Warbirds Replicas P51 Mustang

[Jonathan S]

Everybody thanks for the advise.  I might go with 2 servos.  

Paul did I see you mentioned you had documented how to reverse a servo could you point me to it? 

Thx

Jon

[Paul Johnson 4]

????

[Tim Kearsley]

Jonathan, can't you reverse servo direction in your Tx?  You'd generally only need to reverse a servo direction in the servo itself if you're using a Y lead; if you use a channel per servo you just reverse it at the Tx.

[Jonathan S]

I can but going with 6 channel receiver and will not have enough channels. 

 

 

[Tim Kearsley]

Ah, got you.  Yes, you need a servo reverser or to mod a servo then.  I'm using an 8 channel Rx so just have enough channels! 

[Paul Johnson 4]

Just for you Jonathan Link

[RICHARD WILLS]

Servo reverser is available on Amazon Prime ,£6.99 .    Plugs straight in .

[Tim Kearsley]

Fellow builders, one more question:  What happens around the tailplane area, specifically directly behind where the tailplane sits, as per the photo?  Do you just add a piece of 1/4 inch balsa to fit the top of the fuselage or is it wider to fit in the gap between the elevator halves?

[Paul Johnson 4]

Add a piece Tim, same as sides.

Edited September 19, 2021 by Paul Johnson 4

[Tim Kearsley]

Thank you Paul.  This build is a great learning exercise for me.

[Paul Johnson 4]

Your welcome ?

[RICHARD WILLS]

I wish I'd seen this build thread before I'd started mine . 

[Paul Johnson 4]

What worries me is that you 'started' yours and then moved to another county to get some distance from it...?? I heard Glynn muttering "what am I going to do with it?"

[Glynn]

Glynn is still muttering, and it's still on the shelf.

[Gordon McConnell]

Trevor and Tim,

 

Thanks for the advice on lengthening the flap control arm and also ensuring the servo travel is as far forward as possible when the flaps are retracted. After some experimentation with the servo travel settings in my Graupner MX-16 transmitter, I have more or less eliminated the humming activity on the servos at the extremes of flap travel.

 

One disadvantage is that the full flap angel is a bit reduced, not measured yet but looking like 45 deg. However, I think this will be plenty of flap for landing at least until I get to understand the trim change with flap. 

 

Trevor, I will investigate the ability to set a non-linear profile on the flap control. I am using a rotary control to signal the flaps. I have adjusted the neutral servo position to correspond to around 10- 15 deg flap when the rotary control is around the mid point detent. The idea being to use this setting for take-off. Full rotation on the control knob gives max flap angle. So maybe I have found another way to have a non-linear response. Are you using a 3 position switch or a rotary control on your Frsky tramsmitter?

 

Picture shows the servo arm position with flaps fully up.

 

Gordon

 

 

[Gordon McConnell]

Sorry, Got my Tims and Trevors mixed up. Obviously, the first signs...........

Thanks to both of you for the advice and to the others as well.

 

Gordon

[Trevor]

Glad you’ve got it more or less sorted. You can wind the servo travel up to 110 or 120% if you need a bit more throw on the flaps. It’s Tim who mentioned FRSky. I have a Jeti radio but yes, I use a three position switch for flaps.

[Tim Kearsley]

Yes, I too use a three-position switch for flaps Gordon.   Using a curve on each flap channel makes it child's play to synchronise the end and mid points of the travel for each flap.  I slow the flap movement down also, so that flap up to fully down takes a couple of seconds.  Looks better and is kinder to the hinges etc!

[Jonathan S]

All,

Thanks for all you help so far, I am cracking on slowly.  I did some covering of flaps and all went well some last min fettling to ensure they open and close well. 

 

So next major job is fitting the battery box and cowel. 

The questions I have are:

1. What is the distance between cowl and spinner back plate?

2. Is there any angle built in or have I not build straight? 

3. What's the best way to attach the battery box and what does it glue attach to to hold it in place? 

 

Thanks 

Jon

[Paul Johnson 4]

Jonathan,

Before you add the motor mount/battery box you need to make sure you can get the correct C of G as she is naturally nose heavy. I added a drawing in the topic further back of an extended battery box (make from Birch ply NOT lite ply) to allow you to move the battery further aft. Please go back and read this as otherwise if you use the standard box you may have to add tail weight to achieve the correct C of G. This isn't the end of the world if you have already glued the original in  but it is better not to have to add unnecessary weight.  

 

Edited September 22, 2021 by Paul Johnson 4

[Jonathan S]

Paul,

Thank you as ever for your rapid response. Excuse the basic questions as normal. 

•  I have made a battery box extension (badly) out of ply not sure if lite or birch.
  • Should I ensure it is made from Birch?
  • not sure how your battery box joined to the original box I was thinking of gluing it in place and putting some sheet to connect the two? 
• I have also looked where you have marked your batteries to judge where I might need to put mine as a starter for 10 and thus where the battery box extension might need to go. 
• I don't have a CoG balance so I am currently 3D printing one which should be ready after a visit to B&Q for some threaded rods.

I think maybe I will leave this until the end, my only issue is I might need to locate the ESC below the battery box as mine is too big to go in the nose. Which means I might need to review how I do this and still fix and shape the bottom part below the nose box., but I can have a think tonight. 

 

 

 

 

[Tim Kearsley]

I made the decision (which I think now was a wrong one) to cover my P51 in heat-shrink film.  Given that the wing is completely covered it's a bit late to change that decision!  Would I still be able to use the black/white marker pen technique for panel lines do you think or is film not a suitable surface?  Yet another lesson learned! 

[Paul Johnson 4]

Tim are you referring to the clear film single sided? Shiney or matt?

If shiney, it will still work, very lightly abraid the surface with scotch bright, then undercoat/prime, if matt straight to the prime.

[Paul Johnson 4]

The markers are used on the top coat.

[Paul Johnson 4]

If you are not happy to continue with the film it does come off.... but takes some work and patience.