The Whispering Death

[MThemadhatter]

Well there was a lot of sanding this morning

 

I am using the TLAR principle and to me this looks good. Any defects now I will fill with isopron once the glass is on. Just need to add the last bit of solid balsa at the back of the nacelle top and bottom and I can get on with making hatches and doors.

 

After that its shape the leading edge and glass the wing

 

[MThemadhatter]

A little more progress over the weekend. I have added the fillets at the back of the naccelles, balsa on top and blue foam underneath to save a little wieght behind the C of G.

 

I started to make some blisters for the wheels , but trying to shape them to fit over the compound cure of the nacelle and be the right shape for the wheel is a complete I think have the wheels poke out a bit would be simpler, or maybe vac forming the blister then cutting it to fit over would be easier.

 

I have also finished installing the snakes, to to do this I had to trial fit the tail fins

 

The kink is there to try and make the final bit of the snake straight so that can have the metal rods go a little way into the snake for extra support. The transparent snake is for the rudder cables.

 

 

[Danny Fenton]

Really looking fantastic great job on the nacelles

Cheers

Danny

[Andy Gates]

I agree with Danny, she is looking good.

 

Regarding the U/C doors, could you not make some light glass fibre bulges to fit around the wheel and then fix them to the insides of the doors.

That way you only have to make wheel size cut outs in the doors and GF will probably be stronger than a vac form so will add strength to the door too.

[MThemadhatter]

I have not really got near the Beau the last couple of weeks, been working all the overtime I can get

 

Andy that sounds like a good idea, but I am thinking more that just having the wheels poke out a little.

I have managed to acquire some bits and pieces including some aluminium bar stock for the landing gear. I found a guy on e bay who sells it in 250mm lengths.

 

I have come closer to a decision about the retracts The Eflight ones are £70 cheaper than the lado ones and I can put up with the wheels poking out 12mm more. I am still thinking about some oleo legs though, as my flying patch can be a bit bumpy as can my landings

I have also prepared the power train ready for testing. Which has raised an interesting point, well the article in this months RCME has.

 

In that it suggests it would be better if I connected up the batteries in parrallel to make one common suply for the two ESC's. The idea being that both motor's will see the same voltage and there would be no asymmetric power problems as the batteries go flat.

 

Now the problem here is that the only practical place to put the batteries is in each nacelle. They are roughly 24in apart which I believe would be inviting trouble with battery leads this long. Anyway around this ?

[MThemadhatter]

I have been having one of those days

I decided to test the motor / esc today to see what props I should think about using and how much power I had.

First er, mistake.

Plugged in battery and was rewarded with a loud pop from the some where. On checking the ec3 - ec5 adapter I had made up had it's polarity reversed. So good by to £50 esc

 

Having fixed this problem I then, using the other esc tested the props

 

14x7 7200rpm ~ 450W ~ 30A

14x8 7200rpm ~ 500W ~ 35A

 

These figures are way short of what I was expecting more like 600-700W and 40-50A. So those recommended props I was given are way off. I think I would be flying round at full throttle !!

 

I think I can prop up a bit maybe a 13*10 3 blade or 14*10 2 blade. Starting to worry that I have bought the wrong motors. 100W / lb on a war bird seems a bit low to me.

[Andy Gates]

Sorry to hear of your oops moment, I am sure you and I are not the first to do it either.

 

I have looked at the specs for the motor.

The motors are specified for 5-6 cell packs not the 4 cell that you are running.

650Kv is a bit low for a 4 cell configuration.

 

Looking at your figures I can't see that a 14x10 is going to make much difference from the 14x8 you tested.

I would be tempted to try a 14x7 or 14x8 3 blade prop, that ought to get the current up where you are suggesting you need it.

 

However, I am not so sure that you need shed loads of power.

The 100 w/lb is a guide aimed at single motored machines.

Twins to not hold to the above rule, so for me I would try the 14x8 set up and see how she goes in the air.

 

My Mosquito runs at 90w/lb and is not short of power and flies quite scale like.

My Catalina runs at 111w/lb and is way over powered, ever seen a Catalina go vertical and not stop? Mine can - ooer!

[MThemadhatter]

The reason for the bigger motors is C of G. TN suggested that it needs the weight up front to get the C of G right. Using a smaller 4 cell motor would have needed added weight.

 

I was expecting higher rpm from the motor, ie 14.8 x 620 = 9176 why is it so much lower at 7200 ?

 

In terms of props what I really want is a little more pitch speed. With a 7in pitch the theoretical top speed is about 47mph. I would like a little more in reserve. The idea of a 3 blade prop sounds good but they are hard to find, so far I have found.

 

Graupner 13x10

Gaupner 14x7

Master airscrew 14x9

 

The 14x9 sound's good and should look nice and scale. Its a master though

Thrust HP guestimates 6.22lb for the 13x10 and 8.36lb for the 14x9. So that's 12.44lb and 16.72 lb of thrust respectively. I am guessing at about 12lb weight for the finished model with battery.

Any one got motorcalc for to give guestimates on the Amp and Watts for those props ?

