A Depron Seagull

[Simon Chaddock]

All repaired with a part rebuilt longer nose that allows the battery to move forward about 8 mm.

It spoiled the nbose line a bit but it only added 1 g, now weighs 182 g ready to go but more to the point the CofG is at the same place without the 10 g nose ballast.

Just have to keep trying.  

[Chris Walby]

Hi, Been following as its a very interesting build and development thread. Well done

 

Are you saying you have moved the battery forward, removed 10g of nose ballast, added a longer nose and its still 1 g heavier than the previous AUW? I might be missing something but I would have thought the AUW would have gone down unless the repairs makes up the additional weight?

 

Never ceases to amaze me the level of control and accuracy birds of prey have in all weather conditions. It would be really informative if the subject was studied in depth as to quite what they are doing with wing/tail aerodynamics in sustained flight with what appears to be effortless control. 

[Simon Chaddock]

Chris

Its 1g heavier than in its first guise without the ballast. With the ballast it weighed 191 g.

The extra 1g comes from the longer nose.

I did fly it on the last of the calm days but I think it is still flying tail heavy. Several short flights but each ended in a wing drop (stall?).

The last flight it hit a frozen clump of grass so stopped dead and broke off the right wing at the root but no other damage.

The next step is to move the elevator servo forward as far as possible. A bit harder than it might have been as the servo could not be disconnected so slots had to be cut in 3 formers to allow its wire to be repositioned.

To improve its yaw stability I have added a significant temporary fin extension.

 

I not sure it will make any difference but I have curled up the wing tips a touch.

Hopefully in conjunction with the extra fin area it might reduce its tendency to side slip.

With the weather change there is now no chance of testing it. 

[john davidson 1]

This morning picked up one of the Lidl Pteranadons,  free flight ,fan on top too, but if it flies well  might enlarge for depron rc with a fan on top  Should get a pointer as to CG and perhaps help with the problems you have had with the seagull. my missus has just nabbed the box, says will get it back Christmas Day 

 

ps £5 off fresh turkeys! cheap as chips!

[Rich Griff]

John, may I ask how much was the Pteranodon please, still just shy of £20 ?

[john davidson 1]

This morning picked up one of the Lidl Pteranadons,  free flight ,fan on top too, but if it flies well  might enlarge for depron rc with a fan on top  Should get a pointer as to CG and perhaps help with the prob 

 

It was £20 on Friday, today I was too busy hefting a turkey to pay much attention . pleasant surprise- dug out receipt-£17.90

 

And the turkey was £5 off too, £23 for a medium

[Simon Chaddock]

Just a quick up date the weather was more or less calm enough although the grass at the field was very  long and wet but two short flights, both more or less under control followed by perfect belly landings.

Still ridiculously sensitive in pitch and to any sort of gust.

Once I properly get the hang of flying it a video will follow!

 

I have some further modifications that I might try to tame it a bit further. 

[eflightray]

Long long lime since I looked on here, so apologies for possibly barging in.

 

I have a scratch built Eagle built in Depron. It flies great. It does have a prop on the front though, and a V-tail. But it works.

Sorry if stepping on toes, (I occasionally have a habit of doing so), but you seem to be trying to be trying perhaps too many changes all at once.

Can't you just sort out the glide, stability and controls as a glider or prop power first, then develop the ducted power side. 

Sorry again. My simple brain just tries to come up with the simple method first.

 

Ray - I'll get back to my cave.

[Simon Chaddock]

eflighttray

Don't worry, no toe stepping taken.

This whole project started when I felt I could do better in Depron than the 'printed' Plane Print Seagull which is EDF powered.

Using only thin Depron sheet I knew I could not follow all the smooth curves of the Plane Print design so I made alterations but in the full knowledge the changes would likely result in significant issues with stability and control in what is a fairly extreme layout to start with.

