ronbell

Hi Dave,

First let me thank you for the excellent write up on RCscalebuilder covering your Wingspan bomb bay mod. It answered many of my questions as, like you, I do much better with pictures than written directions. Since you are now my 'designated expert', I wonder if you would be kind enough to give me your thoughts on the following:

I am now getting ready to start on my B-25 and decided that it would make sense to do the bomb bay mod first. After a lot of measuring and scheming, my biggest concern is possible interference between the door mechanism (especially the control rods) and the bombs. The bombs are 6.5" long and the Wngspan bomb bay is 13.5" so there is not much room left when two bombs are end to end. I thought about moving the mechanism to the forward end of the bomb bay, like the real aircraft, so that it would be at the 'pointy end' of the bombs where there is more room but that will not work due to the cross tube for the wing rod. Looking more closely at the innards of the fuselage it looks like the bomb bay could be lengthened to the rear at least 0.5", possibly a little more, to give an overall bomb bay length of at least 14".

From you experience of doing the Wingspan mod, do you know of any reason why this would not work? Obviously I need to decide before I start cutting.

Many thanks.

Ron.

Speedracer2112

I'm not positive on this, but I think my TF B-25 is the "Grand Pumba" of them all. Well over 300 flights. I actually wore out my port engine (OS 81a )and the flyers at the field lost all respect for her presence at the field. She has been "{resting}" for three months now so that she can regain the repect she deserves.

In the process I built her a friend.

SR

norm

Wow, Really nice!

Now Hurry and get 4 new 3 blade 12 x8 MAS props!

Normand

djstar39

My Feedback: (4)

Ron,

I'm out of town on business this week so I won't be able to reply with the benefit of looking at my bomber. I have the bombs nose to tail and there isn't a problem interfering with the opening mechanism at the rear but it does rub the fins just a bit. However, I have the old style bombs. Michael is sending me his newly designed bombs so I'll be able to measure.

I can't remember what's on the other side of either bulkhead. I do know that I mounted miscellaneous switches and a receiver to the forward bulkhead. You would have to lengthen Michael's templates but that's not hard. The hinges will have a little more to cover but that's ok too. I will tell you that getting that rear bulkhead with the servo and hardware in place in those cramped quarters will have you scratching your head. But it can be done. Lengthing the BB would help here. Please be mindful of getting that push pin in the right spot and NOT at an angle. You'll have to sight in from the hole in the fuse while doing this. Mine went in at a slight angle and required me to sand just a bit. Not too bad.

I really can't stress how small those hinge screws are. One slip and they are gone!!! :-) If you're over carpet, a magnet would help. I wasn't... they bounce a long way!

How many bombs are you planning?

More when I get back in town...

Dave

gregory.aldrich1

My Feedback: (9)

Hey all.
That is very impressive Speedracer! Over three hundred flights? Wow, I seriously hope mine lasts as long. I am getting the gyro as Normand strongly suggested and dual glow drivers all in the effort to keep the safety of the Mitchel at a high and the chances of bad luck down. Unfortunately, I have to wait until my tax return comes in to actually order the rest of everything I need. So, building should resume sometime in early February. Still looking for a completion in time for the flying season and our club has a building contest in May I was thinking about entering the Mitchel in. Although, I had hoped I would have the Bomb Bay portion done by then, the cost is prohibitive at this time. I am looking forward to getting back into the build. I lost a little steam since discovering I had the wrong servos for the rudders and didn't have the gyro or glow drivers I decided to install. But the good news is, since I have to wait, I also added paint and other little goodies I wanted to my "wish list" and so I'll be getting her fixed up a little better than planned after all. Hope all is well, Greg

ronbell

Thanks Dave, appreciate the tips about the pins and small screws. I have a reasonable stock of small screws from microfasteners so hopefully I'll be OK even if one or two go bouncing off.

