Feuerlilie / Fire Lily F25 Scratch Build

When I ordered up parts off Fliskits for my Rheintochter build I wildy over ordered to allow for any screw-ups plus I ordered a choice of nose cones to see what worked best. Because I happen to be a genius Rheintochter didn't use much of the stock as I took pains to get it right (well there has to be a first time for everything - even me not screwing up ).

As a result I had a lot of stuff left over including a very long pointy nose cone. I hunted around for something to build and then decided on a Rheinmetall Feuerlilie as it would use the nose up and the last remaining BT70 tube and the stock balsa I had on the shelf would also be used up at the same time plus I could use paints I already had and the whole thing would be powered by the same D12-3s I have in hand.

I did forget to order a spare motor tube (DOH !).....and there goes the genius tag I guess

Fire Lily is a lot simpler than most to build I reckon, the one after this might be Schmetterling once I work out how to do the nose cone transitions, but the headache with Fire Lily is there isn't much data around so I am working from an imperfect plan of the bird plus pictures on the web of one at RAF Cosford. Mine will be a kind of synthetic merge of the two. Just like Rheintochter every pic I look at seems a bit different and as Rheinmetall never got this thing working right my guess is they made mods after each flight.

Anyway enough of the yak - heres the thread.

Firts pic is of the basic components to build the body. A BT70 Tube plus a BT55 with a batch of BT70/BT55 centering rings plus a load of work to turn out some plans based on the technical drawing I found online. The finished kit will be about 18" tall with a wingspan of about 8" for its widest fins/wings.

The back end tube that will eventually hold the motor tube was cut to size and three centreing rings added. I went for three as the bang when this thing ejects given its short length will be quite a bump plus the tube only goes inside the BT70 for a short distance and I wanted it as straight and accurate as possible.

THe exhaust end of the tube where the ejection charge will be was given about three coats of aliphatic glue to toughen it up. The rings are equidistant and once on were filleted with more aliphatic glue. Once assembled the uppermost ring which forms the base of the recovery gear hold was also given a few hits of aliphatic.

The BT70 tube was cut down to size and fitted with a cut down tube coupler that mates to the lower centering ring on the motor mount tube in the previous step. When pushed down into the BT70 tube, if all is well, the protruding bit of the inner tube will be at the right distance for the rear shroud/transition.
Heres the BT70 tube with its lip of centreing ring showing plus the inner tube.

Doing it the way I did it turned out not to be so smart as I had thought - it meant getting glue down inside the BT70 tube was a real pain - as the inner tube had to go in from the top it meant the area to be glued was quite some way down inside the BT70 tube- she may be a short stubby rocket but there is still enough distance in the BT70 to make this sort of job tricky. It did work - with a few heart stoppages when the inner tube and its centreing rings got jammed a few times. I was mindful of the potential for a mishap here and the BT70 centreing rings were sanded down to be less tight in the tube.

Alls well that ends well - and it worked out - heres the two tubes together now with the transition cone/boat tail added. This was made up of card, steamed, glued with a glue stick and finally glued into place with good old aliphatic glue.

The seam of the card stock boat tail is in line with where one of the rear fins will go which will hide the seam nicely.

A quick pic of the body assembly complete with the extra long pointy nose which may end up being sanded down a mite - against the drawings I made up its a bit long. I may decide to shorten it a bit but will decide once the rocket is at a later stage and I can see how its looking as a whole.

The wings were cut out from a relatively thick balsa stock - the forward fins are really more wings - and given some paper coverings. The lines are for later on - I intend to lightly score these as markers for the final paint job when these will be pinstriped a bit (if all goes well).

The leading edges have been given a curve, the real things appears to have pure aerofoil shapes to its wing section but its beyond my ability to get this right and I dont want to have to but more balsa right now.

Final pic for now - a shot of the half made up wings/fins with the body tube to give an idea of how she will look when completed and also to give me some idea as to how its looking in case I need to make changes to the design.

Ausgezeichnet!

When I built my own, somewhat smaller scale F25 (mine is based on BT-55), I contacted the author of the Luft46 site, who sent me this:


It's a scan from a post-war Allied document about the F25, with dimensions and showing a lower tail unit, which ought to help make the model more stable. Not shown on the diagram are the wingtip mini-fins and the detail on the tail fin tips. The Cosford photo shows the tail unit nicely (if you've found the same one I did ) but only shows a half mini-fin on the wingtip. Another photo I saw on luftarchiv.de shows a full mini-fin which is what you're building. So really the only change you may want to make is to add a second tail unit.

