Sterling PT 17
01-30-2003, 01:41 AM
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Sterling PT 17
Walter I received this information from Steve Formelius when I framed out the Sterling kit. It will be of great help to you as it was of me.
I didn't put any negative in and should have. The upper wing needs a couple of degrees. I've got mine at 0 and it climbs under power and dives when power is cut. To get rid of that you need to put in the negative incidence.
I've got an ST3000 on mine (just for fun) and had to add a couple of ounces to the back of it. I built it for a 1.08 ASP with a heavy muffler and had to add a LITTLE weight. They don't fly too fast (induced vs parasitic drag).
General notes - the wire parts need to be checked. Too often they're bent slightly and you wind up building that into the plane and fighting it later. This is true of both the landing gear and the cabane wires. When I design mine, I'm going to use a Ziroli-type attachment.
I've built 5 Stearmans including two of the Sterlings.
1. I can tell you that the drag is high with any bipe, and especially with the legs on a stearman. Thin these down to 1/2 in as soon as you can and taper them.
2. Really take down the stringers and tail balsa down. Scallop the formers if you have to. If you can, copy them onto lighter wood. Put tail bracing wires to compensate for the lighter wood.
3. Use the Klett .60 tailwheel if you don't care about scale that much. If you do, use 1/16th wire and the lightest tailwheel you can.
4. Forget about the mounting rails and just put a regular motor mount on. Put an 1.08 if you want scale + a little speed. Something on the range of a 1.50 4 stroke would do ok too. If yours is a GOOD engine, save it for when you get good at landing. Stearmans don't nose over too often, but believe me, don't use a wood prop unless you bring a few with you.
5. I use the Solartex covering, BUT their light blue is too transparent and their dark blue is too dark. It would probably look good in yellow with the hard surfaces filled and painted.
6. The wire gear WILL bend, breaking the fairings. If you decide to use the abs plastic, use abs cement to put in 4 oz fiberglass cloth and maybe pour in something like silicon rubber. That would strengthen the whole assembly. I was going to try to find some castable silicon or latex and make a product to sell.
7. Flying wires - this plane vibrates so much that hard wires will probably pull out the attachments, cables more or less the same thing. I use heavy elastic thread from the fabric store and replace it when it gets dirty. Just loop it around the base of the struts and leave it there. Don't bother getting fancy.
8. To attach the interplane struts - make the strut rib out of 1/8 in aircraft plywood. Leave a tab sticking up where the struts attach. This should be about 1/2" x 1/2" above the strut plate. Use DuBro 181 ball link on this tab. Measure the distance from the work surface to the front and rear Take out any warps by giving them a hot shower and putting them on a flat surface weighed down with magazines or something. I've done this and it works every time.
For the interplane struts I use 2-25 rod and when the wings are built (DON'T glue the upper wing mounting plates firmly, you may have to rework them) thread the socket portion onto both ends. This will give you 4 struts, two front and two back with about 1/2 of useable adjustment. Now comes the fun - Put on the bottom wing and top wing, level the plane with blocks under the tail until the stab is at 0 degrees. Measure the incidence at the root. If the bottom is 0 you're in good shape. If not, sand the wing saddle till it is. Check the top wing directly above where you measured the bottom wing. If its positive, don't be surprised. This plane was designed to fly on a .60. Move the mounting plates down in front till you get --2 or so. Might wind up with wire sticking up, in which case you can take the plate off and heat the wire to put the bend lower. Now measure the distance from the worksurface to the bottom wingtip. If its not level, block up the wheel till it is. When you get the bottom level, put a level on the top plates and try to make the upper wing level as well. This is the hardest part of the whole procedure. You can kinda bend one side down and see if that's enough, if not, you may have to thin the plate on the high side and block up the low side. You'll be filling these with balsa in a later step anyway.
Now you should have two level wings. The next step is to take out any lateral twist. Look down from the top and both wings MUST be parallel to each other. Again, work the cabane wires till you get them parallel. Recheck everything till you're satisfied they're level, parallel, and not twisted to one side.
When the wings are straight and the incidence is set at 0 on the bottom and -2 on the top roots, put on the struts. Try not to push the wings apart or pull them together. Measure the leading edges from the worksurface and keep them the same distance from the surface left to right and top and bottom. Do the same with the rear struts. When you're satisfied that the ball and socket just pop together with no stress on them that step is done. Bend some 2-56 rod in a tight "V" on both ends to connect the struts together. Use a wire wrap and solder to bind these together. Now you have a wire "N" strut. Cover with balsa and sand to shape.
Now your wings should be as accurate as you can make them. Double check everything now visually - its a step I usually don't do and sometimes regret. If it doesn't look right, check everything again. Fix it now.
Covering - DON'T think of light blue for the wings - believe me. My next covering job is going to be Navy. The Army scheme is great, but its due to the yellow wings and not the fuse. I have one done in white with purple flames on the upper surface of the top wing and around the firewall and cockpit. Not bad but you have to keep your eye on it during stunts.
If this is your first bipe, realize that its supposed to fly and it WILL take some abuse from hardish landings. Come down at a steep angle, level about 3 feet above the runway and bleed off the speed. Don't try to milk it in.
If there are any other hints I can give you, please let me know. I've still got one in the box that I'm going to do sometime in the next year. Right now I have 3, two small Ziroli's and one Sterling. I had the big Ziroli - relatively cheap to build, needed an ST3000 minimum for good flight, and needed 2 1/2 lbs of nose weight. On my small ones, I cut the firewall back 1 1/2 inches, put in a 3/4 in ply firewall and then put a K & B .61 with a tuned pipe on them. They're little rockets and stunt all day long. Most kits wind up with the engine too far forward BTW.