I did some serious internal measuring last night - it is really nice being able to start from the raw fuselage - and it looks to me like there is nothing to stop me from moving the rear Wingspan bulkhead aft until it goes against the next internal former (similar to how the forward bulkhead installs). That will give me a bomb bay opening of 14.5 inches, a full inch longer than the template but still within the main wing, so it won't look 'un-scale' like. The new, all plastic bombs that I have from Wingspan are each 6.5 inches long and I plan to install 8, 4 on each side. Since the controller only handles 6 pylons independently, I plan to double up 2 pairs of pylons to release at the same time.

I have made a modified template but will probably re-measure another couple of dozen times, and then stick pins through at the corners of where I plan to cut, before actually lifting the knife.

This longer bombay should avoid any 'bomb crowding' issues or interference with the door mechanism. It will also make it easier if I follow through on my plan to sheet the inside of the bomb bay and add some scale detailing (phase 2 or 3 of my longer term plans).

Ron.

djstar39

My Feedback: (4)

Ron, you know what this means don't you... you have to take pictures and add to the thread to continue this on. YOU will be the new guru!!

Not sure what retracts you're going with... are you going to put the large air tank above the BB? If you never plan to do the turret, you can put it where they designed it. But...

gregory.aldrich1

My Feedback: (9)

The new Guru, that's funny. Wax on Wax off...Wax on Wax off. LOL
All hail Normand, we are not worthy, we are not worthy. Kidding, just kidding

ronbell

I agree with that Greg - Guru status is not in my future!!! Neither can I place myself even close to the skills and abilities of Normand or Tim Thompson. However, I'll make my best stab at it and have fun along the way. I will try to remember to take and post some pictures as I go. I hope to get started for real this weekend but it will be a relatively slow background project so don't hold your breath

I am using robart retracts and will be putting the large air tank above the bomb bay, probably pretty far back as it doesn't weigh much and I want to put a horizontal bracket for the gyro directly above the main spar. I've got a general idea in my head of where all the electronics bits and pieces will go but the details will get sorted out as I go. At the moment all I can say for sure is that the main receiver will go below the cockpit floor with the air control valve, one battery will probably go up front (per the manual), and everything else will be fitted into the compartment between the cockpit and the bomb bay. There should be plenty of room to fit everything and still allow the 2nd and 3rd batteries to be moved around as needed for balance.

Initially I plan to build everything pretty much per the manual except that I am going to change the interior green to olive drab and omit the 'profile' people. I hope to be able to find reasonable looking pilot and rear gunner busts, and a full figure bombardier/gunner but no luck there as yet - the only nice ones I've seen are from Wingspan but they are way too expensive (I still have 4 servos to buy!!). Hence phase 1 is to get it built and flying with a functional bomb system. Phases 2, 3,... will add detailing as my skills, funding,and inclination allow.

If you're interested then there is some great B-25J detail information on this site : http://www.maam.org/airshow/b25.htm

djstar39

My Feedback: (4)

I do agree that Normand and Tim are the absolute gurus on this project! Ron, sounds like you're putting everything the same place I put mine. I did add a small air tank up front (per the manual) for the brakes on mine. Please see my earlier posts about being piggish and having 7 batteries. Trust me, this bird is solid from TF and handles it with ease with the Saito 82's. Love it!!! Weak point being the nose gear pin (designed that way). The aluminum gear door arms were absolutely perfect. I know I'm going over things already discussed. Sorry... []

You run those engines up in sync and every person at the field will stop and come over!!!

ronbell

I have that to look forward to!!

No problem about repeating stuff - I have spent a lot of time on this site to learn from all you guys that have been there ahead of me. I've never been shy about copying good ideas!!

As for the metal door levers, one of the guys in my club is a professional machinist so I am hoping that I can bribe him into making me a set. My kit came with two pairs of levers; 2 are loose, and 2 are among the push-out bits inside the cowl mounting ring. Don't know if I just got lucky but it means I can give a set to my friend to copy and not worry if he accidentally messes them up.

Brakes would be nice but I'm out of channels and really out of money

djstar39

My Feedback: (4)

If you need an additional set, I'm pretty sure I have them somewhere.

