Topic: Douglas A-20 Boston

I presume you're refering to the canadian trial to validate the cod-strike clearence.

PDR

All right lads! As much as I like the Nimrod (any mark!!) the Comet is staying exactly that............

A COMET!

 

Talk about thread creep!

Right,

Just to try and bring things back on track! ( )

I ordered some Ali tube and Phenolic outer from TNT landing gear last Friday. This is for the tailplane joining system. I was very surprised to see a van pull up today with the parcel in his hand. Very fast service considering they came from the US.

I have the retracts now from Tony Goodger (photos to come) and some wheels on order through our own Mr Clark. I am close to putting together a wood order to Stuart at Solutions. (a fair number of cyparis trees may be hurt in the making of this model!)

Still working on the last details of the plan and should have enough to be printed next week.

I'm off on the long trek to Machrihanish Airbase now for a spot of (not very) relaxing Pulse Jet flying with the Glasgow crowd and hopefully squeeze in some test flying with the Libellula too, now it is on 2.4G.

Later....

We're all still very interested in seeing your Havoc progress Steve 


(P.S. Pete, XW666 was the R1 which ditched in the Moray Firth following an engine fire  )
The Lake Ontario airshow crash was XV239

(P.S. Pete, XW666 was the R1 which ditched in the Moray Firth following an engine fire  )
The Lake Ontario airshow crash was XV239

Picky, picky.

Right then - is this Boston finished yet?

PDR

Turbinlite - Wikipedia, the free encyclopedia
Would have been interesting to see if the turbinlite havoc nightfighter could have been done - big light in the fron 2.700 million candle power - definately different - however im sure this is going to be just as good as the other builds - subscribed

The Night fighter would be nice, but I'm not so sure about flying a black model during our typical british summers! I shall certainly fit the landing lights that are clearly visible just outboard of the engine nacelles, they are retractable too.

A quick update....

My plan has arrived printed by Belair. I have just taken charge of my two Zenoah 62's from Phil and I am collecting the last of the wood on wednesday from Stuart at Solutions......just a few more jobs to do on the current fleet and I hope to be able to make a start soon.......

Steve

A little bit of a start has been made today!

First job is to get myself a kit of parts cut out. Formers and ribs are all a combination of liteply and marine ply, 1/8" mainly. The plans are chopped up and glued onto the wood with Prit-stick.

Where I have double the parts to cut (such as ribs) I will tack glue two sheets of ply together and cut them out as one. That ensures all duplicated parts are identical.



Just the tailplane and fin ribs to be 'marked out' now and I will get cutting!

A few hours later.....



Believe it or not there are 20 fuselage formers there. Most have been cut into four sections that will clad the outside of the basic box structure...more on that a fair bit later!

The next job is to cut the cyparis spars to size.

They will start off as 19 x 12mm, but taper down to 10 x 6mm between the outer edge of the nacelles and the wing tips.



That is tomorrows job though....

(Oh and don't look at the spar on the plan...that was Version 6 when it got sent to the printers, I think I am on Version 10 now!)

Not bad for a mornings work......what did you do in the afternoon

Wandered round Knaresborough and Old Mother Shiptons Cave! Why? 

......I guess I should have seen that one coming

They will start off as 19 x 12mm, but taper down to 10 x 6mm between the outer edge of the nacelles and the wing tips.

I'd like some hints and tips on how best to do this Steve when you get round to doing it

Thanks

Alan

Marked then rough cut on the band saw, then finished by hand with a razor plane was how I did the tapered outer panel spars on the Raider Alan............

Hi Alan,

Yes, pretty much as Phil said only with a slight twist.....I use a large Permagrit sanding block instead of a razor plane.

Mark out your cuts



Rough cut them on the band saw...no need to be deadly accurate just cut to the outer edge of the line or beyond....make sure you don't cross that line though or you'll create a weak spot in the spar.



I clamped all four spars together to sand them...that way you are more likely to keep the sanding block square than just on one little spar.



I have a double taper....so the next cut was marked out (remembering that the spars are now 'handed' left and right)



Two spars together this time (as they wide enough to get away with it!)



