Depron HE 162

[Simon Chaddock]

Stephen

I have only run out of 'proper' 2 & 3 mm Depron, the stuff actually made by Depron. I have a small supply of their 3 mm Aero which is somewhat softer and more flexible.

I have plenty of the the 5 mm underlay which is even softer but is actually very little heavier than the original 3 mm Depron.

 

Original Depron sheet was actually a 'sandwich' foam. The way it was made gave a top and bottom 'skin' that was rather more dense than its core. As a result it was considerably stiffer to bending than a sheet that has the same density all the way though. Most current foam sheet, including Depron Aero is like this.

The 5 mm 'underlay' sheet is made from a softer less dense polystyrene compound specifically chosen for it insulation properties (and its price!).       

[Simon Chaddock]

At long last the fuselage is complete (again!) with the duct permanently glued on.

The Rx has been tested and the elevator checked that the gyro operates in the correct sense to an disturbance.

The next job is to refit the wing. As the duct mountings have been changed the wing aperture will have to adjusted (sanded) to give a good fit.

The servo wires at the moment exit the wing on a Y lead. This will have to be changed to individual leads to allow for the dual ailerons option on the Rx which in turn will permit the differential aileron option on the Tx. 

Edited May 2, 2021 by Simon Chaddock

[Simon Chaddock]

After quite a bit of fitting the wing is back on. Even took it outside in the sunshine!

The ailerons now have 50% differential, about twice as much 'up' as 'down'.

Now we just have to see if it is any more flyable than it was before. ? 

[Simon Chaddock]

This is proving to be quite a saga.

In view of the previous problems the first flight was just a simple straight line hand launch into wind and land within the space available.

No problem at the launch and the initial flight with the gyro keeping things level but after a second or two it began to yaw and to my amazement continued to do so with no input from me just the gyro keeping the wing level. The direction of travel hardly changed. Still only 6 ft from the ground I closed the throttle to get it down before things got any worse. It touched down 'crabbing' at nearly 45 degrees. My only input being slight elevator as it touched down to keep the nose up.

It was behaving as if it was directionally unstable.?

I added a modest amount of nose weight and tried again with exactly the same result (the yaw was in the same direction) only this time the 'leading' wing caught the ground and 'yanked' the wing mounting bolts slightly.

Clearly something was wrong so I stopped before anything worse happened.

 

My guess is the that although the design may be stable flying straight ahead in a yawed state one fin is badly disturbed by the big duct over the wing.

So the alternatives are

a) To add rudders.

b) To increase the fin area.

c) Do both.

At the moment adding working rudders (there would be 4!) is the least favourite from a weight point of view given the He 162's distinct lack of thrust.

Increasing the fin area should be the simplest. I have just enough 2mm Depron  to make two new fins.

If this fails to correct the problem I could still add rudders, they would also be bigger or maybe just retire it as a lightweight project that was just "a step too far". ? 

 

 

        

[Colin Leighfield]

Before I wrote this I’d missed out the last page of your posts, which answered the questions I was asking, so this is the edited second attempt! What a build though Simon! I’ve done some Depron planking and it works well, but the amount of work in doing it on projects like this is huge! The way you are doing it combined with 3D printed formers and ribs is a proper combination of sheer old-fashioned skill and modern technology. You continue to amaze.

The stability problem you describe is similar to what I have seen in the past with planes that have a lot of surface area in front of the c of p and relatively small tail surfaces. Enlarging them would probably sort it out, but it’s non-scale and adds weight where you don’t want it. A larger tailplane would tolerate a rearward c of g a bit better though. It makes you wonder why the original handled as well as it was said to. 

Edited May 4, 2021 by Colin Leighfield

[Simon Chaddock]

Colin

Yes indeed 'Winkle' Brown said it had particularly good control harmonization which is a bit surprising.

I note also that the initial prototypes were criticise for severe Dutch roll which was reduced to tolerable levels by the intervention of Alexander Lippisch  adding the down turned wing tips but it does suggest the airframe had some fundamental stability issues.

I know my Bachem Natter which also had considerable forward fuselage area also had considerable stability issue (although longitudinal in its case) that was not solved until the CofG was brought to just 18% chord and than was on a simple parallel chord wing.

The He 162 wing on the other hand has a pronounced 2:1 root to tip taper but with a straight leading edge. It is difficult to estimate the actual effect that might have on the lift distribution. 

I have made new fins with 30% more area but kept exactly the same proportions.

  

To extract every benefit from the extra area the fin leading edge will be at the same point on the tail plane so the effective fin area will be moved slightly aft.

I will also leave them unpainted for the initial test so the weight gain will be small about 1.6 g per fin.

However the current weather means there is not much chance of doing a test for at least a week.   

[Alan H]

I think the only solution to the yaw instability problem is more fin area. I believe the problem arises from the amount of side area ahead of the CG leading to an adverse yaw moment which is similar or more than the corrective  moment produced by the fins. I'm surprised the full size did not have similar problems but a pilot sitting in the cockpit would make instinctive corrections with the rudder pedals to correct any slip.

[Colin Leighfield]

I’m sure that will improve things Simon. When a skint school-kid, the only things I could afford to make were chuck-gliders! I enjoyed drawing up my own and tested all kinds of ideas, deltas, swept wings, canards etc. I also worked my way through the WW2 fighters and although being profile, they were scale in every other way. Spitfires always flew well, in spite of the fairly small tailplane. I do remember though having problems with the Typhoon. It was completely unstable directionally and would finish up going half sideways into the grass. In desperation I cut the chin radiator off and hey presto! It flew perfectly, though now looking more like the original prototype Tornado than a Typhoon! The point though was it made me aware at a tender age that there has to be a balance between side areas in front of and behind the c of p. I’ve never tried to calculate it!

