24" Sopwith Pup

[Simon Chaddock]

Hi Ron

The answer is yes, the Depron Pup will have exactly the same control system but somewhat simpler to do as all the lines will run outside the airframe. I will post some more pics when the servos are eventually delivered!

If you go back a page there is a pic of how the line is connected a top aileron.

 

Prop testing

The 6x3 draws just 2.8 amps (19 watts) at full power. This may not sound much but its still 60 W/lb! The thrust certainly feels quite adequate so with its 500mAh battery it would have a good 10 minutes at full power.

The correct scale diameter 7x3.5 draws 3.6 amps, giving a still quite a respectable 7.5 minutes duration and 76 W/lb.

The 7x4 has thicker, bigger blades, draws 6.1 amps giving 128W/lb and just under 5 minutes duration.

 

But until those servos arrive its all hypothetical!

[Simon Chaddock]

At last I have the servos!

My usual "glue them in" technique.

The elevator servo sticks out of the side of the fuselage to be cabled up directly to the elevator. Simple but very light.

A video of the elevator test.

The ailerons tomorrow.

[Simon Chaddock]

At last the ailerons. I have painted the line black so at least you can see it!

Servo to LH aileron

Lower to upper aileron

L to R accross the top and so back again to the servo.

It was all done with a single line passing through the ailerons and the tip of the horns. Using the natural stretch of the fine 1.7lb line the whole circuit was placed under tension before the ends of the loop were secured at the servo horn. Only then were the ailerons themselves finally adjusted and secured to be equal and neutral with the servo at midpoint.

It does of course have a bit more friction than the simple straight elevator circuit but it works ok.

[Simon Chaddock]

The final steps.

Due delivery delays the Depron Pup has taken rather longer than intended.

The RC installed. The aileron servo and cables rather get in the way but at least it puts some distance between the radio and ESC.

.

The CofG is 12mm behind the lower LE.

It weighs 4.55oz or nearly half an ounce less than the balsa one. Yes it does have a slightly lighter motor, prop & ESC but then it has a slightly heavier battery and radio.

If it flies well I will add a simple U/C to exactly mimic the balsa Pup.

[Terry Whiting]

Simon,

 

A job well done.

Have you desided where and when the maiden might take place? and if you do not mind me asking, what are the measurements of the chord and wing stagger?

 

Terry

[Simon Chaddock]

Terry

Thank you.

The chord is 4.5 ins (110mm), the stagger 1.5 ins (38mm).

I actually tried to fly the Depron one today as it looked reasonably calm but at the field the wind was probably 5-8 knots or just about the expected flying speed! Did not risk it.

They do look more or less the same.

 

[Terry Whiting]

Simon,

 

Wise man, a fine picture they make too.

 

I have learnt that even my  Widgeon which has a little more weight than your Pup

requires virtually zero breeze.

 

Thanks for the measurements.

 

Terry 

[Simon Chaddock]

The Depron Pup flies!

A rather short flight and rather too much wind. Or rather too much wing incidence and/or CofG too far back meant rather erratic control but no shortage of power.

It certainly drops a wing rather easily so the 'arrival' was a bit rough and not directly into wind. Broke the prop and deranged the rigging a bit but surprisingly all the control runs were undamaged. As I hoped, none of the depron bits suffered at all.

 

So remove the rigging altogether as it plenty strong enough without and the extra 'give' should reduce landing damage.

One advantage of UHU Por is it has a relatively low peel strength so both the cabane struts and the lower wing could be easily prised off the fuselage and re-glued with less incidence.

 

Doing this sort of thing is the exactly what I built it for.

 

Before the next flight (in calmer weather!) it will have a folding 6x4 prop. 

Edited By Simon Chaddock on 10/02/2010 14:36:54

[Terry Whiting]

Hi Simon, 

 

To be quite honest the profile picture gave me the imression you had been a little extravagant with the + incidence. If that was the case, and you were tempted in breezy

conditions  I could imagine the flight being nose upish and wallowey, with next to no control with ailerons due to flying practically in continuous  stall , which would naturally

drop wing as you came back on the throttle.

This is why I suggested adding a rudder to the test model, ailerons are virtually ineffective flying near to the stall, and only exaggerate the problem.

 

In the profile picture it was impossible to see if you had included any down thrust.

This could have been another factor.

 

You know the old saying Simon, if you think you have more than one fault, correct them one at a time, to do them together and she flies, you still do not learnt what was the actual fault.   

 

 

 

[Simon Chaddock]

Terry

As it was a 'test' plane I set the wing incidence the same as the balsa Pup which itself was set to scale.

Here is the undamaged Depron Pup but now without any rigging.

Note the TE of the lower wing is now just above the bottom of the fuselage instead of the scale just below. You cant really see it but the top wing is now set with just a little less than the bottom which should move the CofP back just a bit.