I did achieve the main objective. under half the weight. but what caught me out was just how far forward the CoG had to be with the wing plan form I had chosen. The restricted fuselage volume meant that even moving the battery forward a few mms required a significant structural modification.

The EDF on the other hand has given no problems at all and allows reduced power to be used as a 'glide extender'. So far full power has not been used in flight.

The changes so far have been sequential.

1. Reduce the elevator area. An obvious requirement evident from the very first flight.

2. Move the CoG forward by adding nose weight.

3. Move the CofG still further forward by rebuilding the nose to move the battery forward so that it more than matched the effect of the nose weight.

4. The last test had the benefit of increased fin area. The tail 'volume' of a Seagull is by plane standards very small indeed.

 

The last modification but as yet untested is to adopt smaller twin fins to give a better appearance and improved tail rigidity coupled with a central broad chord elevator. This leaves the outer sections of the tail surface fixed and aerodynamically unaffected by the elevator position.

Overall this layout is 1 g lighter than the previous single fin and full span elevator.😉

I doubt the weather will allow any more testing until the new year.😟

 

 

[john davidson 1]

Sorry to subvert the topic again but just test flew the Pteranodon , flew well with no adjustment , very stable so promising for an enlarged rc version. Lost a vertical fin  after a few flights, small and transparent so back home to make another and glue them on for next time

[Rich Griff]

Hi Jon, interesting...pteranodon, maybe it deserves a thread of its own...3 modes ?

 

Good to hear it flies well.

[john davidson 1]

The seagull, it might fly ok with the transparent vertical fins on the   slightly swept back wingtips and tailerons,  rather than the vertical tail as present, flying wings don't seem to need them?

[Andy Stephenson]

Have you considered using a flight stabiliser instead of using fins at all, it would look even more realistic without them. Not sure how it would work though.

[Simon Chaddock]

Thanks for the comments.

An actual Seagull, as with many birds, needs no fin but then it does have 'stabilised' variable geometry and incidence wings along with a variable area and incidence tail. I wish!

 

To use an RC plane type stabiliser you have to separate the control into separate roll, pitch and yaw functions which almost by definition means an adjustable fin or some form of wing drag brakes. I have gyro stabilised planes than use no rudder function but they do have big fins to ensure natural yaw stability.

I was specifically avoiding using a gyro simply because the Plane Print version manages without one although it is in effect a flying wing using the accurately controlled wing profiles, sections and incidences possible with 3D printing.  

 

What I am aiming for is a configuration that is stable (just) in pitch and yaw without relying on the specific wing aerodynamics of a flying wing and at the same time keeping within my 250g weight limit.

 

Of course mid winter in the UK is not an ideal time to test it but it is getting closer!

 

[Simon Chaddock]

I did some more testing in a quiet spell but the field was extremely soggy so both the Depron Seagull and my feet got very wet in fact it was the water droplets running off the plane that convinced me to stop.

What the testing did show was that in its latest twin fin form it glides nicely - as long as you leave the controls alone, however apply anything like the thrust to maintain height it instantly pitched up and stalled. Its extreme pitch sensitivity coupled with the thrust line well below the centre of drag meant it did this quicker than I could hope to accurately control with the elevator.

What it needs is some form  of thrust/pitch compensation, as in down thrust. With no hope of adjusting the EDF thrust line the only possibility left would be some sort of thrust nozzle deflector.

Indeed Plane Print offer an extension tube on their Seagull to alleviate the same issue.

Rather than an extension added to the existing duct I judged it would be possible to replace the rear section of the duct with a longer one that included an angled down nozzle further aft to provide a nose down pitch with thrust.

After several variations the final duct printed in LW-PLA. The Seagull is of course inverted!

 

It is a 30 degree 'bend' that should move the thrust line at least closer to the centre of drag hopefully without loosing too much thrust.

 

With repeated low pressure anticyclones in the forecast the weather does not look kind for quite some time!   