Et voila! Tapered spars.

Thanks chaps,

So, mandraulic it is then.  No substitute for saw and plane!

Alan

Finally got the ribs and braces finished off today. Surprising how much work there is in that little lot!



and a dry assembly run to prove that things fit where are supposed to.

Managed to get a few hours on the Boston the last couple of days.



To keep the wing sheeting and spars in one piece across the entire span I have devised a new mthod of integrating the nacelle into the wing structure. These 1/4 ply brackets will slot into the ribs and over the top of the spars and allow me to bolt the nacelle on during construction. They won't be removable, I'll simply be using the 6 4mm steel bolts to help transfer the loads into the wing structure.



The center section was framed up last night using Hysol. You can clearly see my 'belt and braces' method for wing retention. I have had to 'break' this wing at just about the worst position so I need not only fly loads to be covered (the steel straps) but also shear forces from landings and the two engines...(the Ali tube). I am not sure that each system by itself would be sufficient, but together I am pretty sure those wing aint going anywhere!



The rest of the wing is being framed as I type, I positioned all the ribs equi distant so I only have to cut one width of shear webbing. I am using this shear web to set the spacing and also help keep the ribs vertical during the 'flimsy' stage of construction.

Today saw the framed up wing dry and ready for a light rub down.....



I had spent a long time working out servo positions, flap and aileron positions etc so all holes and neccessary hard points are installed during this intial 'framing up' stage....consequently the wing is now ready for the first sheeting to go on.

This is new to me...but I decided the sheet this in 2mm lite ply. This is slightly stronger than 1/8" balsa (and slightly heavier) but it doesn't need joining and has a much more even surface finish to it. I was thinking about sheeting each wing half in one go...but quickly realised that was a bad idea. I don't think you would get enough working time with the glue (Aliphatic used here) so I opted to sheet in two sections.....rear of the main spar and forward of the main spar.

I cut the sheet to exact size using my plan (carbon paper between the plan and the sheeting...and marked off the flap and aileron positions too.

All weighted down with pins, clamps and homemade mini sandbags.

The second wing panel has been framed up now.



1/16" ply webbing on both sides of the main spars out to the nacelles helps to keep things rigid and 3/32 balsa webbing out to the wing tips...

It's quite a distinctive wing isn't it Steve?

It's looking great by the way. I'm still impressed by your speed! 

I guess the impression of speed occurs because I haven't been photographing all the preparation for the build. I try to make a complete kit of parts before I begin, all trimmed and sanded to size....so when it comes to the assembly, it all happens quite quickly.





Aileron and flap servo boxes are installed and just need the hard points adding for retaining the servos:



The nacelle hard points are all installed....ready to accept the 4mm steel bolts

The retractable landing lights are now provisionally installed....one on each wing, just outboard of the engine nacelles. I am using 12volt mini halogen bulbs (20watt) that are easily available from DIY stores.. I'll have a 12v NiMh (4000mAh) battery pack drive both of these with a brushed speed controller as the 'on-off' switch. I should get just over 1 hrs operation from one charge...which should be more than enough for a weekends flying.

To start with I made a little sketch to get the shape of the offset hinges just right before transfering it onto some 1.5mm paxolin sheet.



I tacked four laminations together and cut them all out on the scroll saw.



I made up a small set of parts for each landing light...which will use the brass tube as a torque rod. That way I can get the light servo under the same hatch as the outer flap servo.....saves time and strength!



A lite-ply base is glued between the ribs with a smaller square of lite-ply to locate the light unit. This smaller square will be the part of the final sheeting..I thought it was easier to get the sheeting to fit around the square than around the light....

The whole assembly has now been tacked into place with cyano....tonight I'll go around everything with a bit of hysol and fit some locking pins through the brass tube to stop things from ever coming loose.



