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Kressline f5 D/F jet

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Old 09-10-2017, 05:03 AM
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ron Sweeney
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Default Kressline f5 D/F jet

Hi guys, this is a long shot. I have just dug out an old Kressline F5 kit and I need the c of g. It says that it is marked on the plan but it isn't. Does anybody know the position and anything else or any published references?
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Old 09-10-2017, 06:35 AM
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You have the same problem I had. The prints are wrong on the gear location which stopped me from my build. If you have the same cores I have the gear cut out is in front of the spar cutout. The F-5 gear retracts into the belly of the plane not the wing. The CG is just about in the wheel cutout location.
I cheated and found a plan view of the F-5E on Motion RC in the building instructions manual on the last page. If you do a proportional measurement you can get the CG from that. I have not calculated where that is on the core yet as we have a small bit of weather here in Florida we are dealing with. If I still have a house left on Tuesday I will do some calculations and transfer the result to the plans and post them. I suspect the CG from the Motion RC F-5 will be close as I have searched and found no complaints on the CG posted.
John

Last edited by john491; 09-10-2017 at 06:37 AM.
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Old 09-10-2017, 01:54 PM
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ron, has nothing to do with CG, but, that kit would be a great home for a pair of 80-90 mm edf.
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Old 09-10-2017, 02:10 PM
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ron,

there are some threads on "that other site" with cressline info.

https://www.rcgroups.com/forums/show...ne-F5-Agressor

and here

F-20 TIGERSHARK BUILD, CRESSLINE
that warbird guy has some access to the molds/plans, it looks like, from cressline.
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Old 09-11-2017, 07:50 AM
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[QUOTE=john491;12366718]You have the same problem I had. The prints are wrong on the gear location which stopped me from my build. If you have the same cores I have the gear cut out is in front of the spar cutout. The F-5 gear retracts into the belly of the plane not the wing. The CG is just about in the wheel cutout location.
I cheated and found a plan view of the F-5E on Motion RC in the building instructions manual on the last page. If you do a proportional measurement you can get the CG from that. I have not calculated where that is on the core yet as we have a small bit of weather here in Florida we are dealing with. If I still have a house left on Tuesday I will do some calculations and transfer the result to the plans and post them. I suspect the CG from the Motion RC F-5 will be close as I have searched and found no complaints on the CG posted.

John, many thanks for your reply, I thought something looked a bit wrong. Using the gear position it is logical that the balance point is in front of the wheel pivot this appears to be very far forward aerodynamically. I haven't got the foam cores out of the loft so I haven't referenced them yet. I bought this kit at jets over Deland in 1992 when a gang of us Europeans visited. There were so many issues that I put it to one side but at 75 I am now catching up on my 'bucket' list. I have started installing a Wren 44 down one side of the model with the thrust tube exiting only one of the rear thrust outlets, that's complete. I have always been put off by the oversize, non scale intakes, so I have started reducing the intake area. I have completed one side today and it looks more like an F5 now. I fly (amongst others) two BVM mavericks both with Wren turbines. I hope you can dig out the info' you mentioned. My back stop position was the Thorpe brothers F20 which I have built twice. We have all been following your horrendous weather issues on every news bulletin and you have all our best wishes. Ron.

Last edited by ron Sweeney; 09-11-2017 at 07:53 AM. Reason: additional information
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Old 09-11-2017, 07:57 AM
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Originally Posted by mongo View Post
ron,

there are some threads on "that other site" with cressline info.

https://www.rcgroups.com/forums/show...ne-F5-Agressor

and here

F-20 TIGERSHARK BUILD, CRESSLINE
that warbird guy has some access to the molds/plans, it looks like, from cressline.
Thanks, I tried searching but at 75 everything seems to conspire against me but I will try and access the references. Many thanks.
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Old 09-11-2017, 08:21 AM
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Originally Posted by mongo View Post
ron, has nothing to do with CG, but, that kit would be a great home for a pair of 80-90 mm edf.
I'm afraid I am not into edf. I started flying icdf in 1956 with diesel free flight and I never waivered till turbines arrived. I have nothing against edf and the latest foam models are very impressive. I still have two JMP Starfires/0S91 which give me a big kick. Ron.
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Old 09-11-2017, 08:48 AM
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[QUOTE=ron Sweeney;12367055]
Originally Posted by john491 View Post
You have the same problem I had. The prints are wrong on the gear location which stopped me from my build. If you have the same cores I have the gear cut out is in front of the spar cutout. The F-5 gear retracts into the belly of the plane not the wing. The CG is just about in the wheel cutout location.
I cheated and found a plan view of the F-5E on Motion RC in the building instructions manual on the last page. If you do a proportional measurement you can get the CG from that. I have not calculated where that is on the core yet as we have a small bit of weather here in Florida we are dealing with. If I still have a house left on Tuesday I will do some calculations and transfer the result to the plans and post them. I suspect the CG from the Motion RC F-5 will be close as I have searched and found no complaints on the CG posted.

