P38 Documentation
12-22-2002, 04:06 AM
#26
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Fowler flaps; more lore
Paul -
Oh, you are just looking too close at my work!
Very impressive how you drill down into the weak spots so quickly! 
On the prototype, I silver soldered a 3/8" duracollar to a standard 5/16-18 nut. The eight cables go in there with a lot of muscle. The cables WILL flex if you put a lot of stress on them early in the travel of the nut (and thus early in the deployment), but I do not think there will be a lot of stress at this point in the sequence. The cable I am using from the Sullivan package is gold in color and about 3/32" thick - it is pretty stiff. However, I have built a schroud that surrounds the jack screw and cables through about 3/4 of the travel - it makes sure to hold 'em in there. I am not satisfied with the nut and collar approach, and this weekend in fact I am making a single piece out of 1/4" steel which is threaded for the 5/16-18 lead screw and two or four separate holes for the cables.
Looking at the MAN article, it seems possible to use four drive cables and the setup they show. I am sticking with my arrangement because I like the fact that none of the hinge support and tubes show when the flap is deployed. Just personal preference.
I like the sail servo idea. I looked at them also early on, and could not find one that had the power I needed at the right price. But I would say I didn't look too hard, 'cause I was already deep into this design. Where ar you going to get the ACME screw? Small Parts? Recommend you ensure the deployment speed is reasonable - mine go out in about 8 seconds, and I think that is almost too slow. Scale like, but if I am in a pickle, I might want some speed! Although, you know, in full scale flight trainig they tell you to raise and lower the flaps slowly because of the tremendous difference in lift.
Let me know how you sail servo idea comes out. Let's keep this going; it looks like there are others out there who have a lot of unpublished experience with Fowlers that this thread is drawing out.
Oh, you are just looking too close at my work!
Very impressive how you drill down into the weak spots so quickly! On the prototype, I silver soldered a 3/8" duracollar to a standard 5/16-18 nut. The eight cables go in there with a lot of muscle. The cables WILL flex if you put a lot of stress on them early in the travel of the nut (and thus early in the deployment), but I do not think there will be a lot of stress at this point in the sequence. The cable I am using from the Sullivan package is gold in color and about 3/32" thick - it is pretty stiff. However, I have built a schroud that surrounds the jack screw and cables through about 3/4 of the travel - it makes sure to hold 'em in there. I am not satisfied with the nut and collar approach, and this weekend in fact I am making a single piece out of 1/4" steel which is threaded for the 5/16-18 lead screw and two or four separate holes for the cables.
Looking at the MAN article, it seems possible to use four drive cables and the setup they show. I am sticking with my arrangement because I like the fact that none of the hinge support and tubes show when the flap is deployed. Just personal preference.
I like the sail servo idea. I looked at them also early on, and could not find one that had the power I needed at the right price. But I would say I didn't look too hard, 'cause I was already deep into this design. Where ar you going to get the ACME screw? Small Parts? Recommend you ensure the deployment speed is reasonable - mine go out in about 8 seconds, and I think that is almost too slow. Scale like, but if I am in a pickle, I might want some speed! Although, you know, in full scale flight trainig they tell you to raise and lower the flaps slowly because of the tremendous difference in lift.
Let me know how you sail servo idea comes out. Let's keep this going; it looks like there are others out there who have a lot of unpublished experience with Fowlers that this thread is drawing out.
12-23-2002, 04:16 PM
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Fowler Flaps
Lightning Fan,
Thanks for the reply. This is a very interesting conversation. I'm thinking about 5/16x8 acme threaded rod for the jack screw. I can be purchased from an industrial supply house like MSC (www.mscdirect.com). It is not cheap though and the nuts are quite expensive. I was thinking of silver soldering a flat bar across the top of the nut about 2" wide. That would give a nice spot to attach the cables. It could also ride along a rail on each side of the screw to ensure that the nut does not try to turn, but will travel nicely on the screw. I think acme thread will produce much smoother travel with less likelyhood of binding. I can see how your method of a single jack screw works weel for the inner flaps, but how do you handle the outer flaps? The cables would be very long and the wings could not be removed. I am also trying to figure out how to get the extension and drop I want. I am toying with an idea for rails similar to the full size version. I think the sail winch servo will work. They are fairly powerful and proportional. I don't think deployment speed is a problem, you don't want them to move too quickly. On planes with electric flaps like a Cesna, the speed is fairly slow. On mechanical flaps like a Piper, you need to be careful not to move them too quickly. I was flying a Warrior this weekend and needed to go around on a landing with full flaps deployed and I had to be very careful not to raise them too quickly. You could feel the loss of lift as the were retracted, and if I moved them too quickly, I could have dropped into the ground. I don't think there are too many cases where you want to move flaps fast. Where did you get your gears? I figure I can turn down the ends of the screw on my lathe to provide a place for the gerar and bearings.