The light in the retracted position....



and deployed...

lovely work steve........

steve,

i like seeing how this sort of thing is done. one question i do have though is is there any way of adjusting the beam directtion once installed or is it fixed?? i might be wrong but from your pics it looks like the lamps is not parallel to the spars and therefore in my mind not pointing directly forwards. i also suspect that you have thought of this and the spars are not 90 degs to the fuz/direction of travel!!

cheers

nick

Hi Nick,

No, the spars have a slight forward rake so that is why it looks slightly odd......

There is no way of adjustment, that would be getting a bit too clever!

A little more sheeting and wiring inplace.

Wiring is Heavy Duty Silicon twisted cable with Ashlock connectors. I like this system as all wiring is exactly the right length and the connectors cannot be assembled incorrectly at the field and have a locking system too.....about as failsafe as it gets.

Some of you may notice that the leading edge sheeting is balsa and not lite-ply as I had originally planned!

Basically I bottled it when I felt the weight of the wing creeping up! I am sticking to lite-ply for the 'centre' area of the wing, but the leading edge and the flaps and ailerons willbe sheeted in 3/32" balsa!

Don't blame ya mate....the 26 has 2mm lite ply skins on the centre section and 1/8 balsa on the outer panels....more than up to the job. I only use 2milly all over on the 'built like a tank' Skyraider....................

Hi Nick,

No, the spars have a slight forward rake so that is why it looks slightly odd......

There is no way of adjustment, that would be getting a bit too clever!

the above picture illustrates the alignment with the leading edge so the lights will point in the right direction. i knew you would have thought about it!! 

I found the original slide Steve   

Ooh...that's better! Thanks Selleri.

Progress has been a bit slow lately, but I have been working in short bursts!

I decided to make a start on the fuselage. I started by laying some painters 'dust covers' over the plan and then building a basic warren girder structure from 9mm cyparis and balsa. 1/16" ply reinforces the area around the wing cutout and the bomb bay.



Formers installed for nosewheel retract unit, and wing mounts. I added a couple of extra formers to help keep everything in shape around the cavernous bomb bay. When you look at the bottom of the model, the length of the nose gear doors and bomb bay takes up most of the bottom of the fuselage....not leaving much structure around to stop it all flopping about!



The fuselage was then assembled over a plan view, inverted, to ensure everything was 100% square and true. More 9mm balsa and cyparis cross members were added to keep the box shape stable.

Around this box, I am now starting to clad the formers which will give the fuselage the correct shape.

These formers are 1/8" liteply with 6x3mm cyparis stringers.....

Your 8" wheels arrived whilst we were away 

Excellent! Thanks...

fantastic build steve........one wouldn't expect anything else from the main man......

A little more progress over the past week......

Nose wheel retract (unitracts) in place and the steering servo fitted and linked up.



The rest of the lower sub formers have been installed and a few basic stringers added...



1/8" balsa sheeting is then applied.





Where it is hard to sheet, I start to plank in 1/4" x 1/8" strips. This is where I am upto this evening....

Lower sheeting is now complete on the Fuselage.....

Started work on the tail surfaces too....

Tailplane:





Fin:

Rudder....

I thought I would try slightly different take on the 'central core' method. This rudder is pretty big and could see some very high loads if used at high speed, not to mention keeping it rigid to help reduce flutter.

Instead of a sheet balsa core, I opted to build one from 1/4" sq balsa and clad the ribs around it.



The hinge will be 2mm carbon rod which I have used on the P-38 and the Libellula with great results. I find the smaller diameter 'snake' outer tube is a nice fit over the carbon rod to act as a guide and bearing.

This snake tubing is glued to the front of the central core with 1/16" packing strips top and bottom.....



Then 1/8" x 1/4" balsa infront of the snake tubing....



The 1/8" balsa ribs are then trimmed to fit over the core...the 'lip' at the front of the ribs creates a mechanical barrier to the hinge tube stopping it from going anywhere! You can also see the 1/16" ply trailing edge.



This rudder is fabric covered, leaving just the front 'balanced' section of the rudder to be sheeted. I did this with 1/16" balsa soaked for an hour in warm water and then sellotaped into place while it dried.



Some block balsa tips and a good rub down produces this.......