John, many thanks for your reply, I thought something looked a bit wrong. Using the gear position it is logical that the balance point is in front of the wheel pivot this appears to be very far forward aerodynamically. I haven't got the foam cores out of the loft so I haven't referenced them yet. I bought this kit at jets over Deland in 1992 when a gang of us Europeans visited. There were so many issues that I put it to one side but at 75 I am now catching up on my 'bucket' list. I have started installing a Wren 44 down one side of the model with the thrust tube exiting only one of the rear thrust outlets, that's complete. I have always been put off by the oversize, non scale intakes, so I have started reducing the intake area. I have completed one side today and it looks more like an F5 now. I fly (amongst others) two BVM mavericks both with Wren turbines. I hope you can dig out the info' you mentioned. My back stop position was the Thorpe brothers F20 which I have built twice. We have all been following your horrendous weather issues on every news bulletin and you have all our best wishes. Ron.
John, just found the motion rc site.......thanks for the link. What a coincidence that within days of each other two of the same kits rise to the surface. Ron. p.s. I live in North west England in an area of the country that time has forgotten long may it stay that way.
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Old 09-11-2017, 10:25 AM
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Ron,
I have been lurking in the shadows for years trying to answer the CG question. When I found the Motion RC manual I really only lucked out. I was at that Jets over DeLand in 72. I think that was the year I met Bob Parkinson and purchased a Regal Eagle off the tailgate of his station wagon.
I worked out a rough CG from the Motion planform, so here goes. This assumes the same cores, which from the picture posted at the beginning appears is the same.
Assuming leading and trailing edges added to the core the wing root chord will be 420 mm.
The CG is at 90 mm in front of the spar cut out slot. The gear is 40 mm behind the spar cut out slot.
That makes the CG about 110 mm from the leading edge at the fuse without the chines ( extend the leading edge straight to the fuse )
That makes the gear at about 235 mm from the leading edge ( same point ).
I feel this would be a good starting point.
On my kit, I acquired it already started, evidently by someone attempting to follow the prints, so I have a bit to undo to get to the starting point. The elevators were attached with no anhedral ( the amount of which I am still trying to find- I think it is supposed about 7 deg ). The vertical stab was made of a flat slab of balsa so will have to be redone as well. I have been tinkering with going EDF because of the twin pipes, but may spring for a Tam bifurcated pipe before I get to the decision point.
Good luck with your build.
John
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Old 09-12-2017, 01:43 AM
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Originally Posted by john491 View Post
Ron,
I have been lurking in the shadows for years trying to answer the CG question. When I found the Motion RC manual I really only lucked out. I was at that Jets over DeLand in 72. I think that was the year I met Bob Parkinson and purchased a Regal Eagle off the tailgate of his station wagon.
I worked out a rough CG from the Motion planform, so here goes. This assumes the same cores, which from the picture posted at the beginning appears is the same.
Assuming leading and trailing edges added to the core the wing root chord will be 420 mm.
The CG is at 90 mm in front of the spar cut out slot. The gear is 40 mm behind the spar cut out slot.
That makes the CG about 110 mm from the leading edge at the fuse without the chines ( extend the leading edge straight to the fuse )
That makes the gear at about 235 mm from the leading edge ( same point ).
I feel this would be a good starting point.
On my kit, I acquired it already started, evidently by someone attempting to follow the prints, so I have a bit to undo to get to the starting point. The elevators were attached with no anhedral ( the amount of which I am still trying to find- I think it is supposed about 7 deg ). The vertical stab was made of a flat slab of balsa so will have to be redone as well. I have been tinkering with going EDF because of the twin pipes, but may spring for a Tam bifurcated pipe before I get to the decision point.
Good luck with your build.
John
Thanks John for all the info'. I will take it on board. I fly from a grass strip so weight is my enemy. Also the wren gold only gives 10 pound plus' I used a bifurcated pipe in the small yellow aircraft f18 but with such a small model the wing loading was getting a bit too high and no matter how well designed the pipe is there will be a certain amount of thrust loss. Re jets over Deland '92......what a coincidence. Ron.
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