Foam Board SR-71 plans are here!

[Craig A]

Howdy Folks, Craig A back with plans as promised.

OK, so I'm not always fast. They are large sheets, you'll need to tile to print. You'll also have to fasten 2 sheets of foam board together for the first two plan sheets to fit the long parts. The first plan sheet shows the two sheets of foam board connected in a "T" shape in order to get the main wing to fit. Plan sheet 2 shows the foam board sheets connected long side to long side. Here's a couple of pics with a finished (mostly) model. The black stripes on the Nacelles are a 3M double sided velcro strap that is thin like ribbon. They are just holding the nacelles on until I'm finished the model. The front cones are for display and show up decent in the side view. They will look better once painted black. They are friction fit so they can be removed during flight.

As shown, with the EDF unit installed, it weighs in at 539g.

There are some things I'm still messing with but they are minor things, like servo placement, etc. If I hung onto this until I thought it was 100% I'd never post it. If anyone has any questions please let me know and I'll explain what I'm thinking/doing. I'm also open to suggestion for modifications. I am working on a build guide with pictures and instructions and it should be along shortly. This will be a fun build if you like working with the Foam Board!

 

[tesseract]

How heavy?

 

[Craig A]

With what you see so far is 350 grams. There are still some cutouts in the main wing I need to remove and there is still a bottom single layer to add. I'm taking a really wild guess and say the assembled foam will be under 550 grams.
Also, as is the front 200mm of nose is solid, I also plan to hollow that some. The center of Gravity was also displayed in the original print as being 1-1/2 inch behind the junction of the forward (chine?) to the nacelle.

Reminder, I'm a noob, is there a weight I should shoot for?

 

[L Edge]

Suggest that you make the split elevator a set of elevons. You will need ailerons to control the fast roll of the SR-71.
Also, set up differential thrust for rudder action. Have no idea on weight since I used a pair of 64's. You don't really need cw/ccw EDF's

For flying, make sure all of the turns are shallow. Ailerons are super quick. Otherwise, it will roll over and dive down quickly. Last, do not put a high climb, steep descent for the nose will flip the bird over. Fly bird with throttle management to change altitude.

 

[Craig A]

L Edge, thanks for the tips, I appreciate it. On the CW/CCW EDF, I figured that might be overkill but it has been fun. The split elevator halves aren't joined. I had planned to put one servo in the fuse with pushrods that operate both sides together. Elevons would be an easy change. I'm also planning to mount servos in the sides of the nacelles (not blocking the inside). to save on what little control surface there is.
You wouldn't happen to have a picture of yours, would you?

 

[L Edge]

Here is the thread on my EDF SR-71.

https://forum.flitetest.com/index.php?threads/sr-71-takes-flight.63740/

If you notice, I was exploring what losses the inlet tube had, so the 64's were mounted 6 " back and the tube was added for flight to compare as is. Very little thrust was lost.

Watch this video to give you an idea of what can happen.