Skymaster F-18 C of G ???
06-18-2014, 05:12 PM
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Skymaster F-18 C of G ???
I need to fly my F-18 soon and am just setting the CG. I recall two different CG settings. Some people say 120 back from leading edge (about 1/2" behind the front spar) and others say to balance it on the front former.
What do most people find for the best CG?
Mine is the round carbon spar.....Not the flat.....
How much nose weight do most F-18 need. With three batteries in the nose, I still need over 2 lbs to get the CG close to the spar.
What do most people find for the best CG?
Mine is the round carbon spar.....Not the flat.....
How much nose weight do most F-18 need. With three batteries in the nose, I still need over 2 lbs to get the CG close to the spar.
06-18-2014, 06:08 PM
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We flew 2 f18f back in March, one with ordnance and one without....the f18 without ordnance flew first flight at 130mm back from leading edge and it was ok with minor trimmings.
The other flew with CG at 140 as per manufacturer recommendation but was tail heavy despite having two rx batteries just at the start of the nose cone.
Then we moved the batteries fwd and added 60gr of lead and balanced it on 127mm and was much better. The usual take off jump is something you will need to work on also.
The other flew with CG at 140 as per manufacturer recommendation but was tail heavy despite having two rx batteries just at the start of the nose cone.
Then we moved the batteries fwd and added 60gr of lead and balanced it on 127mm and was much better. The usual take off jump is something you will need to work on also.
Last edited by lookilook; 06-19-2014 at 03:08 AM.
06-19-2014, 01:12 AM
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Don´t know exactly where is the CG in my 18, but I will check. Meanwhile I can say it has lead in the nose. probably about 2 lbs.
To get rid of that jump, use takeoff flaps, - lots of it - Mine is set with 45 degrees, the same I use for landing. This plane doesn´t rotate for takeoff.. it coudn´t as the main landing gear is so far behind the CG, I also mix about 5mm of "up" elevator for the pitch trim change.
The full scale F-18 takeoffs smoothly this way... the model is no different, even if you don´t use slats or drop your ailerons.
http://www.youtube.com/watch?v=2rgWyKLQe00
Taking off with this plane without flaps and using full elevator to rotate may result in a sudden "cobra" that will make you wish having a second set of underpants in your flight box...
To get rid of that jump, use takeoff flaps, - lots of it - Mine is set with 45 degrees, the same I use for landing. This plane doesn´t rotate for takeoff.. it coudn´t as the main landing gear is so far behind the CG, I also mix about 5mm of "up" elevator for the pitch trim change.
The full scale F-18 takeoffs smoothly this way... the model is no different, even if you don´t use slats or drop your ailerons.
http://www.youtube.com/watch?v=2rgWyKLQe00
Taking off with this plane without flaps and using full elevator to rotate may result in a sudden "cobra" that will make you wish having a second set of underpants in your flight box...
Last edited by erbroens; 06-19-2014 at 01:45 AM.
06-19-2014, 03:07 AM
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06-19-2014, 06:15 AM
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Haha..well, fortunately since day one I took off always with flaps with it.
At the time I wondered how the heck it could take off with such a weird landing gear position and CG and also no positive attitude on the ground, Those days there was no youtube but the web was full of pictures of the real F-18 taking off with a highly undercambered wing configuration, and realized that this was key for achieving lift and ground effect that allows a smooth takeoff. Tried in the model, and it was a success.
However, a good friend of mine tried to maiden his F-18 without flaps even if I warned him, and with a bigger engine, (I was his caller) During the long takeoff run,with full up elevator the plane suddenly rotated to a "cobra" , flew out of control to the parking lot, and crashed there.. Fortunately nobody was hurt or any car was hit, but the walk to the crash that day was something that I don´t want to anybody experience.
There are more peculiarities with this model, but I think that this is the real turn-off on what most people think this plane is difficult to fly.
At the time I wondered how the heck it could take off with such a weird landing gear position and CG and also no positive attitude on the ground, Those days there was no youtube but the web was full of pictures of the real F-18 taking off with a highly undercambered wing configuration, and realized that this was key for achieving lift and ground effect that allows a smooth takeoff. Tried in the model, and it was a success.
