Warbirds Replicas P51 Mustang

[Paul Johnson 4]

[Tim Kearsley]

OK Paul, thank you for that.  Time to produce some balsa dust!

[Nigel R]

If it is a 1/4" solid sheet control I just rest the thing flat near the edge of the building board.

 

Sand with the grain direction. Keep the block positioned right across the control, but pressure on the trailing edge. Flip the control over regularly. Eyeball regularly to make sure you are not sanding in a curve. It pays to mark a centre line along the trailing edge. Keep at it until the TE is about 1/8" thick. I leave my TE square edged.

 

If you do end up with a slight curve it can be removed using heat and/or shrinking of covering.

[Tim Kearsley]

Thanks Nigel.  I totally agree about marking the centre line.  I do this on leading edges and wing-tips too, as a reference. 

[Eric Robson]

I find on sheet  elevators and rudders, if you put it on the edge of the board and sand only one side to a taper then mark the leading edge down the centre and chamfer one side to the centre you finish up with a symmetrical flying surface .  

[Jonathan S]

Look what arrived today... 

[Eric Robson]

After the first flight the retracts pulled out on landing , I have since refitted them with longer screws that go right through the main plate. Today I had no trouble landing full flaps and gentle touch downs all down hill. Only problem I run out of batteries .  

[Gordon McConnell]

Eric, congrats on a really nice version of the P51D. I am planning the same paint scheme. My build has stalled due work and domestic stuff so it is good to see you flying your model. Hopefully will get back to it in the next two weeks or so.
Couple of questions if you don’t mind. Did you have to dial in any roll trim compensation with the flaps?

You mention running out of batteries. What motor and battery do you have and what is the flight time?

Thanks and good luck with the flying.

Gordon

[Jonathan S]

Eric 

Looks amazing. I hope to fly mine this year... 

[Eric Robson]

2 hours ago, Gordon McConnell said:

Eric, congrats on a really nice version of the P51D. I am planning the same paint scheme. My build has stalled due work and domestic stuff so it is good to see you flying your model. Hopefully will get back to it in the next two weeks or so.
Couple of questions if you don’t mind. Did you have to dial in any roll trim compensation with the flaps?

You mention running out of batteries. What motor and battery do you have and what is the flight time?

Thanks and good luck with the flying.

Gordon

Hi Gordon, when I put the flaps down I did not have to put any roll trim in, it was a little fast at the time  when the flaps were deployed as on our field when the wind was blowing from the east you have to come in high over the electric line for the farm supply then drop quite quickly on to the strip. I still fly by the seat of my pants as they say so   I tend not to use the facilities on the modern TX apart from rates and timer, The batteries I use are 4c 4000 and the motor is a Racestar48/50 800kv which I get 5mins flight with. it is over propped with the 4 blade FMS set up, the lower kv motors should do better times. I am going to try a 2 blade prop next time out and see if that improves duration. It flys to fast for scale with this set up and even on half throttle it is fast it is 5.5 lb without the battery which weighs 15.5 oz .

looking forward to seeing yours and  the other builds .

Eric.

[Paul Johnson 4]

Okay as Eric is out in front I needed to finalize my P51B ready to fly.

Back to Basics and lessons learnt as per Eric's Build.

The kit was designed to fly with a 3200mAh battery and the intention was to use the FMS spinner and propeller.

As most were aware the availability of the Spinner was somewhat dubious so to back this up Richard had an Aluminium one made to ensure we could have an alternative.

A varying number of us opted to go for a larger battery capacity, namely a 4000mAh.

This has generated an issue that has shown itself on my model.

It is very nose heavy, this is a new one as most models I have made all have had tail heavy issues.!

The C of G Eric has got and is comfortable with is as he stated at 90mm from the leading edge at the centre line.

The ideal range for this kit is from 98mm to 108mm but as has been proven you can be a little nose heavy and it flies well.

Unfortunately my kit is too nose heavy to achieve this so I have had to modify mine to suit.

The new spinner, backplate, nut adapter and prop spacer are adding to this issue. The total weight of this being 196gm. Please do not add lightning holes to the backplate this will weaken it and add to prop balancing problems.

