TRF Summer Build Off: Der V-Max

Since I am going with a DRM theme, I figured that a different nose cone is in order. The closest match that I have found in a balsa cone is the BNC80K. Does anyone know of a better match? The other option is to use a shorter, pointed cone to go with the V2 influence but I think that I would prefer a long ogive ala DRM.

I can't turn up the link on my phone, but someone out there has a gallery w/ all the scale dimensions between MMX and 5+ IIRC. I'll keep looking.

https://www-personal.umich.edu/~mbear/redmax.html

The author says grab about a 5:1 ogive and round it over. HTH!

I'm still a couple of days away from the real world yet. I may have a link at home but I want to try and do something that resembles progress. It has been killing me the last few days to catch up on the build threads and not be able to even order parts for my own.

BNC 80 HAH looks about right?

https://www.erockets.biz/semroc-balsa-nose-cone-bth-80-10-5-ogive-sem-bnc-80hah/
https://www.rocketreviews.com/161x-upscale-der-green-max.html

dhbarr said:

BNC 80 HAH looks about right?

https://www.erockets.biz/semroc-balsa-nose-cone-bth-80-10-5-ogive-sem-bnc-80hah/
https://www.rocketreviews.com/161x-upscale-der-green-max.html

Click to expand...

That just may be the ticket! At the very least, it is close enough to look the part.

Yeah, you're making me want to build one now

Screaminhelo said:

At the very least, it is close enough to look the part.

Click to expand...

With that short stature and those canted square fins, you could use anything from a pointy ogive to an elliptical and it would still look the part.

jqavins said:

With that short stature and those canted square fins, you could use anything from a pointy ogive to an elliptical and it would still look the part.

Click to expand...

This build will reflect the evolution of the DRM into the ultimate, sleek tool of destruction, no square fins here.

I like where this one is going...

Hopefully, I will be able to start getting some work done soon. I just got back from restoring the Etropian border (I have learned that those pesky Denovians are nothing but trouble), the yard is a mess and I will never get the sand, sweat and funk out of my stuff.

I will be playing with some alternate options for mounting the tube fins in between applications of paper clay to my mold. I have an idea in my head that looks absolutely wicked. I just hope that I can pull it off before the deadline. Regardless, the rocket will get finished though.

I got something done at lunch! I glued the fins to a short piece of scrap tube. I may just trim the top of the tube and keep them just like this but I have to work out how the motor will be installed for flight. I do have a spark plug boot puller that may fit the bill but I kind of like the idea of cutting away most, if not all of the tube, so that can reach in from the rear to install the motor.

Well, I pieced some scraps together this evening and I may alter the design slightly. The scrap that I used for the main body tube is just a little shorter than would be called for based on the original design. It is only an inch or so shorter but I like the extremes...short and fat or long and lean. I ordered the rest of my parts this evening, so I'll contemplate for a day or two before I commit to cutting anything else. I'll post a picture tomorrow to see what y'all think.

Here is the mock up. I was wrong in the previous post, the mock up is about 6" shorter than designed, the airframe is short by 4" and the nose cone is short by about 2". Since I kind of like the look, I'm going to play around with this and see if it works but I definitely like the longer BNC-80AH nose cone. The one in the image is an 80K if I remember correctly.




Now for the temptation! I just stuck the nose cone on the fin can for grins and I have to admit that I like it! Now this would require a bit of work to fully realize the concept that I am going for here and I figure that my usual commitments and glacial build pace would, most likely, ensure that I would miss the completion deadline. Nevertheless, I think that this idea warrants further exploration.



I just replaced my laptop and for the life of me, I can't get pictures to come out right, every trick to get photos properly oriented just isn't working out for some reason.

First off, let me say that this design is very cool. I was expecting something different based on the name - I was guessing it was somehow a hybrid of the Der V-3 & Der Red Max, though its really nothing like either. Though, I suppose that V-max has a different meaning entirely anyway, I just figured it was a clever play on words. Incidentally, the Der V-3 did use that same nose cone from the V-2 kit (in fact, I parted out a V-2 kit to fix my Der V-3), so you're already tied in there...