Steve
Good luck, KRC
I didn't put any negative in and should have. The upper wing needs a couple of degrees. I've got mine at 0 and it climbs under power and dives when power is cut. To get rid of that you need to put in the negative incidence.
I've got an ST3000 on mine (just for fun) and had to add a couple of ounces to the back of it. I built it for a 1.08 ASP with a heavy muffler and had to add a LITTLE weight. They don't fly too fast (induced vs parasitic drag).
General notes - the wire parts need to be checked. Too often they're bent slightly and you wind up building that into the plane and fighting it later. This is true of both the landing gear and the cabane wires. When I design mine, I'm going to use a Ziroli-type attachment.
I've built 5 Stearmans including two of the Sterlings.
1. I can tell you that the drag is high with any bipe, and especially with the legs on a stearman. Thin these down to 1/2 in as soon as you can and taper them.
2. Really take down the stringers and tail balsa down. Scallop the formers if you have to. If you can, copy them onto lighter wood. Put tail bracing wires to compensate for the lighter wood.
3. Use the Klett .60 tailwheel if you don't care about scale that much. If you do, use 1/16th wire and the lightest tailwheel you can.
4. Forget about the mounting rails and just put a regular motor mount on. Put an 1.08 if you want scale + a little speed. Something on the range of a 1.50 4 stroke would do ok too. If yours is a GOOD engine, save it for when you get good at landing. Stearmans don't nose over too often, but believe me, don't use a wood prop unless you bring a few with you.
5. I use the Solartex covering, BUT their light blue is too transparent and their dark blue is too dark. It would probably look good in yellow with the hard surfaces filled and painted.
6. The wire gear WILL bend, breaking the fairings. If you decide to use the abs plastic, use abs cement to put in 4 oz fiberglass cloth and maybe pour in something like silicon rubber. That would strengthen the whole assembly. I was going to try to find some castable silicon or latex and make a product to sell.
7. Flying wires - this plane vibrates so much that hard wires will probably pull out the attachments, cables more or less the same thing. I use heavy elastic thread from the fabric store and replace it when it gets dirty. Just loop it around the base of the struts and leave it there. Don't bother getting fancy.
8. To attach the interplane struts - make the strut rib out of 1/8 in aircraft plywood. Leave a tab sticking up where the struts attach. This should be about 1/2" x 1/2" above the strut plate. Use DuBro 181 ball link on this tab. Measure the distance from the work surface to the front and rear Take out any warps by giving them a hot shower and putting them on a flat surface weighed down with magazines or something. I've done this and it works every time.
For the interplane struts I use 2-25 rod and when the wings are built (DON'T glue the upper wing mounting plates firmly, you may have to rework them) thread the socket portion onto both ends. This will give you 4 struts, two front and two back with about 1/2 of useable adjustment. Now comes the fun - Put on the bottom wing and top wing, level the plane with blocks under the tail until the stab is at 0 degrees. Measure the incidence at the root. If the bottom is 0 you're in good shape. If not, sand the wing saddle till it is. Check the top wing directly above where you measured the bottom wing. If its positive, don't be surprised. This plane was designed to fly on a .60. Move the mounting plates down in front till you get --2 or so. Might wind up with wire sticking up, in which case you can take the plate off and heat the wire to put the bend lower. Now measure the distance from the worksurface to the bottom wingtip. If its not level, block up the wheel till it is. When you get the bottom level, put a level on the top plates and try to make the upper wing level as well. This is the hardest part of the whole procedure. You can kinda bend one side down and see if that's enough, if not, you may have to thin the plate on the high side and block up the low side. You'll be filling these with balsa in a later step anyway.
Now you should have two level wings. The next step is to take out any lateral twist. Look down from the top and both wings MUST be parallel to each other. Again, work the cabane wires till you get them parallel. Recheck everything till you're satisfied they're level, parallel, and not twisted to one side.
When the wings are straight and the incidence is set at 0 on the bottom and -2 on the top roots, put on the struts. Try not to push the wings apart or pull them together. Measure the leading edges from the worksurface and keep them the same distance from the surface left to right and top and bottom. Do the same with the rear struts. When you're satisfied that the ball and socket just pop together with no stress on them that step is done. Bend some 2-56 rod in a tight "V" on both ends to connect the struts together. Use a wire wrap and solder to bind these together. Now you have a wire "N" strut. Cover with balsa and sand to shape.
Now your wings should be as accurate as you can make them. Double check everything now visually - its a step I usually don't do and sometimes regret. If it doesn't look right, check everything again. Fix it now.
Covering - DON'T think of light blue for the wings - believe me. My next covering job is going to be Navy. The Army scheme is great, but its due to the yellow wings and not the fuse. I have one done in white with purple flames on the upper surface of the top wing and around the firewall and cockpit. Not bad but you have to keep your eye on it during stunts.
If this is your first bipe, realize that its supposed to fly and it WILL take some abuse from hardish landings. Come down at a steep angle, level about 3 feet above the runway and bleed off the speed. Don't try to milk it in.
If there are any other hints I can give you, please let me know. I've still got one in the box that I'm going to do sometime in the next year. Right now I have 3, two small Ziroli's and one Sterling. I had the big Ziroli - relatively cheap to build, needed an ST3000 minimum for good flight, and needed 2 1/2 lbs of nose weight. On my small ones, I cut the firewall back 1 1/2 inches, put in a 3/4 in ply firewall and then put a K & B .61 with a tuned pipe on them. They're little rockets and stunt all day long. Most kits wind up with the engine too far forward BTW.
Steve
Good luck, KRC
