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krproton 10-15-2007 04:49 PM

Top Flite B-25 ARF (Tecnical, tips, suggestions)
1 Attachment(s)
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 instruction manual 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.

krproton 10-15-2007 05:00 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
1 Attachment(s)
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.

krproton 10-15-2007 05:18 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
1 Attachment(s)
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.

Hellcat716 10-15-2007 10:29 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
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.

krproton 10-16-2007 05:50 AM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
Hi Hellcat.

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. [8D]


pettit 10-16-2007 06:19 AM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
Hey Tim. This is a really great idea for the RCU readers.

But you're gonna leave us kit reviewers with nothing to complain about or criticize!

Actually, an addendum with this type of information could be made available on the Top Flite web site for non-RCU readers to access.

There also may be a significant number of B-25 builders who have no internet access at all. They won't get to read any of this.

If it isn't in the manual, they may find a problem and complain about it.

But, on the other hand, who reads the manual anyway?

(I do. How do you think I find all those nit-picky things wrong?)

Good job, Tim, and THANKS!!!

Hellcat716 10-16-2007 10:37 AM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
I fly off pavement so if the model sits well I will go ahead ang give the 2 1/2" a try. They actually measure 2 5/8". Thanks again.

danrc2 10-20-2007 07:40 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
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??


krproton 10-20-2007 11:14 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)

ORIGINAL: danrc2

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??

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.


danrc2 10-21-2007 12:32 AM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
thanks tim for the update and info.


norm 10-23-2007 02:27 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
B-25J Top-Flite Brakes

Whoever is interested there will be brakes made for the B-25 by Robart. The kit will be introduced in the coming weeks and will fit 3.75 or 4.00 inch scale wheels (plastic). Also thank you Tim for all the helpful tips on putting together this plane...I'm still waiting for mine!!! Also the front wheel should be 2.75 inch

I was readind about props in this thread to be used on the B-25. If you are installing OS55's, they should be 11 x 7 APC. If the OS 70 surpass 4s 13 x 6 APC or 12 x 6 3 blades. If Saito's FA82a, 13 x 7 APC or 12x 6-8 3 blade Master Airscrew. My choice is the Saito's FA82a because they are lighter than the OS70 and develop an impressive 1.6 hp for the Saito vs 1.1 fot the OS. Extra HP will be very helpful with and airplane weighing in the 20's pounds.

I have been experiencing with the Seagul Dual Ace simulated engine failure using a gyro on the rudder. I strongly suggest the installation of this device on your rudder in case of an engine failure. The gyro will react instantly before you even hear an engine fail and will counter effect the YAW created by a sudden engine failure. Without a gyro, at any speed and any phase of a flight it is a fatal failure unless you are short final with both engine idling and able to land. The Gyro (gyro approx 150$) may save your B-25 (+/- 2000$ +time put into it) . The only critical scenario remaining, that the gyro may be of only little help, will be on take off where the airspeed is low, on a climb, and you lose either engine and worst if the critical engine is lost (the left engine). You may react by pushing the nose down and maintain full throttle to increase airspeed and go around on one engine. If unable to fly around and the aircraft does not respond positively, it is advisable to land ahead by reducing to idle the remaining engine. In almost all other scenarios the gyro was a success by maintaining the aircraft attitude controllable. You are also able to steer with the ailerons if airspeed permits. Remember that the gyro is not a device intended to continue flying and pursue your flight plan... but it will most certainly fly you back and help you land as soon as advisable.

krproton 10-23-2007 03:14 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
Hi normandouellette.

Thanks for all your additional tips on engines and props.

The gyro sounds like a super idea and I would never agrue against one, but we've designed the Top Flite B-25 so it will not suddenly react if one engine does quit. This isn't to say that a gyro wouldn't be of significant benefit, but if you have enough power you may fly the Top Flite B-25 around on one engine (as we have done during our extensive flight testing program with the O.S. .70 Surpass II). The flying section in the back of the manual goes into detail about this. I just have to say that with our model, it is NOT fatal during any phaise of flight if an engine does quit. We also don't recommend steering the plane around with the ailerons (in an engine-out scenario)--if you get into too much bank angle the plane may snap (roll). With our model, the ailerons should be used to keep the wings level while you "steer the model around" using the rudder(s).

