1/12 scale German A4b

[aerostadt]

Inspired by Tom's conversion of the Estes 2.6" diameter V-2 into the German A4b, I bought Paul Clark's 1/12 scale V-2 advertised on the TRF "Yard Sale" thread . I am in the process of converting this to an A4b.
https://www.rocketryforum.com/threa...estes-v2-into-a-semi-scale-manned-a4b.121175/Paul's V-2 (or A4) has very different construction techniques from the usual model rocket builds. It uses foam board and the polyvinyl (plastic skins).

 

[aerostadt]

Cutting out the foam board I get a lot of pieces for the aft-end.

 

[aerostadt]

Dry fitting these parts I get an idea of what the aft-end is going to look like.

 

[aerostadt]

The servo's were glued into the aft-end and holes were cut out from the skin for the servo's to fit.

 

[burkefj]

That's neat I think if you ditch the PVC shells which will be heavy and went with like a 3 mm or 2 mm depron skin it could be light enough to glide pretty well with an ejection pod.

 

[burkefj]

I'm assuming this is a paper covered foam board correct? If so you could reproduce those parts on 6 mm depron and save some weight as well and build a second one.

 

[aerostadt]

Yes, weight is a definite concern. I am afraid that I am further along than what the posted pictures show so far. The plastic shells are pretty light. Years ago, I converted the Estes 4" diameter V-2 into a Wac Corporal. I went back and weighed my 4" diameter Estes V-2 parts and I get roughly 17.9 oz for the 4" V-2. I'm surprised that it is that light. If I take the cube of the ratio of diameters for Paul's V-2 and the Estes V-2, I get a factor of 2.46 . Multiplying that factor by my V-2 weight of 17.9 oz, I get a scale-up weight of 44 oz. As I recall Paul is stating that his V-2 should be about 30 oz. So, I went ahead and bought Paul's V-2 on the basis that it would be comparatively light. The 30 oz puts Paul's V-2 around the weight of Frank's large BSG Viper. (Of course, my weight will go over and I will not have as much wing surface as Frank's larger Viper. I am weighing as I go along.) The foam board does have paper covering. I am planning on using a pop-pod with a G40 motor. I know Frank has made many models with depron centering rings and depron skin, so that is a definite possibility. My production line is pretty slow, so I do not have plans to build a second A4b. Building this model has taken longer than I thought.

 

[burkefj]

For a 5.5" diameter model, that's pretty heavy with A-4 style wings, My profile model that was effectively 6" weighed about 11 oz in glide but has more effective wing area due to the profile, even if you doubled it to 22 oz in glide, it would come in pretty hot, I don't know what you feel your empty glide weight will wind up...

Yes, weight is a definite concern. I am afraid that I am further along than what the posted pictures show so far. The plastic shells are pretty light. Years ago, I converted the Estes 4" diameter V-2 into a Wac Corporal. I went back and weighed my 4" diameter Estes V-2 parts and I get roughly 17.9 oz for the 4" V-2. I'm surprised that it is that light. If I take the cube of the ratio of diameters for Paul's V-2 and the Estes V-2, I get a factor of 2.46 . Multiplying that factor by my V-2 weight of 17.9 oz, I get a scale-up weight of 44 oz. As I recall Paul is stating that his V-2 should be about 30 oz. So, I went ahead and bought Paul's V-2 on the basis that it would be comparatively light. The 30 oz puts Paul's V-2 around the weight of Frank's large BSG Viper. (Of course, my weight will go over and I will not have as much wing surface as Frank's larger Viper. I am weighing as I go along.) The foam board does have paper covering. I am planning on using a pop-pod with a G40 motor. I know Frank has made many models with depron centering rings and depron skin, so that is a definite possibility. My production line is pretty slow, so I do not have plans to build a second A4b. Building this model has taken longer than I thought.

 

[tab28682]

Very interesting upscale. An A4b at about 5.5" diameter is a nice size scale up from one based on the maxi brute V2.

I printed some nose cone and tail end parts for a 4" version, but need to rework the CAD to reduce wall thickness (less weight) and remove some interior structure. Also need to crank up my printer to use ABS.

I bet that an A4b could be carefully built at 6" in diameter at a little more than the 32 oz takeoff weigh that works best with the H13. very lightweight 3d printed nose and tail come, depon structure, skin and flying surfaces. I know Frank likes to launch vertically, but I woudl be willing to go off at an angle at a slightly higher weight, if need be.

A cool A4b model that size would likely be worth the trouble of automatically released water ballast, or even servo operated water ballast using a small 3d printed valve.

 

[aerostadt]

For a 5.5" diameter model, that's pretty heavy with A-4 style wings, My profile model that was effectively 6" weighed about 11 oz in glide but has more effective wing area due to the profile, even if you doubled it to 22 oz in glide, it would come in pretty hot, I don't know what you feel your empty glide weight will wind up...

Definitely will be heavy. I am trying to keep the weight down. The aft-end section alone was about 15 oz. My 2.6" diameter A4b does not glide that well, but it came down slow enough on the last flight to have no damage. I will go back and measure the gliding weight on the 2.6" diameter A4b.

 

[aerostadt]

I have put some paint on this model.