Depron HE 162

[Simon Chaddock]

I had not considered a HE 162 as a possible winter build but it was suggested and the more I looked at it the more of a challenge it appeared to be.

As an airframe layout it does make a reasonable EDF but the BMW 003 is an early axial turbo jet so had pretty small exhaust although quite reasonable inlet area & geometry.

So the challenge would be to keep the exterior to scale which would mean a relatively small EDF and when coupled with the fact its wing span is less than its length it would have to be seriously light to fly adequately with a hand launch and belly land. A necessity due to the nature of the field I fly from.

My last scratch build was a Folland Gnat where the inlet duct was 3D printed as a complete assembly with a 50 mm EDF which was then used as the 'spine' around which the fuselage was built using Depron formers and a planked Depron skin. It worked well as a process.

The HE 162 was a pretty small plane to start with so using a 50 mm EDF with a scale exhaust it would have a span of no more than 600 mm and with only 1/2 the wing area of the Gnat. It would have to be quite a bit bigger.

My Airbus A350 flies nicely using Emax 2205 racing drone motors turning 3x3.5 four blade props on 4s. The result is electrically more efficient (g/W) than any true EDF an important attribute as battery weight on a true light weight is significant.

With a 3" duct and a scale exhaust the span came out to a more reasonable 970 mm span although it will be 1340 mm long.

It seemed reasonable to concentrate on the duct and motor mount first and if successful to then build the nacelle around it

The characteristic exhaust centre body of the HE 162 neatly reduced the prop swept area to 85% a figure that on previous tests with the A350 gave the greatest (bub not my much!) static thrust.

Printer bed limitations meant the full duct has to be built up from 12 individual parts that took a total of nearly 10 hours to print but at least they all fit together exactly..

The full duct along side the nacelle plan.

A short test run but only with a 2s at this stage.

Only a gentle blow but it is only drawing 1.8A or just 13W.

So far so good but now I have got to buckle down and build the rest of it.

[Simon Chaddock]

The duct with the 2 mm Depron formers.in place.

The first few planks go on.

This of course is just the nacelle that sits on top of the fuselage. The fuselage proper is twice as long!

This is all going to take quite some time.

Edited By Simon Chaddock on 20/01/2021 00:47:47

[Thomas W Shelley]

This looks brilliant - I am going to try using depron from plans this winter. My other depron creations have been fairly simple, 'straight off the top of my head' designs. But I love working with it. Will be interested to see your techniques.

[Simon Chaddock]

Slow going but the basic nacelle planking is complete.

The underside is left open where it will glue onto the fuselage. It will need quite a bit of filling and sanding.

The characteristic exhaust nozzle.

On the basis that everything should be tested at every stage a short video of it running on the intended 4s.

It is drawing a very modest 5.7A delivering 90W. Complete the bacelle weighs 163g.

The rest of the airframe is going to have to be light to fly with such meagre power!

With the current lock down there is no rush.

[Simon Chaddock]

Slow going but the basic nacelle planking is complete.

The underside is left open where it will glue onto the fuselage. It will need quite a bit of filling and sanding.

The characteristic exhaust nozzle.

On the basis that everything should be tested at every stage a short video of it running on the intended 4s.

It is drawing a very modest 5.7A delivering 90W. Complete the bacelle weighs 163g.

The rest of the airframe is going to have to be light to fly with such meagre power!

With the current lock down there is no rush.

[Simon Chaddock]

Apologies for the duplicate post. I only noticed after the 'edit' period was over!

I have slowly been converting the small 3 view into a full size plan. At least the fuselage is now more or less complete.

This is a small 'screen dump' of what is a pretty big file (7133 x 7463 px).

.

Just to give an idea of size those formers are some 3" (75 mm) apart.

The fuselage will be built in 3 pieces, nose including the cockpit,, centre which will mount the nacelle and the tail assembly but it will eventually be a 'one piece' plane..

That wing does does start to look ever so small.

[Simon Chaddock]

A bit of former detail added in the fuselage drawing.

The first part of the fuselage is the centre section from the rear wall of the cockpit to just aft of the nacelle exhaust. Formers F to O.

It will be built as a half shell over the plan.

The set of 20 formers cut out in 2 mm Depron.

There will be temporary top and bottom keel strips pinned on the plan to glue the formers to. It will probably need a number of jury struts as well to keep it square and true once the planked half shell is lifted from the plan.

Edited By Simon Chaddock on 28/01/2021 00:45:50

[Alan H]

Following with interest

[Simon Chaddock]

With the top and bottom temporary keels pinned down the formers can be glued on along with some jury struts the planking can start.

