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Joined: 7/17/2004 From: Cape Town, , SOUTH AFRICA Status: offline
I am currently putting together a Four Star 40 kit. While this is not my first kit build, it will probably be the first kit I finish and fly. I have a nearly completed 1/6 scale J3 Cub that is ready for covering, but I wanted to get experience with a low wing plane after my Hanger 9 Alpha before flying the scale model. (I also have a 1/4 scale tiger moth waiting paitently to be started!!).
I have the wings framed and the leading edges shaped, I decided to sheet the leading edges - more for aesthetics than anything else, and the fuselage is built, with a sheeted turtledeck. I am in the process of installing the servos and now have a few questions:
The first photo is of the servo layout. I have used Sullivan Gold n Rods instead of the supplied nylon pushrods following advice from RCU members regarding thermal expansion of the nylon rods. Is this layout ok? I don't know why it wouldn't be but I have no experience with servo layout other than the ARF I am currently flying. The pushrods do not cross between the servo and the fuselage exit, someone has told me that they should cross to provide slight resistance but surely the less resistance the better?
The second two photos are of the engine mounted on the firewall and the throttle linkage. I have removed the cheeks with the intention of building a balsa cowl. I have lowered the fuel tank by 20mm to allow for the side mounted motor. Does anyone have any suggestions as to how to connect the throttle to the servo? I seems very close to the edge of the firewall.
I am not seeing any issues with your push rods as long as they are secure the full lenght of them. As for the engine it can be done a couple of ways. Dubro makes a 4 stroke kit that mounts right of the edge of the motor mount. It is for all intensive purposes half of a bell crank. Your rod comes from your servo to the bell crank which is mounted on the engine mount about even with the center of your crankcase and then you make a rod that goes to your throttle arm from the bell crank. Another way of doing it is to have your push rod come out low on the carb and it then gets bent 180 degrees going back to the throttle arm. I prefer the bell crank method as it a little more presice, but they both work. Good Luck, Dave
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I believe the throttle arm on the carb can be moved, either that screw in the center or a set screw along the side allows this. Turn it 180 degress and you'll be away from the edge of the firewall and more towards the inside.
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I too am building a 4* with the Saito 56 side mounted... I have already used a Dubro 4-stroke throttle linkage kit to set mine up; It works very smooth.
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You may need room behind your servos for the battery for balance. Is everything glued down and cut? Do a prelim check on your balance before any more glue is laid down.
Looks like you have room to drill the firewall and mount the throttle-be tight to the side, conect to the middle hole on control arm of carb? just a idea! Servo placement looks good but keep checking the balance part to leave room for moving radio gear. I always glue down servo tray ectt. after I complete the build and sometimes after I cover so no LEAD is added-good luck.
< Message edited by frenchie79 -- 2/12/2008 3:51:25 PM >
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quote:
ORIGINAL: frenchie79 Looks like you have room to drill the firewall and mount the throttle-be tight to the side, conect to the middle hole on control arm of carb? just a idea!
That looks like it could work on this one; my engine sits closer to the firewall... My carb is also set to have the needle pointing up thru the cowl for easy adjustments.
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Carrot,
Your servo layout looks fine to me too, as long as there is no way the two servo arms can touch. I have also used the 180 degree bend method for connecting to the throttle and it works great. You can relocate the servo arm to the bottom to give you more room by loosening the set screw on the side of the throttle arm , not the screw in the center of the throttle. That screw is your low end needle valve adjustment. Please don't ask me how I know that
Good luck with your plane. Can't wait to hear a flight report.
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Joined: 7/17/2004 From: Cape Town, , SOUTH AFRICA Status: offline
Acs Guitars - the needle valve on your Saito points up, did you change it around? If so how did you do it? I checked through the engine manual but did not find any info in this regard.
Frenchie79 - I have already glued the servo tray into the rails. I only though about moving it for balance afterwards. I could try and de bond it (tightbond) or put it down to experience and remember next time.
Thanks everyone for the great ideas and photos.
One other point I noticed. I have used the Dave Brown 4045L mount. This is the mount recommended for the Saito 56, however the engine mounting lugs are slightly wider than the mount beams so that the screw holes are not in the beam centre and in fact the front ones "blister the side of the mount close to the bottom edge. Has anyone else experienced this. I do notice that the beams on this mount are slightly narrower than the 2 stroke version, is it possible this is just a mount from a bad batch and another unit may be ok?
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As for rotating the carb, you simply un-bolt it and turn it around. I used the same motor mount and found the same issue in the past but it has yet to pose a problem (The 4* is the Saito's 2nd home). You can tray a Dave Brown FS60 mount if you feel uneasy with using it as-is.
Personally I would try to "pop" the glued in tray free, but it really depends on how much glue coverage you have. My servos will be on a remavable tray right on the CG that also locks in the fuel tank (ARF inspired idea). With the weight I am adding in Balsa to the rear balancing will be no problem with the everything close to the CG and the battery can go Fore or Aft to make up any difference. It is always a good idea to leave the electronics until last.... Lead doesn't fly so why add it to your airframe
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Hi, Carrot! Have built and flown the Four Star 40 (and the Mid Star 40) and can tell you they both flew real nice. No problems. Had O.S. 45's on them. Another flier did have a 4S on his and it flew nice too. Have fun and take your time setting everything straight. You'll be rewarded with a great flying model. Happy building!
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Four Star 40 with Saito 56 - 
