B-29 SUPERFORTRESS BUILD
#202
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RE: B-29 SUPERFORTRESS BUILD THREAD
I can understand that, definitely is a big bird. I'll be watching hope you continue with the build thread, got some good ideas and techniques from watching you build, newer to the hobby scratch building a C-130 with a 65" wingspan. Hope to build a B-29 after
#203
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RE: B-29 SUPERFORTRESS BUILD THREAD
Have been building a Don Smith 169 inch B29 since Easter, the wing is well on the way. I have fitted the 4 DLE 20cc motors, there is a built in 3 degrees down thrust but I can not find any reference to side thrust. Having built a 14 ft Catalina, both motors 3 degrees thrust out wards & a 12 ft 6 inch Spruce Goose, all zero side thrust (figured if you lost one, there's still 3 so it hardly matters, proved correct). Could someone advise me on this. I was also wondering if 4 bladed props have been used on the DLE20's & what size & pitch.
#204
RE: B-29 SUPERFORTRESS BUILD THREAD
You may want to look at the gas engine thread in regards to the prop on the DLE20. I can tell you a 3 blade 15x8 MAS puts quite a load on the DLE20, so even if you are swinging a small 4 blade, it may not have enough power. The DLE20 with a 16x8 has very good power, and a 17X8 is also pretty good, and one of the recommended sizes, so going off those two sizes, you might be able to find something similar. I use an APC for the 16X8 and XOAR for the 17. Good idle, and good top end. The 15X7x3 did work, but top end was a bit low, so it "might" work on this model.
#205
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RE: B-29 SUPERFORTRESS BUILD THREAD
Hello Robwoody
I have started building 169" B-29 last year I have the fuse and tail feathers built. started on the wing and noticed issue with the Robert landing gear fitting in the nacel. started removing ribs and formers to correct the issue and lost interest for the time being. I have DLE engines as well. Let me know what you end up doing with the thrust. If I recall correctly I thing the fin is offset to compensate for the engines not having right thrust.
I have started building 169" B-29 last year I have the fuse and tail feathers built. started on the wing and noticed issue with the Robert landing gear fitting in the nacel. started removing ribs and formers to correct the issue and lost interest for the time being. I have DLE engines as well. Let me know what you end up doing with the thrust. If I recall correctly I thing the fin is offset to compensate for the engines not having right thrust.
#206
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RE: B-29 SUPERFORTRESS BUILD THREAD
The counter clock wise rotation of the engines develops left torque. I do believe that, on the full size, the left side of the B-29 vertical surfaces have a lifting airfoil to offset the torque of the engines. I am not sure about the model though. You can always use the rudder. Dan.
#207
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RE: B-29 SUPERFORTRESS BUILD THREAD
Interesting thought. I haven't found any reference to the rudder or engines being offset. I'll probably off set my engines a degree or two and leave the vertical stab straight. Been working on the bomb bay doors and got them fit. They are removable.
#208
RE: B-29 SUPERFORTRESS BUILD THREAD
Thrust angles are a good thing to watch for. Reason I say this is my friend built a scale model of his Cessna 140, To scale. That was his mistake, he didn't offset the engine and cowl, or the rudder angle to overcome the P-factor. His maiden flight ended rather quickly as the plane flew left on takeoff. It flew very nicely straight and level, but to the left. It went behind a tree, and he chopped throttle after he lost sight of it. Had he kept throttle on it would have circled the tree, flew over the roof of his barn, and he might have been able to recover it. He doesn't fly much rudder and that I think doomed this flight, he might have been able to straighten it out, since ailerons weren't doing jack other than keeping the wings level.
His mistake was not providing enough offset for the engine thrust, so seeing it first hand, really makes an impression....so did his plane, in the ground.
I have a new 4*120 with DLE20 on it, and noticed that I need to add a couple washers to the left mount to correct the left veer when the tail wheel comes up, I had forgotten about that from the first one when I built this one. It just needs a slight correction to the right. Maybe when you do taxi tests with it, getting the nose wheel off with mains on the ground will give you an idea if you need to add thrust angles. I dont fly Trikes, so dont know how else you can find out if you need to adjust the thrust.
That does make me wonder though, on a multi engine plane that doesn't have the prop in front of the rudder, how does P-Factor affect it? If all four engines are 0* thrust, and properly synched, would it even be a factor? My only experience with twins is my Twin Otter and it came as an ARF. Would thrust angles be added in the event of engine failure?
#209
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RE: B-29 SUPERFORTRESS BUILD THREAD
The "P" factor is simply the torque of the engine causing the plane to "yaw" to the left. This can be a serious issue with twins if there is no off set of the engines to compensate for it and if you have an engine out. The arf probably has it already built in. I'm sure it will also cause a 4 engine plane to yaw a bit as well. But with the very large vertical stab and long wing span of the B-29, it might not be as critical. I will definitely put a few degrees of right thrust on the engines.
If anyone out there is still flying one, feel free to comment on how the plane acts and if you have any right/ down thrust compensation with the engines and how much.
If anyone out there is still flying one, feel free to comment on how the plane acts and if you have any right/ down thrust compensation with the engines and how much.
#210
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RUDDER:
Some have asked me in the past how I plan on hooking up the B-29 rudder in a scale manner. The plans show burying the servo in the tail and setting up / attaching the linkage to it before one finishes strip planking the fuse. Also there is the problem of attaching the rudder to the pivot rod the rudder hinges on. I'm not a fan of burying anything and I like to have all components removable if necessary. I also like to keep the tail as light as possible. So this is what I came up with.
