the grunion and the lines went slack when retracted. Where's the post or pic with your mod? Love to see.