However, a good friend of mine tried to maiden his F-18 without flaps even if I warned him, and with a bigger engine, (I was his caller) During the long takeoff run,with full up elevator the plane suddenly rotated to a "cobra" , flew out of control to the parking lot, and crashed there.. Fortunately nobody was hurt or any car was hit, but the walk to the crash that day was something that I don´t want to anybody experience.
There are more peculiarities with this model, but I think that this is the real turn-off on what most people think this plane is difficult to fly.
06-19-2014, 06:50 AM
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we use 30mm of flaps (stage 1) for take off and hold the elevator up on roll out , as soon as the aircraft lifts off we release the stick but still the take off is no where near as smooth as my f16.
Since my last flight i have increased the nose gear strut by 1cm and i may use 45mm of flaps on next take off and see what happens.My f18 has flown only 6 flights and i need more flights to find the best flying setup.
Since my last flight i have increased the nose gear strut by 1cm and i may use 45mm of flaps on next take off and see what happens.My f18 has flown only 6 flights and i need more flights to find the best flying setup.
06-19-2014, 07:08 AM
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I have 15K MAH of battery in the nose of my SM F-18C to get the CG correct. I am on the road and unable to confirm my CG. I use T/O flaps and have a smooth T/O. I have the round spar's and I believe my CG is aft of the main spar, about 25 mm aft of the spar.
My Fai Bao F-18F is a bit of a different animal.
Last edited by whaledriver; 06-19-2014 at 07:11 AM.
06-19-2014, 07:16 AM
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I don't even use take off flaps any more.. The original CG setting from the manual makes it really nose heavy and hard to rotate causing it to leap off the runway
https://www.youtube.com/watch?v=PLrrVC2XjvE
https://www.youtube.com/watch?v=PLrrVC2XjvE
Last edited by basimpsn; 06-19-2014 at 07:22 AM.
06-19-2014, 07:51 AM
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Nice to see you at your club!
This is mine, with a Jetcat P-120 engine, at Joinvile, Brazil.. Using steering and aileron gyros in this flight (same setup I fly this days) with gains on high only when the landing gear is down. Flight is a bit boring in the last half, as a friend of mine tried the F-18 for the first time.. also a broken steering wire at landing.
https://www.youtube.com/watch?v=sMv4X9g6Kwo
This is mine, with a Jetcat P-120 engine, at Joinvile, Brazil.. Using steering and aileron gyros in this flight (same setup I fly this days) with gains on high only when the landing gear is down. Flight is a bit boring in the last half, as a friend of mine tried the F-18 for the first time.. also a broken steering wire at landing.
https://www.youtube.com/watch?v=sMv4X9g6Kwo
06-19-2014, 08:15 AM
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Hi
Lets clarify the most important issue about the SM f-18C .
There were two ver. of the f-18c , the one which was produced by JL and the other produced by FB.
There were some changes from each ver. so pay atten. to which ver. do you have, and this is for your plane
safety.
There are lots of lots of threads about the f-18c cg and here are some of them....
* http://www.rcuniverse.com/forum/rc-j...ty-center.html
* http://www.rcuniverse.com/forum/rc-j...8c-advice.html
* http://www.rcuniverse.com/forum/rc-j...r-f-18-cg.html
* http://www.rcuniverse.com/forum/rc-j...-f-18-c-g.html
* http://www.rcuniverse.com/forum/rc-j...ld-thread.html
* http://www.rcuniverse.com/forum/rc-j...throws-cg.html
* http://www.rcuniverse.com/forum/rc-j...c-g-f-18c.html
and IMO the most informative and the most important ...
* http://www.rcuniverse.com/forum/rc-j...ml#post5351184
pay attention to post no.14 which MNModels written and which is clarify exactly how to determine which ver. and what is the
best CG.
Hope it is help
Avi
Lets clarify the most important issue about the SM f-18C .
There were two ver. of the f-18c , the one which was produced by JL and the other produced by FB.
There were some changes from each ver. so pay atten. to which ver. do you have, and this is for your plane
safety.