[Simon Chaddock]

Calm yesterday so I had a go with the new bigger fins. Better but it still ranks as about the least controllable plane I have!

First flight was in a straight line on purpose. Flies very slowly. The stab rx does its job and keeps everything damped down but it is desperately under powered.

Second light I did manage to coax it round a 180. Too much bank and the drag rose above the thrust available so it was a matter of trading radius to maintain height. The end result was a huge radius turn far too big to be practical for the space available. It never rose above 15 feet. The final 'landing' was still a bit wing low which damaged the wing tip a bit.

The He 162 weighs 671 g or 1.47 lbs. This means it has no more than 60W/lb at full power. A not very realistic figure for any ducted prop arrangement even a slow flying one!

Before attempting to sort out its handling characteristic I will have to install quite a bit more power along with a bigger battery.

A 70 mm true EDF would fit the existing duct but it would have to be 'light' rather than 'powerful'.

The extra weight would likely be ahead of the CofG so it would allow rudder servo(s) to be installed.

This could take a while.

[Simon Chaddock]

After hanging on the wall for nearly a year I decided to have another go with it or rather to see if I could get a bit more thrust and save some weight.

A test rear motor mount retaining the same 2205 drone motor with a scale after body that reduces the nozzle to 95% of the FSA.

It will use a 3 blade 3x4.5 'wide blade' prop rather than the 4 blade 3x3.5.

The duct itself is rolled 3 mm Depron with printed joining pieces.

 It has a printed bell mouth.

Overall this duct is some 20 g lighter than the printed. Not that much but every little helps.

The difference in thrust is remarkable.

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

On a 4s it delivers close to 250 g thrust using 10A (149W). It certainly passes my 'blow the door shut' test. The ESC can be changed for a 30A 6s version if required. ?

This is so much of an advance over the previous arrangement I will simply substitute this duct slightly extended into the HE 162.

It appears the coarser pitch prop is much betterable to handle the effect of the long duct.

No guarantee but I might yet get the Depron HE162 to fly. ?

 

 

[Simon Chaddock]

Having made the decision to instal the test duct into the Depron HE162 the next problem was how to actually do it.

For its size it is a very light basically hollow airframe that relies entirely on its skin for strength and rigidity. The danger being that by cutting open enough area to install the complete duct it could make the rest of the airframe too 'wobbly' to be handlable.

Eventually I bit the bullet and chose to cut the nacelle along the centre line of the duct, either side, front to back. In the process it would destroy the printed duct but that was going to be scrapped anyway. Done this way it would mean the lower half of the duct would remain in place on the fuselage so retaining a degree of fuselage rigidity and not disturbing the wing mounting.

To my relief it actually worked quite well. Note the oversize tail fins installed earlier to try to improve its flight characteristics.

 

Once open it does rather highlight the delicate nature of the structure. It is all just 2 mm Depron. ?

Now I have to work out how to fit and glue in the Depron duct to all the formers without breaking too much of anything.

  

On a lighter note what you don't see in the above picture is my daughter's ChiHuaHua asleep on the bed!

She likes both comfort and human company.?  

 

  

[J D 8]

My daughter had a crazy Spaniel, he once converted an 80 inch glider wing to little bits of balsa and film! 

[Simon Chaddock]

Took some careful fitting and adjustment as well as running the motors wires (0.7 mm magnet wire) all the way along the underside duct it was eventually glued on to the lower half of the nacelle.

Not easy to ensure all 7 formers had glue and made contact with the duct.

The motor wires have been brought forward into the cockpit.

I intend to use an 850 mAh 5s LiPo. Its current ESC is only good to 4s so before going any further with restoring the fuselage the next job is to temporarily install a 6s ESC and a servo tester so the duct can be tested at full power.

Compared to the space inside the fuselage the ESC and UBEC are both tiny and light.?

With the motor now right at the back of the duct I expect the battery will have to well forward so the internal layout of the cockpit/battery hatch will have to be substantially altered. Never that simple with such a light construction. ?   

[Simon Chaddock]

Fitting the top part of the nacelle back proved to be quite an exercise as the Depron duct is 6mm larger OD compared to the single wall  printed one so it required an insert or both the skin and the formers either side.

It also requires quite a bit of "skin adjustment" to get it to match up cleanly with the printed inlet and exhaust.

The canopy and windscreen have been removed. The ESC, UBEC and battery box are rather "lost" in the huge space!

What was the removable canopy will be fixed in place. The windscreen will now be removable and become the battery hatch.

I am still not exactly over confident it will fly

 

 

 

 

[Simon Chaddock]

The story continues.

To my surprise it did fly passably well but at the time my head mounted video camera didn't.☹️

Tried again a few days later.

https://www.youtube.com/watch?v=gU7vrjDt8pg

For some reason the power failed completely just after the launch. No control so the result was inevitable.?

Repairs took nearly 2 weeks but today it flew and the video worked. ?

https://www.youtube.com/watch?v=vjx8ApC0DDw&t=105s

The video did not like the bright white clouds so nearly 2 minutes had to be edited out.

I does fly 'silly' slow for an EDF.