Working with 2mm Depron formers requires the plank holding down pins to be very accurately placed.

Planking is started with two narrow parallel planks set 90 degree apart to quickly give some stability to the formers. Thereafter each plank is shaped and curved to fit as closely as possible to its neighbour. It is not a job to be rushed but 2mm is quick to sand.

It does take a degree of faith to believe such a flimsy structure will ever be rigid enough.

It does help if you have done similar before.

[john stones 1 - Moderator]

You like a challenge Simon, nice choice.

[Simon Chaddock]

Slow going but the planking is complete for the fuselage centre section half shell.

The pins mark the final plank. It is always the hardest to make fit and when you have there is the problem of where to place the pins!

The half shell has actually been lifted from the plan but is 'resting' lightly weighted whilst the glue hardens.

The next step is the most likely to cause a problem as until much of the skin is added on the other side the whole thing is pretty flexible.so it need care not to build in a twist.

With the keel strips removed the other half of the formers can be glued in place.

It is a bit of an exercise in the control of "wobbliness" so there are quite a few temporary Depron jury struts to try and keep things 'true and square'.

The first few planks on the other half will be quite narrow to limit the forces put on the structure but fortunately 2mm Depron is pretty flexible and can be hand formed so each plank fits just resting in place - well almost.

If I have guessed the likely all up weight correctly it will have a wing loading of about 4 oz/sq ft. Fly like an EDF it will not!

[Simon Chaddock]

With the centre fuselage planking complete I just had to create the mountings so the engine nacelle could be mounted on top.

It does rather show just how big the cockpit is going to be.

The HE162 used a wing of limited span but with a remarkably broad root chord.

The wing plan in position under the centre fuselage gives an idea of what it will look like.

The strait leading edge and severe taper mean the spar has significant forward sweep which may give a light weight Depron wing structure a torsion problem.

We shall see.

[Simon Chaddock]

I decided to use 3D printed wing rids as the wing is a straight taper and CURA has a scaling option so all the ribs can be created from a single master CAD file. ?

My usual light weight build using the Depron as a stressed skin with a single Depron whear web with a very small amount of 2 mm hard balsa inserted in the 2mm skin.

The ribs glued onto the bottom skin with the Depron shearweb inserted between the ribs.

The top skin with the inserted balsa flange is only added as far as the shear web. This creates a 'D' box spar that make the wing rigid enough to be lifted from the plan.

With the other side built in exactly the same way the wing halves are joined with an all round Depron doubler. The balsa flanges use external doublers as well. The HE 162 only has modest dihedral. The down turned tips will be added only when the wing is complete.

I just had to place the wing on the fuselage to see what it looked like.?

So far so good.

Next task is to add the aileron servos so the wing skin can be completed.

Edited February 11, 2021 by Simon Chaddock
Missing words

[Piers Bowlan]

Simon, amazing work, as usual. You mentioned in your post of 24 January about converting your 'small three view drawing into a full sized plan'. I am particularly interested to know what software you are using to generate all the multiple cross sections. Is it a standard CAD package? Sorry if you have covered this in another thread somewhere. Many thanks.

[Simon Chaddock]

Piers

Sorry to say in my case there is nothing clever about generating the 'extra' cross sections it is just plain 'eyeball'!

The side and top views give the height and width of the additional sections but the actual profile is just a case of 'interpreting' the difference between two 'known' sections.

I am sure there are CAD packages that allow a full 3 dimension shape to be "tweeked" to give the desired profile but such are beyond my capabilities..

Adjust formers during a build is one of the reasons why I like to make then out of Depron. It is easy to locally sand or add bits on to give a 'smooth' profile as the planks are added. Of course the formers do have to be about right to start with hence I end up more satisfied with some builds than with others.

I am embarrassed to say there are a couple of formers on the HE 162 fuselage that have resulted in a slight 'wasting'.

In this case formers M an N would have benefitted from a extra mm or two in the right place to achieve a constant fuselage taper.

It is not that noticeable unless you look carefully or take the right picture!

I'll know if I ever build another. ?

Of course the wing ribs which were generated by the 3D printing software have produced a smooth continuous wing taper.

 

Edited February 11, 2021 by Simon Chaddock

[Simon Chaddock]

A little more progress with the wing. Fitting the aileron servos and completing the top skin.

 

As this is strictly a super light weight I judge that 3/7 g servo will be quite adequate.

At least with the printed lattice girder ribs there is no problem running the servo wires

The top skin added. A 6 mm Depton leading edge and ailerons yet to be fitted.

 

In the above state the wing weighs 137g. It will be taken no further at this stage so its back to the fuselage.

