A very unusual fighter plane

[Erfolg]

I should also have added that it is the "Tailless" issue.

 

From what I have read, the various Me 163 and the 263, were landed very much like conventional aircraft. In doing so they used flaps and slats. Not a high alpha or high drag, high AoA approach. I am guessing that is why he favioured thick wings, relatively as in the Vulcan.

 

I seem to remember that the Concord, thin wing was solved by Busemann who I thought worked at Farnborough (seems I am wring), although it has been suggested that wing tip arrangement was developed via his contribution.

 

The envisaged power plant for the projected aircraft, was a reflection of the state of Germany, they had run out of most materials, petro chemical fuels, and also armed forces manpower. With hindsight, many of the campaigns were about securing or denying assets, such as north Africa (oil), Rumania (oil). The shortage of acess to quanties of Nickel, Chrome, Aluminum gives an insight to what appears to be strange decisions. Although the fundemental works on alloys etc, by AG Farben helped the post war (2) developments and understading of structures at atomic lattice level. 

[Simon Chaddock]

Made a start on building the P13a.

The fuselage, although it includes 1/3 of the wing span, is built as a half shell over the plan. Once the 3mm formers are in place it is 'planked' with 3 mm Depron.

This view shows the substantial wing section even at 1/3 span from the C/L

Once the half shell is complete and the glue hard the next tricky bit is inserting the complete nose to tail duct including the EDF so it lies exactly half into the formers.

Then the other side of the formers can be glued into place and the skinning completed.

Simple to say but rather more difficult to achieve however when complete the result is a lightweight basically hollow structure where all the loads are carried just by the skin.   

 

Edited January 11, 2023 by Simon Chaddock

[Simon Chaddock]

Slowly moving forward.

The half shell complete and a test fit of the rear portion of the duct.

All the formers had slightly undersize semi circular cut outs in them so quite a bit of sanding to get hem all to just touch the duct all round and it be 'submerged' exactly half way in.

The first nose former is sacrificial and will be carefully removed when the EDF and inlet duct section are added.

Its unconventional shape and structure means there is quite a bit of 'working out how to do it' as you go along.

The other half should in theory be easier, provided you can remember how you did the first.      

Edited January 14, 2023 by Simon Chaddock

[Simon Chaddock]

Some real progress. The full duct and EDF are in.

Note the rubber band holding the nose planking to the duct once the first former has been removed and the magnet wire motor leads brought back from the EDF. Purposely over long because I am not at all sure where the ESC and battery will need to end up.

 The next and very satisfying job is to fit the other half of the formers as at last you feel you actually getting somewhere.🙂

[Simon Chaddock]

Slowly moving on. Skinning progressing on the 'fuselage'.

This picture does rather highlight just how empty it is inside. The wings and fin will have quite a bit of empty too!

On the plus side it does mean the structure will be really rigid despite using just 3 mm Depron with no reinforcing anywhere. 

 

[Simon Chaddock]

The 'fuselage' skin is complete.

The EDF slot is flanked by dummy extensions to give the appearance of the scale slot.

 

Should look ok when all the exhaust is painted black.

It is quite light. Including the 55 mm EDF it weighs 145g. With a 1500 mAh 3s it is still just under 250g so hopefully not too far from 350g when complete. That would give over 200W/lb so hopefully sufficient thrust but whether it will be aerodynamically stable and controllable is another matter! 😲

[john davidson 1]

 Is the outlet area larger than the intake, would result in a loss of speed and less stress on the motor

[Simon Chaddock]

john d 1

The outlet is actually the FSA whereas the inlet is closer to 110%, not ideal. The inlet is exact scale although for efficiency the exhaust slot is a not true scale 'thin'. 

The biggest losses are in the length of the duct and converting the round to a rectangular slot.

To fly it will rely heavily on being very light! 

[Erfolg]

I totally agree with you Simon, the loss from the transition is greater than you tend to suspect. My first thoughts were perhaps a plenum chamber sizing where the transition takes place, then comes the but, then there would be a loss from reaccelerating the air.

 

Would a cheat type slot not help, and avert some of the full impact from the geometry.

 

Where is the pulverised coal hopper? 🙂

[john davidson 1]

13 hours ago, Simon Chaddock said:

john d 1

The outlet is actually the FSA whereas the inlet is closer to 110%, not ideal. The inlet is exact scale although for efficiency the exhaust slot is a not true scale 'thin'. 