To be stable, mine needed quite a lot of plasticene in the nose, and that's a plastic cone so the stuff went right to the tip where it would do the most good.

Hi Adrian, Thanks for that - I had found it anyway and I suspect from a web server your running as it was listed as 'Adrian Directory' from recall. I found it while digging about but discarded the data as by the time I found it I had already cut the wings out and papered and have no more balsa. Partner is moaning a lot about me spending endless cash on rockets and filling up our tiny flat

Its interesting that once again there seems to be an amazing disparity between sources as to what the wretched thing actually looked like. Some pics I found seem to suggest a delta, others a swept wing, the tail unit seems to differ between sources as well. I seem to recall from TV Jones book 'Most Secret War' at one point at the end of the War the Russians carted a lot of stuff off and offered to share it with the Brits a Brit was dispatched to check over the consignment but wasn't expert enough to realise the Russians were packing the crates with old tractor parts so who knows maybe a lot of this stuff was mashed together from what they found - I used to have a book called 'Last Year of the Luftwaffe' and there were some pics in that of factories as they were when they fell into Allied hands and they were mostly quite a mess - bits of planes, engines etc everywhere so perhaps its not surprising a low priority project may have fallen into serious disrepair and stuff like Rheintochter and Feuerlilie which never made it into service may well have been assembled from parts of assorted prototypes which explains the disparity between images.

By the way did you notice on some of those pics you posted of the Rheintochter that the rear engine unit had a yellow paint on marked as RAE Farnborough - interesting I thought.

If this one needs a serious nose weight I have a long wood drill so I can drill down quite some way and hopefully that will be enough. My next project will probably be Schmetterling once I figure out how to do the really complex nose assembly. It will have a second tail unit but the 'T' part on mine is somewhat longer than shown on your diagram.

I think I also found a pic of your Fire Lily online - at least I am pretty sure its yours as its located at https://www.macs.hw.ac.uk/~adrian/rockets/

:wave::w:

Astro-Baby said:

Hi Adrian, Thanks for that - I had found it anyway and I suspect from a web server your running as it was listed as 'Adrian Directory' from recall. I found it while digging about but discarded the data as by the time I found it I had already cut the wings out and papered and have no more balsa. Partner is moaning a lot about me spending endless cash on rockets and filling up our tiny flat

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I saw you had already done a good job on the wings so didn't point out that the plan shows swept rather than delta. The main point is that you can build a second tail unit which will make the model more symmetric as well as doubling the tail area for the purpose of stability.

Its interesting that once again there seems to be an amazing disparity between sources as to what the wretched thing actually looked like. Some pics I found seem to suggest a delta, others a swept wing, the tail unit seems to differ between sources as well.

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I've seen various drawings showing various layouts, but both the actual photos I've seen agree with the swept wing and double tail. Those photos are the Cosford one and the luftarchiv.de one.

By the way did you notice on some of those pics you posted of the Rheintochter that the rear engine unit had a yellow paint on marked as RAE Farnborough - interesting I thought.

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Yes, both the booster and sustainer show markings saying "RAE". They're travelled a long way, from Germany to Britain and then back again.

If this one needs a serious nose weight I have a long wood drill so I can drill down quite some way and hopefully that will be enough. My next project will probably be Schmetterling once I figure out how to do the really complex nose assembly. It will have a second tail unit but the 'T' part on mine is somewhat longer than shown on your diagram.

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You're still following the Luft46 plan. So did I at first, and it looked like this. I've still got the airframe but when I got the plan, I built another one, then took the nose off the old one and put it on the new one.

I think I also found a pic of your Fire Lily online - at least I am pretty sure its yours as its located at https://www.macs.hw.ac.uk/~adrian/rockets/

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Yes, that's mine, and you'll find my F55 there as well.

Yup - my one will have twin tails but somewhat larger rear fins than is shown by the Cosford pics. How did the F55 fly ? I saw an article which said the real one had stability issues, maybe because the planned powerplant wasn't fitted so they had to run on a lower power alternate motor.

I was originally going with the F55 but I didn't have enough tube or a nose cone to make one in anything except a teeny size and I prefer bigger as my eyesight isn't great for fine work and also because I really wanted something to fly off the D12s I have.

Schmetterling (planned at the moment) is being a pain as I just cant find a cone/frustrum template calculator that can handle the complex nosecone. My geometry ability can handle off centre cones and even cones with tubes but I just can work out the technique to handle a cone joining a cone which also shares the same base - its a real perisher. I am considering a papier mache one instead which I think would work. I am thinking in terms of sculpting a positive mold in something like modelling clay than using papier mache to cover possibly with a filler or epoxy coat to strengthen it and add a ply base to the whole thing - what do you think ? Doable or am I nutty ?