 

 

 

Edited January 9, 2023 by Simon Chaddock

[john davidson 1]

Have you built  reflex into the wing?, absolutely vital for stability in a flying wing

 

I went back to look at the previous photos  and it seem you have no reflex, it is surprising  what a difference it makes , even in free flight. Raising the elevons might help

Edited January 9, 2023 by john davidson 1
spelling

[Simon Chaddock]

john

Technically it is not a flying wing, just a very close coupled and rather small tail plane! I was expecting it to be twitchy and it is.

What I hope is that there is enough longitudinal stability to be controllable. The fact it will now glide without any input suggest it is just stable but with so little reserve that virtually any pitch disturbance takes it outside the stable flight region.

 

The whole concept was always an experiment so success was by no means guaranteed although it did achieve one of its goals to be under 250g.😉

It may well prove to be impossible to achieve stable powered flight with its current configuration. In that case some sort of rebuild will have to be considered.

Edited January 9, 2023 by Simon Chaddock

[john davidson 1]

Reflex  or washout is desirable in most wings , look at the Spitfire ,I agree the Gull is not a flying wing ,just  very short coupled as you say and this must be where the instability lies, the tail does not have the power to recover from a dive caused by tip vortex. My daughter gave  me Martin Simons book on model aerodynamics for Christmas  so sorry to be so pedantic

Edited January 9, 2023 by john davidson 1
more thoughts

[Simon Chaddock]

Really calm today so the Depron Seagull had another test.

The downward faxing thrust tube coupled with a vary slight right thrust component has transformed it flight characteristics Still a bit sluggish in roll but it can now fly hands off for many seconds.

Very sensitive in pitch but it can easily perform a tight loop!

The only outstanding issue is it is using a 'park fly' Rx with a single very short aerial. Get the plane lined up wrong with the Tx and it looses signal and it takes a full 3 seconds to re acquire it.😲 A new Rx is the next task.

Now confident enough in its flight characteristics to make flight video.

The really calm weather seems to have moved on so it is currently "hanging on the wall".

 

[Simon Chaddock]

I was just about calm enough today for a flight video. It is rather short as I had forgotten how to set up the video camera properly so it stopped at 1;22.

https://www.youtube.com/watch?v=kodYniSccCA

Pity the video stopped as a bit latter on it demonstrated how well it glided. Being sub 250 g it is very effected by turbulence a situation made worse by it rather limited pitch stability.

But is does fly.

[John Wagg]

The first half of this video has might be of interest :-

 

 

 

[john stones 1 - Moderator]

Looks good airborne Simon, can see it's easily upset pitch wise, impressive though. 👍

[Richard Harris]

Great work as always Simon, you now need to add some sort of toothpaste dispenser!

[MattyB]

13 hours ago, Simon Chaddock said:

I was just about calm enough today for a flight video. It is rather short as I had forgotten how to set up the video camera properly so it stopped at 1;22.

 

Pity the video stopped as a bit latter on it demonstrated how well it glided. Being sub 250 g it is very effected by turbulence a situation made worse by it rather limited pitch stability.

But is does fly.

 

Vry impressive Simon. The phugoid oscillations would indicate to me that it is still a smidgeon tail heavy, but given what you have already done to address that I'm guessing going any further would be very difficult. On that basis I think I'd be chucking in a gyro stabilised receiver (or aftermarket gyro like the Guardian) and seeing if that helps - they can do great things with models that have marginal pitch stability.

[Simon Chaddock]

MattyB

I would agree that moving the CofG a touch further forward would likely increase the pitch stability. I have moved the elevator servo as far forward as the ducting will allow and both the battery and the rx are already up against the 'beak' bulkhead!

So short of rebuilding the whole nose (again!) the only other option is to use a slightly heavier battery although the space is very limited. It currently has a 450mAh 3s at 42g. I suspect a 500mAh version could add 10+g but of course just at moment there is a world shortage of small LiPo!