1/4 scale electric Bell P39 Airacobra build (designed by Jerry Bates)

[Craig Spence]

[Nick Somerville]

Looks great Craig. Lovely sharp lines

and with the inset Proskin/g10 you have a super durable edge that better emulates an alloy skin.

[Craig Spence]

1 hour ago, Nick Somerville said:

Looks great Craig. Lovely sharp lines

and with the inset Proskin/g10 you have a super durable edge that better emulates an alloy skin.

Thanks very much Nick, I’m trying to figure out how I can make the hinge recesses sharper.

I may cut back the covering and use CA on the edges and sand back but not sure at moment.

 

I’ll see what it looks like once i prime it.

[Craig Spence]

Been at something of a standstill lately whilst still waiting for retracts.
A lot of weekends away and only building during the week has been slow.

Anyway, I’ve decided I’ve gotta get on.
I’ve told the retract manufacturer to not drill mounting holes and he’s given me the dimensions of the nose unit.
I’ve made a template but it’s a very thin drilling area, I had two attempts and I’m happy where I’m at with bolts and t-nuts but always can be better.
Localised reinforcement will be added at a later date.

I’ve done some sheeting on the flank but I have to leave the fairing area until the wings are built.
Added more stringers as well.
I’ve installed the air tank as well which is a good fit.

There’s a lot of thought that has to go into this model as it’s an enclosed fuselage and needs pull throughs for cables everywhere.

A lot of work to get done this year but I’m enjoying the challenge.

Hopefully next week when I’m back from Rome I can get a lot more done.

[Craig Spence]

Not looking pretty yet but I now have the main sheeting complete on the fuz.
I’ll have to wait until I build the wings before I can do the fairings and intakes.

I can and will do the fin, stab fairings and fin trailing edge with G10.

In the coming weeks I’ll have this filled, sanded and then stored so I can start the wings.

Looking forward to getting the retracts and then I can start some other works.

The pen on the model is basically areas I have to fill with thin slithers of balsa which takes a lot of time and I’ll come back to this later.

[Craig Spence]

Started the fin fillet build up with lightweight filler and it’s going ok. By no means perfect though, I intend to get it as close as possible and then pick up the rest in the finishing stages (the idea being to use as little P38 as possible).

Over the time before glassing it will crack but I intend to add finishing resin which will help prevent this until glassed.

I’ve also applied finishing resin to the foam on the fin. This will hopefully stop the shrinking dope eating the foam (yet to see if this works but I’m sure I can sort if something goes wrong).

Plan to cover the fin soon as well as glassing the stab to help form the tail fillets.

Retracts are now due end of august but I suspect I’ll be too busy with the wings by then.

Hopefully get moving on this more in the winter months but just too busy with work, business and flying at the moment.

 

Cheers 

[Craig Spence]

After a long break holidaying I’ve restarted on the project.
Fuselage has had a rough sand and put to the side.
Framed up the wing and sat down for a while whilst I figured out wiring routes, tube mounting etc…

Quite happy so far and can’t wait to get the top sheeting on.

Still waiting on retracts though so can’t sheet the bottom until I have them, what I can do though is make both wings, mount to fuselage and finish the fuz 😃😃

Quite excited about the next phases.

Cheers 

[Craig Spence]

Bit of upper wing sheeting tonight.
The blue lines help me with rib positioning, I’ve changed my method for sheeting which helps it going on straight and quicker.

I use a combination of thick CA and UHU Hart (thick CA for ribs and UHU Hart for joining sheets together). This enables me to position and rub the sheeting down on the ribs, I still pin it for positioning but it’s not required.

I’ve also glued on the G10 flap trailing edge.

Tomorrow I will hopefully get the aileron G10 trailing edge on and another sheet & maybe start the aileron whilst waiting for wood for the leading edge.

[Craig Spence]

Finished sheeting the top of the wing and I then flipped it over to give re enforcement.
There is only shear webbing detailed for one spar on one side but I decided to do shear webbing on the the two central spars on both sides.

After that I put the wing to one side as I need supplies.
I then moved to the aileron which was trickier than I first thought.

The detailed hinge line did not allow for downward movement so I trimmed the hinges and opened up the sheeted hinge openings.
Then, the end of the aileron (outboard) requires the 1/4” strip to bend down to make the profile. This didn’t work so I cut the last bit of sheeting off and built it up with scrap balsa.

Hopefully tomorrow I can pick up supplies and get moving on the interesting stuff (aileron, flap servos and linkages).

[Craig Spence]

Short day building today figuring out the flaps.
The plan calls for a continuous piano hinge but there’s not many places that do a hinge as fine as is required.

I decided to use flat hinges and recessed the trailing edge for them.
Then I drilled out the leading edge of the flap.
As securing them is difficult because it’s so thin I drilled and secured them with 3mm carbon dowel.

Later I will epoxy extra blocks to them for added security.

After all that I’m sure I’ve also save quite a bit of weight, the piano hinges with screws carries a lot of weight.

[Craig Spence]

It’s been a bit slower over the past two days.
Managed to hinge the flap and aileron.

As it’s bottom hinged and sheeting covers the hinges it doesn’t give much meat for the hinge so I’ve had to recess spars, add blocks and key up all hinges.

I’ve also been sanding the topside of the frise aileron to give clearance of the trailing edge when moving. It’s a tricky part of the wing build but now one half has been sussed the next part should go smoothly. 

Still have servos to add, wiring routes and to figure out fixing it to the fuz.

Looking forward to it.

[Craig Spence]

Port wing has now been constructed and top sheeted.