The biggest losses are in the length of the duct and converting the round to a rectangular slot.

To fly it will rely heavily on being very light! 

FSA? Full Scale Area?   Agree with Erfolg , entry must be much more than exhaust even if achieved by cheat holes, the exit can then be modified to get the speed of flight, usually very slightly less than the area of the fan. Generous entry probably minimises losses and then I try to put the fan as near to the exit as possible. Suck it and see!

Edited January 21, 2023 by john davidson 1

[Simon Chaddock]

FSA = Fan Swept Area. The area of the fan less its hub.

My bench testing has shown that maximum static thrust is achieved with the exhaust nozzle at 85% of the FSA although the thrust reduction is only 2% with the nozzle at 90%. These figures only apply with a relatively short exhaust tube which the P13a definitely does not have.  

 

I would agree that the inlet is best at 120% FSA but in this case this was not possible at the chosen scale and a 55 mm EDF.

Testing the full length duct so far shows about 350g static thrust which should give a thrust to weight ratio close to 1:1. I can always go to 4s if necessary.

 

Interesting to note that the "bare" EDF (no duct just its bell mouth) gave nearly twice the static thrust.

The penalty of a long and unusual shape duct?

[Simon Chaddock]

Erflog

The only details I can find suggest the intention was to use a bituminous coal filled 'basket' that rotated to give an even burn.

It would be lit by a gas burner once the plane achieved the ram jet self sustaining speed. The theoretical flight time was 45 minutes!

The wings of the P13 folded up to allow the 'basket' to be quickly replaced.

Quite bizarre!

Its hard to imagine a coal 'basket' could provide the required energy, let alone not destroy the pressure waves required for a ram jet to function.

 

A coal basket was apparently tested in a wind tunnel by ram jet maker Kronach Lorin right at the end of the war. 

  

[Erfolg]

Simon

 

I was joking, obviously not very well.😧

 

I do have some details of the envisaged arrangement, just need to find them. Personally I found it hard to believe it would work (effectively), never mind for 45 minutes, or in a combat scenario. In some respects it reminds me of a fluidised bed, as many coal fired stations used. I guess the grit coming out of the back, could peppered the screen of the enemy.

 

I do agree the very long duct (relative to diameter) is not helpful.

 

I have been designing a Douglas X3 for some years now, Like yourself, keeping the weight down, and creating a goodish duct (with my limited printing skills) has not been, well, easy.

[Erfolg]

What has immediately come to hand is the tailless Luftwaffe booklet. Their are drawings, perhaps described as sketches and description of the aircraft. 

 

My impression is that the whole project was somewhat conceptual, supported by some theoretical data. As you stated there was postulated 1760 ib of coal, getting on towards a ton of coal. The wing area 130 ft^2. I would guess that the energy available was assessed against the Brayton cycle, although what is envsaged was not a closed loop cycle. Still surprised that anything like the performance suggested would practically be achieved, missing like a country mile. Probably a little like the Sterling cycle, promises a lot in efficiency, just cannot be made to deliver.

 

I now understand why a Delta, with a slot exhaust. The engine motor, was a large wheel/grate, mounted in plan. In the grate was to be inserted cylindrical hollow pressed shapes or bulky coal pressed into plates. There is also mention of Pine cooked in oil or paraffin, sized at 10*10*10 mm. All seems to be based in a hope that it can be burnt t a very high rate.

The principal of operation is based on the Lorin tube/pipe. I vaguely remember that about WW1 an aircraft based on the concept was actually flown some how. 

 

Anyway the 13 needed rocket assist  to get it actually into the theoretical window that it could work.

 

I am not surprised that the USA team were somewhat surprised that the project was allowed to even start.

Edited January 22, 2023 by Erfolg

[Paul De Tourtoulon]

I followed Bob Violettes book, with a constant area from the blade area to the outlet at the end of the tube and it worked for me,

ground thrust isn't everything, don't forget a fan is just an air accelerator.