Regarding the F-40, keep in mind that those ducts are pretty standard shaped NACA ducts - it isn't anything particularly specific to Ferrari (even though that car used a lot of them!). That shape is commonly accepted as having the lowest drag for an inlet/scoop/duct. You might even be able to buy a small, ready-made piece that you can adapt for your purpose. My question is: with the motor as far up in the tube as your sketch shows, won't it be tough to install/remove/get the ignitor into? Won't the lower tube get pretty toasted below it?

EXPjawa said:

My question is: with the motor as far up in the tube as your sketch shows, won't it be tough to install/remove/get the ignitor into? Won't the lower tube get pretty toasted below it?

Click to expand...

Those are valid concerns. First take a look at the photo here. On that, my first GDS Saturn (on both, actually), I used an estes Screw-on retainer. Even with that, it took a little effort to get the motor in. The igniter had to either be added before the motor went in or, if after, it required a long igniter that could be secured below. As for burning, that is not a given. The lower body is almost 3" and the motor is 29mm. On two flights, there was a lot of splatter in the tube but it wasn't really burned. The nozzles overlapped the ID of the lower body and they suffered a bit. Screaminhelo, if you are concerned, you might consider adding a light, removable telescoping tune the the lower part of the body. There have been many threads talking about treatments to protect from burning. I don't know how these will work if you actually have the motor plume scorching the.

EXPjawa said:

First off, let me say that this design is very cool. I was expecting something different based on the name - I was guessing it was somehow a hybrid of the Der V-3 & Der Red Max, though its really nothing like either. Though, I suppose that V-max has a different meaning entirely anyway, I just figured it was a clever play on words. Incidentally, the Der V-3 did use that same nose cone from the V-2 kit (in fact, I parted out a V-2 kit to fix my Der V-3), so you're already tied in there...

Click to expand...

Der V-Max came from the inspiration for the colors, red and black makes for a purty rocket but I am honor bound to ensure that the color combination is clearly tied to something other than the University of Georgia (War Eagle!!!). I decided to use the BNC-80AH cone to have a bit more of the DRM shape to help make the connection.

EXPjawa said:

Regarding the F-40, keep in mind that those ducts are pretty standard shaped NACA ducts - it isn't anything particularly specific to Ferrari (even though that car used a lot of them!). That shape is commonly accepted as having the lowest drag for an inlet/scoop/duct. You might even be able to buy a small, ready-made piece that you can adapt for your purpose.

Click to expand...

I got the inspiration at work, I am a helicopter mechanic and aviation nut in general, anyway, I saw the cockpit blower inlet and decided that I just had to give it a shot. I designed the master from the original specs from the test program. I am planning to squish mold fiberglass ducts, it shouldn't be too difficult.

EXPjawa said:

My question is: with the motor as far up in the tube as your sketch shows, won't it be tough to install/remove/get the ignitor into?

Click to expand...

As for motor installation, this one will be easier than the DGS model since I am dealing with a 29mm motor and a 2.6" tube. The other one was an 18mm motor and a 29mm tube. I also have some spark plug boot pliers that I may be able to use to help ease flight prep a bit. I also have some design options available to help ease this issue if necessary.

EXPjawa said:

Won't the lower tube get pretty toasted below it?

Click to expand...

The motor placement is relying on some of the principles of dynamic gas stabilization. I am not really counting on additional stability from DGS, though it could impart some benefit, I am really looking for the exhaust to draw air in through the inlets which will maintain a barrier of cool air between the exhaust stream and the aft tube. I experimented with the DGS concept last year with a much smaller margin between the the diameter of the motor and the aft tube and, while a bit charred, the fin can survived quite well.

rstaff3 said:

Those are valid concerns. First take a look at the photo here. On that, my first GDS Saturn (on both, actually), I used an estes Screw-on retainer. Even with that, it took a little effort to get the motor in. The igniter had to either be added before the motor went in or, if after, it required a long igniter that could be secured below. As for burning, that is not a given. The lower body is almost 3" and the motor is 29mm. On two flights, there was a lot of splatter in the tube but it wasn't really burned. The nozzles overlapped the ID of the lower body and they suffered a bit. Screaminhelo, if you are concerned, you might consider adding a light, removable telescoping tune the the lower part of the body. There have been many threads talking about treatments to protect from burning. I don't know how these will work if you actually have the motor plume scorching the.