[MThemadhatter]

Right I stuck a 15x8 graupner g-sonic on it this morning and got 7000rpm at 42A after 30 sec's at full throttle. This gave approx 650W.

 

I don't know what this means though

[Ton van Munsteren]

For me I never look at the Watts only look at the amps draw by the motor , static thrust and propspeed M/sec.

 

For me having minimum 80% of the models weight in static trust and a prop speed of minimum 18 m/sec makes it for me sure that the flight has good performance to start with. (for a sport model no 3D)

 

Think with the prop you mention 15x8 you would have a static thrust of about 3300 gram and a speed of 18 m/sec which for me would be more than enogh for flight.

 

Ian sure you will have a good performance using the power for 80% and would be more than enough for a good flight.

 

Ton

[Keith Simmons]

The Motorcalc is only a guide as actual testing sometimes give different results. I like to use Master series 3 bladed props as they use more wattage, are less economical than 2 bladed but it looks right and as long as it flies right, I am happy. I normally use more powerful motors and use less juice rather than use motors at their max watt rating as I want them to last longer if possible. I have 10x8, 12x6 , 13x8 and 16x8 props, all 3 bladed for my different warbirds.

[MThemadhatter]

Thanks for the advice guys.

 

Ton, your right the 15x8 would be a good match but, its actually lager than scale which means a I run out of ground clearance. The props on the real thing are 3.88m diameter so a 14in prop is about scale size.

 

I have bought a 14x10 two blade graupner G-sonic and a 14x9 3 blade MS and will try them out soon.

 

I have plenty of thrust,1:1 or better with those set ups it is the pitch speed that concerned me a little.

 

Any way I am now in the process of preparing to make the FG doors and finish sheeting and stripping the fuse.

 

Watch this space...

[MThemadhatter]

Well I have spent the day building and it has not gone well.

 

I bought my retracts and oleo legs with some xmas money

 

Things started out ok I have made the first set of undercarriage doors.

 

I then went on to the finish the fuse.

 

Again I found it impossible to sheet the underside , I really don't how your supposed to sheet a compound curve as shown on the plans and I ended up strip planking most of it and sheeting the straight bits .

 

However the results are not er brilliant. After all the effort and care I took making sure the fuse was built square its not. There is a big ripple just behind the wing seat, and it's worse on one side. I am going to try sanding it all to look something like a beaufighter fuselage but I am about ready to give up on this, really wish I had not bought the UC

[Danny Fenton]

you mustn't give up now you have done brilliantly, and you are so close. can you show a picture of the problem, maybe we can make some suggestions?Cheers Danny

[MThemadhatter]

Here you go

 

It looks like one of the formers , the one in the middle of the wing seat is to small and it only really showed once the sheeting was on.Or the one behind it is to big

 

The fuse is straight though. Also if anyone else builds this put the 4mm balsa on the bottom of the formers first then do the sides not the other way round as suggested by the plan. Getting it to bend and stick to the formers is a nightmare.

 

I will take it out and sand it to death tomorrow and see what I can do. My order from lado shipped yesterday

[Danny Fenton]

I had a bulkhead on my Spitfire that was scaled incorrectly from the smaller version. fortunately I spotted it in time. before you sand the sides and potentially make them too thin, think about adding wood on the inside to keep the strength. You may have to fatten the fus to match the fat bulkhead.

let us know how you get on, but don't give up

cheers

Danny

 

[MThemadhatter]

Right I have had a good sanding session today and examined the problem more carefully.

 

Here is what it looked like after some rough shaping

 

 

What has happened is the sheeting as buckled in between the formers. I think I can fix this by running a knife along the join and re positioning it. You can also see that the transition between the side sheeting and thick bottom sheeting is a little uneven at this point. I can see some filler in my future.

 

Also this part of the fuse is cosmetic as it will be cut out and stuck on the bottom of the wing. You can see the cut line I left for reference. If I end up with any thin areas I will put some of the heavier glass cloth I have on the inside.

 

I have since drawn on with a soft pencil all the shaping points. There is going to be a lot of sanding being done over the next few days

 

I think my despair last night was brought on by to much planking and the cost of the 95 degree lado retracts.

I have done some more glassing today

Here are the moulds of the nacelles that I will cut the UC doors from.

 

To make these I covered the nacelle in cling film secure in place with double sided sticky tape. To my joy the cling film peels off the cured epoxy.

 

I have used this stuff

 

 

Thanks to Danny for the idea of using the Jenny brush in his glassing video

 

Here is the battery hatches being made

 

Cling film on

 

Glass and epoxy on

 

 

The are I have glassed again is much bigger than the hatch needs to be. The fibretech stuff is very easy to use and does not smell, a plus as I am doing this in the dining room.

 

Now back to that sanding.

 

 

[MThemadhatter]

I have done some motor testing today

 

With a master airscrew 14x9

 

 

And a graupner g-sonic 14x10

 

 

Results where taken after 30 seconds at WOT on a freshly charged 3300mAh 14.8V 45C Turnigy nano tech lipo. And then reduced to half throttle.