Paul
Thanks for the reply. This is a very interesting conversation. I'm thinking about 5/16x8 acme threaded rod for the jack screw. I can be purchased from an industrial supply house like MSC (www.mscdirect.com). It is not cheap though and the nuts are quite expensive. I was thinking of silver soldering a flat bar across the top of the nut about 2" wide. That would give a nice spot to attach the cables. It could also ride along a rail on each side of the screw to ensure that the nut does not try to turn, but will travel nicely on the screw. I think acme thread will produce much smoother travel with less likelyhood of binding. I can see how your method of a single jack screw works weel for the inner flaps, but how do you handle the outer flaps? The cables would be very long and the wings could not be removed. I am also trying to figure out how to get the extension and drop I want. I am toying with an idea for rails similar to the full size version. I think the sail winch servo will work. They are fairly powerful and proportional. I don't think deployment speed is a problem, you don't want them to move too quickly. On planes with electric flaps like a Cesna, the speed is fairly slow. On mechanical flaps like a Piper, you need to be careful not to move them too quickly. I was flying a Warrior this weekend and needed to go around on a landing with full flaps deployed and I had to be very careful not to raise them too quickly. You could feel the loss of lift as the were retracted, and if I moved them too quickly, I could have dropped into the ground. I don't think there are too many cases where you want to move flaps fast. Where did you get your gears? I figure I can turn down the ends of the screw on my lathe to provide a place for the gerar and bearings.
Paul
12-31-2002, 05:29 PM
#29
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P38 Documentation
Paul - here's a little more info - sorry for the late reply.
I worked on this a lot over the last couple of weeks and so far have three flap bays routed with controls on the actual airframe, as well as the "real" servo built and installed.
Regarding the outer wing panel removal, the outer tubes break between the panels. To remove the outer, you loosen the setscrew on the servo which holds the cables. Now the outer can be pulled, along with the cables. To reinstall, the cables are fed back into the inner panel tubes, shove the panel in and reset the setscrew on the cables. The worst run is the innermost cable on the outer panel - the loop is required so the cable exits perpendicular to the chord - it is EXACTLY 48" long, which is what Sullivan provides in he #514 GoldnRod product.
I've attached another sketch with some part numbers, the cable routing and more details on my servo. I can tell you this so far - the servo is very powerfull over the full range - it is very difficult to stop it from moving - I do not have force measurements yet. Installing the cables and extension tubes AFTER the wing is built requires a lot of surgery.
I think your question about the cables flexing at the servo still needs to be addressed in a better fashion - I'm working that. I'll try to post some photos soon - a buddy is coming over with a digital camera.
I worked on this a lot over the last couple of weeks and so far have three flap bays routed with controls on the actual airframe, as well as the "real" servo built and installed.
Regarding the outer wing panel removal, the outer tubes break between the panels. To remove the outer, you loosen the setscrew on the servo which holds the cables. Now the outer can be pulled, along with the cables. To reinstall, the cables are fed back into the inner panel tubes, shove the panel in and reset the setscrew on the cables. The worst run is the innermost cable on the outer panel - the loop is required so the cable exits perpendicular to the chord - it is EXACTLY 48" long, which is what Sullivan provides in he #514 GoldnRod product.
I've attached another sketch with some part numbers, the cable routing and more details on my servo. I can tell you this so far - the servo is very powerfull over the full range - it is very difficult to stop it from moving - I do not have force measurements yet. Installing the cables and extension tubes AFTER the wing is built requires a lot of surgery.
I think your question about the cables flexing at the servo still needs to be addressed in a better fashion - I'm working that. I'll try to post some photos soon - a buddy is coming over with a digital camera.
11-05-2003, 02:26 PM
#39
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RE: P38 Documentation
Great pictures...I'm sure by now you have finished the project. Do you have photos at which to look at? I'm considering building one of these monsters.
thanks,
BadBart
thanks,
BadBart
11-06-2003, 11:17 PM
#40
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RE: P38 Documentation
Alas, no. She has taken a back seat to a P-82 ARF which I have been flying all season to get "Twin-time". Lot of work, at my job (yech), to pay for engines and such as well. I'm hoping to get back to her this winter, and finish. What engines are you considering? Don't do what I did - try to go cheap and buy US41's ... the net is full of advice not to do this, so now I'm stuck with two new US41's with no home. If you haven't done the Twin thing yet, I think flying a junker 2 stoke glow twin gives you a learning curve that I would not want to have to climb on the P-38. Stay in touch, let me know how it goes.