[Simon Chaddock]

With the tail assembly built. also in 2 mm Depron, the parts made so far can be placed together.

So it now begins to actually look like a HE 162 rather just the parts of one. ?

The nose is next.

With the relatively heavy motor at the back of the nacelle and a very light airframe I suspect the battery and most of the other RC bits will have to be crammed right in the nose to achieve a suitable CofG particularly as the motor only draws 5A on a 4s so it could manage on a really small light battery.

This is my 'You have got to joking picture' but does show the nature of the problem.?

My original intention to save was to make it a 'one piece' plane but it is surprising bulky so I shall have to work out how to make it come to bits without a significant weight penalty. The problem with such a lightweight structure is there is nowhere locally strong enough to to bolt anything together.  

Edited February 13, 2021 by Simon Chaddock

[Simon Chaddock]

The fuselage nose has proved a bit of a nightmare although largely my own fault as to save Depron I chose to use 3D printed formers as their slight extra weight would not go amiss in the nose given I expect it to be short of nose weight.

As before built as a half shell over the plan the problem was simply you can't stick pins into a printed former so each plank had to be held down with tape.  This in turn meant the next plank could not be added until the glue had set firm and the tape removed which slows the planking process down by at least 50%.

Note even the printed nose cone is in two halves.?

As I expect the battery and everything else will be in the nose the cockpit canopy is planked and treated as part of the fuselage skin.

After two days solid the half shell is lifted and the other side of the formers added.

 

The rearmost former is a temporary 'lash up' just for planking. It will be removed before the nose is glued to the rest of the fuselage   

Now to do the same planking all over again.?

A suitable hatch, or hatches, will be cut into the nose section to install the battery box, ESC and Rx once the likely position of the battery is determined.

[john stones 1 - Moderator]

You have some patience and nimble fingers Simon, I would end up in a straight jacket attempting that. ?

[Simon Chaddock]

john

Cheers but I can assure you it gets harder and harder each time.  

I must say a nice foam BNF gets more and more appealing.

 

[Simon Chaddock]

After a bit of perseverance the nose is complete and glued onto the fuselage.

 

As I have no idea where the battery will have to go and with such a 'light weight' ballast is to be avoided if at all possible so the hatch(s?) to install the battery box, ESC and rx will be cut once as basic CofG  test has been performed. It will need the elevator servo(s) and ideally the motor wiring in place in position to do that.

It is slowly coming together.   

[Simon Chaddock]

With the structure substantially complete and the wing bolts in place it is possible to not only work out if a 'workable' CofG but the airframe can undergo my standard 'strength test'. At the normal flying weight can it be supported by just its wing tips?

 

Not exactly scientific but its puts a root bending load roughly equivalent to pulling 4g. My guess is it could easily support quite a bit more but at this stage I didn't want to break anything. ?

The next task was to see where the battery had to be placed with two 3.7 elevator servos placed on the tail plane to give a CofG at 25% of the mean chord.

The answer is a long way forward! ?

The ESC and Rx also well forward will ease things a bit. This will also have the side effect of making the weight of all the wiring almost CofG neutral.

The final problem yet to be solved is how to launch it? As its wing loading is so low I do not expect it will require much of a 'shove' but the fuselage is way too big to grip so it may require 'bowling ball' type finger holes in the underside as I did with the bigger & heavier AN124. 

  

 

 

Edited February 22, 2021 by Simon Chaddock

[Simon Chaddock]

After adding the elevator servos to the tail plane I have come across a problem with the long servo wires (1500 mm!) that are required with the receiver paced in the nose.

This video demonstrates the effect.

Both servos work normally on short 50 mm leads and either shows the same effect when coupled to to the long one.

I thought it might the result of voltage drop but with the servo running the drop from measured across each each end was only 0.01 V. Not really surprising as the tiny servo moving but off load only draws 170 mA.

It follows it must be the servo signal that is being effected by the length of the wire.

I am just surprised I have not noticed this effect of some of my larger lightweights that use the same type of servo.

Any ideas?  

[Martin Harris - Moderator]

Would a few turns of the servo lead onto ferrite rings close to the receiver be worth a try?

[Dad_flyer]

You have not got the motor running, so if it is interference it cannot be from inside the model. What does it do outside the house? Mains frequency is the same as the servo refresh rate,

Twisted wires should also help to reduce pickup instead of a ferrite.

I think I heard that some receivers only output 0V/3.3V on the signal line, as that is the voltage of the internal logic in the microprocessors. It should be fine on a servo expecting 0V/5V as it is above a 2.5V threshold, but it is not that far above. Unfortunately one would need an oscilloscope to test that.

Edited February 23, 2021 by Dad_flyer
Clarity