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-   -   Hangar 9 B-25 ARF: Building and Modifications (https://www.rcuniverse.com/forum/rc-warbirds-warplanes-200/6549627-hangar-9-b-25-arf-building-modifications.html)

CorsairJock 10-28-2007 12:25 PM

Hangar 9 B-25 ARF: Building and Modifications
Starting this new thread, and hoping that the focus can be kept on the subject (Hangar 9 B-25J ARF).


I am also hoping that posts to this thread are informative and meaningful to those who own or are planning to own this ARF. In order to accomplish this, I am hoping to keep out the nuisance posts which eventually number so many, that it makes it extremely difficult for those seeking real information to find it.

That said; I have some rules for this thread. The rules are totally un-enforceable: anyone and everyone has the right to totally disregard any and all of them. To me tho, they are a common sense approach to keeping this thread as informative as possible, without having posts that are meaningless to the majority us us.


1) If all you want to do is say "Hi" to someone else; please PM or e-mail them. Why create a post which contributes nothing, while taking up space and making it more difficult and time consuming to some person to find genuine information concerning the topic of discussion?

2) Remember: there is an "Edit" button. Please don't waste (cyber) space by posting a 'whoops', and then creating another post to correct. Use the "Edit" button to correct your post, rather than creating another post. Again; having many posts which contribute little or nothing makes it more difficult and time consuming for others to find the important posts. Have some consideration for those who will be trying to learn something from this thread.

3) Don't use this thread to assert which B-25 ARF is better. There are already threads for that. If you want a thread about the Top Flite B-25 (or any other B-25), feel free to start one. Most people will agree that the Top Flite B-25 is more detailed, larger, and more expensive. So why make it more difficult for those of us that have chosen the Hangar9 B-25, regardless of the differences?

Those are the rules. As stated earlier: they are totally unenforcible, and anyone has the right to be as inconsiderate as they choose to be. We are all jerks (*ssholes) at times; please don't be one that takes your turn at it more often then others.

What I DO encourage is contributions from others.

If you have a Hangar 9 B-25: tell us about it. Post pictures of it and PLEASE provide details:
1) which engines are you using?
2) did you install retacts?
3) what radio gear are you using?
4) anything special about your's (modifications)?
5) HOW MUCH DOES IT WEIGH? And this is a big one in my opinion, so please find a way to accurately weigh it.

If you have ideas for modifications, please post them here. That is the main purpose of this thread: to share ideas on how to make these B-25s better looking/ more scale accurate, and/ or better flying. Hopefully, I can meet some of you next summer at warbird events, and we can do some formation flying.

Questions are welcome also, but please read all previous posts, OR check the table of contents to see if has already been asked and answered. Engine choice questions are inevitable, so again; please read what has already been posted.


I will attempt to post 'contents' pages and keep them up to date. Since a post can only be editted within a certain time frame (I don't know how long, but here is an 'expiration date' on being able to edit a post), I will begin with post 2 as the 1st table of contents, and will attempt to have every 100th post be an updated table of contents. Thus, if you are looking for the most up to date table of contents; always look around the 'century' posts (100, 200, etc.). I may not always be able to post them right on the 'century' posts, but they will be nearby (101, 102, etc).


Here are some links you may find useful:

If you really want to voice your opinion on which is better (Top Flite or Hangar 9), here is the place to do it:

If you want more general info and/ or general discussion on the Hangar 9 B-25:

Here is a thread with discussion and pictures of full scale B-25s, for ANY B-25 project:

Lastly, a Doolittle Raider web-site:

A lot of words already in his post, so I'll end it for now.

CorsairJock 10-28-2007 12:26 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
Table of Contents (#1) Number preceeding subject refers to post number

3, 21) Converting to a B-25B/ Doolittle Raider/ tailcone mod

11 ~ 12, 16, 18) Alternative retracts options, and scale wheel sizes

15) Cowl mods

28) Mounting Elevator Servo on the Stab

CorsairJock 10-28-2007 12:42 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
1 Attachment(s)
I intend to build mine as a B-25B/ Doolittle Raider. Since doing some research, I have discovered that the co-pilot of aircraft #14 (14th to take off from the U.S.S. Hornet), Lt. Jack A. Sims, was from my hometown of Kalamazoo, MI. That said: I intend to model mine after that #14 aircraft, which had the numbers "02297" on the tail.

Converting a B-25J into a B-25B (as flown by the Doolittle Raiders) is not that difficult. The most difficult step would be fabricating a tail-gunner/ tail-cone 'blister'

I have begun that process by removing some of the balsa block on the tail on my B-25, hollowing it out, and adhering 2 layers of .75 oz/ yd glass cloth to the 'former'.

The 1st and 2nd pics show the part that I sawed off, held in position (with 2 pins) where it used to be attached to give a rough idea of how to saw it off.

