24" Sopwith Pup

[Terry Whiting]

Simon,

 

Have you thought of GWS Hyper Drive props, I have used them on small models, and are very forgiving. Being extremely thin and flexible I replace folders with them.

BRC are doing a good range of them.  

[Malcolm Fisher]

Hi Simon,

 

A belated comment re the clothes horse or sewn hinges. I have used them with closed loop systems with no problems - at least on rudders and elevators. I must admit that I haven't yet tried a closed loop aileron set up but I don't think it would make any real difference - especially if there is some tension and elasticity in the loop material as you have used..

 

Malcolm

[Simon Chaddock]

A quick up date

The Depron Pup crashed again but as before the basic Depron bits are still sound.

The ailerons appear distinctly ineffectual if things get just a bit out of shape, I suspect due to aileron yaw compounded by the small fin area.

I am going to put in some aileron differential coupled with a proper rudder.

[Terry Whiting]

Simon,

 

Sorry to hear of another failed test, but i'm pleased you are now contemplating a 'rudder'.

Did the slight  negative wing incidence help, or was the flight too short to evaluate?

Is there any possible means of test gliding? as this could show if the problem was/is power torque related.

 

Terry

[Biggles' Elder Brother - Moderator]

The test glide idea might be  sound. As you say Simon, with these smaller models everything happens so quickly you've hardly got a chance to figure out what's out of kilter before the ground rushes up and brings things to an abrupt halt! With a couple of test glides you'd at least have a chance to check that she tracks reasonably straight

 

BEB

[Simon Chaddock]

In the last two 'flights' it has banked the opposite way! 

In both cases it appeared to pull away strongly with very gentle climb but what has surprised me was the complete lack of aileron authority. The bank increased despite opposite aileron and just continued until I suspect the inside wing tip was stalled and dropped. In both cases it hit the ground nose down with almost vertical bank having turned though about 90 degrees.

So I am thinking either the ailerons are simply not effective enough and/or the CofG is too far back. 

As suggested, a test glide (over the longest grass I can find) should help identify the problem.

[Biggles' Elder Brother - Moderator]

It could well be a bad case of adverse yaw. It banks, say left, you put in right aileron, but the increasing drag on the down going left aileron just keeps on pulling it left - slowing the left wing until it tip stalls. Result of course is you feel the ailerons are ineffective - when in reality they are "working" extra hard - producing the exact opposite effect of what you want!

 

If this does turn out to be the problem then you might need that rudder as Terry suggests!

 

BEB

[Always broke]

I find with my 1/3rd scale pup that I lead with the rudder on turns. Also I have about a 25% movement on the downward Aileron to 100% on the upward aileron. This seams to work very well. I would have thought the rudder is essential in the model you are building.

 

[Terry Whiting]

Simon,

 

If the model was mine,  I would disconnect the aileron servo, secure the ailerons with 4 small pieces masking tape, and plug the rudder servo in it's place.

I would then test glide without radio.  If required add plasticine as ballast  until I had a satisfactory glide.

If satisfied, use the height of a step ladder to extend glide with radio on and use elevator, and rudder only. If all was well my next glide I would open the throttle very gingerly.

 

I hope i'm not being a pain, just want to see this plane fly.

 

Terry

 

 

 

 

[Simon Chaddock]

Terry

Thanks for the ideas but I think I might have found the answer.

I have two TXs both on the same frequency. One has rather an old NiCd in it so I tend to use it for testing set ups on the bench, the other I fly with.

The Endurance and the Wing Dragon both work fine on the 'flying' TX but I did set up the Depron Pup with the other one as I built it.

Then I had a terrible thought, were the aileron directions set the same on both TXs?

 

I am hugely embarrassed, it was not a lack of control but the wrong control, which is why it banked and crashed so readily both to the left and to the right - I was telling it to!

 

So we try again but boy! am I glad this is not happening to the scale Pup.

[Biggles' Elder Brother - Moderator]

Its exactly as I said - adverse yaw - its just that the cause is different

 

Well at least you have found it!

 

BEB

[Terry Whiting]

Simon,

 

I think we have all suffered the same dilemma in our modelling lives,

 but it takes a man to hold his hand up and admit his error to the world.

Hope all goes well on the next test.

 

TW  

[Klippy]

Echo that Terry

[Simon Chaddock]

Thanks for the kind sentiments but I glad to report it flies!

However word the ridiculous comes to mind.

It flies ridiculously slowly and is ridiculously twitchy, nevertheless, these pics were taken straight from the field after it had flown twice!

