Dynasoar Rocketry IntR/Ceptor D-2.3 RC motor flight

I finally got a 12 pack of reloads to try. I built one of my IntR/Ceptor kits but left off the carbon spar to save weight, and fit an 18mm motor mount. AUW is 141 grams, which is a bit heavy for this motor but I wanted to see if I could fly it on one of these kits as an option for folks, since the casing is inexpensive. I did not need any nose weight at all so that saves one ounce compared to the 24mm version, the 18mm motor is about .7 ounces lighter and the spar saved a few more grams, and I did some other foam reduction. I would have switched to a lighter battery but the balance point was perfect as is. I could have saved about 8 grams using lighter servos. The 24mm version is 8 ounces rtf with an E-6 as a reference. I think a good weight would be about 4 ounces rtf for a sport plane like mine, I think I could maybe get as low as 4.5..

It was really windy today, 11-12 mph gusty, but I wanted to try anyway. Used an 8' rail. I had to stand there and hold the wing so that the wing gusts wouldn't twist the rail buttons out of the foam. Had a very slight dip in the wind and had my wife hit the button, very fast off the rail, about 4 seconds in, the thrust starts to be approx 1:1 and I had to pitch into the wind. glide was very docile at 4.5 ounces glide weight. I'm going to try some more launches tomorrow as there is supposed to be no wind. I know fighting a head wind robbed some of the altitude, so we'll see how it does in calm conditions. Model was dead stable and hands off for most of the boost which is great given the high wind.

If I chop off the wing tip pods and go to a single vertical stab instead of the twin tails, it wouldn't look like an Interceptor any more but may save a few more grams in the tail and mean I could use a slightly smaller battery as well.

Anyway, wip. Interestingly the o rings don't compress much but there were no issues, just filled the ejection well with JB as per the instructions, grease and install the guts. About an 8 second burn. Guts came out easily after the flight and wiped clean easily.

Frank

I got six flights this morning in dead calm and it flew really well, really straight and not sluggish at all, just a bit of pitch over near burnout was required to keep up the airspeed. CG shift is pretty minimal so I had to keep a few grams of nose weight in place or the glide wasn't stable. It's so light it doesn't have much penetration so the altitude is good but the glide is slightly shorter than the heavier version with 24mm mount. Flew two more this afternoon, here is the last flight. I like the 18mm reloads, very clean just wipe the forward end and re-lube and reload, didn't find any hard baked residue at all, I did need to build the reload with the igniter in place as the nozzle was too small to insert it after it was built. With a 15% discount, the 12 pack motors come out to about $4.67 per motor compared to around $6.50 for the E-6.

[video=youtube;onakXqCaZE0]https://www.youtube.com/watch?v=onakXqCaZE0&feature=youtu.be[/video]

Here she is with the rest of the stickershock decals applied.

Cool that it works with the existing model!

Frank, where did you get the D2.3s at a 15% discount?

Have you thought about a slight overall scale down to get the weight of the model closer to 4 oz?

I will likely do a SR-71 model optimally sized for the D2.3 to add the my fleet, or perhaps a B-70.

Well, I did remove the spar and a doubler which saved about 6-7 grams. My goal was to see if I could take my lightest kit and modify it to use the d2.3 as a way to see if people would like that, as the casing is cheaper to get into and the reloads are less expensive. So it did work with little modification, but I don't know if the flight time/performance is good enough for people to be interested, they'd have to let me know. Right now there are no comments so I'm assuming not.

Right now the model is using about 5 grams of nose weight, so not much, it's pretty optimum at 143 grams. I'm afraid if I shorten it at all to downsize, I'd have to just make up for CG with nose weight and be back to where I started. The foam component with pushrods/horns is only 2.2 ounces(62grams) of the weight, the rest is servos 2x11 grams, battery 16 grams, motor 28 grams, receiver and wire for battery 10 grams, nose weight 5 grams. I could switch to 3 gram servos, so get back 16 grams, and maybe remove some/all of the nose weight because of the lighter servos, so maybe 122 grams or 4.3 ounces.
The initial spike in thrust is high so you want to watch flutter in an un-spar-ed wing so you can't go too light.

The SR-71 CG location is further forward than this model by another 3-4 inches for a 39" long model, so will take more nose weight relative to the IntR/Ceptor as an example, again downsizing may not buy as much.

Mike at bay area rocketry got two 12 packs of the d 2.3's and sold me one for 15% off retail which is his normal thing, I saw him at a launch this weekend and he had the other 12 pack still. He doesn't list it, you'd have to call him.

Frank

tab28682 said:

Cool that it works with the existing model!

Frank, where did you get the D2.3s at a 15% discount?

Have you thought about a slight overall scale down to get the weight of the model closer to 4 oz?

I will likely do a SR-71 model optimally sized for the D2.3 to add the my fleet, or perhaps a B-70.

Click to expand...

My D2.3 loads have made it to buyrocketmotors.com and I will pick them up this week.

I hear you on the SR-71 needing more weight to make the required CG but I do think that a scale down can end up with enough weight reduction over all to do decently on the D2.3. Could do the planform in 3mm Depron with a bit of 1x3mm carbon strip as needed. The fuse and nacelle profiles could stay at 6mm.

Might do the XB-70 or another model to avoid the need to paint the SR-71 black, though.