The 3rd and 4th pics show the results, now waiting for me to fabricate a 'plexi-glass' tail-cone blister.

The 5th pic is an actual photo of one of the Doolittle Raiders while aboard the U.S.S. Hornet, showing the gun blister I intend to replicate. Note the absense of the tail-gunner 'greenhouse' which was located above the stablizer on later models (including the B-25J).
Actually tho, on the Doolittle Raider aircraft: these were not real machine guns. Jimmy Doolittle came up with the idea of installing broomsticks thru the plexiglass, painting them black (as well as the 'elevation slots'), to intimdate would be attacking Japanese fighters.

6th pic is a drawing of the #16 aircraft

For a follow up on this mod, go to post 21

jasonred007 10-28-2007 01:16 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
Actually the reason that the were broom sticks is because they took all the guns out to load up with fuel for the long run, and to take off from a carrier fully loaded with fuel,guns and ammo they were simlpy too heavy. Good luck on your build. I have a KMP with 2 OS 91s they are kind of heavy but fly great. I have decided to steer away from H9 because of some bad luck with their products lately, but I must say they certainly look like wonderful planes. Good luck and happy flying Jason

timothy thompson 10-28-2007 02:10 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
top turret and gun in nose were real. tail guns were the only ones with broomsticks

reincarnate 10-28-2007 07:26 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
Question Jock. Do you plan on operable gear door or bomb bay doors? Thanks for taking the lead and starting this thread.

NCIS 10-28-2007 07:28 PM

RE: Hangar 9 B-25 ARF: Building and Modifications

I don't understand why you buy an ARF and then go through all the trouble of modifying it to look like the real thing. Why don't you just build one off plans and then modify that so it looks exactly like what you are striving for? I'm not trying to be critical just wondering.


mobyal 10-28-2007 08:35 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
Jock --
I've bitten the bullet and had my LHS order one for me. It'll have to be one of the second run, as apparently H9 is sold out of them for now. Delivery estimated in early Dec.
I've also ordered the Robart Retracts designed for the plane, the JR servo set, PCM receiver and two EVO 46s for power, based on local reports that say the 36 seems underpowered.
I'll look forward to following this thread along and learning from it. Hopefully it'll make mine go together faster.

CorsairJock 10-28-2007 09:38 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
YES, I would like to be able to drop 4 bombs, as the Doolittle Raiders did. However, it looks like it will be difficult to drop 4, may have to settle for 2 (lack of room under the wing).

I work 7 days a week, and many of them 12+ hour days. It still take less time for me to modify an ARF than it does to build from a kit. I work all these hours in hopes that I can retire in 2 years, THEN I will start building more kits. ALSO: it is easier to spot scale indescepencies in an already completed model than in a box full of un-assembled parts.

having lost my H9 Hellcat due to some *SSHOLE turning on his Tx while I was flying, I will not trust this plane to72 MHz. I intend to use 2.4 GHz with this warbird, as well as all my others. As for the .46 choice: I agree, the video of the .36s climbout did not seem all that impressive to me. This from someone who typically (by most people's standards) likes to under-power his warbirds.

BTW: I have ordered retracts and RoboStruts from Tower and the total cost will be about $265 (without air kit). Details tomorrow.

Also: I have been in contact with Bill Fulmer (RC Report), and he will be providing the grafix (Doolittle Raiders markings) at a VERY reasonable cost. If you would like some custom graphics from Bill, here is his web-site:

timothy thompson 10-28-2007 11:25 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
you can make a plug from balsa and heat clear plastic and pull her down to make the bubble. dont need a vacum forming device.

stick a dowl in the bottom of the plug and clamp in a vice then heat the plastic and pull! putting the clear sheet in a frame is better

you couldnt build a b-25 for the price of the kit so whats wrong with jock modifying I think its a great idea!!

CorsairJock 10-31-2007 08:07 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
A few facts about this ARF: the full scale has a wingspan of 67 ft, 7 in, or 811". Adversized span ofthe H9 B-25 is 80.7", making it for all practical purposes: 1/10 scale.

I have determined thru measurements taken from a 1/48 scale plastic kit, and calculations that the correct scale wheel size should be about 4 3/8" dia for the mains, 3" dia for the nose. As the included mains are about 3 1/4" dia, I decided that I wanted to install larger (yet lighter) main wheels on mine.
I intend to install 4" mains on mine, and a 3" nose wheel on mine.

Doing so with the retracts that are especially made for this kit may cause problems, so I decided to purchase a set of Robart retracts and seperate RoboStruts so that I could cut the struts to correct length.

SO, I placed 2 seperate orders with Tower Hobbies (so that I could use $25 off coupon twice), ordering the "550RS 90 Degree Main Gear RoboStrut Ready" mains (which APPEARED to be the same ones that come with the B-25 retract kit), and a "560RS 105 Deg Nose Fire/Belly Mount RoboStrut Ready", as well as the RoboStruts

Main retracts arrived today, along with 1 RoboStrut.
Maybe there's something to be said for buying the retract kit made for this plane.

