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Skymaster F18F c of g position

Old 08-07-2006, 04:49 AM
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Springbok Flyer
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Default Skymaster F18F c of g position

Hi guys

A friend of mine last Saturday had a fatal crash with his F18E due to the C of G being too far back. The position was set as per the instructions and the jet was going fast enough on take of. He is a very experienced pilot of 30 years standing and many jetflights. Over 350 on turbines alone. He did not grab a hand full of up stick either - just in case you were wondering.

My F18F is waiting to fly and I will appreciate input from any Skymaster F18E or F18F pilots regarding the C of G and throw settings on their aircraft.

Please, any pilots who have successfully flown either of these F18's are asked to reply.

Thank you for sharing your experience.

Cheers

Springbok Flyer
Old 08-07-2006, 08:47 AM
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Default RE: Skymaster F18F c of g position

I have the F18E with two flights on her. I set my c/g and control throws up per the instructions and it's hard to believe your friend was able to get this plane rotate without a ton of up stick. Now I did make the mistake of setting my tails with too much up trim as the plans are fuzzy about where the zero position is and after she rotated the climb out was near vertical until I added allot of down trim but the c/g feels correct and I am not a high time turbine pilot. I have the first flight video if you would like to see it.
Old 08-07-2006, 09:02 AM
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Default RE: Skymaster F18F c of g position

Hi Springbok Flyer

Sounds like you should be in sunny South Africa! Not that our Springbok rugby team is doing very well at the moment!

I had the misfortune of seeing the same aircraft suffer the same fate 2 weeks ago. It was also rumoured that 2 previous F 18's showed signs of nose heavyness so these fellows erred on the side of tailheavy. Unfortunately the total plane was lost as it caught fire on impact, even the turbine was a write-off!

Best you wait for some good news from other F18 pilots.

I don't know if Ali has one in his arsenal?

Zane
Old 08-07-2006, 09:38 AM
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Default RE: Skymaster F18F c of g position

Michel from Chile has as much time on the F18F as anyone. He will probably help with some info.

Regards

Jim
Old 08-07-2006, 10:21 AM
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Default RE: Skymaster F18F c of g position

The "leap-off" takeoff on the F-18 does have nothing to do with the SM CG factory settings (that is very conservative) it is about the scale main landing gear position, designed for carrier operations that simply compromise ground rotation abilities (not required at all on the carrier flight deck) with more fuselage and tail protection at typical carrier landings.

Fortunately, there is a simple way to avoid this problem using flaps at takeoff. They help the plane leave ground in a flatter attitude without needing a lot of elevator input, making a smooth rotation.

And sorry to hear about the crashes.. the F-18 is a nice and forgiving aircraft to fly, as long you know its characteristics.

Enrique
Old 08-07-2006, 10:53 AM
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Default RE: Skymaster F18F c of g position

ORIGINAL: Jascat100

Michel from Chile has as much time on the F18F as anyone. He will probably help with some info.

Regards

Jim
Thanks for the words Jim, my F-18F is flying great every weekend.

Springbok, I found very strage that your friends F-18 was tail heavy if you had the CG as instructions say. I have the CG at 140mm as mannual and the F-18 flys great. I have even tested it at 150mm and no problems at all. Maybe the problem was something else.
I also have all the throws as Skymaster instructions, I would recomend though if you are using the external tanks and missiles to lower the elevator throw a bit. If not just go as the instructions say and you will be ok. Remember to use some expo on the elevators and ailerons.

Rotation problem is as Enrique says, using flaps and let the jet run as far as posible will help in getting smooth takeoffs. Also try to set the nose gear as long as posible in order to give the F-18 a positive AOA when sitting on the wheels, this will also help on takeoffs.

Here are a couple of videos of mine flying...

http://www.jetsrc.com/videos/F-18F_MT_JetsRC_Hi.wmv
http://www.jetsrc.com/videos/f-18F_JetsRC.wmv

The F-18F is a great jet and flying is very predictable and stable, don't be afraid of it. It can also fly extremelly slow, so this is great for short landings. You can have this bird in full stop in about 40 meters, but don't try to do this on your first flights..

Hope this helps...

Michel

Old 08-07-2006, 08:31 PM
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Default RE: Skymaster F18F c of g position

Thank you Michel and others

Your input is most appreciated.

Just for the record, some details: The F18E was equipped with a FunSonic set to 33lbs and total take off weight was 45lbs. Runway was hard, short grass with a 15 knot head wind. The vertical attitude was instantaneous upon application of elevator for rotation.

