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

[Eric Robson]

It will have a similar effect as the stepped elevators on a lot of WW2 aircraft, as the surface is moved up or down the air flow will assist the pilot as it moves into the airstream

 

Typed at the same time as Craig's reply

Edited May 17, 2022 by Eric Robson

[Craig Spence]

20 minutes ago, Eric Robson said:

It will have a similar effect as the stepped elevators on a lot of WW2 aircraft, as the surface is moved up or down the air flow will assist the pilot as it moves into the airstream

 

Typed at the same time as Craig's reply

That’s how I read it Eric ?

Unusual build but very different I think ?

[Danny Fenton]

Ailerons I can understand Craig, as you are trying to introduce an element of drag and cause yaw on the upgoing aileron. Thus balancing the turn with minimal rudder.

 

Elevator and rudder are a different kettle of fish. The offset hinge is to make the moment arm shorter and therefore the forces lighter. However the leading edge of the surface, (unlike an aileron) should not introduce drag and protrude into the airflow.

 

Here is the elevator of my P-51 as an example.

 

 

 

Ignore the counterbalance weight towards the tip.

 

I would ignore the funny stuff the modern 3D capable aircraft get up to

 

Perhaps others would like to comment, I am no expert and bow to smarter peeps than me.

 

Cheers

Danny

 

[Craig Spence]

3 minutes ago, Danny Fenton said:

Ailerons I can understand Craig, as you are trying to introduce an element of drag and cause yaw on the upgoing aileron. Thus balancing the turn with minimal rudder.

 

Elevator and rudder are a different kettle of fish. The offset hinge is to make the moment arm shorter and therefore the forces lighter. However the leading edge of the surface, (unlike an aileron) should not introduce drag and protrude into the airflow.

 

Here is the elevator of my P-51 as an example.

 

 

 

Ignore the counterbalance weight towards the tip.

 

I would ignore the funny stuff the modern 3D capable aircraft get up to

 

Perhaps others would like to comment, I am no expert and bow to smarter peeps than me.

 

Cheers

Danny

 

Mate, it’s not a question what 3D pilots do or any otter pilot does. It’s scale and designed for a purpose as stated in the article I posted.

 

It’s not for yaw like a fris’ ailerons (not sure that’s the right spelling though ?).

 

It was designed like that on the full scale planes to reduce the amount of force a pilot had to put into the stick for the manoeuvres.

 

The exposed edge got caught by air which made pulling the full surface easier in a nut shell.

 

Since most planes are hydraulic, electric or pneumatic now or all 3 (A10) there’s no requirement for that design any more.

Hence why you only see it on some warbirds.

It is as the real one was built for the reasons detailed in the article ?

[Ron Gray]

These shots may (or may not!) help.

 

Full size tail, shot from beneath

 

 

From above (different 'plane)

 

 

 

[Craig Spence]

11 minutes ago, Ron Gray said:

These shots may (or may not!) help.

 

Full size tail, shot from beneath

 

 

From above (different 'plane)

 

 

 

Thanks Ron, it does help a great deal and much appreciated ??

The hinge points are bang on as plan and the leading edge does go above the trailing edge of the stab.

 

I have a trailing edge to add yet which will help (although only 1/8th”).

I won’t have a great deal of movement on the elevators so they won’t be much above like on the video.

 

I may however put more of a chamfer on the leading edge of the elevators but only once I have the trailing edge complete on the stab and it’s in situ on the plane.

 

I don’t suppose you have anymore photos?

The only one that was in the UK got shipped off a couple of years ago.

[Craig Spence]

Tonight’s work, just added ribs to one stab and also sheeted the other stab.

I think I should have the tail plane 80% complete by the end of this week.

[Ron Gray]

Here you go:

 

https://www.ipms.nl/walkarounds/walkaround-vliegtuigen-props/2013-walkaround-p39-cobra

 

https://inchhighguy.wordpress.com/2021/08/15/bell-p-39-airacobra-walk-around/

https://www.net-maquettes.com/pictures/bell-p-39n-airacobra/

http://www.primeportal.net/hangar/scott_dimmick/p-39q/

https://www.cybermodeler.com/aircraft/p-39/p-39_walk.shtml

 

Edited May 18, 2022 by Ron Gray

[Craig Spence]

20 minutes ago, Ron Gray said:

Here you go:

 

https://www.ipms.nl/walkarounds/walkaround-vliegtuigen-props/2013-walkaround-p39-cobra

 

https://inchhighguy.wordpress.com/2021/08/15/bell-p-39-airacobra-walk-around/

https://www.net-maquettes.com/pictures/bell-p-39n-airacobra/

http://www.primeportal.net/hangar/scott_dimmick/p-39q/

https://www.cybermodeler.com/aircraft/p-39/p-39_walk.shtml

 

Thanks Ron, I have some of these already ?

