Warbirds Replicas P51 Mustang

[Tim Kearsley]

To those who have progressed to the flying stage, have any of you added weight at the tail?  As I mentioned in an earlier post, I'm intending to make the next flights with the FMS 14 X 8 prop and aluminium spinner. A very quick, rough check today shows that I'm going to need around 60g at the tail to move the CG into the 95 - 100mm range.  This is with a 4S, 3300mAh battery, as far back as I can get it.

[Trevor]

Ah, you see, I knew there had to be some benefit from all the time I spent fitting a steerable, retractable tailwheel ?

[Tim Kearsley]

There's always a positive aspect if you look for it Gordon!

 

[Eric Robson]

2 hours ago, Tim Kearsley said:

To those who have progressed to the flying stage, have any of you added weight at the tail?  As I mentioned in an earlier post, I'm intending to make the next flights with the FMS 14 X 8 prop and aluminium spinner. A very quick, rough check today shows that I'm going to need around 60g at the tail to move the CG into the 95 - 100mm range.  This is with a 4S, 3300mAh battery, as far back as I can get it.

Hi Tim,

my P51 D balanced with a 4s 4000 as far forward as I can get it and also fly's ok with a 4s 3600 in the same position 

[Paul Johnson 4]

Eric weren't you using the plastic spinner and a 2 blade prop?

 

[Graham Davies 3]

3 hours ago, Tim Kearsley said:

To those who have progressed to the flying stage, have any of you added weight at the tail?  As I mentioned in an earlier post, I'm intending to make the next flights with the FMS 14 X 8 prop and aluminium spinner. A very quick, rough check today shows that I'm going to need around 60g at the tail to move the CG into the 95 - 100mm range.  This is with a 4S, 3300mAh battery, as far back as I can get it.

Are you sure about that Tim? If we assume (conservatively) that the tail is twice as long as the nose, 60g at the back means your prop and spinner are 120g heavier than the ones you've taken off. They seem excessively lardy! 

 

If it flew OK before, mark the balance on the wing and then recheck with the new spinner. If it does need 60g, it's not exactly a lot.

 

Graham

[Tim Kearsley]

4 minutes ago, Graham Davies 3 said:

Are you sure about that Tim? If we assume (conservatively) that the tail is twice as long as the nose, 60g at the back means your prop and spinner are 120g heavier than the ones you've taken off. They seem excessively lardy! 

 

If it flew OK before, mark the balance on the wing and then recheck with the new spinner. If it does need 60g, it's not exactly a lot.

 

Graham

Well, there are a few factors here Graham.  The first flights had the CG in the 90 to 95mm back range.  I thought the CG needed to come back a bit as the model seemed a bit sluggish and needed quite a lot of up elevator trim.  So I thought I'd try and bring it back 5mm.  It seems that the combination of a heavier prop/spinner combination and aiming for a more rearward CG needed an extra 40g of weight (I already had 20g at the tail).

 

I suppose CG position is a bit subjective.

[Graham Davies 3]

Thanks Tim, that's a bit clearer now. I don't think I'd worry about 60g of weight to get the C of G right though. The WW1 bird boys would be delirious if they got away with 60g up front!

[Tim Kearsley]

Fair comment Graham!  The other factor, which I'd forgotten, is that I used a slightly larger, and heavier, motor than most have used I think.  I need to make slightly more careful measurements to be sure and then if some extra tail weight is needed so be it. 

[Eric Robson]

3 hours ago, Paul Johnson 4 said:

Eric weren't you using the plastic spinner and a 2 blade prop?

 

Yes Paul I still am but my motor is also smaller than Tim's from what he says. From what I can remember it is a 60 -70 ic equivalent, I have one in my 65" span Me 109 and it is quite a lump.

[Tim Kearsley]

The motor I used is the NTM Propdrive 5050 580kV.  The spec reckons it weighs 331g.

[Eric Robson]

Hi Tim ,

my motor weighs 219g. it is a Racestar 4250 800kv and plastic spinner +2 blade prop save we a lot of weight. 

[Tim Kearsley]

6 hours ago, Eric Robson said:

Hi Tim ,

my motor weighs 219g. it is a Racestar 4250 800kv and plastic spinner +2 blade prop save we a lot of weight. 

That's a big saving compared to what I'm using Eric.  Ah well, the benefit of hindsight......