Since the crash we've had Duke from Hawaii Jets tell us that the c of g as per the instructions are wrong and that they (Hawaii Jets) have told Skymaster so on numerous occassions. He maintains that the c of g as per the instructions is flyable but extremely sensitive. He recommend that the c of g get set between the leading edge flap notch to 1/8" behind this notch. That is quite a long way in front of the instruction position. He does however say that at this position it is difficult to spin the F18.

Please can you tell me where the neutral potition is for the leading edge of the stab.

Cheers mate

Springbok Flyer
Old 08-07-2006, 11:41 PM
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Default RE: Skymaster F18F c of g position

Michel,

Do you mix any elevator in with the flaps when you extend them?

Thanks,

Beave
Old 08-08-2006, 09:03 AM
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Default RE: Skymaster F18F c of g position

Hi guys,

I have been watching this issue with interest and I agree entirely with the comments about the gear configuration being the primary reason for rotation problems with the F18. I have a skymaster F18c and I have shimmed my nose retract down approx 6mm at the rear and 4 mm at the front to enable the nosewheels to retract. This has the added effect that the nose is lifted on the ground for takeoff roll. I also was unhappy with the softness of the ist stage spring in the noseleg. I suspected that this would compress at full power allowing the model to adopt a nosedown attitude on its takeoff roll as I have had this problem with another F18.

The solution: I made a Delrin spacer cylinder to fit inside the lower part of the noseleg to prevent the first stage spring from compressing. Sure I have lost some travel in the compression strut, but it wold have been disadvantageous to have it anyway! The spacer is 17.5mm long, inner diameter 5mm and outer diameter 8.5mm. The model looks good now on its wheels, sitting with a relatively good positive AOA at rest....approx 1.5 to 2degrees positive incidence at the wingtips. Add some flap into the equation and I reckon I will have the problem solved. I expect relatively smooth rotation now.

The large yellow F18 seems to have always rotated better than other versions of the F18 I have seen. If you look at it, it has a higher nose attitude than other F18's on the market....I think there is good reason for that!

Best of luck.

Craig.
Old 08-08-2006, 09:45 AM
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Default RE: Skymaster F18F c of g position

ORIGINAL: Springbok Flyer
Since the crash we've had Duke from Hawaii Jets tell us that the c of g as per the instructions are wrong and that they (Hawaii Jets) have told Skymaster so on numerous occassions. He maintains that the c of g as per the instructions is flyable but extremely sensitive. He recommend that the c of g get set between the leading edge flap notch to 1/8" behind this notch. That is quite a long way in front of the instruction position. He does however say that at this position it is difficult to spin the F18.

Please can you tell me where the neutral potition is for the leading edge of the stab.

Cheers mate

Springbok Flyer
I got a picture I think was send by Duke a while back, if this is not your picture Duke sorry, my head is playing tricks on me...
Actually the CG shown in this picture is very close to the one Skymaster recomends. You can go as far as the foward spar and the jet will fly with no problems. Behind that, I have not tested it.

I don't havre the jet with me right know, I will check the stab neutral and let you know.

Michel
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Old 08-08-2006, 09:47 AM
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Default RE: Skymaster F18F c of g position

ORIGINAL: bevar

Michel,

Do you mix any elevator in with the flaps when you extend them?

Thanks,

Beave
Hi Beave, yes I do mix elevator and flap. I need some up elevator when flaps are applyed as the F-18 will pull the nose down. I am not sure how much but it is not a lot. As I said before the jet is not with me at this moment.
Anyway, if you have a 9Z or similar you can actualy trim this in the air.

Michel
Old 08-08-2006, 07:38 PM
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Default RE: Skymaster F18F c of g position

Michel and others

Thanks again. I do believe that Duke is an excellent source of information and certainly has the expertise to advise me competently.

Only one thing is worrying me. There seems to be a misunderstanding as to the c of g position when it comes to the F18C on the one hand and the F18E and F18F on the other hand. From what I can tell, the F18C c of G is better behind the front set of wing mounting bolts. Whilst the F18E and F18F c of g is better between the leading edge flap notch and the position as per the instructions. I further believe the undercarriage position, hence rotation problem, to be more particular to the C than to the E and or F. By all accounts, the C is considerably different in many respects from the E and the F.

Therefor I think we need to be very careful not to confuse the c of g on the C to that of the E and F.

As for the picture, is that a C or an E? I look forward to getting your measurement on the stab neutral position.

Thanks

Springbok Flyer
Old 08-08-2006, 09:02 PM
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Default RE: Skymaster F18F c of g position

Hi all

The picture is of the F-18E, and I do think that is the one I sent to you Michel! By the way great job with your F-18F!