 

First the cross brace to prevent a prop blade dropping between the cabane struts.

The struts have been moved back, reducing the stagger so effectively moving the CofG forward a bit.

I suspect the CofG needs to go forward just a bit more.

It has plenty of power, I only used 3/4. Although the wind was very light (about 3 knots) it certainly notices every little bit of turbulence.

It appeared to fly ever so fast on the downwind leg (10 knots?) yet when I cut the power on approach it just stood still and 'parachuted' down well short of the anticipated landing spot.

Now we got to see how well it will fly.

 

Edited By Simon Chaddock on 19/02/2010 14:52:54

[Biggles' Elder Brother - Moderator]

Weeeeeeee!

 

Congratualtions Simon. Another step towards the "big day" with the "real thing"!

 

BEB

[Terry Whiting]

Simon,

I'm really pleased for you.

I see you did make provision for a rudder, did you have to use it?

I suppose being  twitchy could be due to  the lightness, and the amount of aileron  control surface to model weight.  It might be worth trying rudder only, this I think would give some indication to the power of your ailerons, and may be the need for reducing their overall travel.

 

My little Widgeon which is about 3oz heavier is surprising how little rudder movement is required in the turn.

 

Just  thoughts.

 

TW   

 

[Doug Ireland]

Unfortunately its a mistake all too easy to make! Bet you won't do it again though

[Simon Chaddock]

Terry

The first task was to remount the motor as the original had been loosened after the abortive initial flights. The motor is in exactly the same relative position although the firewall has been doubled up.

As the Depron Pup is intended to be a 'test' for the scale one I have not yet installed a rudder, although as you suggest it may be advantageous.

 

Along time ago I did a combined rudder/aileron set up (all from a single servo) on a big lightweight glider but in that case is was done to improve the turn response compared to using rudder only.

With a bit of servo rearrangement I could do the same on the Pup(s) with virtually no weight penalty.

 

Before that however I will gradually reinstall the rigging to see what effect it has on the performance, hopefully it will just add drag rather than effect the flight characteristics in any way.

Now I know it flies I can reduce some of the twitch by reducing the elevator travel. 

[Terry Whiting]

Simon.

 

I assumed the twitch was aileron, but I see now it's pitch twitch, so you could well be right with your assumption of a rearward balance point. Still it's nice to know she flies, and will be great once trimmed.

 

TW 

[Simon Chaddock]

Terry

Although it is pretty twitchy both in pitch and roll under power, it did settle down quite a bit when gliding. I thus deduce that the primary problem is elevator sensitivity resulting in a pitch up/wing drop followed by nose down/ aileron over correction sort of thing.

If Sunday is as calm as today (I was working) I will have another go with reduced elevator throw. 

[Stephen Grigg]

Wow now this is a thread to be  very proud of congratulations so far its been like a good novel,way above my comfort zone,I admire your modelling skills

[Terry Whiting]

Simon.

 

Although to scale these control surfaces are extremely powerful for the model's weight.

 

When I converted the Widgeon from free flight  to RC  I was experiencing the very same problems with elevator and rudder. I was in fact letting RC cloud my mind. It had been

flying beautifully as a free flight so WHY??

It then dawned on me the only trim I  had on the fin was  1"x 1/4" piece of soft thin aluminium, and the stabilizer was trimmed with pieces of thin card.

 In my conversion  my rudder was 50% of the fin area, and  the elevator was 25% of the tail plane area.

 

Today my FULL  throws are about 3/32" either way, and I couldn't guess how little

control movement are required in flight.  

Edited By Terry Whiting on 21/02/2010 10:49:06

[Simon Chaddock]

Terry

You are probably right. I have reduced the elevator travel by going in one hole on the servo horn, it may have to come in further.

 

I could have tested it today, the wind was light enough, but the thought of flying a white plane on a snow covered field in the freezing cold overcame my desire to try!

[Terry Whiting]

Hi Simon,

 

How is the world in your area ? , certainly not test flight weather in Hertfordshire.

I think this winter will make flyers think more of the advantages of indoor flying.

It is certainly making me think. 

 

TW

[Simon Chaddock]

Yes Terry if only I had access to (or could afford) something like a sports hall!

 

I have got ready a couple of times but as soon as you get to an open space the wind seems so much stronger. I will just have to wait.

 

I am looking at fitting a bigger 900mAh battery to the Depron Pup. With a small modification it will just fit and a bit of extra weight (20gm) ahead of the CofG probably wont go amiss.

 

I might fit such a batter in the scale Pup as well.