It looks like once I have arrived at a good solution I will have to rework the scale Pup a bit, probably with a touch of negative incidence on the tailplane.

Friday looks to be the calmest day in the NW.

[Terry Whiting]

Simon,

 

Truly hope all goes well Friday.

 

As for a touch of negative incidence on the scale Pup tail plane, isn't that going to

accentuate the problem,?  

[Simon Chaddock]

Terry

 Er, it depends on what you take negative incidence to mean.

As the wings on the scale Pup are rather permanently fixed I intend to reduce their effective incidence by raising the leading edge of the tailplane.

It will cause the fuselage to fly slightly nose down but it will add a touch of down thrust into the bargain.

All this is still some way off as the Depron version must fly properly first, eventually with the Flycam on board as well. 

[Terry Whiting]

Simon,

 

I understand, but in my book that has always been  positive tail plane incidence, but you did have me worried.

 

 

[Simon Chaddock]

Weather forecasting wrong again, much too much wind so I tested the Endurance2 instead.

[Simon Chaddock]

I have come against a small problem with the 'closed loop' lne coupled with surface tape hinges on the Depron Pup ailerons.

I tensioned the loop quite a bit to ensure there was no free play but unfortunately this results in a net vertical force on the aileron (downwards on the upper, upwards on the lower) which of course tries to peel the tape away.

I am thus having to re-engineer the ailerons to put the tape at the centre line to better resist this force.

Fortunately, but originally for different reasons, the scale Pup ailerons are already mounted this way.     

 

Edited By Simon Chaddock on 13/02/2010 22:45:28

[Terry Whiting]

Simon,

 

Would those 10mm wide pin hinges be of use, they are extremely thin, I have used them in 3mm balsa, but I have no dealing  with depron.

[Simon Chaddock]

Terry

I am sure proper pin hinges is the answer and if this was any other than a 'test' plane I would probably use something like that.

I have elected to use paper hinges fixed on the aileron centre line and sand its leading edge back either side to allow 45 degrees movement up and down.

It is probably not a long life solution but is very light and flexible, quite important when you have 4 to move with just a 3.7 gram servo.

[Callum Smith 1]

Simon,

 

I've just been reading through and want to thank you for a very interesting build blog! It's certainly inspired me!

[Simon Chaddock]

Callum

I am glad you are inspired but 24" span planes are not the easiest things to fly as they react very fast so unless it is set up exactly right the inevitable crash just happens that much quicker.

The cheap & tough(er) Depron Pup has piled in twice already but with just minor repairs is still going.

[Malcolm Fisher]

Simon,

 

Regarding your hinges, I'm surprised that you haven't considered the old fashioned sewn types as we use to use many years ago on C/L models. They are very light, friction free, cheap and easy to apply. Another possibillity is to use paper in the form of "clothes horse" type hinges which could also be managed using adhesive tape of some sort - again light and easy to do.

 

Malcolm

[Simon Chaddock]

Malcolm

Yes I have in the past used both the types you mention.

 

I did consider using the clothes horse type (I wonder how many people know what they are?) but in a closed loop system it is important that the hinge pivot point remains constant otherwise the cable tension is likely to change as the ailerons move.

If the centre line paper hinges fail they will indeed be replaced with a clothes horse type and trust the changes in line tension are not too significant. 

 

[Toni Reynaud]

Hi Simon,

I have seen a lightweight depron model with hinges formed from a bead of UHU Por - put on thin and left to dry, it forms a tough flexible joint quite nicely. Just a thought. 

[Simon Chaddock]

Thanks Toni

It had not occurred to me to make the complete hinge that way although when fixing my paper hinges a small excess of POR formed an accidental hinge. I had to cut it away and it was amazingly tough.

I shall have to remember that one for the future. 

[Sheldon Holy]

Hinges on small models eh?

 

On balsa or depron, UHU-POR is absolutely brilliant!

It's a contact glue, so apply to both sides, wait 20 mins then push together. The hinge is very strong and very flexible.

 

Sheldon

[Simon Chaddock]

The 6x4 folding prop with the fixed 6x3 below.

It is intended just to save the prop on landing as restarting in flight could be very dodgy because a blade might end up between the cabane struts. I did try a prop saver but found  the band had to be very weak to ensure the prop came off without damaging the motor mounting.

As delivered the blades were extremely thick (they were marked '6x4 d'. Does anybody know what the d stands for?) so I thinned them down by about 50% but they are still about twice as thick as those super thin 6x3 blades. A same brand folding 11x6 does not have the 'd' mark and its blades are much thinner.

Balancing a folding prop is not easy so I made a small balance beam scale and carefully sanded until they exactly balanced each other.