The larger battery is a further 100 gm.

Method:

In MY case I made a new battery box to make this longer reaching further back towards the cockpit.

 

The servos for the rudder and elevator had to be moved further aft and the snakes shortened to allow room for the extended box and also helped shift some of the weight aft.

I was able to do this as I had fitted the box in place with screws to make it removable, see back in thread for info.

A recess was added  to the former to the rear of the front former 10mm high and at about 45 degrees, mirroring the one on the front former to allow the battery to enter the bay.

A small plate from ply was fitted to fill the hole created from removing this section.

With it all reassembled it was fitted to my balancer and I have set my C of G at 100mm.

This I am happy with.

 

Anyone that has glued the battery box in place there is an easy fix for this should you want to use the heavier spinner and battery.

You can achieve this by creating a small 'Add On' box to extend the original.

Start by removing the rear of the battery box from the inside of the fuselage using a dremel or similar tool.

Next fabricate an add on box to extend this recess.

Glue in using some triangular section balsa to reinforce and support it in place.

 

I have attached a pdf drawing full size of an extension box should anyone wish to use it, feel free to make it longer should you want.

 

Battery box extension.pdf

 

 

[Ron Gray]

Good work there Paul. 

[Trevor]

Hello Paul. Any chance of a pic of where your battery has ended up? The batteries I have to hand are 4s x 5000mah so will be a bit heavier than yours. I’d already decided to make the battery box removable and have left the rear end off in anticipation of having to extend it. I am also considering shortening the cowl a touch but cutting the rear flange off cost me a bit of spilt blood and it’s fitting well at the moment so I’m not sure I want to tackle trimming it again.

 

Trevor

[Paul Johnson 4]

If you go to 5000mAh you'll have to go further back.

I found the standard turnigy batteries are too fat, high, the  nanotechnology ones are thinner and fit ok

[Eric Robson]

I flew mine today with the FMS spinner and blades replaced by a 13 5.6 2 blade prop and no spinner as I did not have one suitable. The  FMS spinner and prop weigh 1/4 lb  the APC  weighs 1oz. the c of g is now 100mm back and despite a very strong wind it performed as well as the 4 blade prop set up. the first landing was when a strong gust came over the strip and it floated on then wind sheer caused it to drop it held straight and level and despite hitting the ground hard the undercarriage took it . there was 34% left in the battery after 5.5 mins flight. the second flight still in very strong wind was good and the landing perfect as I done it when the wind was steady, I did not use flaps at all as the wind was to strong. I need to change the connectors on my watt meter then I can check the motor output. 

Eric. 

Edited April 11, 2021 by Eric Robson
spelling

[Eric Robson]

3 hours ago, Ron Gray said:

Good work there Paul. 

Let down by the uneven spacing of the cable ties.

[Trevor]

Thanks Paul. I’ve already opened up the rear hatch formers to take the fatter batteries so hopefully there will be enough scope for adjustment. I’m feeling a lot better about adding the retractable tailwheel now!

 

Trevor

[Ron Gray]

1 hour ago, Eric Robson said:

Let down by the uneven spacing of the cable ties.

Yes, I spotted that too Eric, becoming a bit of a worrying trend ?

[Paul Johnson 4]

I like to be trendy?

[Graham R]

Just to say thanks to contributors of this thread and good to see p51's starting to maiden.I have enjoyed his thread and I look forward starting mine in the near future after finishing the rebuild of my bf109. It fell and broke the fuz and t/plane having done a nice tail slide when putting it away. An unintentional maiden that's taken a time to fix.

[Paul Johnson 4]

Graham an unintentional maiden will get anyone into trouble....

