24" Sopwith Pup

[John Bunting]

With that power-to-weight ratio, Simon, I would think you'll never need to use full throttle!

(By the way, what's 'WOT' ? Haven't come across that one before.)

Further to Ken Lighten's advice a week ago, I have now received four sizes of foam cord, for tyres, that I ordered  from Vintage Car  Supplies: 4, 6, 8, and 10 mm, which should do for WW1 type wheels from about 3 to 12 cm diameter. It's very light weight, black, and can be stuck end-to-end with cyano to form a ring, taking care of course to get the ends properly lined up. The cyano makes a rather hard joint: possibly something like rubber solution as used for puncture repairs might be softer, but I haven't tried that yet.

 As I have three metres of each size, I' ll be happy to pass on enough for one pair of wheels to anyone here who can use it.  As it's pretty cheap, it's Christmas, and I'm feeling generous I don't want any payment for it: just give a few pounds to any charity of your choice.

Edited By Timbo - Administrator on 19/12/2009 13:14:29

[Tim Mackey]

WOT = Wide Open Throttle

[Malcolm Fisher]

Great progress Simon.

 

I can only remember having one model which needed tail weight. No matter how lightly I built the back end, I almost always needed extra church roof on the front end.

 

I hope that, when your Pup eventually flies, someone will be there with a suitable camera to record the event to share with us.

 

Malcolm

[Pierre Marais]

Hi Simon, good to see your Hong Kong parcel arrived before Christmas - seems like the power  setup is more than adequate! Hope you achieve correct CG without adding any nose/tail weight. I'm curious to know what wing incidences you'll use - e.g. is it better to set top & bottom wings at different incidences to get one wing to stall before the other; or do one set equal incidences top & bottom. Anyway, I don't want to run ahead of the build - will wait until you reach that part of the setup.  (PS. you were correct w.r.t. the Guillows SE5 needing more extensive weight saving than just the wheels - I have trimmed away most of the heavy bulkheads, fuselage longerons and wing trailing edge - but compared to the lean structure of your pup the Guillows SE5 is still a "porker" - using 4 servos does not help!

 

John, thanks for your generosity but I think shipping to South Africa will cost much more than the total cost of your purchase - good tip though (I'll investigate if there's a local supplier for the foam chord)

[Simon Chaddock]

Pierre

I will set the wing incidence, like the original, the same on both wings. If this Pup flies anything like my earlier CL one the scale wing section will produce a sudden stall with a strong nose down pitch. This does result in an almost instant recovery provided you have the height so again just like the original you must not stall on approach.

 

I am still waiting for the radio and as everything has to be squashed right up the front I want all the bits to hand, so I have made a start on fixing the wings.

This is not something I really wanted to do as it will make fitting the battery/ESC/radio a bit more difficult but never mind.

No its not broken, its pin jointed! All loads will be carried by the wires.

Actually the joints are small strips of acetate cryo glued in.

It may look crazy but it is light and strong yet hopefully will pull out before the structure breaks.

All the struts will be done the same way.

[Simon Chaddock]

The lower wings with cotton jury bracing.

It weighs 1.5 ounces so under 5 still looks possible.  

The cabane struts.

Made from 2 laminations of 1/32 strip with the acetate "joiners" glued between them.

Once the top wing is fixed in place the inter plane struts will be added and the jury rigging removed.

[Terry Whiting]

Hi Simon,

A few pages back I stated concern about the power output of the tests you ran, and your last tests you stated the 5Amp was more than adequate, and I totally agree. as that equates to 35W. With the Pup that is 7W per oz

 

This made me check on some of my models.

 

My converted Westland Widgeon from rubber to Electric is 7.25oz, it flies on 1.6 oz per oz.      My 7lb Lancaster flies on 50W per LB  = (3.1W per oz),     The 8lb Sopwith 1&1/2 Strutter flies on 56W pr LB =(3.5W per oz   The Lanc and Strutter only require this power on take off, and they are no slouches on take off.

 

I hope I'm reading into this a non existing problem.

 

Regards  Terry

 

 

Edited By Terry Whiting on 23/12/2009 10:46:02

Edited By Terry Whiting on 23/12/2009 11:15:27

[Simon Chaddock]

Terry

Thanks for the info. Your Widgeon (is that 1.6 W per oz?) is the nearest.

 

In my tests I was more concerned at the possibility of damaging the tiny 500mAh 2s if I fully opened the throttle with a big scale diameter prop rather than the thrust available, which I am sure is more than sufficient.

At the bottom end of the scale my "endurance" Wing Dragon kept up on 0.75 W per oz and the 2 hour version now under construction should manage on even less!

[Terry Whiting]

Simon, 

Yes, I should have stated  Watts

 

The Widgeon's power train was  from the fuselage of a smashed foamy Tiger Moth given to me, I salvaged two mimi servos, a GWS   4-8 cell  2Amp ESC . very small  unlabled brushed geared motor with a reduction of 6-1.

The receiver had no case, but thought to be GWS,  the battery was a very small 7 cell Nicad  both  were discarded. 

This lead to the Widgeon's conversion.   

 

Your endurance   ' Wing Dragon' construction  sounds interesting

[Simon Chaddock]

I originally intended to install the battery in the top of the fuselage under a removable hatch however a trial installation of the top wing soon convinced me this would not work.

With the cabane struts fully braced you would not even be able to open the hatch, let alone get the battery out, so on to plan "B" - a single 500mAh LiPo on either side of the servos, inserted from underneath.