I cut out and made a removable hatch underneath the tail for the rudder rod to slip up from the bottom. I made up a little bracket with a 1/8th wheel collar silver soldered to it that is mounted in the bottom of the rudder. Once the rod and rudder are in place, I can tighten the set screws which secure the rudder to the rod. Then I have a steering arm attached at the bottom of the rod to control the movement of the rudder. The rudder servo is now located in the rear bomb bay with a HD push rod to the tail. Sounds simple enough? See pics.
Some have asked me in the past how I plan on hooking up the B-29 rudder in a scale manner. The plans show burying the servo in the tail and setting up / attaching the linkage to it before one finishes strip planking the fuse. Also there is the problem of attaching the rudder to the pivot rod the rudder hinges on. I'm not a fan of burying anything and I like to have all components removable if necessary. I also like to keep the tail as light as possible. So this is what I came up with.
I cut out and made a removable hatch underneath the tail for the rudder rod to slip up from the bottom. I made up a little bracket with a 1/8th wheel collar silver soldered to it that is mounted in the bottom of the rudder. Once the rod and rudder are in place, I can tighten the set screws which secure the rudder to the rod. Then I have a steering arm attached at the bottom of the rod to control the movement of the rudder. The rudder servo is now located in the rear bomb bay with a HD push rod to the tail. Sounds simple enough? See pics.
Last edited by Warbird Man; 08-25-2013 at 07:10 PM.
#211
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The flight control surfaces on the B-29 were fabric covered. (rudder, elevators & ailerons) The kit controls are fully sheeted so to simulated the ribs I added some rib tape to the elevators and ailerons for a little more detail. The rudder when built came out undersized. So I had to add some length to the back. I also added some balsa strips to simulate the scale ribs locations ( see previous post pic) and covered with fabric.
#212
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Well after spending the last couple of weeks of just "prime fill and sand", I finally got the plane back on it's feet. Getting close to painting but first I need to finish setting up all the engines and fitting the cowls. The real trick is going to be how I'm going to fit a fuel tank, ignition module, ignition battery, switch, fueler, and throttle servo in each of the nacelles. Definitely gonna be a tight fit.
#215
Well after spending the last couple of weeks of just "prime fill and sand", I finally got the plane back on it's feet. Getting close to painting but first I need to finish setting up all the engines and fitting the cowls. The real trick is going to be how I'm going to fit a fuel tank, ignition module, ignition battery, switch, fueler, and throttle servo in each of the nacelles. Definitely gonna be a tight fit.
I have a very similar setup to yours on my B-25. I have Century Jet retracts with Robart wheels and brakes. They work great together. I set up one battery in the fuse that runs out to a charge/switch on the side of the nacelle and then to the ignition. That saved plenty of room for tank and ignition and allowed for one very large battery. You could use 2 batteries linking your inboard and outboard engines together. That way you only have to charge 2 batteries and they can be charge from either side of the plane. With your removeable wing/engine setup you could put both switches on the inboard nacelle. Just a thought.
By the way, Bruce can easily add an inch to that gear if you need it. Really enjoying your build...lots of good ideas!
#217
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Thanks guys.
T-55, I thought about that but I'm skeptical of radio interference from running ignition battery leads down the wings. Did you have any trouble with your set up?
Bruce is a good guy to work with but it's way too late in the build to change the length of the struts. The wheels when retracted just barley fit and are 1/16th away from the formers as is. And I would have to put even smaller tanks in the nacelles. Another reason to build the 14' er. over the 12. One should be able to put the tanks in the wings at that size.
T-55, I thought about that but I'm skeptical of radio interference from running ignition battery leads down the wings. Did you have any trouble with your set up?
Bruce is a good guy to work with but it's way too late in the build to change the length of the struts. The wheels when retracted just barley fit and are 1/16th away from the formers as is. And I would have to put even smaller tanks in the nacelles. Another reason to build the 14' er. over the 12. One should be able to put the tanks in the wings at that size.
#218
WM-
No problems with this setup. The battery is actually in the bottom of the nose gear well and the wires run through the fuse to the wings and then out the wing to the nacelle and plug into the switch and the switch goes to the ignition. the battery/ignition wire also runs together with the choke and throttle servos through the wing. Never a glitch! I'm using a 3500 mAh SR NiCd for nose weight I have 2 battery outputs for the ignitions.
No problems with this setup. The battery is actually in the bottom of the nose gear well and the wires run through the fuse to the wings and then out the wing to the nacelle and plug into the switch and the switch goes to the ignition. the battery/ignition wire also runs together with the choke and throttle servos through the wing. Never a glitch! I'm using a 3500 mAh SR NiCd for nose weight I have 2 battery outputs for the ignitions.
#220
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Everytwin i have ever built or flown has had 0 degrees side thrust on the left engine(s) and 1 or 2 degrees right thrust in the right engine(s).
You will never be able to get rid of P-factor in the design of a propeller propelled plane, its just not possible (until you go to jets). The only way to limit and counter-act P-factor is by learning to use the rudder, that stick still moves once the throttle gets to full!
You will never be able to get rid of P-factor in the design of a propeller propelled plane, its just not possible (until you go to jets). The only way to limit and counter-act P-factor is by learning to use the rudder, that stick still moves once the throttle gets to full!
#221
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I was thinking about the same thing. zero right thrust on 1 and 2 (left engines) 1 degree on 3 and 2 on 4. I'll put 1 degree down on all. (if that make any sense). As far as electrics, that might be easier but just not into them on anything I can fit a gasser on.