We're similar... I'm not very original or innovative but I can copy with the best of them!!!

gregory.aldrich1

My Feedback: (9)

I finally was able to make it over to friends place to make the metal door levers. He also is a machinist and has some pretty impressive equipment in his garage. Half the fun was drinking a cold one and BS-ing our way through the process of making these arms. One thing I did was to plan on removing the small plastic washers at the same time I replaced the arms (levers). Also, because of the size of screw that was provided to secure the levers, I tapped out for and added a slightly larger and longer screw. I noticed the more I adjusted, the more the screw provided was working it's way looser and looser. It occurred to me that eventually it would happen in flight, well maybe, but I wasn't willing to find out. Also, the ply levers provided were 1/8 inch thick and so was the small portion of the brass bushing provided for the lever to pivot on. I removed .0020 thickness off the new aluminum arms so I could really tighten up the screw and prevent any loosening without binding up the new lever. Now I just have to readjust the motion and fine tune the whole mess again. Very difficult to duplicate the arms I had already ground so I just need to redo the whole adjustment process again, no sweat.
Once the remainder of the parts I need arrive (glow drivers, gyro etc..) I'll get back into the build full speed again.
I can definitely agree with Ron, Normand and Tim Thompson have given tons to this thread and should be recognized for it. It is so unfortunate that Tim suddenly passed as he did. He was a remarkable craftsman! The stuff he made out of just.....stuff! Very impressive. Never met the man but felt the loss to this hobby when I read he had passed.
DJ, I don't know who is going to be more excited, the spectators or myself. When I fire this baby up, I'm thinking the butterflies are going to return all over again. Haven't felt them in a long time. Time and money investment in this project tell me I am going to be nervous! Worth it though. Looking forward to the pics Ron. I'm with you, this baby will be done in phases. It's a marathon, not a sprint. Hopefully I will have as much success as Speed racer, 300 plus flights! WOW

djstar39

My Feedback: (4)

Folks,

For the record... SpeedRacer is a class act! I had mentioned that I needed to find the spring hinges for the nose gear door after the pin failure and the door being ripped off as it slid along the grass. SR sent me a spare set of hinges he had absolutely free out of the kindness of his heart. Wouldn't even allow me to pay him for shipping! I don't know him and have never met him.

THAT is why I love this hobby! Guys like that who just love the hobby and go out of there way for others.

Greg, I am no expert pilot by any stretch... This B-25 is actually one of the easiest warbirds I fly! As my buddy says, 'I almost wet myself' when I fly my P-51 1.50. Once I get through my checklist... takeoffs, circuits, bomb runs, and landings are pretty routine. The hardest thing I had to get used to is that it is so big it appears to be going slow (compared to a fighter) and I wanted to run it close to full throttle. Not necessary. Also had to learn to be patient in the turns. It's a big plane and needs lots of room (and time) to get around. At first I was a little heavy handed getting the bank angle way too high to hurry up and get around the turn like a fighter. Time to be patient here. Of course, can't let it get too slow!

I also have a video where I deployed flaps on downwind going way too fast. Ballooned like crazy on me. Didn't do that again.

She's a crowd pleaser! If you set her up to minimize the risk of an engine out, then it's just plain ole fun flyin!!

gregory.aldrich1

My Feedback: (9)

DJ, I remember reading a ways back in the thread when that happened to you and SR hooked you up. I feel the same way about this hobby. I mean, flying the planes and building them is fun enough, but when you realize the people (most) involved next to you are really good people and they will give you the shirt off they're back to help you out to be successful, it draws you in and makes this hobby that much more attractive. Good honest friends and a camaraderie found within this hobby is something you don't find very often in these days we are in. It's a good way to spend one's time.

ronbell

Are you guys aware that the real Executive Sweet is still flying at airshows around Southern California?  Here is a link to some great pictures:

http://www.air-and-space.com/2007102...ve%20Sweet.htm

Ron.

gregory.aldrich1

My Feedback: (9)