Obviously a single cell has no balance plug so this will have to be wired up.

This layout has the advantage of leaving planty of space above the servos for the ESC and radio.

[Simon Chaddock]

Not much progress over the holiday - to much DIY but at last the radio arrived.

The TX & RX crystals were provided and it seems to work ok with my Futaba 6A.

No case so it has a 'slot in' balsa mount which will be glued directly to the back of the firewall. A convenient place but I do wonder if it might actually put the radio rather too close to the motor.

Just after the first test run using all the 'flight' components.

Its slow going because it seems like almost everything seems to need some sort of modification to fit.

[Terry Whiting]

Simon,

That is a beautiful little receiver, but I think you would be wise keeping it well away from

the motor and ESC. I sure do when using 35 meg with electric.

 

[Simon Chaddock]

The last (hopefully) of the 'specials', the 500mAh 'saddle' battery made up from 2 Walkera single cells.

With all the RC bits in and tested the top cowl goes on.

Top wing next, then connect up the ailerons.
 

 

[Simon Chaddock]

The next unsolved problem is the cowling for the Monosoupape.

Unlike the neat full circle one for the 80 hp Le Rhone, the Mono had a rather angular 'horse shoe' type so I thought I would try and fabricate it out of 1/32 balsa and cover it with foil, to match the rest of the fairing.

Front and side are sheet but the radius bit is made up of 40 little wedge shaped 1/8 balsa blocks in two rings carefully sanded to profile inside and out.

It weighs just 2.1gm like this but that will rise to 3 when it is covered in foil and the 4 little air scoops added.

It works ok but a bit like the rest of this plane it is more an exercise in light weight carpentry than a sensible way to make an engine cowling!

[Pierre Marais]

Very impressive Simon! Your project is a great example of miniature (&lightweight)  engineering - can't wait for your next installment!

[Terry Whiting]

Simon,

 

If you do not mind me asking, what is the weight of those two combined cells,?

 

Terry

[Simon Chaddock]

The completed cowling, all foil covered with its external braces and extra air slots.

Not quite a neat as would have liked but keeping weight to an absolute minimum was the primary objective.

Terry. The connected pair of batteries weigh 24.4 gm (0.86 oz).

[Biggles' Elder Brother - Moderator]

Simon, what's the CoG situation looking like? I can see that you've "stuffed as much up front" as you can but as I am sure you know pups and camels are notorius for coming out tail heavy!

 

beautiful work by the way - this is one of my favourite build blogs I've been following it from the start!

 

BEB

[Simon Chaddock]

Thanks BEB.

With everything installed, less the top wing, the balance point is just about at the lower wing leading edge which if my calculations (and feel) are correct it will be very slightly nose heavy. We shall see.     

[Sheldon Holy]

What an amazing project! Brilliant workmanship there.

But, are you sure those Walkera cells are 500 mah? I have a couple and they are 400mah. Where did you get them from? Mine came wih a walker 4G3. Just wondering, you must know what your on about though! Maybe it woule be an idea to get a smaller esc?

Are you just having one servo for all four ailerons? Or are you using connecting pushrods to connect driven bottom ailerons? I am asking as it would be amazingly fidly to have another one of those flishing-line setups on the top wing with the wires coming down the cabane struts! I guess you must have mentioned this and i didn't notice.

 

Sheldon

[Simon Chaddock]

sheldon

They came direct from Hong Kong & are very small but this is what is says!

Lets hope it really does what is says on the tin!

All four ailerons will be driven by one 3.7 gm servo connected up "pull/pull", just as in the full size. This Sopwith Dove pic shows the principle.

From the servo in the fuselage though the lower RH wing, turn 90, out under to the aileron horn, up through the aileron to the upper aileron, through the aileron, over the horn, into the top wing, turn 90, right across inside the top wing , turn 90, out over to the RH horn, down through the  aileron to the lower aileron, through the lower aileron, over the horn, into the LH wing, turn 90, through the wing back to the servo.

Fidley? maybe but elegantly simple and light.

Well thats the intention.

Edited By Simon Chaddock on 09/01/2010 00:57:58

[Terry Whiting]

Simon,

I'm sure you must be right with your balance calculations, but that balance point seems extremely forward.

 

 

[Sheldon Holy]

Wow... Fidley, definately! Simple, I guess. Elegant, unless it's perfect you'll find yourself with a wing warping mechanism! I think it'll be fine, especially by looking at the brilliant building I agree with Terry - the balance point seems awfully far forward... will we have a video of the maiden?

 

Sheldon

[Biggles' Elder Brother - Moderator]

Monoplane flyers are used to the CoG at about 1/3 wing chord. But you have to remember that its not unusual for the balance point of a biplane to be close to the leading edge of the lower wing. The important thing of course is that its in front of the effective, combined, centre of lift. Because of the wing stagger the combined centre of lift of a biplane can be much further forward than you'd think - in extreme cases it can be in front of the leading edge of the lower wing!

 

So I don't think its too far forward at the moment - forward, maybe, but not too much yet. Anyway better that way than the alternative

 

BEB

[Malcolm Fisher]

I'm with BEB on this having once built a C/L biplane and set the CG at about the normal place on the lower wing for a monoplane. First attempt at flight managed threequarters of a loop from take off and an instant rekitting and pushed the crankshaft through the engine backplate...

Malcolm