Yet another He 162

[Erfolg]

Although I have a number of models waiting to have pretty much first flights or improvements (hopefully), I cannot resist building, especially something which I see as a challenge.

 

I bought a 50 mm fan from 4 max to try and build a Douglas X3. I slowly came to the conclusion that I could see more problems, that I had few immediate possible answers, which particularly to where the CG would end up. Also there was, and still are issues on how to 3D print a inlet and outlet duct.

 

My mind then drifted to the He 162 (design proposal/study) that was a free plan, a few months back. Also I have followed the TN series of DF, particularly the Grumman Panther and the Jet Provost. I Have always liked a bit of challenge, but possibly doable. In the past a Bachem Natter was such a model, finally flying successfully this year, now I think, hmm I could cut the wing area down to much nearer true scale, I then think why bother, the taileron control worked much to many peoples surprise, especially the unusual proportions.

 

So this model is a low priority build, drawing on TNs designs, and a low consideration of the HE free plan as how it could be done.

 

So far I am concentrating on the power pod and wing. The wing has been essentially a general copy of TNs proportions. This has dictated the size of the duct, which is scaled from a 1/72 Airfix model (built probably when a teenager). Another issue is I am still learning about design using Autodesk Ulitmate 360, I would benefit from some formal lessons, as I now seem to be a poor learner, and seem to lack intuition. I have piles of books with 162 info and pictures.

 

This is as far as I have got.

 

 

[Erfolg]

Missing pictures

 

[john davidson 1]

An X3 model would have to be semi scale I would think, with much increased wing area, certainly  a challenge?

[Erfolg]

John, I am not completely convinced it would be necessary to deviate to fat from scale, to model an X3.

 

 The proportions at not that far from a EE TSR2, which I understand has been modelled by some, which includes TN?

 

One of the dilemmas I wrestled with is where the motor/fan unit should go, I was thinking right at the back, with the Lipo in-front, between a bifurcated inlet duct, with a cheater inlet between the two wings. I could not convince myself that it could all be made to balance without some lead. I was surprised the nose length ratio to chord length at the root, was very similar to the TSR-2. it looks far more dramatic due the slender nose on the X3. Where as the TSR2 nose is quite chunky, probably for all the avionics.

 

What finally killed the project with me, is that wanting to try my hand using Depron, I wanted to use the duct work as part of the structural strength and my abilities at 3d printing where/are not up to the task, That is why the duct on the 162 is as it is.

[Simon Chaddock]

Erfolg

There is nothing wrong about building an HE162.

But I shall have to have a good think about the viability of a Douglas X3.😉

[Erfolg]

Simon, as with our Bachem models, I can anticipate that getting the CG in an acceptable position without using lead could be an issue.

 

I learnt quite a bit from both my Me 263 (Ju 248), in that I could cut down the Blue foam a lot more than I did, more of an issue was that the ply chasis, I used for the UC needed lightening a lot more to keep the weight down. It flew, although not as well as the 163, that used the same wing (cloud models).

 

In case of the Bachem, if you remember I wanted a pusher prop, then ended up with a tractor. In that case, I found just from taking moments, I could not get an acceptable CG without it being a tractor prop. Perhaps more interestingly, the tailerons worked really well and I could cut down the wing area to nearer scale, as it flew really well (being a plain wing could have been a benefit).. There was an issue in that I used an old Futaba 35, and it glitched. I could and cannot be bothered developing the model further. The paint job was a prototype development airframe that I saw in the Deutsches Museum Munchen (I was concerned about seeing it).

 

I have used Depron previously, although I have always used it in sheet form. The picture is of the first, the second model used a different grade of Depron? which was not as rigid. Which meant I needed 4 servos to effectively drive the Elevons, as the control surface flexed, even with a Bamboo longitudinal stiffener.

 

So where does all of this take me, well, I want to keep the weight down, but as when and where we worked, I want a robust, everyday, reliable model. In this case I want to use Depron, as I no longer have any amount of Blue Foam. I am not keen on the idea of planks, although I could go there, and glass cover the body as with the other foam models to obtain a ding resistant model.

 

You probably have gathered that the wing will be a mixed material fabrication, in construction.

 

I have noticed that the TN DFs have a constant thickness section. Without looking up the curves for a NACA 000 series airfoil, I can only guess that at these chord lengths, it has a similar effect to washing out. Have you any opinion or experience?

[Simon Chaddock]

Erfolg

I still have a bit of "true"  6mm white Depron now 7 years old and it is amazing just how rigid it is.

 

I have built quite a large He162 (56" span) out of primarily 3mm 'modern' Depron.

 

Strictly not a true EDF but a 3 blade 3x4 ducted prop using a Emax 2205 'drone' motor on an 850mAh 5s. The prop is near the back of the nacelle.

It has not flown nearly as well as it should given its reasonable aerodynamic proportions, light weight and wing area. Maybe I was too frightened of the limited thrust so set the CoG too far aft. In addition I flew it bank and yank which was probably a mistake as the side area ahead of the CoG is nearly as big as that aft. It just did not turn until it achieved a considerable angle of bank, about 45 degrees, which then resulted is a rapid nose drop.

