Topic: Douglas A-20 Boston

Centre section of the tailplane is also coming togther. I really like the dihedral tail of the Boston....

TNT ali tubes and phenolics used here, from the states.



Then the elevators...

These are much smaller and thinner than the rudder, so I went back to a 1/16" traditional balsa core. I added 1/16" ply trailing edge to keep things strong and hopefully leave a tidy and thin trailing edge.



The 1/16" balsa wouldn't be near strong enough to stop the elevators from warping while covering or distorting under flight loads. I strengthened the core by adding diagonal strips of 3/16" sq...tapered towards the trailing edge. I also used some balsa block instead of sheeting the leading edge. The end result is a very strong and rigid structure, and it still needs covering yet!

Hi Steve, nice work!!
 
Will you use one servo per elevator? And what servo would that be?

How do you work out the torque requirement?

What servo will you use on the rudder?

Hi Alasdair,

Yes, there will be one servo per control surface. I like this system as it gives direct and slop free linkages with fewer parts to each linkage (which could fail over time).

As for working out the control forces...this one is a giant can of worms! I think that it is such a complex area of any model aircraft that no formula can realistically take into account all the forces acting on a control surface. As a very loose guide I use some of the excel spreadsheets like....:

Servo Calc

This can give you a rough idea of the forces, and the moments/angles to use on the linkages...but is not comprehensive and I always add a safety margin (about 20%) to the final figures.

I work out that I need about 6.5 kg.cms for the elevators at 30 degrees of travel and a whopping 120mph airspeed. I have installed JR 8411's with 11kg.cms so they will be way more than needed!

Servo Calc also works out that I would need 16kg.cms for the rudder to move 30 degrees at 100mph (wholly unrealistic to use such huge control throws at such high speeds) I have fitted a Hitec 7955TG here which at 18-24kg.cms is again way over the top, but I can be sure that it is not going to struggle!

Hope this helps....not overly scientific, though!

Steve

Here's a photo of the elevator linkage....



Twin fiberglass sheet control horns with a dubro 3mm ball link. 3mm threaded rod, with a section of Ali tube over the top to tidy it up.

Servo mount is made from angled aluminium section cut to about 1/2" widths. 2mm bolts and nylocs will hold it all in place.

To hold the tailplane on....I made some 3/32" paxolin 'tongues'. One 4mm bolt will hold each tailplane half in place.



The tailplane is nearly complete.....



Just need to fettle some of the edges and sheet the lower part of the center section......

And a quick motivational photo session......!

Looking good Steve 

Cheers Jamie,

I seem to have been building tailplanes and fins for weeks now!

Just be thankful you didn't decide to build a Constellation then 

Tailplanes and fins beats fibreglassing any day of the week! I haven't been into my shed since the beginning of August 

Just be thankful you didn't decide to build a Constellation then 

True...'cause that would also look rather silly with Phil and gang buzzing about in formation with Fighters and the like!!

I guess there can be rather tedious bits to all builds I just know that I if i stop half way through and do something else it is twice as hard to go back and finish the old job!

True...'cause that would also look rather silly with Phil and gang buzzing about in formation with Fighters and the like!!

Not in M.A.T.S. colours!  

Test flight before Christmas?     

What a jolly good idea.......a C-69 Constellation.......have I asked you what you're building next Steve ....it'd be quite nice at 1/5

I know where a nearly finished one is for sale....must be about 1/5 or 1/6 th scale!!! Four radials for power!

....I couldn't possibly comment

In an attempt to get the model sitting on its wheels in time for the LMA Gaydon event I have have made a start on the basic nacelle construction.

The undercarriage is from Unitracts....quite a basic set but they work really well and should never give any problems. Wheels are from Fighteraces (not sure were Phil got them from) but at just over £25 for a pair of 8" wheels...they are brilliant value and light too.

That's a 7" ruler for scale!



I'll spend some time tarting up the legs and hubs later.....


Primarily all 1/4" marine ply...The only exceptions are the firewalls and the undercarriage retract mounts which are laminted up to 1/2".

Here is one assembly while clamped up while the Hysol cures...

While the nacelles cure I have been do a spot of work on the top side of the fus....next big job here is to glue the wing and tailplane centre sections on...but that will have to wait until the weather improves and I can assemble it all outside.

'tis looking good steve!!   

Managed to get the model on its wheels in time for Gaydon....other that I have not done a huge amount, just little jobs here and there....

I have beenworking on planking the last of the upper fuselage sheeting this week.

All planked in 1/8" balsa...about 1/4" wide over the tight radii and around 5/8" everywhere else that normal sheeting won't go over....

