build DB Mighty Barnstormer

[EarlyBird]

On 09/12/2024 at 16:49, kc said:

If the balsa is dented why not try the old trick of a drip of water on the dent?

Thanks that's works a treat. 

After what seems like hours of sanding and scraping and more sanding this is what it looks like. 

 

That's going to have to do, is my thoughts at the moment as there is lots of wing left to sand. 

 

Steve

 

[Keith Evans 3]

Did you actually fit a dihedral brace before you glued the wing halves together ?

[EarlyBird]

9 hours ago, Keith Evans 3 said:

Did you actually fit a dihedral brace before you glued the wing halves together ?

Hi Keith, yes I used the ply braces that was supplied. They are not obvious but they are there in this photo.

 

Steve

 

[EarlyBird]

Eventually I have had to turn it over so you can all have a look at the mess. After a lot of sanding I have chopped out the sheeting for the struts. 

 

 

Steve

[kc]

Doesn't look bad - maybe just insert a sliver of balsa into any gaps.  Covering will go right over and conceal it but nobody will look under the wing!

[EarlyBird]

Not bad at all now the sanding is completed and the cabane struts are  test fitted. 

Time to start the covering. 

 

Steve

[EarlyBird]

The covering has started and in effort to minimise the number of joints I have wrapped the top and bottom covering which has worked well for the first two panels. Then I made a mistake, oh well it happens. 

 

That's what happens when you use a heat gun next to the edge apart from that the piece I cut accurately ended up being an inch short. Obviously I was having an off day and should have taken the day off. 

 

Steve

[EarlyBird]

And fixed, well patched to anyway which gave me a chance to practice my repair skills. 

 

Steve

[EarlyBird]

I decided to do the wing tips first simply because they are the hard part. 

 

 

 

All went well and did not seem very difficult at all I guess this is because I have been building for five years so I thought how can I make this more difficult the answer was covered the leading edge top and bottom in one piece. The results are not brilliant but it is done and more to the point is that I have learned something which is what I try to do all the time. I did find a clear covering hid absolutely nothing and all minor mistakes were opened for all to see. I guess that I need more practice. Looking at the amount of black especially in the center I'm wondering how to apply some yellow covering as trim.

 

Steve

[Andy Stephenson]

Self-adhesive trim material works best but will only come out as nice as the rest of your covering if you apply it wet. Put a little washing up liquid in a bowl of water and remove the backing underwater then slide it to the position you want and squeegee out the water from underneath with a tissue until there are no bubbles left, leave it to dry overnight as any remaining water will find its way through the material.

[EarlyBird]

Thanks Andy, as I was faced with a lot of triangular off cuts I had to give it a go. 

 

 

It worked out well as there were only half a dozen bubbles which quickly disappeared when a light touch with a pin was applied followed by a little bit of heat. I think the problems I've had before is that I was using two much heat and when bubbles appeared I added more heat and made it worse so this time the iron will set at 100 degrees centigrade and move over the film quite quickly. The edges were given special attention with the iron to make sure that they were well stuck. Now I I'm going to practice a bit more by adding more trim to the leading edge. 

 

 

When I have decided on this spacing and the number to have on each Wing it will be finished don't hold your breath 

 

Steve

[EarlyBird]

Decided on two diamonds and space them accordingly. 

 

It looks like the answer is for keep the iron moving and do not allow it to rest in one position.

 

Steve

[Ron Gray]

Yes, a double diamond works wonders. 

[EarlyBird]

After a couple of days off and  my double diamond on Christmas Day. Oh dear time to add some more.

 

Cheat lines and finished with another double diamond. 

 

 

More decoration to come? Or I could start the fuselage. Or I could finish the Peter Miller builds. 

 

Steve

Edited December 29, 2024 by EarlyBird

[Nick Cripps]

Clean and simple, it looks good as it is, Steve.

 

Time to get back to gluing balsa sticks together.

[EarlyBird]

38 minutes ago, Nick Cripps said:

Time to get back to gluing balsa sticks together.

Yes it must be as I am either ill or having withdrawal symptoms I think it's the latter. 

 

Steve

[EarlyBird]

Two balsa sticks glued together. 

 

 

The rest of the chaos is due to me making the parts required. The additional pack included the formers that you can see I just have to make the straight bits. 

