Boeing Vertol BV234 Chinook G-BISP

[Jamie @ Sovereign Hobbies]

Whilst the Scottish National Scale Model Show we're just back from was bad use of our time in a business sense, I can find a positive slant on it if I consider that we paid £200 to find out that the public seemed to quite like my little motorised aeroplane and helicopter. The moving parts seemed to catch peoples' eyes from some distance and they'd come over to look and talk about it.

 

 

 

Notwithstanding that I have no real idea where I may go that would allow anyone to see it, I have decided I'd like to pluck the Revell 1/48 Chinook that I bought in Devon with my then fiancee (we've been married 17 years now) out of the stash and build it as one of British Airways Helicopters' BV234s which I still have some childhood memories of. I did ask my dad @skyscooter if he had a favourite out of the fleet, and the response was that G-BISP and G-BISR were the best ones. From an engineering point of view, I interpret that to mean those two worked fairly well more than the rest of them did.

 

 

I'm consciously avoiding G-BWFC which was a bad time for dad, although by way of showing it's a small world indeed, @Duncan B is friends with the captain who survived the fairly horrific crash's son.

 

What the show at Perth did demonstrate was that the HH-3E and HC-130P models aren't actually very good. They were unreliable over the weekend and needed a fairly bit of impromtu repair. I told various people that I hadn't really thought them through properly and failed to make sufficient effort because I honestly wasn't confident it was all going to work.

 

In the interests of not repeating avoidable mistakes, this time I'm trying to be a bit more methodical and plan out the whirly bits.

 

I've started by attempting a scale drawing of the Chinook HC1 as kitted, from which I will adapt. I have a Cricut Maker which does cut plasticard well, so will cut new fuselage side inserts with the cabin windows using that in due course.

 

 

Next I studied various photographs of the BV-234 and marked up the differences. There are more detail differences yet to capture, but for now I'm concentrating on big chunks of plastic in need of carving up.

 

 

Which upon removing the original layer leaves me with something close to a BV 234 civil Chinook. I had some discussion with dad about the differences, and the relocated undercarriage was a new one, despite him knowing the civil machines literally inside out. It seems the MH-47E which first flew in 1991 is pretty much a BV 234 with military gadgets added and indeed it looks very similar in most respects except the cabin windows. The wheels are in a different place on the MH-47E compared to the CH-47A/D too, I discovered just today.

 

 

As the Chinook has counter rotating and intermeshing rotors, just having two motors won't be good enough for this. They need to be properly geared together, so I've spent a bit of time on RS Components' website choosing mitre gears, spur gears and ball bearings to suit the required purpose. I've ordered a 300rpm geared motor from eBay, but can't confirm the precise dimensions until it arrives. It'll fit inside though - there's plenty space. The transmission will be 3mm diameter steel shafts. I will design a cradle structure to hold the ball bearings in place, and plan to insert the whole thing in through the floor. I won't use most of the Revell interior hence - the BV 234 was completely different inside anyhow and the small windows won't permit much viewing of the interior.

 

I have two options for the drive layout, and will probably go for Option B as it's simpler and cheaper, needing 2 fewer spur gears and 2 fewer ball bearings. It took me until I saw Option A to realise I could just flip round one of the mitre gears and still achieve the correct rotational direction on each rotor mast.

 

Option A

 

Option B

 

I'll sleep on this and will try to order the gears and bearings tomorrow

 

Power will be external again. I have superimposed D cell batteries on the above layout and they're both too tight and will probably squash the undercarriage.

 

Thanks for reading.

 

 

[dnl42]

This looks interesting! 

 

An Arduino would do a fabulous job of spinning the rotors and running the lights.

[Jamie @ Sovereign Hobbies]

2 minutes ago, dnl42 said:

This looks interesting! 

 

An Arduino would do a fabulous job of spinning the rotors and running the lights.

 

I like the idea but fear I would require a LOT of "community support" on that. I'd find myself out of my depth opening the packaging!