Astro-Baby said:

Yup - my one will have twin tails but somewhat larger rear fins than is shown by the Cosford pics. How did the F55 fly ? I saw an article which said the real one had stability issues, maybe because the planned powerplant wasn't fitted so they had to run on a lower power alternate motor.

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The articles I've read indicate that the first flights of the F55, powered by a cluster of solid-fuel motors because the intended liquid-fuel motor was not available, were successful. The final test flight with the liquid-fuelled motor was not. Besides, I don't have access to a liquid-fuel motor either, so I went with a cluster of four solid-fuel motors - C6-5's to be exact. The rocket flies fine but for some reason the wingtips always get damaged, even though I fit a larger parachute than I've used in a similar size rocket with more conventional fins which recovers without damage. One detail not obvious in photos but specifically mentioned in another document I got from the Luft46 author is that the wingtip mini-fins are angled so that the leading edge is slightly closer to the fuselage than is the trailing edge.

Schmetterling (planned at the moment) is being a pain as I just cant find a cone/frustrum template calculator that can handle the complex nosecone. My geometry ability can handle off centre cones and even cones with tubes but I just can work out the technique to handle a cone joining a cone which also shares the same base - its a real perisher. I am considering a papier mache one instead which I think would work. I am thinking in terms of sculpting a positive mold in something like modelling clay than using papier mache to cover possibly with a filler or epoxy coat to strengthen it and add a ply base to the whole thing - what do you think ? Doable or am I nutty ?

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Having seen your previous work, I am sure you could manage it. I'd probably start off trying to do it with paper transitions and end up with so many additions and patches that it would effectively be papier mache. Just to complicate matters even more, from some photos I've seen, the shorter cone is actually a small propellor, probably part of the fuse mechanism...

Ooh dont big me up there

I read the propeller was to provide electrical power for it. I was planning, if i ever build it, to have the prop working. It shouldnt be too hard to do. A simple cone, coiple of basic blades on it and probably a small dowel given a hit of wax as the spindle for it pr perhaps a small bit of wire.

Mine would have to have a slightly more simplified body as the rear end of the real thing also looks a bit complex, rather like a flattened boat tail. It might be possible to do it with some balsa formers but the skin would be quite a compex template I think.

A quick update - a bit of patient work has turned out the fins, heres the almost complete set papered and left under a pile of books for some time to make sure they are nice and flat.

The main fins have been given a sanding to give the front edges a slightly rounded shape - the main fins are also thicker than the smaller rear fins. The one not showing are the small rounded fins at the end of the main fins/wings - these turned out to be horrendous to get right and I must have made about 5 or six that just didndt look right or were ruined by over heavy sanding.

They are now done and will appear in the next pics.

The fins have all been filled at their edges and sanded smooth and, if I say so myself, everything is looking good.

And after spending some time over the last few days gluing all the fins on here she is minus final sanding, filling and paint.

The fin alignment is probably the best I have ever done to be honest and she looks very clean - I'll try not to mess it all up with paint later on

The small wingtip fins are now on the end of the wings and these, after a few attempts, came out fine (just dont look in the waste bin where half a forest is laying in wrecked bits of wood trying to get these right).

I am still waiting on the motor mount and some odds and ends for the recovery gear and until that gets here I can calculate weight for the nose. I am estimating even with that big nose of balsa she will need noseweight. CP according to my primitive model and rough and ready calcs will be approximately halfway along the root of the big forward wings/fins.

Anyway heres the pics so far.

With the CP that high it looks like a lot of core drilling on that balsa nose cone to fit lead weight and epoxy! Too bad you can't get a composite motor.

Well so long as the CG comes forward a bit I am sure she will be fine - Perseus II has a very narrow CP/CG ratio and works fine. So long as I can get the CG a bit forward - and with that huge nose on it that shouldn't be a problem I am sure all will be well and even if it isn't and she flies wild theres lots more stuff to build Sea Dart, Schmetterling, Thunderbird 3 and Goddards L13 (from Fliskits) so its not like I am short of stuff to do.

To be honest a few rockets being destroyed would be a help in finding space and partner would be ever so happy too

The larger horizontal tail fins mean that your model won't need the CG to be quite as far forward as mine. One thing does concern me, though. Judging by the photo of the fins by themselves, the tail units are glued straight onto the tail cone. Is that cone just rolled card, or is it paper over a solid core? If it's just rolled card then it may not provide a solid enough base for the tail fins.