 

Steve

[EarlyBird]

All the straight bits made and glued in place. 

 

 

That's one side made and if anyone is any any doubt I am not following the plan. The reason being that's my chosen engine, Saito FG 21, has its own mounting directly to the firewall. This has made me not using the wood engine mounts. It is my thinking that the engine mounts are part of the strength. Therefore I'm following Peter Miller method of using a ply doubler for strength. The engine mounts are also used to impart down thrust and side thrust which are now included in the firewall. Next I need to make the ply doublers.

 

Steve

[EarlyBird]

One doubler test fitted. 

 

 

Take it apart and build the second side on top of the first so that they are in identical then the second doubler. 

 

Steve

[kc]

Do you think side and downthrust are actually needed?   Modern thoughts seem to differ from old designers on this point!     I remember that Peter Miller thought side or downthrust unnecessary on his designs.

 

A Barnstormer 63 with electric power that I acquired seems to have a trace of downthrust and barely any sidethrust.   My view is that such little sidethrust is not worth the effort in offsetting the mounting to make the prop come out in the right place.  Same with downthrust.    I suggest asking for opinions before committing to angle the bulkhead!

 

The bulkhead might need reinforcement to doubler - I always found balsa triangle unsatisfactory even on 40 size glow models -I used hardwood instead.

 

 

[John Rickett 102]

I’d agree that built-in side and downthrusts are unnecessary with modern radios, the same result can be obtained with a bit of programmable mixing – progressively increased down thrust with advancing throttle, and increased right rudder with advancing throttle. What built-in angles are required is a bit of a guess for a given power output and if its not right you are stuck with it. Using the radio to obtain the trim required can be fine tuned once the first flights have been made.

 

My start point would be a 5% offset at max throttle, if that’s wrong it doesn’t matter just add more or less for the next flight.

 

Also, making the bulkhead/fuselage joints using a tab and slot arrangement, similar to the two formers in your photo, will impart considerably more strength than butt joints, won't add weight or take up useful space. The bulkhead joint is the one where the strongest glue available should be used, Hysol takes some beating!         

[Don Fry]

17 minutes ago, John Rickett 102 said:

I’d agree that built-in side and downthrusts are unnecessary with modern radios, the same result can be obtained with a bit of programmable mixing – progressively increased down thrust with advancing throttle, and increased right rudder with advancing throttle. What built-in angles are required is a bit of a guess for a given power output and if its not right you are stuck with it. Using the radio to obtain the trim required can be fine tuned once the first flights have been made.

 

My start point would be a 5% offset at max throttle, if that’s wrong it doesn’t matter just add more or less for the next flight.

 

Also, making the bulkhead/fuselage joints using a tab and slot arrangement, similar to the two formers in your photo, will impart considerably more strength than butt joints, won't add weight or take up useful space. The bulkhead joint is the one where the strongest glue available should be used, Hysol takes some beating!         

So what happens, build up speed with power, mixes cut in, cut throttle, does it not dive left. Not saying a bit of mix can’t fine tune, but the airframe thrust angles need to be about right first. Not saying it’s easy, but it has to be done. 

[John Rickett 102]

 

Don, The mixing doesn't 'cut in' its always there - zero mixing at idle and maximum (whatever you've set) at full throttle. I use Futaba, but I'd expect all makes nowadays will have the facility to not only have the mixing linear but follow whatever curve is desired.

Its worked well for me on a draggy biplane and I have one model which, ordinarily, will put its nose down with increased power, setting a mix to apply proportional 'up' elevator with increasing throttle has cured that one.

Built-in side and down thrust is a throw-over from free flight days and simple analogue radios, if you want to make a model of an old design exactly as originally designed, that's absolutely fine, however the facility now exists, in just about all transmitters I'd think, to be able to let the electronics take the guess work out of it.     

Edited January 4 by John Rickett 102

[Don Fry]

We will agree to disagree. An aircraft wot needs down elevator to fly staight and level at full clic will dive if that power is taken off. To avoid it, the operator applies up until the excess speed bleeds off, or gets the thrust lines sorted. Thats physics, not fashion.

[GrumpyGnome]

What do the F3A fliers do? They want ultra-straight lines with no deviation.......