 

14x9x3 43.13A 614W 6300RPM Pitch speed 54mph Thrust 6.4lb

11.75A 174W 4050RPM Pitch speed 35mph

 

14x10 38.30A 530W 6330RPM Pitch speed 60mph Thrust 4.62lb

12.11A 185W 4440RPM Pitch speed 38mph

 

Looking at these results I think the 14x9x3 seems the better choice. I am wondering if I will get better results when I use a 4500mAh lipo in terms of the voltage stability ?

 

In hind sight I should have chosen the motors to spin the MS 14x7x3 as they make a pusher version of this prop and I could have had them spinning different ways.

 

The keen eyed will have noticed the motors have lost thier nice red finish. When I masked them up to grind indents so that the M4 mounting bolts would fit the masking tape pulled the paint away

 

[Andy Gates]

The figures for the 14x9 3 blade looks good.

 

Don't forget that you will be running 2 sets of these so they will be helping each other.

I would expect the motors to run faster than your static results indicate so that will almost certainly increase the pitch speed.

 

Your current figures show that you are only pulling 15C from your 45C lipo so the current drop should not be excessive,but greater capacity will of course help this but at a weight penalty. Wiegh up the difference before you commit yourself or the plane.

 

I assume you are still going to use one pack per motor because 2 motors are really going to drag the voltage down under full load on a single pack.

 

I suspect you are going to have quite a lively machine on your hands.

 

I know I may be teaching grandmother to suck eggs with my next comment, but I really would not worry too much about the torque effects of having both props running the same way.

Fly it like the full size machine, on take off open the throttle progresively keeping the tail straight with the rudder and let it get steady before lifting it off the ground.

If you wollop the throttle wide open in one hit, you will be fighting it right through the take off and climb out until you reduce the throttle again.

[MThemadhatter]

Thanks for the advice. Your right about the torque effect and my Lysander will reward you with a ground loop if you try slamming the throttle open.

 

I plan to use a 4.5Ah battery on each side, partly for duration and partly for balance. I would have preferred to wire them up in parrallel but its not practical, I would be stuffing the nacelles full of capacitors. I will probably go for either a pair of these or these , probably the former as the two "identical" turnidgy batteries I have are not consistent in power output.

 

I have received some more goodies in the post and have been trying my hand at metal work.

 

 

My first attempt at the cross piece

 

 

Am now realising why the cheap drill bits I bought where cheap I have enough alloy bar for two more and a new set of drills on order lol. I have of course also been sanding, there is no end to the sanding with the beau fuselage....

 

[MThemadhatter]

Had the day off today so I have put the time to good use

I have a whole week off at the end of the month so I want to get the wing ready for glassing. So today I have profiled the leading edge.

To help with this I made a some templates

 

 

This is to help me make the "second" cuts on the leading edge. The top and bottom of the leading edge have already been sanded to the wing

 

 

With the template I can make sure that the second cut is the same along the length of the wing . You can see above that I have also used a marker to colour the front edge of the so its easier to see where I have sanded.

 

I then make the third cut,

 

And finally I use a strip of sand paper, wrap it around the leading edge and then pull it backwards and forwards to smooth off the profile.

 

Again on the outer wing panel

 

 

I have also been working on the fuse and have pretty much finished off shaping it to the correct profile

 

I have fixed the belly sheeting on the right side , here it is before sanding

 

It looks much better now.

 

 

 

[Ton van Munsteren]

Great pickies and a great build keep up the good work.

Looks like there's still a lot of sanding to do, but the shape is getting better all the time so your on the right track.

Always a nasty job all that sanding.

 

Ton

[MThemadhatter]

Yeah and it makes such a mess I find that it's one of those jobs that you get wrong if you think to much about it lol

[MThemadhatter]

I sanded some more the of the fuse today, and I think the bottom and sides are pretty much done.

 

Just need to go round with the red devil filler and fill in any small in perfections. I then add the remaining top section of balsa but before I do that I need to shape the tale fin so that I can dry fit it and fit the top piece around it.

 

Once I have done that I will cut out the belly pan section and test fit the wing, which also needs more sanding and the aileron hinge shrouds added.

 

[MThemadhatter]

This week I have started glassing

I started off by doing one part of the plane.

I used the belly pan

 

I am using fibretech, or as they are called now Bucks composites

 

 

I used a jenny brush and squeegee to apply the epoxy, on larger surfaces I will use a roller.

 

The results where quite good but I have some pin hole's on one section where the epoxy has soaked into the balsa

 

So I did the "optional" step of sealing the balsa for everything else. This consists of thinning the activated epoxy with 20% epoxy thinners, painting a very thin coat over the components and then wipe it off with some absorbent paper. Once its dried I then lightly sanded the parts before applying the glass.

 

 

I will put the flow coat on later when I have more parts ready for it.

 

Today I have finished prepping the wing and put the sealing coat on.

 

I have already put the glassed the nacceles

 

It was easier than I thought it would be to get the glass fibre around the nacelle.

 

 

 

I am going to put the glass on in three sections on the underside of the wing tomorrow and to help me I have made these templates to cut the fibre glass sections.