A Depron Seagull

[MattyB]

2 hours ago, Max Z said:

Matty, can you give a link to an explanation on how this is done? I am not unfamiliar with openTX, but would appreciate some guidance.

 

 

This video explains it @Max Z:

 

 

As you can see it is very simple to do, but is potentially a bit risky to have enabled all the time (an accidental flick of the momentary switch during a roll could have very "interesting" results!). To avoid this I always limit instant trim to only a single flight mode; this is easily done by setting a special function based on AND that requires SH to be hit AND the correct FM to be selected.

 

When maidening a new model I then take off in the flight mode where instant trim is active, set the trim once I am at height, then immediately change to another flight mode. Hey presto, your out of trim model is flying straight and level and there is no danger of any incident occuring due to an accidental activation of instant trim. Once back from the maiden I then make any adjustments needed to the linkage/servos/subtrim etc, then disable instant trim altogether - unless you do something dramatic to the model configuration it should be close enough to trimmed out that it will never be needed again.

 

[Stephen Jones]

51 minutes ago, Simon Chaddock said:

Given the rather horrible weather for even attempting to fly such a thing I have done a bit of decorating.

It now has a proper Seagull 'hooked' beak and its a bit creepy but that is a picture on an actual seagull's left eye.

And thanks to edit flip horizontal there is RH version on the other side 

Having a rather novel no spar lightweight structure I did my usual wing tip test just to be sure. If in a ready to fly condition it can be lifted by its extreme wingtips it gives a bending moment at the wing root equivalent to pulling about a 4g manoeuvre.

It flexes a bit but nowhere near to failure.

With a 1210 mm span it is a bit smaller than the 1500 mm span of the Plane Print Seagull but at 181 g it is only 1/3 the weight. 😉

A nose down thrust test on the scales showed 105 g. Should be enough, just. 

 

Looking good Simon. 👍

 

 

[Simon Chaddock]

I made use of the murky but flat calm conditions yesterday to have a go test flying the Depron Seagull but with limited success however no damage.

It has sufficient thrust in fact i never used full power. The best 'flight' I achieved was about 20 feet before control was lost.  

I fear it has two issues. A bit tail heavy coupled with extreme pitch sensitivity. The problem is one has a huge effect on the other making a reasonable diagnosis rather difficult.

After several low power glide attempts I ended up with virtually all the elevator down trim dialled in which almost certainly removed what little pitch stability it may have had. Unfortunately Its extreme pitch sensitivity and at low altitude made any 'recovery' stick input almost impossible resulting in either a nose plant or an immediate stall. 😟 

Just as well it flies so slowly!

I gave up after 5 minutes as the very wet grass meant water droplets were running of the fuselage!

 

The fact the wings have both compound sweep and taper makes even estimating a 'safe' CofG none too easy.      

The proposed remedy is to move the battery forward as far as possible and significantly reduce the chord of the elevator with a corresponding increase in the area of the tail plane.

Hopefully this will result in a slight nose heavy CofG position requiring slight 'up' elevator (refex?) so giving a degree of pitch stability. It after all more a flying wing than an conventional plane.

Well that's the plan.

[MattyB]

Could you configure it as a flying wing instead using elevons for pitch?

[Simon Chaddock]

MattyB

I probably could but the wings were built without any twist or washout so likely would not be pitch stable.

In addition when the elevons were acting as elevators the moment arm around the centre of pressure would be even shorter than it is with the current layout.

 

The Plane Print Seagull has true flying wing elevons but without knowing exactly the wing incidence configuration (it would all be 'hidden' in the print files) I elected to use a conventional elevator knowing the very short tail moment would make things difficult and it has!

 

A start on the modifications.

The battery hatch has been extended forward.

With an even bigger temporary cut out underneath to release the Rx that was right at the nose.

 

The Rx was turned round and placed in the belly beneath the EDF. This will allow the battery to go right up against the nose former so moving its centre of mass forward by some 40 mm. This should be sufficient to move the CofG forward a bit as at 43 g the battery is over 20% of the Seagull's flying weight. 🙂  

[Eric Robson]

On 25/11/2022 at 15:43, Shaun Walsh said:

For true realism it needs a servo operated pump that dispenses white toothpaste from an orifice at the bottom.

As long as it doesn't hit the fan

[Simon Chaddock]

With all the skin made good and a new longer battery hatch it does not look any different apart from the ragged black on the top side of the wing tips.

The 450 mAh 3s is now squeezed in right up against the nose.

The tail outline is unchanged but the elevator has less than half the area and is 25 mm further aft.

The all weight has increased by 1g to 182 g.

Just need the right condition to try again.

 

[GrumpyGnome]

Good luck!

[Simon Chaddock]

With the current calm weather I had another go.

Better but still very twitchy in pitch despite the reduced elevator. I am still sure it is tail heavy so no 'flight' was attempted just low power extended glides. In each case effective control was always lost after travelling about 30.

The next step is to add some weight into the beak. Its quite a long way forward so I 'guestimate' just 10 g would make a noticeable difference.

New LW-PLA nose with 10 g of lead inside the beak.

I hate lugging dead weight lead around so ultimately the answer may be to simply use a bigger heavier (600 mAh?) battery.

 

[GrumpyGnome]

Yes, I'd try a heavier battery if you can shoe-horn it in .....

[Ron Gray]

7 hours ago, Simon Chaddock said:

I hate lugging dead weight lead

It’s never dead weight if it makes it fly!

[Simon Chaddock]

The extra 10g right in the nose made all the difference - it flies!

Still horrendously sensitive in pitch despite the reduced elevator and touchy in roll, It drops a wing ever so easily. It climbed gently to abut 50 feet on reduced power. Made two close in circuits no problem as it flies so slowly.