When I built mine, I cut slots into the tail cone. The tail fins have tabs extending in to the motor mount tube. The tail cone therefore plays no structural role, it's just decorative. The extra wood didn't do the CG any good but it does mean the rocket has done 19 flights so far and still has its fins.

Adrian,

You may well be right - I may have been over-optimistic about the properties of card stock when soaked with CA. In my thinking about the tail section I considered three approaches which were;

1/ Have an internal fillet of wood that ran down inside the boattail in line with the fin and anchored to the boat tail and the interior tube. Three successive attempts to get the fillets right resulted in failure. Really down to my inability to get the dimensioning right (though I did try very hard). Sirius Rocketry do this on one of their kits (Phobos I think) as an aid to the forming of the tail cone and presumably for increased strength.

2/ Mate the rear fins directly to the interior tube and have the tail cone made up of two halves - I rejected this as it seemed to involve fiddly stuff like allowances for the thickness of the fins and also trying to form a perfect half cone which I saw as likely to be a huge headache. Doing this for the Rheintochter rear nozzles was very awkward and the results were not 100%.

3/ Simple approach - just form the boat tail onto the rocket, glue fins on and give both a couple of hits of CA. This worked quite well on the Fliskits Thunderbird and the small rear fins that mate to the cardstock boat tail are pretty rigid.
In practice this produced a simple solution and one that looks ok BUT you are right to raise this as the finished item, even when filleted with epoxy along the fin root and with both fin and boat tail hit with two coats of CA has produced a somewhat flexible fin. Its not super wobbly but given the fact that the Rheintochter cracked a fin on launch and I do wonder if what nobbled it was stress caused by oscillation in the fin I do wonder of Fire Lilly will be very survivable in this regard.

To be honest I didnt think of cutting slots - I did consider having a pair of lug running through the boattail to the tube - I considered bamboo skewers for this which worked well on Thunderbird to improve the strength of the large rear fins which join to the boosters on a very small area but never pursued this idea at all.

I normally fly off a very soft landing ground with lots of long grass and two rockets have tumbled down intact when chutes failed (including Rheintochter) so I am moderately comfortable about landing but perhaps a tiny bit concerned about flexing under launch and flight conditions.

It may be the paint will add some rigidity to the structure - it has done with other rockets. With all being well in other respects I wil find out in two weeks when I hope to launch Fire Lily when my two boys are available to help out lugging stuff about for me - my youngest would never forgive me if I launched without him around

Latest pics....................

Nosecone has now been drilled out (had to go buy something for this) - an extra long drill/auger to get down to the pointy bit ready for weight once I know what the finished bird weighs and can measure its CG/CP. This will have a large dowel inserted later with the ring for the chute and shock cord.
The rear end of the bird still needs its engine mount (waiting on a delivery for that).

Final pic is the bird mostly undercoated, spray can ran out hence the bit of white showing through - its going to need a bit more sanding and finishing before a second undercoat and its final paint.

Astro-Baby said:

2/ Mate the rear fins directly to the interior tube and have the tail cone made up of two halves - I rejected this as it seemed to involve fiddly stuff like allowances for the thickness of the fins and also trying to form a perfect half cone which I saw as likely to be a huge headache. Doing this for the Rheintochter rear nozzles was very awkward and the results were not 100%.

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Making a tail cone of two halves is easy. You just make the full cone, coat it in CA to make it rigid, then cut it in half. Cut a strip off each half which is as wide as the fins are thick, glue the fins in place and fillet them, then glue the cones into place. The only difficult bit is getting the cone right in the first place.

I normally fly off a very soft landing ground with lots of long grass and two rockets have tumbled down intact when chutes failed (including Rheintochter) so I am moderately comfortable about landing but perhaps a tiny bit concerned about flexing under launch and flight conditions.

It may be the paint will add some rigidity to the structure - it has done with other rockets. With all being well in other respects I wil find out in two weeks when I hope to launch Fire Lily when my two boys are available to help out lugging stuff about for me - my youngest would never forgive me if I launched without him around

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The idea of gluing the fins to the internal tube wasn't to make them stronger during landing, it was to keep them rigid during flight. If anything it's a disadvantage during landing, I'd rather have the fin come away cleanly at the root than break part way along the fin, then it's easier to just stick back on.

Paint won't add any structural strength unless you slap it on so thickly that the paint alone will probably double the rocket's mass. You could make a second paper cone, glue it round the original, then coat that again in CA and sand down where it meets the body tube; that will do far more for the structure than any reasonable amount of paint, with far less additional weight.