[Jinxman]

Popcorn opened for this one, watching with interest...

[Ryan Hothersall]

I understand these are ex British Airways machines. 
 

N237CH. 

 

N238CH. 

 

These were passing through Adelaide, South Australia in preparation to be loaded into a container ship at Port Adelaide. 

[Duncan B]

This should be good.

 

Duncan B

[Jamie @ Sovereign Hobbies]

Continuing with thoughts and planning before cutting plastic, I've laid out roughly where the internal crutch would need to go and roughly what it would look like.

 

 

This is sufficient for me to start taking some internal measurements of the fuselage halves, especially at pinch points e.g. the rotor pylons and just check everything is going to fit. With Option B here, which right now is my favourite, I want to confirm that the green spur gear and ball bearing at the aft end will fit in the pylon. I could possibly extend the red shaft and aft purple shaft to lower those green components down in the fuselage 10mm, but it's best to make an informed decision using measurements!

[Jamie @ Sovereign Hobbies]

I've only actually flown in RAF Chinooks (that I can remember anyway - I certainly flew in BAH/BIH S-61Ns once or twice) but the noise inside will be familiar to everyone who's been in one I'm sure!

 

 

 

9 minutes ago, Ryan Hothersall said:

I understand these are ex British Airways machines. 
 

N237CH. 

 

 

N238CH. 

 

 

These were passing through Adelaide, South Australia in preparation to be loaded into a container ship at Port Adelaide. 

 

I understand they are ex G-BISR and G-BISN respectively  I haven't seen a 234 in a LONG time here!

[Jamie @ Sovereign Hobbies]

I've got my first plastic bits out of the box. The fuselage halves are bowed and will need some Basic Modelling Skills^(TM) applied to join them, but that's down the line. Right now, tape is good enough.

 

 

This thinking ahead thing is paying off.

 

 

Option B as it currently stands doesn't fit. The internal width at the location of the aft spur gear and ballbearing is 12.5mm, but the width of the spinny bits plus structure to hold them (remember I want to avoid just smooshing working parts into gaps and ending up with wobbly rotors like the HH-3E did ) will be approximately 14mm. It could be narrowed slightly, but this will still be Oh So Close, and I don't want any foul-ups.

 

 

The options are either:

1) Revert to Option A with two idler shafts, moving the green shaft ball bearing and mitre gear forward and slightly downwards away from this pinch point in the pylon, or;

2) Lower the whole power train down into the fuselage and extend the forward idler (red) shaft and aft purple shaft.

 

Of these, I'm currently leaning towards Option A, but I'll do some more digital scribbling. I haven't ordered the bits yet pending this.

[Jochen Barett]

Interesting concept with the slanted central drive shaft. If you were German, you'd have to do it with a horizontal central drive shaft and CV joints or double Cardan joints.

The other valid German option would be two motors synchronized via a fiber optic cable and (at least!) two Arduinos, RPM controlled via a quartz stabilized circuit.

 

Anyway, option A may be simpler because it is a symetrical solution even though it has more parts than option B. About how much money (difference between A and B ) are we talking when talking about bearings, shafts, and gears?

Edited May 18, 2022 by Jochen Barett
B and ) produce an unintended emoji if not seperated by a blank

[Jamie @ Sovereign Hobbies]

51 minutes ago, Jochen Barett said:

Interesting concept with the slanted central drive shaft. If you were German, you'd have to do it with a horizontal central drive shaft and CV joints or double Cardan joints.

The other valid German option would be two motors synchronized via a fiber optic cable and (at least!) two Arduinos, RPM controlled via a quartz stabilized circuit.

 

Anyway, option A may be simpler because it is a symetrical solution even though it has more parts than option B. About how much money (difference between A and B ) are we talking when talking about bearings, shafts, and gears?