Hey Ron.
Yeah, I have seen many sites where the suite is featured in pictures. It's one of the things that make this model a little more interesting to me, the fact that it is still a functioning full scale warbird. Have you noticed that there is no nose art on the starboard side? The TF model decals come with two, one for each side, but it appears that the full scale only has one side done. I'm thinking allot of WWII craft only had the port side nose art because it took allot of time and effort to get those things done. Has anyone else omitted the starboard side nose art to favor the full size bird? Anyone....anyone?
Greg

ronbell

Hi Greg,

Even at my age I am too young to know for sure but my understanding is that the primary nose art is always on the left side. On single seat aircraft, like fighters, the pilot selects the name and artwork and sometimes the starboard side is 'given' to the ground crew (probably the crew chief) to add their chosen artwork. Perhaps there is/was a similar convention for bombers. Like you, I'd be very interested to know for sure.

By the way, after remeasuring and finding a mistake, I measured and checked many more times before finally picking up the saw and cutting out the belly section for the bomb bay. Luckily, after finding my first error, I decided to build in a 1/4 inch safety margin. That saved my butt as I completely missed the fact that the formers have a 1/4 inch cross member glued across their center on the forward face. Bottom line is that I got lucky and now my forward and rear bomb bay bulkheads are a perfect fit to the edge of the sheeting where I cut and I have a 14 inch bomb bay opening. That isa full 1/2 inch longer that the Wingspan template and should solve any interference issue at the rear between the door mechanism and the bomb fins.

I'd insert some pictures but I am not sure how to do it on this site - it keeps asking for a url to the pictures??? I've no doubt that it is simple enough once you know how. Perhaps someone will send idiot 101 instructions. Update -manged to get one of my pictures to upload

Anyway, I am finishing up the door mechanism piece, using a retract servo, and will then move my attention to all the tasks that will be easier to do while I have such great access to the inside of the fuselage. Things like mounting the air tank, gyro, bomb release controller, and the like. After those are done I'll finish up the bomb bay and doors.

Ron.

acerc

Hello all.
Great thread ya'll have here. Looking to get into one of these in the next cuople of week's. Right now in the collect info mode, and there's alot of it.

Two question's if ya'll don't mind.
1 What's the all up weight with all the added detail's, glassing,rotating turret, bombbay with bomb'setc?
2 Any opinion's on two stroke 90's, have two on the shelf is why I ask.

djstar39

My Feedback: (4)

Ron,

Looking really good! Great to hear you found your mistake before cutting into her! On the retract servo for the door opening... not sure how that will work as retract servos aren't adjustable and and move the full 180 degrees each time. I would have to look at mine but I think I fine tuned the door movement using travel adjust with a standard servo (can't use travel adjust on a retract servo).

Dave

gregory.aldrich1

My Feedback: (9)

Hey Dave, Greg here
Got a question about your fuel choice for the saitos you run. What kind of fuel do you favor? The reason I ask is this, I have been using Morgan fuels "omega" 15 % in all my two and four strokes since I started in this hobby. Over time, my ability to get out and fly as often as I did in the beginning has changed. Being a single father makes it tougher even though he does like to go out and hang with the guys. Anyway, since my engines sometimes sit all winter until the next flying season, even though I do treat with lubes to keep them smooth, they still seem to develope a gummy residue and I end up having to "tweak" them again before I get decent performance out of them. I have always used O.S. two strokes and Saito and Magnum four strokes. They reall love the omega 15%, but I am tired of dealing with the dried castor build up. So, I decided, since these saitos are new, I would switch to the "cool power" from morgan. Also, I am going to break them in with 10% nitro and if I can get the proper RPM's out of them with the 10%, I'll probably stick with it. Also, the cool power, being fully synthetic lube, I will have less issue with caking of lubricants.
I guess my question is, since you have said and I guessed originally that the saito 82's would be a good choice, I was wondering what percent of nitro are you using. Curious if you use 10 or 15 percent to get the "more than enough" power you have said you get with the saito 82.
Thanks man, Greg