[Paul Johnson 4]

I wouldn't worry too much Tim, if you want to use the scale 4 blade prop Eric's 800kv wouldn't cope with it so it's really dependent on what you want. The NTM 5050 580KV is a beast of a motor and will spin the 4 blade with no effort. I'm using one to turn a 16x10x3 with no effort. 

Horses for courses ....

[RICHARD WILLS]

I suppose if you look at it like this :

My Blue nose P51 weighs 6.5lb old money . Thats 100 ounces roughly .  60grams is less than three ounces . 

So if you strap a 3% load under any of our planes , even a world champion aerobatic flyer wouldnt detect it . 

We all hate adding ballast , but in the big picture.....

Stick the lead on and forget it Tim .

?

[Eric Robson]

15 hours ago, Tim Kearsley said:

That's a big saving compared to what I'm using Eric.  Ah well, the benefit of hindsight......

A big saving on money too Tim, when I bought the motors from Banggood they were £15 each so I bought four two of which are in my Ju 88. Our grass strip is good but not many times in the year are the conditions perfect for tail draggers with retracts and most times finish up with a nose over so I prefer 2 blade props as they have a chance. Even trying to take off some times is difficult which is frustrating with IC as a nose over means a trip back to the pits to restart. All good fun.

[RICHARD WILLS]

Further thoughts on battery placement . If you skipped Pauls mod to move the battery pack "coffin " further back , then why not just cut out the back end of the existing coffin , so that the battery can slide further back . The pack cant really go anywhere if you put in some sort of end stop at the wind screen end and consequently it will not need a complete extension to the box at the back end . Simply a stop buffer . How about chopping out the end with a hacksaw blade ? Long reach and manageable ?

[Tim Kearsley]

Have you got a spy in my workshop Mr. Wills?  That is exactly what I did with my battery box!  I even did it with a hacksaw blade - bit spooky!

[RICHARD WILLS]

Ask Glynn . He thinks I'm a witch . The all seeing eye is watching over you all . 

Perhaps this is a development ? Maybe we wont need to write things down soon . 

My theory is , by feeding you all my kits , you gradually start thinking like me . 

Frightening though that might be , once you welcome half a dozen puppets into your life , talk to yourself and do the voice for your dog , you will feel much more liberated . Also you will be able to bodge up your models , using Mcdonalds coffee stirrers and bits of cardboard.

The internal dialogue does get a bit tiresome sometimes , but a compulsory double whiskey at 9pm does tend to get them settled down for the night . 

[Paul Johnson 4]

That is why Richard moved to the west country, to be closer to stonehenge...

[Graham Davies 3]

10 hours ago, RICHARD WILLS said:

Ask Glynn . He thinks I'm a witch . The all seeing eye is watching over you all . 

Perhaps this is a development ? Maybe we wont need to write things down soon . 

My theory is , by feeding you all my kits , you gradually start thinking like me . 

Frightening though that might be , once you welcome half a dozen puppets into your life , talk to yourself and do the voice for your dog , you will feel much more liberated . Also you will be able to bodge up your models , using Mcdonalds coffee stirrers and bits of cardboard.

The internal dialogue does get a bit tiresome sometimes , but a compulsory double whiskey at 9pm does tend to get them settled down for the night . 

Surely you've all heard that celestial voice when puzzling over a piece of a warbird? "Nah, just do ...... it'll be fine."

 

Just me? Right.

 

NURSE!!!

[Eric Robson]

Richard, you are about 20 years behind me as the artful bodger. Cereal packets are much cheaper than balsa and ply for fillets etc.

[RICHARD WILLS]

Maybe we should start a new thread , called how to bodge things up and fake a good build ?

Would it mean that the newer guys would realise that everyone was fallible and that the learning curve was only 5 degrees instead of 45 ?

Or would those faithful disciples stop following the Gurus , when they realise that the prototypes are made of papier mache and lolly sticks ? (Anyway , whats wrong with that ? ) ?

 

[Graham R]

11 minutes ago, RICHARD WILLS said:

when they realise that the prototypes are made of papier mache and lolly sticks ? (Anyway , whats wrong with that ? ) ?

If it works go for it!!

 

8 hours ago, Graham Davies 3 said:

by feeding you all my kits , you gradually start thinking like me

I have thought for a long time that you have been infecting our wood with your or the boys DNA which we then absorb. How many of your clones do you reckon are kicking around?

[Jonathan S]

Nearly finished covering the wing.  

Question is do we need to use sanding sealer over the brown paper if I am going electric? 

 

Thanks 

Jon