A little bit of work to the front framing....

I am building the Boston III which has the lovely glazed nose with angled sides (some have the 'stepped' sides). I also plan on doing detailing the inside as best I can..so I need to start now and build the structure up similar to the fullsize....

All of this to date is made from 1/8" marine ply. About 8mm in depth and all designed on Adobe Illustrator, printed onto A4 sheets of paper and then tacked onto the wood before cutting out. I roughly go around the shape with a bandsaw and fretsaw and then finish off the sides on a sanding wheel. Seems to make a reasonable job of things...



Have to admit it was a real pain to get things to fit...and a fair amount of trial and error was needed to square things up....

Unfortunately this is about as far as things are going to get for a while....

I have had to take a job in Doha, Qatar (Middle East) which will stop work on the Boston for about 2 1/2 years!

I'm sure I'll find something to do out there, modelling wise, but for now the Boston will have to be packed away in a crate and stored.....

 

Steve,

How are you planning the glazing for the nose?

It's a similar nose to the He111, but that uses mainly flat(ish) panels apart from right at the nose.


Mark

Hi Mark,

I plan on making a plug around this existing frame and taking a fibreglass mould (female) from it. I'll then make a male plug from resin. I'm not sure how many sections I'll make it in yet. Probably just left and right halves. These plugs will then be sent off to a vac-forming company to do the biz.

The initial mould will then be broken down to about this stage and the moulding applied.
Steve

Steve,
I'm glad you are getting advancement in your career (flying what? for whom?) but on a selfish level I am disappointed that I will not see you and your models at the events next year.

Is the family going out there with you?
All the best, & stay online. You can at least hand out advice.

Hi Alasdair,

I am off to fly A319's, A320's, and A321's for Qatar Airways...... Just my wife, the little one and I going out there.

I'm sure I be around RCMF a fair bit while out there...need to pass the long turnarounds somehow!

Cheers

Steve

tell them you cant come till the twins finished       wish you the best with your new job,  hurry back

Cheers Alan!

Not sure they will be overly sympathetic!!

I'm sure I'll find something to do out there, modelling wise, but for now the Boston will have to be packed away in a crate and stored.....

 

Ohhhh I wonder what  

C U Friday mate

Good luck Steve! When I was out there they didn't allow model flying at all  . Maybe it's changed  . Will miss your build threads. 

Cheers, Alex

Ohhhh I wonder what

   

Hi Alex - They do fly models out there at the moment, but it tends to only be early in the mornings and generally only in the winter too....for obvious reasons!

I was going to get a jet to fly out there, but I have been persuaded (and I see good reason for it too!!) that sand and Gas turbines don't mix very well! So it looks like a building project out there.....I had another plan of taking the Boston with me...but it is just too big and needs too many tools to complete. So to Plan C! Details will emerge on this site in good time!!

Crate is now made....this will be home for a Boston III for the next few years! I have tried to make it as air tight as possible and installed a couple of moisture traps as it will get stored in what is essentially a glorified barn in deepest Lincolnshire!

Other than that I have no more to say other than thank you for looking in....progress will resume shortly!

Steve

You should just pay Fighteraces to finish it for when you get back!!

You should just pay Fighteraces to finish it for when you get back!!

is the waiting list that long?? ;-)

You should just pay Fighteraces to finish it for when you get back!!

If I could afford it, I might have!

I hope it's not clearing off to deepest darkest Lincolnshire yet mate....coz as I never got a chance to look at it at Gaydon, I was hoping for a guided tour on Saturday  

is the waiting list that long?? ;-)

9-12 months & counting at the moment

 

Uh oh....

Just sealed the lid about an hour ago and it will probably be leaving a couple of hours before you get here! Sorry!

I was trying to hold off on packing it away...but I got the telex from 'upstairs' requiring room in the garage for storage. Not wanting boxes of 'unsavory things' like towels and bedding resting on my bare balsawork I thought it wise to get it somewhere safe!

 

Awwww, no more building. Such a shame, however, hope you and yours have a goodtime out there Steve.

Charlie C

...it will get stored in what is essentially a glorified barn in deepest Lincolnshire!
Steve

That's no way to talk about your father's house Steve! 

All the best in Qatar.

Paul

I was trying to hold off on packing it away...but I got the telex from 'upstairs' requiring room in the garage for storage. Not wanting boxes of 'unsavory things' like towels and bedding resting on my bare balsawork I thought it wise to get it somewhere safe!

I don't know....it's a few weeks before you go and she's that organised already......I'll have to have a word