 

Retracts will be on their way soon 😃

[Nigel R]

Nice work. Ailerons and flaps look like quite the challenge to get accurately and firmly attached.

 

[Craig Spence]

1 hour ago, Nigel R said:

Nice work. Ailerons and flaps look like quite the challenge to get accurately and firmly attached.

 

Thanks Nigel, the flaps are ok apart from the hinging it’s the ailerons that are the most work.

 

Once both wings are complete I will have a better idea for line on the trailing edge.

 

Cheers

[Martian]

progressing well Criag it's looking very impressive

[Craig Spence]

1 hour ago, Martian said:

progressing well Criag it's looking very impressive

Thanks very much, I’ve just got to stick with it until the retracts turn up.

then I’ve got a lot of work with fitting, alignment etc..

 

looking forward to it

[Craig Spence]

Getting excited now, spoke to Century Jet and my retracts are now ready and just waiting to get packaged and sent off.

Really can’t wait to get these and install them, it will really help with me getting the wing finished now and once that’s done the fuselage.

[Nick Somerville]

Can you explain  the operation of the retracts and the mounting of them, Craig. Such seemingly small surface area and just one hole on each side of the mounts.  Wings looking great btw.

[Craig Spence]

12 minutes ago, Nick Somerville said:

Can you explain  the operation of the retracts and the mounting of them, Craig. Such seemingly small surface area and just one hole on each side of the mounts.  Wings looking great btw.

Hi Nick, thanks very much.

I won’t have them for a few weeks yet but I’ve been speaking with them on and off throughout the process.

 

As I knew the retracts wouldn’t be here for some time I decided to build the fuz at risk, I couldn’t go by his holes and made a template for my own and sealed it up. So I asked them to supply the nose leg with no mounting holes.

 

The thin rails maybe a problem but I’m sure I’ll be able to sort this.

 

The mains are in question at the moment due to depth of unit, I’ve asked for the dimensions of the unit and I’ll check this soon but it’s the same detail with the mains.

 

I will make best fit with these when they arrive, the supplied mounting plates with the kit will be no good for the retracts in the photos and I’ll make a different one from 1/4” birch ply.

 

Id normally do 1” by 1/2” hard wood rails but weight really is going to be an issue with this plane.

[Craig Spence]

It’s been a long time since I posted on here and that’s mainly because I’ve been massively let down by the retracts manufacturer!

 

I won’t go too in depth but there not fit for purpose and I now stand another long wait to get new ones which has been a massive blow to progress.

 

In the background I’ve partially sheeted the starboard wing and will soon do the port.

This will enable me to joint the wings to the fuz and adjust as required.

 

I can then do the Fuz fairings.

 

ince that’s done I’ll be sending the wings away with plans to my new retract manufacturer who will make retracts that work for me.

 

Onwards & upwards 

[Craig Spence]

I’ve also commissioned fighteraces to make my scale spinner.

looking forward to getting this as I know it will the right quality.

 

[Craig Spence]

Haven’t done any building for quite a while now, work, play & weather all getting in the way 😂
Also have been a bit disheartened by the issues with the retracts.

Anyway, I’ve offered the wings to the fuz today for the first time and there almost bang on for alignment.
Tubes have been tacked in with thick CA for now and I will secure later with epoxy and discs.
I will need to add fillets to the inner wing ribs due to gaps but apart from that it’s all good.

This has set me up nicely for the new year so I can work on the fuz and tail plane whilst I’m having new retracts made from scratch! Again! 😂

Merry Christmas and Happy New Year to all.

[Craig Spence]

First week back at work all I wanted to do this weekend was sleep 😂
Anyway, managed to drag myself into the workshop today and started the port fairing which is and will continue to be a tough one.

The forward and aft parts will be shaped from foam or balsa later, the intakes at the front most likely to be balsa.

In other news as well, I’ve got a gentlemen working on the retracts so hopefully they’ll be updates to come in the coming months.

Hope you all had a good Christmas and new year.

Cheers 

[Craig Spence]

Slow progress but progress all the same.
I thought I’d really take my time on the filets and leading edge intake as there such prominent features for me.

The fillet will be rough sanded to profile and I’ll build up the outboard edge with 1/16th sheeting and filler. It’s very thin towards the end so will have to be strong hence the G10.

The leading edge intake I decided to carve from solid block and still a fair way off.
The idea behind this is I get a solid join at the front and I’ll hollow this out before flying in position.

This is one of my wing joining options (not detailed on plan). I plan to bolt the leading edge of the fuz to leading edge of the wing through the intakes.

They’ll be another bolt position behind the main spar which will be bolted through the wheel well.
This will keep external non scale fixings invisible.

Gonna loose this weekend building as I’ve got plans and also next weekend so it’s working after work every night until I can take some time off to concentrate on this fully.

Cheers all.

[Craig Spence]

Been off the build this week as I had an accident last weekend resulting in a few broken ribs.
Anyway, did a bit today and it’s setting me up for a repeat on the starboard side.

The leading edge intake has had rough fairings added. I then carved out the air intake and hollowed out the inside.

This hollowed out area along with the leading edge of the wing will serve as one of the wing fixing points.

I also had to take fill the area behind the intake, this part is far from finished and is a difficult curve to meet. I think this will be picked up in the glassing stage.

Everything I’ve done to now is to save weight as this plane will be heavy due to the set up in the nose.

Retracts are still an issue I’m trying to resolve but the fuz nose gear should be done in the near future now it’s in the right hands.

Cheers all.