*** Ultra Sport Brotherhood ***
#2653
Join Date: Oct 2007
Location: SortlandSortland, NORWAY
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Hi guys. Im well into my us60 build now and everything seems to come out ok. Today I started working on the firewall but I just cant figure out what the manual tries to tell me regarding cutting down the firewall for a 2 stroke engine.I will be using an os 75 engine on it. The firewall fits the nose of the plane perfectly as it is and if I cut it I will have to pry the fuselage together in the front to mate with the firewall. Can someone please explain? Also, when I turned the fuselage right side up after gluing it I noticed that the stab base is slightly tilted in relation to the fuse even tough it is fully seated against f6 and f6 is fully seated against the balsa triangles on the bottom of the fuse.question is if the fuse has the right angle or the stab base is
Last edited by larscato; 02-05-2015 at 12:20 PM.
#2654
Join Date: Nov 2005
Location: Lincoln,
NE
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Hi guys. Im well into my us60 build now and everything seems to come out ok. Today I started working on the firewall but I just cant figure out what the manual tries to tell me regarding cutting down the firewall for a 2 stroke engine.I will be using an os 75 engine on it. The firewall fits the nose of the plane perfectly as it is and if I cut it I will have to pry the fuselage together in the front to mate with the firewall. Can someone please explain? Also, when I turned the fuselage right side up after gluing it I noticed that the stab base is slightly tilted in relation to the fuse even tough it is fully seated against f6 and f6 is fully seated against the balsa triangles on the bottom of the fuse.question is if the fuse has the right angle or the stab base is
#2655
Join Date: Oct 2007
Location: SortlandSortland, NORWAY
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In theory the firewall needs to be bigger if the nr4 firewall spacers are used because the fuselage is wider the further back you get. however, the firewall fits snuggly between the fuselage sides even with the nr2 spacers for 2 stroke engine installed so I just dont get why I should make the firewall narrower and then force the fuse sides to mate with it..?
#2656
Join Date: Oct 2007
Location: SortlandSortland, NORWAY
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In theory the firewall needs to be bigger if the nr4 firewall spacers are used because the fuselage is wider the further back you get. however, the firewall fits snuggly between the fuselage sides even with the nr2 spacers for 2 stroke engine installed so I just dont get why I should make the firewall narrower and then force the fuse sides to mate with it..?
#2658
Join Date: Nov 2005
Location: Lincoln,
NE
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In theory the firewall needs to be bigger if the nr4 firewall spacers are used because the fuselage is wider the further back you get. however, the firewall fits snuggly between the fuselage sides even with the nr2 spacers for 2 stroke engine installed so I just dont get why I should make the firewall narrower and then force the fuse sides to mate with it..?
#2659
Join Date: Nov 2005
Location: Lincoln,
NE
Posts: 167
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In theory the firewall needs to be bigger if the nr4 firewall spacers are used because the fuselage is wider the further back you get. however, the firewall fits snuggly between the fuselage sides even with the nr2 spacers for 2 stroke engine installed so I just dont get why I should make the firewall narrower and then force the fuse sides to mate with it..?
#2660
Join Date: Oct 2007
Location: SortlandSortland, NORWAY
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thanx guys. I will cut the firewall down then. It makes sense to make a smooth curve down to the spinner as jrf said. The reason it just seems a bit odd is that the plans show the firewall at least 2,5-3 mm narrower than the 4 cycle firewall and it requires a great deal of force to pry the rather stiff fuselage sides together to mate with the firewall.
#2661
Join Date: Mar 2013
Location: Winnipeg,
MB, CANADA
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Hi larscato,
I am wondering if the difference is not to make the plane balance better, a four stroke being heavier will be closer in while a two stroke being lighter will need to be further out? If this is the case I would leave well enough alone unless you have a means to take off the correct amount evenly from both sides of the firewall.
Do your fuse front top and bottom fit well now and if so will you have to also shave these down. I have only experience with the US40 and it incorporates the differences by using different inner fuse side extensions for the proper setback. An aluminum spinner will make up for the difference in weight I would think.