I am sure it should fly well enough. Perhaps in calmer summer weather I will try again.

As far as washout goes I believe a swept wing has natural aerodynamic washout and any flexing tends to add to it. Certainly my airliner swept wing planes tend have very forgiving characteristics despite having no washout built in.

My 162 has no washout and the wing is pretty rigid. If you include the fact the wing is aerodynamically slightly swept forward maybe that is part of the reason it flies poorly. I am conscious that until Lippisch added the down turned tips and t

he "ears" at the trailing edge of the wing roots the characteristics of the full size were "unacceptable". 

[Erfolg]

Well Simon the 162 looks the business.

 

I can confirm that the earlier Depron I have, is far superior from our perspective. The foam board is rather spongy, when the paper is removed.

 

Time will tell how well it can be sanded. The old stuff could be sanded quite well, if sanded slowly, with light pressure.

 

I do not think Lippisch played any role with the Heinkel.  In Eric Browns "Wings of the Luftwaffe", he wrote that the 162 was the nicest handling aircraft of WW2. By that I take it that the aircraft was OK. In theory a swept forward wing should handle well at the stall, although the 162 has not much of forward sweep, unlike the Junkers 287 & the Grumman X29. That is if the wing does not twist from the flying loads. I guess that the torsionally rigid wing is difficult to build in practice.

 

Anyway back to your model, how thick is the body skin?  Have you used a cambered wing section? Or as TN a symmetrical section? Are the body  formers Depron or PLA? Where is the Lipo, is it in a internal box? Where is the elevator servo, is the drive a split rod to each halve, if so have you used ball type attachments? Is the duct attached to the body with a bottom hatch or a detachable duct (which seems messy to arm the battery?

 

Now you are thinking what does he not desire to know! Well my whole career was based on using others experiences.

 

 

[Simon Chaddock]

Erfplg

All the skin (wing, fuselage and tail) is 3mm Depron or rather the modern equivalent.

To save weight the body formers (actually half formers) are all 3mm Depron so the body could be built over the plan as a half shell.   

Apart from the cockpit which are PLA to give the maximum possible internal volume.

The LiPo is right up in the nose. The windscreen is removable to get at it rather than the cockpit canopy!

The wing section follows that drawn on the 3view I used. The ribs are PLA structures

No idea how scale it is.

There elevators have individual servos buried in the tail plane so no mechanical link required.

The duct is permanently built onto the fuselage. The wing slides into the aperture between the nacelle and the fuselage and is retained by 4 nylon bolts. Not the easiest arrangement to rig but I felt a 'fixed' nacelle was essential.

As the battery is in the nose it is easy to arm as the last action.

Since the picture I have incorporated rudders. The servo is in the fuselage just ahead of the duct with external pull/pull lines back to a bell crank at the centre of the tail plane with thin carbon rods to each slightly over size fin & rudder.

   

It works well but it has not yet flown with the rudders.

Despite all the effort my He 162 has so far proved to be my most disappointing scale plane. Maybe I was just lucky with the others. 

The downturned wings tips to reduce the Dutch roll effect of the 4 degree dihedral were credited to Lippisch and were known as Lippisch-Ohren or Lippisch Ears, according to Wikipedia.

 

 

[Erfolg]

I have made the first tentative start, with respect to the airframe. I decided to wrap the duct with the Depron sheet, after having removed the paper by wetting, then peeling/rubbing it of. I had considered using multiple slices, as with a sliced bread loaf, In the end going for the Swiss roll approach. Two reason, the first material waste, perhaps more importantly, the amount of adhesive I suspected that would be used.

 

The adhesive used is Polyurethane (Gorilla). Partly because the UHU Por I had was no longer viable. I was interested how the Polyurethane would sand. Not bad, although not great either. My other concern was how would the art board sand, as some of my recent Depron look alike did not sand well. The art board is much better than I thought it might be.

 

The first picture is after wrapping, the second is sanded down to shape. In retrospect I could have made the item a bit smaller, plus overall lighter. I would now do the thing slightly differently, with potential benefit.

 

I am now having second thoughts about the model. As a one time engineer I liked the idea, that an external motor/fan would be easier to maintain, or switch for another, I could even change the motor combination without taking the whole of the body apart. I particularly liked the short duct, reducing losses by a significant amount. I even liked that the motor could be over the CG. I even like that the Froude number for the 162 body is much better than a lot of WW" and early jets, which were often like (tuby) barrels.

 

Personally I had discounted the Meteor and Canberra, as the spars had to have a potentially heavy transfer rings mid span. Now I am thinking, perhaps I could live with limitations.

 

Back on the 162, I have started the process of agonising, how to deal with the body, as I like robustness aand light weight, using a material I am less familiar. Thankfully Christmas is here and I can deliberate with good  cause whist enjoying? family life, get togethers, hopefully in harmony.