There are lots of lots of threads about the f-18c cg and here are some of them....
* http://www.rcuniverse.com/forum/rc-j...ty-center.html
* http://www.rcuniverse.com/forum/rc-j...8c-advice.html
* http://www.rcuniverse.com/forum/rc-j...r-f-18-cg.html
* http://www.rcuniverse.com/forum/rc-j...-f-18-c-g.html
* http://www.rcuniverse.com/forum/rc-j...ld-thread.html
* http://www.rcuniverse.com/forum/rc-j...throws-cg.html
* http://www.rcuniverse.com/forum/rc-j...c-g-f-18c.html
and IMO the most informative and the most important ...
* http://www.rcuniverse.com/forum/rc-j...ml#post5351184
pay attention to post no.14 which MNModels written and which is clarify exactly how to determine which ver. and what is the
best CG.
Hope it is help
Avi
06-19-2014, 08:27 AM
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Here are the 2 skymaster F18F maiden flights at ladies mile salt lake in Cyprus with settings as described on my first post. http://www.youtube.com/watch?v=10_t_...ature=youtu.be
06-19-2014, 10:50 AM
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Thanks for all the tips. I think I will start around the front spar or a few mm back. Should take about 2.2 lbs of lead. I will also take off with a good amount of flap to help with the lift off.....
09-09-2015, 11:05 AM
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Gear doors installed. As are airlines, but rip all those out as they need to be redone. cylinders installed but some may need to be redone.
Flaps and ails and rudders have hinge points installed on the one side but not fully installed, which is good so you can properly position them on the wings and vertical fin.
Flaps and ails and rudders have hinge points installed on the one side but not fully installed, which is good so you can properly position them on the wings and vertical fin.
09-09-2015, 11:33 AM
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No, What I mention is pretty typical of any ARF these days. Getting leak free airline system and reliable doors takes a bit of experience to get right.
The structure on this one is good. I boroscoped it. Has dual ball bearing elev and carbon rods. A nice pipe. That's all good.
The whole CG confusion is unfortunate.
The structure on this one is good. I boroscoped it. Has dual ball bearing elev and carbon rods. A nice pipe. That's all good.
The whole CG confusion is unfortunate.
10-28-2015, 06:19 PM
#21
Ok, its official...
My F-18C is weeks out, and I need to start my shopping for her...
K140G in my shop now, should I go 180? This is the "C" version and not the larger F
Servos?
actuator's?
I plan on building her super light, so any recommendations, I would appreciate.
My F-18C is weeks out, and I need to start my shopping for her...
K140G in my shop now, should I go 180? This is the "C" version and not the larger F
Servos?
actuator's?
I plan on building her super light, so any recommendations, I would appreciate.
10-28-2015, 08:03 PM
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Db, you will find the 140 a good match for the 'C'. Dont skimp on the servos for the flaps & stabs, minimum 15kg. Thin 4kg for the ailerons will be fine
10-29-2015, 04:23 AM
#24
I am "building" a Skymaster F-18c right now and I will be going with the 180 for power. I thought about it a lot and it just makes more sense, it is the same size as the 140 with 8lbs more thrust. I want to fly with all the missiles and drop tanks also. The Skymaster bifurcated pipe is a bad design in my opinion, especially with the bigger engines, it will start to fail at the top and bottom of the split. The CG discussion is interesting, so much confusion! I'm thinking of starting at around 140mm and 145mm back from the leading edge.
I had pretty good luck with my Skymaster F-18F gear doors, but the air cylinders in this F-18c are leaking all over the place. Getting the gear right is always something that I spend a lot of time on.
I had pretty good luck with my Skymaster F-18F gear doors, but the air cylinders in this F-18c are leaking all over the place. Getting the gear right is always something that I spend a lot of time on.
10-29-2015, 04:44 AM
#25
Yeah if you don't mind I'd like to keep this active since mine will be here in a few weeks it will be a Blue Angel F-18C, I planned on Building it light. I had a Skymaster F- 15 that I bought used that all the cylinders were hysoled at every seam. Did your cylinders come installed? was it an extreme Arf? What about the airlines did you use the Skymaster or did you replace them?