Click to expand...

I believe that if I have enough inlet area relative to the ID of the fin can, it will work out O.K. I still have not calculated the flat plate area of the inlets, but I will add additional cut out area in the tube aft of the inlet trunks if I need a bit more to ensure adequate air flow.

Screaminhelo said:

This is the master for an NACA style inlet.

Click to expand...

EXPjawa said:

Regarding the F-40, keep in mind that those ducts are pretty standard shaped NACA ducts - it isn't anything particularly specific to Ferrari (even though that car used a lot of them!).

Click to expand...

Just to make things clear, it was moi who gave the F-40 reference...Screaminhelo noted the NACA inlet in the OP.

Screaminhelo said:

...
The motor placement is relying on some of the principles of dynamic gas stabilization. I am not really counting on additional stability from DGS, though it could impart some benefit, I am really looking for the exhaust to draw air in through the inlets which will maintain a barrier of cool air between the exhaust stream and the aft tube. I experimented with the DGS concept last year with a much smaller margin between the the diameter of the motor and the aft tube and, while a bit charred, the fin can survived quite well.

Click to expand...

Would the infrared heat radiating out still cause some charring or browning?

Yay aluminum tape!

Cabernut said:

Would the infrared heat radiating out still cause some charring or browning?

Click to expand...

There was some slight browning after one F and one G flight. Hence my suggestion for a replaceable stuffer.

dhbarr said:

Yay aluminum tape!

Click to expand...

When I have subjected metal tape to a direct motor burn, I still got some damage as it breached a little. At a minimum, I consider it a replaceable item. That still might be good for this one because I don't expect a ton of burning.

Screaminhelo said:

I believe that if I have enough inlet area relative to the ID of the fin can, it will work out O.K. I still have not calculated the flat plate area of the inlets, but I will add additional cut out area in the tube aft of the inlet trunks if I need a bit more to ensure adequate air flow.

Click to expand...

I think you will be OK but you might look at Dean Black's reference design for a GDS rocket to estimate how much air gap you need. Oh, I see your earlier responses about GDS. Note that the diagram I attached is newer than the one in the Apogee article.

Yeah, for reflecting IR only, no good with direct impingement.

Thanks for the new info Dick. The PoF article is where I took my inlet area ratios from, so an update on this may be very useful.

BTW, do you remember how much clearance you had with your Saturn V? I should have just over 1/2". My gut feeling is that this should be adequate but I am not ruling out lining the tube to protect it from the heat. Thing is, I am trying to to keep this reasonably light. There may be a few things that I have to do in the end to get this to work that negate my efforts to reduce weight though.

Glad to be of help. That one was lost to tree. I got it down after a month but it was mush. I will see if I have any notes and can measure my new one later tonight. I followed his original design to size the air gap. After the 1st flight, his new diagram was out and I added some extra holes. It flew better with the extra holes.

Fortunately, I am not reliant on GDS for stability. The height of the tube fins did end up rather low after I had a brilliant idea but the addition of a ring and the inherent drag of tubes and rings should balance things out. Any stibility that I get from the DGS attributes is a bonus. I like the idea because it allows me more freedom in motor placement. Since this is only my second attempt at it, consider this a bit of a research build as well.

The GDS reference also provides some guidance on how much of a gap you need to get enough airflow to keep Krushnik from killing you.

It appears that I had a 1.5 gap on a 2.8" tube and then added four 1"x"1.25" vents below that for the 2nd flight. The first flight clearly suffered from Krushnik but the 2nd didn't. Not that there wasn't some thrust loss but it wasn't clearly evident.

On the new one I have a 2" gap and 4 similar vents. I increased in because I experimented with a smaller diameter entry into the GDS tube (don't ask...bad mindim). It was stable but the thrust really was diminished.

I am estimating the current inlet area at 3 square inches. Since I am.using 2.6" tube, I will need to add another 3.75 inches of inlet area. I should get parts on the door step this weekend, so I will be able to start start getting things worked out.

I'm really interested in ducted rockets. I'll be watching your progress, especially the fiery part