Hi Springbok

The F-18C and F-18E and F are very different as far as the CG is due to the LEX being quite a bit larger on the Superhornet E/F than the F-18C.
Old 08-09-2006, 09:07 AM
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Default RE: Skymaster F18F c of g position

Thanks Duke

Now all I need is the correct neutral position of the stab ............... then my F18F can fly.

Cheers

Springbok Flyer
Old 09-05-2006, 01:57 AM
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Default RE: Skymaster F18F c of g position

William

On the F18E. have you still got the C of G in the original position? Please could you measure the position for me. The instructions quote 140 to 160 mm from the leading edge where the wing joins the fuz. According to a few of the other guys they are quoting 120 to 125 mm by comparisson or 1/8 of an inch behind the step in the wing to fuz joint.

I have also been trying to get the neutral position on the stab. Please check that and let me know too.

Again, thanks for your help.

Cheers

Springbok Flyer
Old 09-05-2006, 07:25 AM
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Default RE: Skymaster F18F c of g position

My C/G is on the aft side of the foreward cross brace, I actually hung the plane from this brace when i was completing the C/G.so I stayed withen the 140 to 160mm range. My stab is neutral 1/4 above the Z shape panel extending from the flap trailing edge or 3 1/8" below the fuselage/vertical stab seperation line, if this makes no sense I will take a photo later today for you but all measurements are taken at the leading edge of the stab.
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Old 09-05-2006, 08:32 AM
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Default RE: Skymaster F18F c of g position

Yes, please post a pic for us. Michel, if you could take a pic of yours too that would be great. Maybe you could do one flaps up and one flaps down?

Thanks,

Beave

ORIGINAL: foster4u

My C/G is on the aft side of the foreward cross brace, I actually hung the plane from this brace when i was completing the C/G.so I stayed withen the 140 to 160mm range. My stab is neutral 1/4 above the Z shape panel extending from the flap trailing edge or 3 1/8" below the fuselage/vertical stab seperation line, if this makes no sense I will take a photo later today for you but all measurements are taken at the leading edge of the stab.
Old 09-05-2006, 10:04 AM
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Default RE: Skymaster F18F c of g position

Hi guys, I don't have the F-18 with me right know, also I am days of been a father for the second time so the bird is off limits for a couple of weeks... You know how it is...

Anyway CG at 140mm as stated by the factory.... The jet flys really great here, no bad tendencies and very stable. Same thing with flaps, factory settings are perfect, I would suggest using a bit more flap for takeoff for geting a smooth rotation.

For elevator start with a 0 degree setting and trim in the air, in mine I had to add a bit of trimimg.

For landings first slow down the F-18 a bit and then apply flaps, the faster you go the more down the nose will want to go. Again this is not something to get scared off, that is why I sugested using a mix to apply a bit of up elevator when lowering the flaps. But if you don't do the mix you will just have to apply some up elevator when lowering the flaps.

Michel
Old 09-05-2006, 01:34 PM
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Default RE: Skymaster F18F c of g position

Michel,

Congrats on the new baby!!
Old 09-05-2006, 01:52 PM
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Default RE: Skymaster F18F c of g position

Thanks Shawn, it is going to be a girl....UFFFF(Second one...) I am surounded by women know... I am crossing my fingers that at least one will like jets...

How is little Shawn???
Old 09-05-2006, 07:03 PM
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Default RE: Skymaster F18F c of g position

Hi,

He's absolutely excellent. He gave us a couple of health scares early on, but he's tip-top these days. Very smart, very strong, very coordinated and very effectionate. He's a lot of fun.
Old 09-05-2006, 08:05 PM
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Default RE: Skymaster F18F c of g position

William

Fantastic, thank you.

Cheers mate

Springbok Flyer
Old 09-05-2006, 08:10 PM
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Default RE: Skymaster F18F c of g position

Michel

Thanks mate, all the input is appreciated.

Hope the 'delivery' is smooth and both mother and girl are in good health.

Cheers

Springbok Flyer
Old 09-19-2006, 08:03 AM
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Default RE: Skymaster F18F c of g position


We have test flown the F-18F this weekend to conform some CG issues that was of some concern. Please take a look at the link below, at a post in another thread I did regarding this issue.


http://www.rcuniverse.com/forum/m_4753018/tm.htm






Old 06-04-2007, 09:21 PM
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Default RE: Skymaster F18F c of g position

Call me 305 300-1800 ASAP i have to tell you about my F-18 F from Skyamster dont flyit YET if you havent call ME ASAP my name is Marvin

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