[Peter Jenkins]

The interesting thing with slender deltas is that they seem not to stall even at very high AOAs.  I did a flow visualisation project for my 3rd year aerodynamics project and one of the examples was a slender delta that I just cut out of hardboard and hung up using strings in the wind tunnel.  When I turned on the smoke generator you would see two vortices form just aft of the wing LE and stay attached out to the wing tip.  I had got the wing to 80 deg of incidence(!) and both vortices remained intact.  However, a yaw of even 5 deg resulted in the vortex on the less swept wing beginning to form and then degenerating.  The vortex on the more swept wing was unaffected.  This would have given a might roll input towards the stalled wing of course!  However, the power needed to maintain an 80 deg AOA would have far exceeded anything that could fit in such an aircraft!  Most slender deltas therefore, do not stall in the classic sense but get to the point where increasing AOA will eventually require full power and recovery from that situation can only be achieved by reducing AOA.  If you are low on approach then clearly that is not a good place to find yourself!  That's why Concorde didn't have flaps because it could generate a lot of drag without them.

[Simon Chaddock]

Peter

Agreed but unfortunately the P13 is definitely not a slim delta.

I expect it will generate lift, and drag, at a typical "delta" high angle of attack but at lower angles I fear the L/D ratio will not improve due to the very thick symmetrical wing section. This could mean it will only have the power to fly slowly despite having a pretty good thrust to weight ratio.

 

Both my scale thin wing deltas, Concorde and Fairey FD2, have lower thrust to weight ratios yet fly well enough but do simply run out of thrust if the angle of attack gets too high.

[Simon Chaddock]

The fin built but not yet fixed.

The hatch will be added when I have some idea where the battery needs to go.

To call it a fin is a bit of a stretch.

 

It is hugely thick!

I have a suspicion the aerodynamic stability rules are going to be as unusual as it configuration.😲

[David Ovenden]

5 hours ago, Simon Chaddock said:

The fin built but not yet fixed.

The hatch will be added when I have some idea where the battery needs to go.

To call it a fin is a bit of a stretch.

 

It is hugely thick!

You could call it a VFC.

The vertical fuselage component. 

[cymaz]

Interesting project. Ive found this article, you may have already seen it 

 

https://hushkit.net/2019/03/29/the-lippisch-p-13-supersonic-wonder-plane-or-nazi-coke-head-an-assessment-by-former-british-technical-liaison/

[cymaz]

https://cults3d.com/en/3d-model/game/1-10-scale-lippisch-p-13a-rc-model-600mm-wingspan

[Simon Chaddock]

cymaz

That is an interesting printed P13a. It certainly flies and pretty quickly.

In the information on the web site I can't see any mention of its all up weight. Also it shows a short thrust tube that appears to exit out of the underside. In other words it does not use a full length duct exhausting as a slot at the rear which probably explains the substantial thrust figure it achieves.  

[john stones 1 - Moderator]

You like a callenge Simon, hope I get to see it in the flesh.

 

[MattyB]

10 hours ago, cymaz said:

https://cults3d.com/en/3d-model/game/1-10-scale-lippisch-p-13a-rc-model-600mm-wingspan

 

Wow, that seems to fly pretty damn well all things considered!

 

 

[Erfolg]

Even when in my prime, the speed and size of the model would have been well beyond my capabilities.

 

There seems to be a lot files to print it out, which puts me off trying to print it out for static purposes.

 

I do wonder where the Lipo is, as I have found on my own deltas, that the Lipo needs to be up front, balancing out the lighter motor at the back. Avoiding the need for Pb. I notice that Simon has gone the other way, motor up front, Lipo somewhere near the back (I guess).

 

As for the real project, Arado would appear to have undertaken an in-depth study (Hans Welland) of various configurations of Delta's, pre-war I understand. Their preferred configuration being the 1*1*1 (isosceles). It appears that a French manufacturer (Payne) produced an essentially Delta, (supposedly in the Musee of air Paris).

 

It appears that the RLM decided the 13a would not be useful in the short term, telling Lippisch to move onto the 15 (Diana) a jet powered revised version. The sketch I have seen is potentially easier to configure into a viable model, having a short through duct.

 

I suspect that or Simon, it is the challenge that grabs him, of the 13.

 

In the case of the UK Deltas, there were a myriad of them, like the Avro 707, in support of the Vulcan, in addition to many others. Modified FD 2 in line with the Bussmann contribution to Concord, and the modified later Vulcan wing tips.

 

In reality a whole pile of aircraft in support or lending data to a raft of aircraft, who did what and why is now lost in time. Many making claims to being the first. What I have read about Lippisch, he had more than one version for the same event. Most rely on his book "Memories (errinarrung)", which does not always tie in well, with other sources.

Edited January 25, 2023 by Erfolg