Now that I think of it, maybe it would be best to connect the gyro to the roll axis (ailerons) instead of rudder. In our engine-our scenario, this would help you keep the wings level. Hmm, this will probably open up another can of worms! :eek:

Now, as for an engine quitting on takeoff...well that's a whole other ball game! [X(]

Michel 10-23-2007 03:32 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
Greetings Gentemen

I ll be keeping a close eye on this thread . Hopefully I will be a caller for one of these babies , and might have the honner to help assemble one . Norm , I heard that you got youre kit in , thats great . THE PROJECT IS AFOOT

Michel ;)[8D]

jbarnes 10-23-2007 04:05 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
For those of us that have not used a gyro before could you describe the setup and programming that is necessary to use a gyro?

kthmarks 10-23-2007 07:35 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)

ORIGINAL: krproton
Now, as for an engine quitting on takeoff...well that's a whole other ball game! [X(]
Can you say........ JATO DOH! :D

krproton 10-23-2007 09:21 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)

ORIGINAL: kthmarks

ORIGINAL: krproton
Now, as for an engine quitting on takeoff...well that's a whole other ball game! [X(]
Can you say........ JATO DOH! :D

That's so crazy it just might work![sm=spinnyeyes.gif]

n9331v 10-23-2007 09:32 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
Check in

timothy thompson 10-23-2007 10:29 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
This is a j model, Dolittle used a b. Totally different cowls and short stacks. To convert to a B it will take a lot of work. nose was different too A neat conversion would be a solid nose J with 8 50 cal and a cannon

norm 10-23-2007 10:51 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
Re Gyro for the B-25

I have been experiencing with the Seagull dual ace in preperation to fly the twin B-25RC model and tested with and without gyro assistance. The test were conducted by simulating engine failure by programing one engine to idle while the other one follows the throttle stick at the flip of a switch.
I have decided to follow those test for the simple reason that i was told many different thing on the event of engine failure. I soon realized that amazingly planes reacts like planes. I have flown numerous full scale and have reviewed the emergency procedure in the event of an engine failure. all procedures dictates (in sequence of importance for those steps that interest us) 1- full power on operative engine. 2 control yaw with rudder....dead foot dead engine, and for those who fly "foot on the ball". I was told otherwise for the Seagull and to my surprize the emergency procedure was right. I am surprized how model aircrafts behave like real aircrafts. When a twin engine aircraf model or full scale has an engine failure, it is obvious that the operative engine will whant to turn the aircraft on its vertical axis. The RC pilot will immediately whant to control the aircraft with the ailerons... and maybe the design of the aircraft may permit to do so but if the rudder has a yaw damper (gyro) the aircraft will be correcrted at approximately 85% then you only have to control the plane lightly with the ailerons. Model aircrafts reacts abruptly most of the time and the Gyro on the rudder in case of an engine failure is your best bet. Still has to be tested on the B-25...I would be "ALL IN" on the rudder for a gyro. As far as installing another gyro on the ailerons well as an rc pilot the natural reaction is to try and level the plane when we see it roll. No gyro would beat me. The gyro has been tested extensively these last few weeks and i conclude that it is the best insurance against engine failure is a gyro installed on the rudder.
For those who are not familiar with Gyro installed on airplanes, well you can download the instructions on the JR G500A gyro. it explains well the installation and use of the Gyro. This device will not fly the plane for you but will assist you immediately at a critical moment often when you dont know that you have an engine failure.

timothy thompson 10-23-2007 11:10 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
go e power

norm 10-23-2007 11:12 PM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
BTW I am receiving my B-25 on 10/24 tomorow morning!!! Cannot wait to see it! I will work on it to exaustion every day until it is perfect. I will keep you posted on my experience. Tim, if you read this, is the B.25 tail heavy with the OS70's. By design it looks Tail heravy and rerading the instructions it is suggested to install the battery in the noze section below the noze gunner section. I presume that the aircraft is tail heavy. Also for my model I have the MCD472TE glow driver to assist the glow plugs when idling...and maby avoid an engine failure if the low setting is too rich on the carb. I will build and fly this aircraft slightly noze heavy at first...will keep you informed

norm 10-24-2007 07:04 AM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
E power is good for cordless tools.

danrc2 10-24-2007 07:45 AM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
nothing is better then hearing twin 4 stroke flying through the air!!!!!!!

norm 10-24-2007 09:24 AM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
"Nothins is better then hearing twin four strokes". I would disagree with that, my wife too!!! but as far as model aircraft I fully agree that it is a melody to hear twin four strokes and nothing as far as model engine beat that on warbirds. Have you ever heard two Black & Decker drills at the same time? Ha Ha HA!

timothy thompson 10-24-2007 10:10 AM

RE: Top Flite B-25 ARF (Tecnical, tips, suggestions)
tell that to greg hahn he used e power on the tf b-25. go ahead and loose a engine and watch the fun! Please read the red info. I am surprised at your antiquated approach have you evn seeen what is out there for electrics. The sound can be gotten with speakers and actual recordings.

E power will make a twin reliable and no holes in the cowl to boot

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