To ACERC, I have not finished my bird yet so I can't comment on all up weight. To my knowledge, there was only one guy on this thread who had glassed his bird and I do believe he flew it successfully. As to all up weight, he may have mentioned in a post on here, but you'll have to go back and read through to find it. I couldn't begin to tell you where to look. It took me about 20 hours of reading ot get through this thread and it all seems a little blurry to me now.
As for the 90's you have laying around. My thoughts are they would be fine. I think your only issue may be weight and clearance. You may end up cutting a bunch of cowling out for them to fit. Depends on the brand too. I know my Saito 100 worked just about as well as my Magnum 120 as far as comparisons go. What I mean to say is, depending on what type of four stroke 90 you are talking about will determine how suitable they are for the Mitchel. Most have gone with O.S. 70's, Saito 82's and there have been a couple who have put twins in the cowls as well, all seem to be satisfied except for one guy who said the 70's were "just enough" and wished he had gone bigger. One of the reasons I did, and also Dave said he had more than enough power with the Saito 82's, Normand too I think if my memory serves me right. I think a guy put YS four strokes too. I would check your actual HP output for the 90's you have against data from the engines I listed and do your own comparisons from there. Good luck.

Mot of everything else I needed is going to be arriving Monday, so I plan on getting back into the thick of building again next week sometime. Looking forward to firing up the motors and starting the break in. That's why I picked up four gallons of fuel today! Yeehaw!

ronbell

Thanks Dave,

I believe that I will be OK with the retract servo.  I like it because of the operational speed.  Although I could adjust the travel through the channel expander that is driving it, I would not be able to use the servo speed function of the TX so the bomb doors would snap open and closed with a standard servo - not what I want.  I have used some helicopter linkage parts to tweak Michaels mechanism a little and reckon that I now have a comfortable amount of travel such that by setting the length of the linkage to the doors when the doors are closed they will open adequately to both look good and allow the bombs to drop.  Fingers crossed!!

Progress is a little slow right now as I am taking advantage of the great internal access to plan out and install all the items that will be hidden when I sheet in the bomb bay; air tank, gyro, bomb release system, matchboxes, and channel expanders.  This needs to be done now so that I can plan access to the items that will need trimming during set-up.  It is also a heck of a lot easier right now!!  This should keep me out of mischief for a while [8D]

ACERC - Welcome to the TF B-25J 'club'.  Now I am no longer the newbie!!!  I believe that you will quickly grow to love this aircraft.  I will leave others who are more qualified to respond to your engine question.  I am using OS FS72-A's.  I was going to use FS81's but the power difference was slight and I liked the fit and weight of the 72's better.  Time will tell if I made a good choice but I believe so.

Ron.

djstar39

My Feedback: (4)

Greg, I was runnning Wildcat 2 and 4 cycle 15% in my Saito 82's but was about 900 rpm lower than optimum which caused me to feel on the edge of having enough power. Last summer I switched to Heli 30% and got the 900 rpm's I was looking for. Now this is just me because I think Normand is just fine with his rpm's at the lower nitro amount. He is using perry pumps but that probably doesn't account for 900 rpm.

I really tried everything I could think of to get the RPM's up around the 9400 mark and the only thing that got me there was the 30% nitro. Not really happy about that with the cost of fuel.

Dave

acerc

gregory.aldrich1       
Those were two supertiger 90's- 14.73cc.  Measurement wise they fit,barely. Prop wise looking at 13-8 smaller if 3blade. Weight probably around 23lbs. I'm looking at the Top-flite arf for less work or down size a ziroli 101 to 88 inch+ a year to build.

gregory.aldrich1

My Feedback: (9)

ACERC, if your talking about two 90 2 strokes, those would be way too much power. The ARF calls for 46 2 strokes. Myself, being one to overpower most everything, I might push it to 60 2 strokes, but no more than that. Now if they are four strokes, I guess if you can fit them, why not? lol