Talking of paint, if you have a well stocked model shop, look for Tamiya sprays. They do a spray can version of RLM 76 Lichtblau, which is what I believe to be the colour seen on the Cosford specimen and on the black and white photo on luftarchiv.de, and which I used on my Feuerlilie F55. (My F25 is small enough that I just painted it by hand.)

Theres a real shortage of hobby shops round here that stock anything really. This F25 will be the same color as RheintoxhterI have a can left over from the RT build and the space and defense budget is strapped

The fins....well after the epoxy fillet dried they seemed to get a bit more rigid. I think they are probably ok but with those large tail surfaces acting as a lever on them they tend to feel more wobbly than perhaps they are.
The finish is coming up well so I am going go leave as is and see what happens. If its a ripper on launch and the fina fall off I will rebuild but I really want, just for once, to get somethingaat least approaching sodmeisters quality of finish and this one is getting close...at least if I squint my eyes a bit

With some time spare this week I managed to get the final paint job done. Here she is......

The nose cone is actually just the forward side of the white band - the rest is fake nosecone (ie real body tube) - I did this to more closely resemble the one in pictures I have. She is a bit of a mish mash of styles with larger rear fins than the one in the pics and also with delta wings rather than swept back ones as I worked from what may be a faulty original plan.

The pics arent high enough quality to see the scored in panel lines on the wings.

I finally managed to get a good finish - the ultra matt green I got from Halfords covers up a multitude of sins It was left over from the Rheintochter build. The whole things has been made of scrap parts left over from the Rhinetochter build so a a good use of spare resources. I was under a bit of a nag about the costs of my hobby so I had to keep things under some control for this. The kevlar shock cord was recovered from a rocket crash and pretty much all I had to buy for this was the motor mount (that hasnt got here yet so she is not fully completed) and some elaticated nylon for the shock cord. The parachute will be run up from some Mylar I have on hand.

Anyway here is the nearly finished Fire Lily missing only its motor mount and some small parts of the recovery system.

She has been a very easy build (compared to Rheintochter everything probably is )

Still some distance from the legendary sodmesiter quality of finish but with each build I am getting better and sharper and although there is a long way to go yet I really felt with this one I was starting to see some results from practice.

No transfers - its all done with paint on this one - the narrow black band near the tail isnst on the pics but I added it on just to give it a slightly better line to the eye. It also helps draw the eye away from any glitches on the boat tail seam

Heres a few more pics of her including one with her sister 3rd Reich missile the Rheintochter.

Oh, forgot to mention - if anyone wants the plans for this with the fin templates and the rear boat tail transition hit me up on PM and include your email addy and I will email them to you.

Astro-Baby said:

With some time spare this week I managed to get the final paint job done. Here she is......

The nose cone is actually just the forward side of the white band - the rest is fake nosecone (ie real body tube) - I did this to more closely resemble the one in pictures I have. She is a bit of a mish mash of styles with larger rear fins than the one in the pics and also with delta wings rather than swept back ones as I worked from what may be a faulty original plan.

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It looks good! The black band round the tail is indeed visible on the photos. The red tip on the nose looks neatly done, too.

Some of the score lines on the wings are also visible, especially in the head-on photo. Try pointing the model towards a window or even put a torch in front of it so that the score lines cast better shadows from the light ahead.

My model is based on the luftarchiv.de photo which shows no such white ring and the black not extending quite as far back. So I did the exact opposite to you. The model's nose extends too far back compared to the luftarchiv.de photo, so I painted a light blue ring around the base of the nose cone to give the illusion that it's part of the body. I should have copied the Cosford photo and you should have copied the luftarchiv.de photo, then no such trickery would have been needed on either model. :lol:

With any luck you'll get to see the real one in a day or two!

You probably know this Adrian but I get red to look bright by undercoating with something bright - white is good but a bright yellow or very pale grey works as well. The red tip was handpainted with a Tamiya Acrylic which I used for some astro gear agas back that needed a bit of tarting up.

Typical on the nose cones though eh ? - Its very hard to know what was the definitive look because none of this stuff ever made it to production

Looking good and it should fly well too.

JUst for completeness - heres a final few pictures showing;

• The motor tube in place
• The wooden dowel that goes into the nosecone - the nose cone has a piece of plumbers lead inside, topped up with epoxy and then a wooden dowel made of basswood glued into place.
• The recovery gear - bin bag parachute cos once again I made the recovery space a bit tight

and finally...a few pics of the now fully completed Fire Lily all ready for its firts flight. If the weather holds up I may get to fly her this weekend.