[Gordon McConnell]

On 10/04/2021 at 23:43, Eric Robson said:

Hi Gordon, when I put the flaps down I did not have to put any roll trim in, it was a little fast at the time  when the flaps were deployed as on our field when the wind was blowing from the east you have to come in high over the electric line for the farm supply then drop quite quickly on to the strip. I still fly by the seat of my pants as they say so   I tend not to use the facilities on the modern TX apart from rates and timer, The batteries I use are 4c 4000 and the motor is a Racestar48/50 800kv which I get 5mins flight with. it is over propped with the 4 blade FMS set up, the lower kv motors should do better times. I am going to try a 2 blade prop next time out and see if that improves duration. It flys to fast for scale with this set up and even on half throttle it is fast it is 5.5 lb without the battery which weighs 15.5 oz .

looking forward to seeing yours and  the other builds .

Eric.

Eric,

Thanks for the information. Encouraging that the flaps deployment does not induce any roll. But then you have made sure the wings are symmetric and the flaps mechanism extends both flaps exactly in sync!! ? I have a 4S 4200 battery and an Overlander 580kv motor, possibly a little bit heavier than your set up. I have the FMS prop and an FWS spinner if needed. I have not had a watt meter on it yet, nor have I got to the stage of weighing the model. Speed is nice but the ability to fly at scale like speed is good too. The obvious secret is to keep as light as possible to lower the wing loading.

Thanks again and happy flying.

 

[Gordon McConnell]

On 11/04/2021 at 12:48, Paul Johnson 4 said:

Okay as Eric is out in front I needed to finalize my P51B ready to fly.

Back to Basics and lessons learnt as per Eric's Build.

The kit was designed to fly with a 3200mAh battery and the intention was to use the FMS spinner and propeller.

As most were aware the availability of the Spinner was somewhat dubious so to back this up Richard had an Aluminium one made to ensure we could have an alternative.

A varying number of us opted to go for a larger battery capacity, namely a 4000mAh.

This has generated an issue that has shown itself on my model.

It is very nose heavy, this is a new one as most models I have made all have had tail heavy issues.!

The C of G Eric has got and is comfortable with is as he stated at 90mm from the leading edge at the centre line.

The ideal range for this kit is from 98mm to 108mm but as has been proven you can be a little nose heavy and it flies well.

Unfortunately my kit is too nose heavy to achieve this so I have had to modify mine to suit.

The new spinner, backplate, nut adapter and prop spacer are adding to this issue. The total weight of this being 196gm. Please do not add lightning holes to the backplate this will weaken it and add to prop balancing problems.

The larger battery is a further 100 gm.

Method:

In MY case I made a new battery box to make this longer reaching further back towards the cockpit.

 

The servos for the rudder and elevator had to be moved further aft and the snakes shortened to allow room for the extended box and also helped shift some of the weight aft.

I was able to do this as I had fitted the box in place with screws to make it removable, see back in thread for info.

A recess was added  to the former to the rear of the front former 10mm high and at about 45 degrees, mirroring the one on the front former to allow the battery to enter the bay.

A small plate from ply was fitted to fill the hole created from removing this section.

With it all reassembled it was fitted to my balancer and I have set my C of G at 100mm.

This I am happy with.

 

Anyone that has glued the battery box in place there is an easy fix for this should you want to use the heavier spinner and battery.

You can achieve this by creating a small 'Add On' box to extend the original.

Start by removing the rear of the battery box from the inside of the fuselage using a dremel or similar tool.

Next fabricate an add on box to extend this recess.

Glue in using some triangular section balsa to reinforce and support it in place.

 

I have attached a pdf drawing full size of an extension box should anyone wish to use it, feel free to make it longer should you want.

 

Battery box extension.pdf 1.44 kB · 11 downloads

 

 

Paul,

Great past on the CG position and your mods to manage it. Not at that stage yet so no worries now that you have defined the changes to bring the CG further back. 

Thanks for all your very helpful inputs, including the cable ties!

Gordon

[Gordon McConnell]

Just now, Gordon McConnell said:

Paul,

Great past on the CG position and your mods to manage it. Not at that stage yet so no worries now that you have defined the changes to bring the CG further back. 

Thanks for all your very helpful inputs, including the cable ties!

Gordon

Should be .....post.....not past!

[Jonathan S]

Guys another question.  The front of the wing the plate that the dowels goes into, is that attached to the leading edge or attached instead of the leading edge.  I cannot make out from Paul's photos how this part sits. 

 

Thanks 

Jon