Just make sure the 2 stroke is not longer than the four stroke, if it is then your upper and lower chin blocks may be to short, even so you can glue on some extensions.
Calvi
I just went back and looked at your pics again, it sure looks good to me. I like your glue fillets, I like to do the same all the way back to the rear of the wing saddle.
I am wondering if the difference is not to make the plane balance better, a four stroke being heavier will be closer in while a two stroke being lighter will need to be further out? If this is the case I would leave well enough alone unless you have a means to take off the correct amount evenly from both sides of the firewall.
Do your fuse front top and bottom fit well now and if so will you have to also shave these down. I have only experience with the US40 and it incorporates the differences by using different inner fuse side extensions for the proper setback. An aluminum spinner will make up for the difference in weight I would think.
Just make sure the 2 stroke is not longer than the four stroke, if it is then your upper and lower chin blocks may be to short, even so you can glue on some extensions.
Calvi
I just went back and looked at your pics again, it sure looks good to me. I like your glue fillets, I like to do the same all the way back to the rear of the wing saddle.
Last edited by Calvinman; 02-06-2015 at 06:17 AM.
#2662
Join Date: Oct 2007
Location: SortlandSortland, NORWAY
Posts: 85
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I will have to shave of the top and bottom of the firewall to blend with the top and bottom of the fuse. The thing that confuses me is the fact that the manual tells me to shave of the with of the firewall when using a 2 stroke engine even though the firewall slides right in as it is. I have used the correct spacers and the with of the fuselage is set by the top and bottom. 3 things could be wrong here. 1: I have made a mistake earlier in the fuselage build that im not aware of, 2: there is something wrong in the manual or 3: Im just plain stupid. My bet is on the last one...
#2668
Join Date: Nov 2005
Location: Lincoln,
NE
Posts: 167
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Hi larscato,
I am wondering if the difference is not to make the plane balance better, a four stroke being heavier will be closer in while a two stroke being lighter will need to be further out? If this is the case I would leave well enough alone unless you have a means to take off the correct amount evenly from both sides of the firewall.
Do your fuse front top and bottom fit well now and if so will you have to also shave these down. I have only experience with the US40 and it incorporates the differences by using different inner fuse side extensions for the proper setback. An aluminum spinner will make up for the difference in weight I would think.
Just make sure the 2 stroke is not longer than the four stroke, if it is then your upper and lower chin blocks may be to short, even so you can glue on some extensions.
Calvi
I just went back and looked at your pics again, it sure looks good to me. I like your glue fillets, I like to do the same all the way back to the rear of the wing saddle.
I am wondering if the difference is not to make the plane balance better, a four stroke being heavier will be closer in while a two stroke being lighter will need to be further out? If this is the case I would leave well enough alone unless you have a means to take off the correct amount evenly from both sides of the firewall.
Do your fuse front top and bottom fit well now and if so will you have to also shave these down. I have only experience with the US40 and it incorporates the differences by using different inner fuse side extensions for the proper setback. An aluminum spinner will make up for the difference in weight I would think.
Just make sure the 2 stroke is not longer than the four stroke, if it is then your upper and lower chin blocks may be to short, even so you can glue on some extensions.
Calvi
I just went back and looked at your pics again, it sure looks good to me. I like your glue fillets, I like to do the same all the way back to the rear of the wing saddle.
#2671
Join Date: Oct 2007
Location: SortlandSortland, NORWAY
Posts: 85
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thanx for all the input guys. Firewall is in and it came out nice. Yesterday I glued the turtledeck formers and stringers into place and started working on the sheeting. Im wondering on how to do this because if I lay the turtledeck sheeting flush with the bottom of the formers it doesent line up with the fuselage side and I will have to sand the fuselage side down for a nice transition. If I edge glue the turtledeck sheeting to the top of the fuselage sheeting making them flush the turtledeck sheeting will not touch the former at the bottom. The manual tells me to glue the bottom of the sheeting first. Do they mean edge gluing it flush with the fuselage sheeting?