First off: those RoboStruts sure are a tight fit (even with paint sanded off) in the RoboStrut ready retracts. I'll have to cut them to proper length then force them in somehow.

Second: I ordered the wrong mains. The correct ones would be the 530 series mains, which are also known as reverse (so called because the cylinder is on the opposite side as the retracted strut). In other words: the cylinders are at the front part of the retracts, NOT the rear. The ones I have can be made to fit using 1 of 2 methods:
1) slight modification to the retract bays, involving removing some plywood. A spruce brace can be added later.
2) reversing the truinions on the retracts, alsth this may be more work than 1)

Either way, my advice is get the correct ones: the 530 series. They cost about $7 more a set, but will save building time.

Ordered 3 H9 1/10 scale WW II US pilot busts from Horizon today: MAN are THEY EXPENSIVE! $9.50 EACH. Thats just shy of $30 for 3!
Williams Brothers busts are about 1/3 the cost, but they do not make 1/10 scale.

CorsairJock 11-01-2007 08:05 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
Remainder of retracts arrived today, YES: the "Left Offset" is the correct way to go on the nosewheel RoboStrut (unlike the right offset ones which appear to be coming with the H9 and Top Flite B-25 retract kits).

tevans55 11-07-2007 05:53 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
1 Attachment(s)
Jim- I posted this scan on the other thread also...New B-25. This is a scan of the new CJ bomber pilot. I purchased the bust version.

tevans55 11-07-2007 06:01 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
Jim- Are you going to make a mold to form your blister over and if so how are you going to actually mold the blister...heat gun or something else? Also what type of clear plastic are you going to use and where can it be purchased?

tevans55 11-14-2007 10:09 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
1 Attachment(s)
I started working on the engine nacelles and discovered that the vents around the cowl look pretty good when you open them up. They will also provide improved airflow through the cowl.

tevans55 11-15-2007 11:42 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
1 Attachment(s)
Here are the new Century Jet retracts for the B-25...this is a nice durable set of retracts for $365 and the kit includes everything. I threw the wheels on to get a little more pespective. Wheels are 3.50 mains and 2.75 nose. I also included the new bomber pilot busts that just came out. I know you already have purchased this stuff for your B-25 but I thought others might want to consider other options. These retracts are custom made for the H9 B-25.

mobyal 11-20-2007 05:31 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
Found it.
Thanks, tevans

tevans55 11-21-2007 02:04 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
1 Attachment(s)
Here are pics of my CJ's ready to install. Had to build up mounting blocks to fit properly. Nose gear tank will share front compartment with SR 2200 ma flat battery pack. Also have started changing colors used on pilots.

One-O-Wonder 11-21-2007 08:54 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
Living at 6000 ft here in Colorado and having one of the H9 B-25s that came with the Evo 36s, I decided to test fly the engines in another airframe. I fly an Ultra Stick on skiis during the winter with an Evo 46. I installed a motor mount that the Evo36s fit and yesterday I flew the stick briefly ( temp was falling and begining to snow). The Evolution started right up and ran fine from the start. After tweaking the main needle a little bit I poured the coal to it and the Evo flew the stick rather well. Not the power of the 46 but not a dog either. I only flew it for about 5 minutes but that was long enough to assure me two EVO 36s will fly the B-25. Btw I had an APC 10x6 on it. I'm going to test fly the engine with an APC 10x5 and at Master Airscrew 9x7 three blade also. One of my friends also got the plane with the two free Evo 36s. He's going to use Saitos on his so he gave me his two Evo 36s. I guess I'll be flying four engines on the stick. Life is good!!!!!

tevans55 11-22-2007 04:14 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
Have you had any ideas as where you are going to place your battery switch and retract filler valve? By the way, the guys at CJ suggested that I use clear silicon around all the places where wood contacts fiberglass inside the engine nacelles. I tried it and it appears to provide a much better bond than epoxy.

CorsairJock 11-23-2007 01:28 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
1 Attachment(s)

ORIGINAL: tevans55
Have you had any ideas as where you are going to place your battery switch and retract filler valve? ................
I haven't got that far yet, but with an EASILY removable belly hatch: there is no excuse for having any either of them (switch, filler valve) exposed.

With 4 straight days of no work, Iwill be making some progress on mine this (Thanksgiving) weekend.

I refuse to be like so many others here, and keep posting threads (sometimes several consecutive) posts with little value. I prefer instead to use the "EDIT" button. Therefor, what I post today will probably be changed/ modified/ with pictures added by the end of this long weekend.