 

What I do not like is that the equation for drag on a body, has a much larger cross sectional area than some other piston type models

[Simon Chaddock]

Erfolg

As you surmise the HE162 may have a reasonable aerodynamic layout but the fuselage + duct has a considerable cross section and a substantial surface area when compared to its modest wing span. This suggest that you may have to squeeze in a pretty powerful EDF to overcome the form and skin drag with the result it may end up as a "fast flyer" unless it is remarkably light overall.

[Erfolg]

Simon

 

I have started or changed my initial plan, to one where I have produced a body, this will enable me to more closely estimate the finished weight. From that I will have a better grip on the wing area required at a 20-23 oz m^2 loading. If wing comes out large, It could well be a bin job. In reality being very semi-scale, there is some latitude.

 

You mentioned the anhedral tips being there as a cure for Dutch Rolling. One source suggests that they were introduced after V1 (Versuch) to cure wing vibration, generated from the tips. Being vortex attenuators, an to improve longitudinal snaking. I have just been reading about Luftwaffe Emergency Fighter Competition, it is of passing interest that all(maybe most) tenders with very low aspect wings, have the same tips. Again of passing interest, if the Germans had managed to stagger forward to 1945, it was obvious (particularly with hindsight) that the Heinkel turbine was never going to be a viable motor. On that basis the 162 and 262 was as good as would get.

[Erfolg]

Christmas is now over. During the period, most definitely family time. Puts my hobby back into perspective.

 

I have started on a body, being an ex-engineer plagiarism is my thing. On that basis I have the RCM&E free plan to hand. Whilst sketching out the body, I did realise that engineers like circles and straight lines. Unfortunately the real world forces complications like curves. The freebee has the circles, but all of my reference sources show the body at least in parts are more egg shaped. The problem seemed to be the real UC forced a widening of the lower body.

 

I am most definitely not a slave to absolute accuracy, as my models deviate from this philosophy to make them very semi-scale. Yet another side tells me, unless there is a practical reason, keep thing scalish.

 

As to the real design I have borrowed extensively from Simon and others, because all engineering knowledge comes from others efforts. 

 

Yet there is one issue at least unresolved, that is the hatch into the model for a lipo, I do not like the free plan very much, mainly because of the motor wires and the need to arm the model, fasten at least one screw, for me a bit clunky. I prefer a bottom hatch, yet this weakens the monocoque shell. A big hatch makes working easier at the expense of strength, a small hatch, well my banana fingers have difficulties. All require an aperture compensation.

 

By the way I made a mistake on the drafting for former position 5. When doing the profiles I think I have made a mistake in the potions of the template contour position, hence the former line. I bodged a correction, did not bother with my former contour view.

 

Feed back and suggestions on the way forward will be appreciated.

 

 

[alan p]

In my 162 12" jetex scaled up for 50mm fan I used the cockpit canopy as a battery hatch, a tonged at the front, small magnet a back to secure . Takes a 3s.

[Erfolg]

I have now back tracked, as I did not realise there were issues that are relevant, I was so busy thinking about so much that concerned me , initially some very relevant things did not register.

 

Alan's posting did not come up in my in tray, for some reason.

 

Now I can see others solutions to problems did not register

 

So what did I initially not register, that the 162 had a wing. I was fixated on the duct to body junction (ignoring the wing completely), the other thing on my mind is the Lipo access. To date I am still disturbed by the issues. It is the issue of avoiding excessive weight, as interfaces often disproportionally (in full size also) increase the weight, At the same time I want to keep things secure.

 

Normally I would rough out a design, not overly concerned with detail, relying on tried and tested generic solutions. Any issues normally are identified during the process. In this case, just drawing bits and pieces on taped together A4, has not worked well at all.

[Simon Chaddock]

It does very much depend on the battery position but my "go to" is to use the cockpit canopy as the battery hatch on scale EDFs.

On my somewhat bigger HE 162 that has a 76 mm EDF (actually a quad motor and 3x3.5 3 blade prop!) is so light it means the equally small 5s LiPo battery has to go so far forward the windscreen is the hatch. The actual canopy is fixed and provides significant stiffness to the nose.

I was going to say "It works for me" but to be honest I can't as so far my Volksjager flies horribly!   

 

[Erfolg]

Thanks for your reply Simon, not  thinking through has caused me what to do problems, it seems that I have become very formulaic in my adhoc designs using balsa ply standard design. 

 

I am now thinking of a two hatch approach, the canopy and either the bolt on (as Alan) or a belly hatch. The pity is that the battery box was conceived as a structural member with end loading. Which will require some stress compensation re-enforcement.

 

I was hoping to get all the major bits pretty much fabricated so as to decide if the wing as partially made would provided a wing loading circa 20-22 oz ft^-2 loading, or if some extra area needs finding.

[Simon Chaddock]

Erfplg

At 20-22 oz/sqft it certainly wont be a "slow" flyer.

Even my Bombardier Dash 8 Q400 with a wing span less than the fuselage length has a wing loading that is not quite at that level. It does hand launch but does rely on the generous thrust from its twin props to accelerate to the 'control' flying speed before anything goes too far wrong.