 

Most of the controller stuff is way beyond my clanky brain sadly! If I could 3D model and 3D print, the best solution, I think, would be to print new bevel gears with the correct angles which is how the real thing does it. I can't do either of those things though so unless someone is about to volunteer I'm stuck with using 90 deg commercially available items.   I would honestly rather have that shaft horizontal running along the cabin roof but everything is a compromise in the end!

 

Your question about cost is a good one though. The difference is about £4, since the spur gears come in a pack of 5 anyway and it's only 2 ball bearings which are different. That said, the act of laying this all out did cause me to change my shopping list last night when I realised I had simply chosen components which were not compatible with one another!

 

I spent lunchtime making adjustments:

 

Option A has been tweaked slightly to line up bearings and remove the need for one additional mounting plate. Hardly transformational, but a small optimisation.

 

 

Whilst Option B with some changes looks like it would now work. Everything still fits that used to fit, and the thing which didn't fit now does fit. Bringing the widest spinny-roundy bits forward a smidgeon opens the internal width of the rear pylon out to 14.7mm which allows either of these options to work.

 

 

[Jochen Barett]

51 minutes ago, Jamie @ Sovereign Hobbies said:

 

Most of the controller stuff is way beyond my clanky brain sadly! If I could 3D model and 3D print, the best solution, I think, would be to print new bevel gears with the correct angles which is how the real thing does it. I can't do either of those things though so unless someone is about to volunteer I'm stuck with using 90 deg commercially available items.   I would honestly rather have that shaft horizontal running along the cabin roof but everything is a compromise in the end!

+++

Forget about two motors and controller. Even an expert will produce chopped or at least tangled rotor blades every now and then.

 

A 3D printed miter gear would probably suffer from suboptimum gear tooth surfaces, but considering the rpm (low) and the torque (low) involved you may get away with a 90° miter gear used at 80° and/or 100° for quite some time. Maybe worth a try on some sort of mockup. On the other hand I bet somebody already 3D printed a miniature CV joint.

[dnl42]

One Arduino should be sufficient Here's one suggested board that has two stepper ports, four RC servo ports, and other devices. It's a 30mm square board. Other choices are also available

You can keep 2 stepper motors synchronized, but they don't have the smoothest motion. A NEMA-8 stepper is about 20mm square by 33mm long with a 4mm shaft. A pair could indeed make the mechanics relatively simple.

Amazon.com (but not .co.uk?) have these universals with 3mm bores. Back in the day I would use rubber or plastic tubing as a low-torque universal joint for RC boats, but they age and inevitably fail.

[Jamie @ Sovereign Hobbies]

20 minutes ago, Jochen Barett said:

Forget about two motors and controller. Even an expert will produce chopped or at least tangled rotor blades every now and then.

 

A 3D printed miter gear would probably suffer from suboptimum gear tooth surfaces, but considering the rpm (low) and the torque (low) involved you may get away with a 90° miter gear used at 80° and/or 100° for quite some time. Maybe worth a try on some sort of mockup. On the other hand I bet somebody already 3D printed a miniature CV joint.

 

I'll do the mock-up. It won't take long to do and should give indicative results pretty quickly. Thanks!

 

15 minutes ago, dnl42 said:

One Arduino should be sufficient Here's one suggested board that has two stepper ports, four RC servo ports, and other devices. It's a 30mm square board. Other choices are also available

You can keep 2 stepper motors synchronized, but they don't have the smoothest motion. A NEMA-8 stepper is about 20mm square by 33mm long with a 4mm shaft. A pair could indeed make the mechanics relatively simple.

Amazon.com (but not .co.uk?) have these universals with 3mm bores. Back in the day I would use rubber or plastic tubing as a low-torque universal joint for RC boats, but they age and inevitably fail.

 

Hmm. This stuff is all new to me and whilst it does look clever, it's also a rather expensive solution to a fairly simple problem going by those prices. There's no learning curve at all nor any special skills needed for a handful of plastic gears and cheap ball bearings  No issues with lumpy motors either for that matter. The size of those stepper motors would mean they couldn't be located where they needed to be, so the majority of the the gears and shafts would still be needed - only without the mechanical certainty of the big shaft down the middle guaranteeing the rotors remain synchronised under all circumstances.