After about 2 minutes it looked like there was a radio problem as it dived from 50 feet almost vertically into the frosty ground!

The result was inevitable.

 

Although the battery was separated in the crash every thing worked as soon as it was plugged back in.

All quite mendable.

On careful examination it looks like it was not a radio signal problem but a suspect Rx connector from the UBEC so no Rx power! or anything else come to that.

 

Now I know it can more or less be controlled in flight I will repair it as is and put on some serious elevator expo.

Next proper flight will be have a video.

Then a rebuild forward fuselage big enough for the heavier battery and possibly a "gyro" Rx too!  

 

 

    

 

 

[GrumpyGnome]

Proper 'good news, bad news' story! Looking forward to a video if it soaring......... like a bird.

 

Nice one Simon.

[Nick Cripps]

And if you need more nose weight, put a chip in its beak!

[Rich Griff]

Extremely good design and engineering happening with this project I feel.

 

As to nose weight, a mars bar !

 

One dam flying rat took one clean out of my hand as I was trying to eat it !

[MattyB]

12 hours ago, Simon Chaddock said:

The extra 10g right in the nose made all the difference - it flies!

Still horrendously sensitive in pitch despite the reduced elevator and touchy in roll, It drops a wing ever so easily. It climbed gently to abut 50 feet on reduced power. Made two close in circuits no problem as it flies so slowly.

After about 2 minutes it looked like there was a radio problem as it dived from 50 feet almost vertically into the frosty ground!

The result was inevitable.

 

Although the battery was separated in the crash every thing worked as soon as it was plugged back in.

All quite mendable.

On careful examination it looks like it was not a radio signal problem but a suspect Rx connector from the UBEC so no Rx power! or anything else come to that.

 

Now I know it can more or less be controlled in flight I will repair it as is and put on some serious elevator expo.

Next proper flight will be have a video.

Then a rebuild forward fuselage big enough for the heavier battery and possibly a "gyro" Rx too!

Well done, good stuff. I nearly recommended a gyro or FC last time, but I agree you were right to try and take it with nose weight first. On balance perhaps with a platform like this, configuring it aerodynamically as a plank flying wing with elevons may be the best bet, but obviously that would need an entirely different wing at this point. Perhaps for a v2?!

[Andy J]

I made several bird designs with a V tail. All had a tendency to perform what I called the dive of death. Model would fly nicely but very sensitive in pitch until without warning it would put its nose down and enter a dive which was impossible  to recover from.

[Ron Gray]

Ah, maybe that’s why they became extinct!

[Andy J]

Simon, have you thought about including a gyro to improve stability?

[Simon Chaddock]

All mended.

As the elevator is so sensitive I have fitted proper hinges rather than its original top tape hinge to ensure consistent movement at small angles!

  

We shill see.  

[John Wagg]

Just conjecture but would the very fast airflow under the elevator, due to the EDF, have an adverse effect.?

I could imagine any down elevator being much more effective than up.?

 

If you did think about fitting a stabiliser/gyro then the Byme A is quite small, about the size of a postage stamp.

It does need though an SBUS input and a three position switch programmed to operate it.

Although if the model goes into a death dive I very much doubt it would be able to rescue the situation.

Edited December 12, 2022 by John Wagg

[Denis Watkins]

The beauty of a stabiliser is that it has already detected and started to correct the direction of flight before you even see it yourself.

A properly installed stabiliser would avoid a death dive, though such a dive does sound like a stall.

[Andy J]

Not convinced my bird designs entered a deep stall as had one come down from a very high altitude. Seem to recall it just appeared to increase speed in the dive without a change in pitch. However this was some years ago and can't really recall the events of the day, only the fact that it came down on a secure high speed car test track. Had to go knocking on the security post door to recover the model.

 

Did wonder if it is a tail blanking effect similar to the issues found with the flying flea design.

 

Well impressed with your Depron work Simon. Gave it using it myself some years back as there was little longevity in the models. All my Depron builds including a enlarged Eagle design now reside in the loft. One day I may think of setting them free to fly again.

[Simon Chaddock]

I have been told and I can fully appreciate that a "bird" layout particularly with a gull wing that incorporates both for and aft sweep as well as a relatively thick wing section is likely to suffer significant centre of pressure changes with angle of attack. The changes might well exceed the natural stability forces available its small tail volume. In other words there could be AOA regimes where it becomes unstable. If you couple that with limited elevator authority to tame the pitch twitchiness it could end up beyond recovery control.

It may come down to flying within a limited speed range but that has to be judged adequately from the ground.   😲

I never expected it would be easy to get right.

After all very few of my conventional layout planes fly perfectly first time either! 😉

 

Andy

As far a Depron longevity goes it is the energy absorbing crumple ability of light weight structures that impressed me. What is damaged is lost but the remainder is structurally undamaged to far less a degree than in a balsa structure. This has allowed me to keep Depron planes repaired and flying for a many years.

My oldest all Depron plane in full working order and still flown is now 11 years old and it is an EDF!

[Simon Chaddock]

The testing continues. There is some improvement in control each time but........

Several short flights but the last ended up with a series porpoises and the ground is of course now frozen solid.

It still feels like it is tail heavy even with the 10g nose ballast. I expect if it had a reasonable tail moment it would probably fly adequately. 

No problem with repairs but the whole nose section is suffering from "crash fatigue" so will have to be partly rebuilt. At the same time I will extend it a bit so the battery can be moved forward to adjust the CofG without using nose ballast.

To be continued.

 

I fear is will come down to "Can it be persuaded to fly properly before it get wrecked?"