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Joined: 8/5/2007 From: Champaign,
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Please allow me to introduce my self. My name is Tim and I am one of the people who developed the 1/9th Top Flite B-25 ARF. I work in the R&D department at Hobbico and did the in-house development work and wrote the instructionmanual for this model. Another R&D member (who has more scale and twin engine experience) was the primary test pilot.
I have been posting on the other thread on this site about the Top Flite B-25, but now that the kits are in stock and will be shipping soon, all the speculation (When will it be available? How much does it cost? What are the specifications?) is over, so I think it is time to start a new thread with actual technical data, tips/suggestions.
Now that I have had the opportunity to assemble and fly my own B-25 (leftover from final production samples) on my own personal time, I have learned many helpful tips and suggestions that I would like to pass onto those who may be purchasing one of these models in the future. I don't intend this thread to replace the service that our Product Support department provides, but hopefully I will be able to answer some of your more technical questions that only someone who has built and flown one of these models could answer. I will try to visit this thread often, but please be patient if I am not able to answer right away.
I've already posted a few photos of my model in the other thread, but for those of you who may not have seen it, below is repeat of one of them (I didn't have all the cockpit parts installed at the time the photo was taken--darn!).
To those of you who will be building and flying one of these models soon, please feel free to post what you have learned and your suggestions as well!
That said, following is my first post in this thread about the Top Flite B-25.
< Message edited by krproton -- 10/16/2007 12:02:57 AM >
Posts: 365
Joined: 8/5/2007 From: Champaign,
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This is a list of helpful tips for the Top Flite 1/9th B-25 Mitchell ARF:
These are some of the things I have learned after building and flying my own B-25 on my own time after work. On my own time without deadlines, I am able to devote more time, use my creativity and let my ideas flow to come up with even more improvements and suggestions that may not be appropriate for or fit in the instruction manual without making it hundreds of pages long. I am sure many of you will develop many more ideas that we can all use:
1. Always remove the screw-in tail-gunner machine gun barrels and the nose-gunner canopy when carrying/transporting the model. This makes the fuselage much shorter so it is easier to handle and the guns cannot be broken off. 2. When at the flying field, place barriers (such as your flight box, Tx case, soccer cones, etc.) in front of the nose-gunner canopy and behind the tail guns. This will protect them from getting broken off when spectators or other pilots walk by or stand near the model. 3. For planes with retracts, never run the engines without the gear locked and pressurized. Otherwise, without pressure, engine vibration may cause the gear to collapse. Alternately, the engines could be run with the fuselage resting in the included stand. 4. The best way to carry this plane is while it is not in its stand. This way both hands will be free to hold the model. But to make transport even easier, purchase a second stand separately (TOPA1721, retail price = $9.99). Keep one stand in your vehicle and another stand on your workbench or wherever you store the model. Then, all you have to do is transport the model from one stand to the other without making additional trips to retrieve the stand. 5. It will be easier to add the “stars-and-bars” decals to the fuselage BEFORE gluing on the waist guns/waist gun windows. 6. (Photo 1) Rather than permanently gluing on the top turret, use small wood screws to hold it on. This way, the turret may be removed if the guns or barrels ever require repair. #2 screws are suitable, but if you can find even smaller hobby wood screws those would be better. (Try www.microfasteners.com) 7. For those using Robart retracts, in some cases the nylon clevis on the outboard pushrod for the main landing gear doors (photographed on page 18, step 16) may rub against the aft end of the air cylinder as the bellcrank lever rotates downward to pull the doors closed. If this is the case, the lever may be moved aft slightly (approximately 1/16” should do it) by placing a washer made from 1/16” plywood (or regular #4 washers) under the lever. This will move the lever—and the clevis attached to it—away from the air cylinder to provide the required clearance. 8. There are probably dozens of ways to enhance the scale appearance of this model. One way would be to cut the floor out of the tail-gunner cockpit. Then, more details may be added down inside the cockpit and inside the fuselage. If you don’t wish to do this immediately, but plan to add details later, rather than permanently gluing on the tail-gunner canopy with CA, tack-glue the canopy with a few dabs of R/C 56 or RTV silicone. Then, the canopy can be removed later when you are ready to add your details in the tail-gunner cockpit. 9. Another suggestion regarding the levers that pull the gear doors closed; The thin, plastic washers (step 5, page 16 and step 1 page 29) may not be required. Using the washers may increase the thickness of the bellcrank levers and nose gear door lever so that they do not “float” on the brass bushings. Try mounting the levers without the thin plastic washers first. If, when you tighten the screws that hold on the levers the levers rotate smoothly, leave the washers out. 10. When finally ready to fly your B-25, make certain you have COMPLETE CONFIDENCE in your engines. This will reduce the anxiety of your first flight allowing you to devote all of your concentration to flying the model without being distracted by the worry of an engine quitting. To get this confidence in your engines, make certain you spend plenty of time running the engines on the ground, on the model with the cowls in place (if you intend to make your first flights with the cowls). Synchronizing the engines is good, but it is more important to spend time making certain they both run reliably. 