 

Now if there's some small gadget that can be fed a sound sample and play it, I'm all ears. No pun intended!

[Jamie @ Sovereign Hobbies]

I've ordered the parts now, so there is a (hopefully short!) wait whilst they are posted to me. In the mean time, I plan to start designing the new fuselage sides and saddle tanks to modify the kit.

[Jamie @ Sovereign Hobbies]

Before committing to plastic, I'm trying paper print-outs of planned inserts to check how they fit and to convince myself that my planned cut lines make some sense!

 

[perdu]

This jumped to the top of my watch list Jamie

 

Fabulous idea

[Jamie @ Sovereign Hobbies]

18 minutes ago, perdu said:

This jumped to the top of my watch list Jamie

 

Fabulous idea

 

Thank you Bill. I'll make an effort to maintain some sort of pace with this one.

 

In the mean time, I've noticed another mistake. The large light green spur gear is too large to fit in the fuselage there. It's a reminder to think in 3D rather that 2D!

 

 

The solution is to lower the green shaft in the fuselage so that spur gear doesn't extend above the cabin roof (as the gear is wider than the inside of the pylon). This effectively means the green shaft, motor and so on are the same in Option A and B. The only difference therefore is Option A has one extra shaft. There may be 2 spare ball bearings coming in the above order - which isn't the end of the world.

 

 

[hendie]

I'm right behind Bill at the bar waiting for him to get the beers in.  Great project and some nice interesting challenges.

 

Not wishing to complicate matters (and you've already forked out some moolah) but have you considered belt drives? By using one central motor driving timing pulleys, you could eliminate the 90 degree gearing and using toothed drive belts  would also synchronise the rotors.  I had a quick look on the web and the pulleys are only 3 or 4 bucks each.

I'm not near my CAD machine just now but could sketch it out for you if my wild ramblings above don't make any sense

 

 

*edit*  just remembered the Chinook has counter rotating blades so it's not as simple a problem as I first blabbed about. One side would have to be a cross belt drive to achieve the counter rotation.

[jackroadkill]

Nice one, Jamie.  I shall watch with interest.

[Back in the Saddle]

This looks good!

 

Low tech would be my preferred option - keep it simple. Good to see somebody else using paper cutouts at the design stage too!😁

[dnl42]

This is all very interesting! 

 

I suppose 2 shafts are needed forward so you can avoid intruding into the cockpit? Could you get rid of the 2nd shaft back aft by moving the bevel gear aft of the vertical shaft? You'd need a thrust bearing in that case.

 

 

[k5054nz]

I'm very, very excited about this!

[perdu]

8 hours ago, hendie said:

I'm right behind Bill at the bar waiting for him to get the beers in.  Great project and some nice interesting challenges.

 

Not wishing to complicate matters (and you've already forked out some moolah) but have you considered belt drives? By using one central motor driving timing pulleys, you could eliminate the 90 degree gearing and using toothed drive belts  would also synchronise the rotors.  I had a quick look on the web and the pulleys are only 3 or 4 bucks each.

I'm not near my CAD machine just now but could sketch it out for you if my wild ramblings above don't make any sense

 

 

*edit*  just remembered the Chinook has counter rotating blades so it's not as simple a problem as I first blabbed about. One side would have to be a cross belt drive to achieve the counter rotation.

I am in favour of the Shropshire brews these days, Pete might advise but they do have Kinver in if that's to your taste or there is always Hell a fine German brew since 1308, nod when you are ready.

 

Jamie will need a preferably printed chassis for the rotor gear, I'm sure something can be cobbled up for it.

 

I'm sure angled drive off a horizontal shaft is the way ahead.

 

I have been giving head space to it since Jamie announced it to us.