I was hoping you did a walk around 

 

thanks again

[Ron Gray]

54 minutes ago, Craig Spence said:

I was hoping you did a walk around

Nah, only the walk I did was through Google!

[Piers Bowlan]

The Aerocobra has aerodynamically balanced control surfaces to reduce control loads. The p39 is unusual in that they extend the full width of the elevators whereas it is generally more usual to involve part of the control surface, notably the top section of the rudder of aircraft with unpowered controls (generally light aircraft and warbirds). An alternative solution to reduce aerodynamic control loads is a balance tab. Incidentally, an ‘anti-servo tab’ has the opposite effect and fitted to an all flying tailplane to increase loads. Aircraft with powered controls don’t usually have aerodynamically balanced controls.

As Craig said earlier, frise ailerons produce drag on the down-going aileron to help counteract adverse yaw.

 

Awesome model build, following with interest ?

Edited May 18, 2022 by Piers Bowlan

[Piers Bowlan]

Should have been ‘ increase drag on upgoing aileron to increase drag’ Opps ?

[Craig Spence]

1 hour ago, Piers Bowlan said:

The Aerocobra has aerodynamically balanced control surfaces to reduce control loads. The p39 is unusual in that they extend the full width of the elevators whereas it is generally more usual to involve part of the control surface, notably the top section of the rudder of aircraft with unpowered controls (generally light aircraft and warbirds). An alternative solution to reduce aerodynamic control loads is a balance tab. Incidentally, an ‘anti-servo tab’ has the opposite effect and fitted to an all flying tailplane to increase loads. Aircraft with powered controls don’t usually have aerodynamically balanced controls.

As Craig said earlier, frise ailerons produce drag on the down-going aileron to help counteract adverse yaw.

 

Awesome model build, following with interest ?

Thanks very much, greatly appreciated ?

[Craig Spence]

Fitted both stabiliser half’s and screwed in place. 
They’ve taken really well and the alignment with the fin looks bang on so happy with that.

Over the weekend I should be able to fit both elevators and give it dry run to see if movements are ok.

Then I’ve gotta figure out control horn fixing, I’ll probably use G10 and epoxy in place.

[Craig Spence]

Last night I decided to glue the hinges into the stab.
One of them unfortunately pulled slightly off center but apart from aesthetic it works superbly. The plan for that one is to sand to suit.

Also functioned both dry and they worked well with the fuselage hinge in. 

All that’s left to do with these is a trailing edge, trim tab, glass and covering - said very quick but will of course take time.

Have a great bank holiday weekend everyone ??

[Martian]

Looking very impressive 

[Craig Spence]

21 minutes ago, Martian said:

Looking very impressive 

Thanks Martian ?

[Nick Somerville]

Looking good. It’s always a relief to complete any close fitting scale hinged control surfaces and have free full movement. Having a removable pin is a real bonus too.

[Craig Spence]

42 minutes ago, Nick Somerville said:

Looking good. It’s always a relief to complete any close fitting scale hinged control surfaces and have free full movement. Having a removable pin is a real bonus too.

Thanks Nick and your right, it’s very satisfying as well.

I think the planned hinge system is great, JB has done a great job designing this.

[Craig Spence]

Not much done over the weekend due to celebrating too much and having fun.
Now I’m back at work I may get some work done ?

Made up some control horns for the elevators and epoxied in place, should be able to finish off and cover the elevators this week.

The rudder will have to wait until I flip the fuz again in future but that all depends on when the retracts arrive.

Have a good week everyone ?

[Craig Spence]

Elevator tab and 1 coat sand & sealer done tonight.
Cut out some lightening holes as well.
Also trial fitted the linkage to the elevator and it all works well ?

Looking forward to covering these in the coming days with nylon and dope. Waiting for pinking strips and other bits so should have near completed elevators by end of the week and maybe/ hopefully nearly done on the stab.

Edited June 6, 2022 by Craig Spence

[Craig Spence]

Elevator tab and 1 coat sand & sealer done tonight.
Cut out some lightening holes as well.
Also trial fitted the linkage to the elevator and it all works well ?

Looking forward to covering these in the coming days with nylon and dope. Waiting for pinking strips and other bits so should have near completed elevators by end of the week and maybe/ hopefully nearly done on the stab.

Edited June 6, 2022 by Craig Spence

[Craig Spence]

First attempt at nylon & dope tonight & it all seems well so far (I’ve done tissue and dope but the method is different to what I did).
Got some tips off a good friend which has massively helped.

Tomorrow I’ll do the other sides & then wait for pinking tapes.

[Craig Spence]

I don’t normally finish parts until the constructions done but I’m still waiting on retracts so why not.
Rib stitching applied and rib tapes stick on, I only hope when it’s painted that this will show as at present it’s too subtle.

Anyway, I’ve got another to finish and then off to bed.

Hope your all having a good weekend ??

[Craig Spence]

One G10 trailing edge glued on today as a trial fit which has went quite well
I should get the rest on quite soon I think.