11. If switching to Robart wheels, use a 2-3/4” nose wheel and 3-3/4” or 4” main wheels. (4” wheels are probably closer to scale). 12. When mounting the top turret, the openings for the machine guns may need to be cut lower so that the turret can be fit over the guns after they have been glued to the fuselage. 13. A tube for guiding the elevator and rudder servo wires has been added inside the fuselage. The tube may not be large enough to accommodate both wires, so guide one set of wires (either for the elevator or rudders) through the tube and the other set of wires down through the fuselage. 14. There is also an antenna tube that has been added in the fuselage for guiding the Rx antanna-- 15. When mounting the waist gun windows, glue only the top and bottom or only the sides of the windows to the fuselage. This way, if you ever break off one of the waist gun machine gun barrels, it will be possible to remove the windows for repair. Or, same as suggested for the top turret, use small screws to mount the waist gun windows to the fuselage instead of permanently gluing them on. 16. Note that the 1/4-20 x 2” nylon wing bolts that secure the outboard wing panels to the inboard wing panels screw in only about two turns. This is normal. 17. In several places the instruction manual reminds you to harden screw holes in wood with thin CA. However, this is not necessary for the four screws that mount the nose-gunner canopy. The mounting blocks are hardwood and already grab the screws tightly. Adding thin CA here could make it too difficult to remove and install the screws. 18. (Photo 2) If you encounter difficulty when installing the throttle servos in the lower throttle servo mounting rails (step 1, page 11), you may cut approximately 3/16” from the end of the forward rail and support. 19. (Photo 3) Drill 5/32” holes where shown to accommodate the 1/16” drill and a screw driver when mounting the throttle servos in the lower throttle servo mounting locations. 20. (Photo 4) When drilling the aluminum wing tubes for mounting the inboard and inboard wing panels (step 5, page 33 and step 7, page 34), for perfection, use 1/8” and 3/32” brass tubes (available from K&S in 12” lengths) as guides. (The holes in the wings may first need to be drilled with a 1/8” drill so the 1/8” tubes will fit.) These “guides” will center the drill. But because the inside diameter of the smaller (3/32”) tube is only 1/16”, pilot holes will first have to be drilled with a 1/16” drill. After drilling the pilot holes, remove the panel you are mounting and the tube, enlarge the hole with a #43 drill for tapping, tap the threads, then mount the panel. 21. Keep the small scraps of MonoKote you cut from the fuselage sides when installing the side gun packs (step 5, page 39). These scraps may be used for minor repairs/patches if ever required. 22. When flying from paved runways, reduce the nose steering servo throw. Nose wheel steering is sensitive and if there is too much throw it will be too easy to overcorrect steering inputs during takeoff causing the model to veer too far one way or the other. 23. Also regarding nose steering, as the nose wheel is sensitive to steering inputs, it is a good idea to make a few practice takeoff runs down the runway and trim the nose wheel so that the model tracks straight. The wind direction seems to affect the model’s tracking during takeoff, so whenever the wind velocity or direction changes, the nose wheel may require trim changes so that the model will track straight. This is most important when flying from paved runways.
< Message edited by krproton -- 10/16/2007 12:12:15 PM >
Posts: 365
Joined: 8/5/2007 From: Champaign,
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Here is my second post in this thread about the Top Flite B-25 ARF. It contains suggestions on how to prepare the MonoKote covering on your new ARF when it comes out of the box. All of these techniques were developed using Top Flite MonoKote, but may also apply to other brands of covering as well. (Be careful--some types/brands of covering require less heat.) For the most part, the covering job on todays ARFs is fantastic and better than most modelers could do, but the bottom line is this; you should probably expect to do a little preparation work to the covering on an ARF--I feel this is part of the trade off you accept when purchasing a model that has been mass-produced. With the B-25 for example, you should expect to spend one to two hours using the following techniques to go over the covering to bring it up to perfection. You will be rewarded with a model that will look good and should stay looking good as long as you own it. Occasionally, it may be necessary to bring it back into the work shop for touch-up, but the better the job you do now and the more time you take up front, the less that will have to be done later;
How to tighten MonoKote covering on ARF models:
Tightening the covering over control surfaces that have ribs and open structure (such as elevators and ailerons) requires different techniques than tightening covering over sheeted areas. For this process it will be helpful to have two covering irons—one with a protective covering sock, and another without a covering sock. Both irons should be set to approximately 320 – 350-degrees F.
For this example an elevator from a Top Flite B-25 ARF will be used. But the same techniques apply to any control surface that has ribs.
Photo 1. Use a tissue dampened with naptha (lighter fluid) to clean off any adhesive left from masking tape that may have been used to hold the parts together during shipping. This will not hurt the MonoKote and easily wipes the glue away.