1st order of business in the tailcone. I asked Dan Gipe (owner of Wing Mfg.) if he would assist me in producing a B-25B tailcone which could be used for the H9 B-25 as well as his Wing Mfg B-25 (which at 84" span is slightly larger). Turns out that Wing Mfg. ALREADY makes/ sells a B-25B tailcone, so the Wing Mfg. B-25J can be convereted to the B-25B. So, I handed $8 to him (list price) and he gave one to me. If YOU are interested in buying one of these, here is a link to the Wing Mfg. B-25 parts web-page, which has the blister listed (Part #PK1001-B):

Now for the hard part: that tailcone does NOT match the contour of the H9 B-25 tail. Probably the Wing Mfg version is more true to scale. In particular, in order for the Wing Mfg. tailcone to work on mine, I will need to:
1) round the bottom of the fuselage more (only at the extreme tail end of the fuselage).
2) flatten the top of the fuselage to match the aft of the horizontal stab .
3) Make the sides parallel (again, only at the extreme tail end of the fuselage).

To accomplish all of that: the covering will need to be removed in that area. Oh well, I had already decided to recover the entire airplane with FLAT covering (CoveRite flat olive and flat dove gray).
The covering has now been removed, and I am ready to begine sanding to the correct shape. NOTE: you do NOT have to remove ALLof the covering as I did for this mod: it is only necessary to remove the fuselage covering from about the elevators aft.

The 1st 3 pics show the tail without the clear tailcone. The first 2 show after intial sanding, and a piece of 1/4" thick sheet has been added to the top of the fuselage (AFTER sanding the top slat/ removing the top sheeting there). The 3rd shows after sanding the newly installed 1/4" sheet to match the contours of the rest of the fuselage.

The last 2 pics show the clear tail cone taped on, to show how it will look. It is barely visible in pic 4, but pic 5 shows it to good effect.

There is a lot of work/ sanding involved in this mod in order to make the Wing Mfg. tailcone fit properly. Some of you may find it easier to just make your own tailcone, to match the contour of the H9 B-25. Personally tho, I was not looking forward to fabricating the tailcone, and I am glad that Wing Mfg offers one, altho it IS a lot of work making it fit right. The tailcone itself also had to be sanded quite a bit to make it fit.

jbarnes 11-23-2007 03:33 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
I too picked up on these bombers this week. I'm thinking about the electric conversion. Do any of you have any history with SkyShark electric combo's. They have their 50 size combo which is similar to the Eflite 46. Using SkyShark combo pricing saves about $250 over the Eflite combo. I'm keeping mine fixed gear as a B25 trainer while I wait for the new KMP B25 to come out. I currently own their OV10 running twin Evo 26cc gas engines and its a nice plane. I understand their new B25 will be all composite with lots of detail and probably lots of $$$ too. Love the H9 stuff so I couldn't pass this B25 up. Any electric advice you can give this electric rookie would be appreciated. Thanks, Jerry.

timothy thompson 11-23-2007 05:59 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
the b-25 j had slab sides. the b model was rounded thats the difference. It will not be possible to convert as the shape of the fuse is completely different. I checked all my fathers data and manuals and the J fuselage shape is correct! the b is an entirely different bird

CaptainHook 11-23-2007 10:31 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
Just stumbled accross the deal at the LHS. $400 with Evo .36's installed. Special deal going on I guess and I wish I hadn't dumped a load of cash on the Top Flite at this point so now I have two B-25's to build this winter.:D Looking forward to following both threads here on RCU before I begin the builds.

BillPTC 11-26-2007 12:56 PM

RE: Hangar 9 B-25 ARF: Building and Modifications
Lost mine last week on test fly.
Used EVO 36 and all stock setup. 10x4 EVO 3 blade props. No retracts. Two 2500 NiMH batteries with 2 MPI switches with volt regulators.
Two tanks on ground and third tank high speed taxi on grass field.
Take off was good and went to 125+ feet. flew 5 minutes in race track pattern. chopped throttle to observe stall, only got mushy and throttled up. Also slowed 1/3 throttle and put flaps down. Half flap no notice different, full flap little nose up. Every thing Ok. 5 note wind down runway. 2/3 throttle level flight, 100 feet initiated left turn flying into wind, nose pitched up, left wing dropped, stalled and flipped over and started spin down. Cut engines and could not get it out of spin. Straight into lake nose first. Lost fus from cockpit forward. Wing, engines radio and tail OK. Just put new fus on.
I cut throttle because I was thought I had lost left engine making left turn caused flip over. Others said no, both engines going fine. Plane had balanced out on the spot OK with both batteries forward. Radio worked because I was able to cut engines. Batteries and radio battery check out with high voltage.
Flying upwind slowed down and couple said tail was down. Flying down wind level and faster.
Left engine was 10,000 rpm and right engine was around 9800 rpm. I slowed left engine down by radio to match right.
I am going to add half inch to CG for next test flight.
Bill PTC

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