 

Started thinking of it up in the ceiling but of course there is a better chance for it if its anchored at floor level if we can get the drive up into the pylon easily.

 

Thinking...

[Jamie @ Sovereign Hobbies]

10 hours ago, hendie said:

I'm right behind Bill at the bar waiting for him to get the beers in.  Great project and some nice interesting challenges.

 

Not wishing to complicate matters (and you've already forked out some moolah) but have you considered belt drives? By using one central motor driving timing pulleys, you could eliminate the 90 degree gearing and using toothed drive belts  would also synchronise the rotors.  I had a quick look on the web and the pulleys are only 3 or 4 bucks each.

I'm not near my CAD machine just now but could sketch it out for you if my wild ramblings above don't make any sense

 

 

*edit*  just remembered the Chinook has counter rotating blades so it's not as simple a problem as I first blabbed about. One side would have to be a cross belt drive to achieve the counter rotation.

 

Hi, I did think of a belt which is common for tail rotor drives in RC helicopters, but I chickened out as belt length and tension becomes important and there's still the issue of the forward tilted rotor heads and the need to drive the forward rotormast which sits above the cockpit, so I'd still need that red idler shaft in there to get the power "upstairs" without encroaching into the cockpit which would be pretty noticeable I think 😕

 

9 hours ago, jackroadkill said:

Nice one, Jamie.  I shall watch with interest.

 

Thank you! I hope I don't disappoint!

 

9 hours ago, Back in the Saddle said:

This looks good!

 

Low tech would be my preferred option - keep it simple. Good to see somebody else using paper cutouts at the design stage too!😁

 

Thanks! I am attracted to predictable solutions, and my hope is that this one looks more elaborate than it really is, because I'll put more effort into the external bodywork of this one than I did on the resin HH-3E on the assumption that this one is going to work  

 

8 hours ago, dnl42 said:

This is all very interesting! 

 

I suppose 2 shafts are needed forward so you can avoid intruding into the cockpit? Could you get rid of the 2nd shaft back aft by moving the bevel gear aft of the vertical shaft? You'd need a thrust bearing in that case.

 

 

 

Exactly, it's because without that red idler shaft the forward shaft would be between the pilots' seats. As for the shaft at the back, yes I believe we can - that's basically the "Option B" that I didn't think of until after I'd drawn the retrospectively named "Option A"  I will need to relocate that ballbearing to aft of the gear though to pick up the thrust load on the shaft. I'll make a note to do that now actually...

 

7 hours ago, k5054nz said:

I'm very, very excited about this!

 

Thanks! As above, I hope I don't disappoint!

 

1 hour ago, perdu said:

I am in favour of the Shropshire brews these days, Pete might advise but they do have Kinver in if that's to your taste or there is always Hell a fine German brew since 1308, nod when you are ready.

 

Jamie will need a preferably printed chassis for the rotor gear, I'm sure something can be cobbled up for it.

 

I'm sure angled drive off a horizontal shaft is the way ahead.

 

I have been giving head space to it since Jamie announced it to us.

 

Started thinking of it up in the ceiling but of course there is a better chance for it if its anchored at floor level if we can get the drive up into the pylon easily.

 

Thinking...

 

Hi Bill, I'm not much into breaking new ground so I'm effectively copying the real one with the horizontal shaft. My only real "even better if" (mein gott, I sound very corporate - I wish my mortgage was paid off so I could get a proper job and stop playing BS Bingo for a living!) would be to have custom made bevel gears with the right pressure angles. My dad remembers the aft rotor mast being tilted 1.5 degrees forward compared to the datum line and the forward mast being tilted 5 degrees forward. Custom gears would allow me to have the shaft horizontal along the cabin roof and be able to put some seats inside like wot scale modellers are supposed to do. The best I can do with commercial gears is to tilt the horizontal shaft to minimise the angular difference between the not-horizontal shaft and the not-vertical shafts to the point the gears won't really notice.