Photo 2. When tightening covering on a control surface that has open structure with ribs, the covering must first be SECURELY bonded to the trailing edge and tips. Otherwise, when tightening the rest of the covering on the top and bottom, it may pull away. First, use the iron with a covering sock to bond the covering to the trailing edge. Press hard and make sure the covering is thoroughly attached.
Photo 3. The next thing is to make vent holes in the bottom of the covering which will allow heated, expanding air to escape. Otherwise, during the shrinking process, the air inside will expand, thus stretching the covering—exactly the opposite of what you are trying to achieve! Use a pin to poke small holes in the covering between each rib. (For future reference, the next time you are building a kit, a small (1/16” – 1/8”) brass tube sharpened on the end can be used to cut vent holes in each rib and another vent hole cut in the tip or root end to allow air to escape.)
Photo 4. After the covering has been bonded to the trailing edge and tips and the vent holes have been punched, the covering may be tightened. A covering iron with a protective covering sock is preferred, but sometimes does not transfer enough heat. If unable to remove all the wrinkles, use a covering iron without a covering sock. (Here, a Top Flite iron is set to about “2-1/2”.) Use care NOT to let the iron contact the trailing edge—otherwise, the covering may loosen and pull away. Once the covering has been tightened with the bare iron, go back over it again with the other iron that has the sock. Press down to bond the covering to the ribs and any other structure underneath.
Tightening covering over sheeted areas requires a different technique… Photo 5. The covering must be securely tightened and bonded to the sheeting. Use the iron with the covering sock. First, without applying pressure, glide the iron over the wrinkle. Once the wrinkle disappears, go over the spot again this time applying pressure to bond the covering to the sheeting. If a bubble forms, allow the area to cool for a few seconds and go over the spot again this time pressing down harder and moving the iron faster so less heat is transferred. In some cases vent holes must be punctured in the covering over the bubble. Use a sharp, new #11 blade to poke vent holes, then go over the area again with the iron.
In some cases, where the sheeting is thin or soft and over unsupported areas (such as between wing ribs or between stringers and bulkheads), the sheeting will bend inward when pressing down on the iron. This stretches the covering as the sheeting bows inward—again, exactly the opposite of what is trying to be achieved. In these areas, glide the iron over the covering using little or no pressure. If you still cannot get the wrinkles to disappear, use an iron without a protective sock set to higher heat. This will shrink the covering and remove the wrinkle. Then go back over the area with your iron with a covering sock applying little or no pressure to bond the tightened (but “floating”) covering to the sheeting.
Photo 6. Where necessary (and possible), reach inside the model and push outward on the sheeting allowing you to press hard on the iron and bond the covering to the wood.
< Message edited by krproton -- 10/16/2007 4:07:43 AM >
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Joined: 9/10/2003 From: Las Vegas, NV, USA Status: offline
I have purchased the robart gear and tires. I went with the 4" main wheels and I went with a 2 1/2" nose wheel. Do you think the 2 1/2" nose wheel is alright or should I get the 2 3/4" nose wheel as you have mentioned? Thanks again for this thread.
Hmm, good question about that nose wheel size. If it's easy for you to return it I'd do that. But if it's a hassle you could just give the 2-1/2" wheel a try and see how the model sits on the ground--check the ground stance. As long as the nose doesn't appear to sit too low I guess you'd be okay. But the smaller wheel would also probably put a little more stress on the strut, so if you fly from a rough field I'd be even more inclined to exchange the 2-1/2" for the 2-3/4". But if you fly from pavement or a nice grass field most of the time you'd probably be okay with the smaller wheel. I guess the bottom line is that I don't have a definitive answer for you, but I don't think it's going to be a major problem.
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Joined: 10/10/2005 From: Frackville,
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tim, did you do any more testing on the props. before you said those graupner props where not the best choice. that it was between the apc 13x6 or the masterair screw 12x8. did you find out any more on the props??
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Joined: 8/5/2007 From: Champaign,
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quote:
ORIGINAL: danrc2
tim, did you do any more testing on the props. before you said those graupner props where not the best choice. that it was between the apc 13x6 or the masterair screw 12x8. did you find out any more on the props??
thanks dan
Hi Dan.
I don't think I've done any more testing since that last post. To re cap, I think the APC 13 x 6 would probably be the best 2-blade and probably better than the Master Airscrew 12 x 8 3-blade, but if you insist on using a 3-blade, I think the Master Airscrew 12 x 8 is the best of the ones I've tested (between the MAS 12 x 6 and 12 x 8 3-blade and the Graupner 12 x 8 3-blade).
Put another way, going by my memory, I believe the APC 13 x 6 performs better than the MAS 12 x 8, but it's been a long time since I've flown the APC (on one of the prototype B-25s). To be certain, I would like to fly the MAS and the APC back-to-back, but I haven't yet. Going to be really windy tomorrow so I doubt I'll be flying. Maybe after work one day this week.
I'll let you know if I do more flying and have more info for you.
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