This page will detail these two unique aircraft through web info and photo interpretation.
This web page is in no way related to or sanctioned by Boeing, NASA or the US Air Force. All photos of the full-size aircraft belong to Boeing, NASA, or the USAF unless otherwise noted.
The goal is to end up with flyable R/C models. Check back often for updates. A simple build thread is presented in the pull-down tab above and will be updated as appropriate. This is not intended for and may not be used for any commercial purposes whatsoever.
Specs for each aircraft vary. Often numbers are given in metric units with conversion to US customary. These often seem rounded and vary from site to site. The X-40 dimensions were found in more than one place. NASA is usually particular about getting details right and the following were found on a Dryden site so we’ll go with those. The X-37 dimensions came from a Boeing site and a fact sheet released by the Air Force.
X-40A
- Wingspan 11′ 6″
- Length 21′ 5″
- Height 7′ 5″
- Weight 2650 lb
X-37B
- Wingspan 14′ 11″
- Length 29′ 3″
- Height 9′ 6″
- Weight 11,000 lb
So comparing the photos below, it looks like the wing for the X-40 is slightly smaller than the X-37. The tail surfaces are also smaller. The distinguished ramp on the back of the 40 is also missing from the 37. Its hard to speculate but it could have been removed to reduce pitching moments at higher speeds. The 40 was only meant to do landing tests. This could explain the smaller wing. Maybe it was sized to increase wing loading to mimic 37 flare on landing? The side flares on both models at the rear is interesting. Maybe a packaging issue or its used to move the CP aft. The wing plan form looks slightly different in the limited photos I have seen. Maybe the double delta (crank) on the 37 is to help with super to transonic stability. The shadows in the first photo above shows the double delta on both models but its really hard to see anywhere else on the X-40.
While I am an Aerospace Engineer, its been a long time since I did aero work and I wasn’t that hard core anyways. Again, only speculation. Those tricky Aerodynamicists 
I just want to build and fly a cool scale model with completely different Reynolds numbers anyways…
I’ll leave it to the reader to do their own research if they are more interested.
This composite photo has been scaled (and reversed) to compare the differences.
I’ll work up some numbers as I go along. Currently the 1/10 scale Depron model of the X-40 is flying and providing experience for optimizing CG and control throws. The goal is to build a same-scale X-37 from more traditional building techniques (balsa) with operating spoiler and retracts. I’ll eventually post plans for both. The X-40 can be built in a few evenings and is fun to fly. It does require some intermediate skills. The larger X-37 with retracts should be even more fun!
10/18/11
The templates and some basic intructions are done and posted for the X-40. The point was to figure out the CG range and control throws. I also wanted to see how it flew mixing in flaps. I wanted to get some flying experience on it before building the X-37 and flying it onto a hard runway.
After drawing the wing, I scaled it up 125%. I wanted a better chance of being successful. It would also allow me to ballast it up and see how the X-37 might fly. It ended up with a 16.5 inch wingspan and is 25.5 inches long. It weighs 8 oz ready to fly. It uses a simple flat bottom airfoil that ends up around 12% thick with the formed top piece. It uses a 3/16 round carbon spar for simplicity.
Basic construction before assembly.
Ready for radio equipment.
Waiting on final graphics.
10/21/11
It flys! We flew it about 10 times. I flew it 4 or 5 times to get the CG about right. Then I wanted someone else to fly it for second opinions. After 5 or 6 more flights, we found the aft limit and on the last flight, the forward limit. Only a few of the flights were very nice. Near the end we had limited the elevator throw to de0sensitize it and forgot to put in an ‘emergency’ rate. We were pretty excited and the crowd at the local field was anxious to see the next flight. It went in pretty hard but since its depron, it was a pretty easy fix and paint touch up. A wing broke so I added an additional spar a little further aft. Its ready for more testing…
This was just before the first flight.
First flight CG was at the heavy line. It seemed to flew best about 1/8 inch behind the dot which was the calculated 25% chord of the wing. It flew light. Next time out I’ll add some ballast and try it with a faster approach.
10/28/11
Success! About 20 more flights today. The battery was moved forward and the Receiver ended up where the battery was. It also has a quarter in the nose (8.2 oz now) It flies quite well. I ended up mixing elevons to elevator. It allows for smoother (alpha) control and takes out some of the pitchiness we were experiencing. It’s essentially killing lift as we add elevator so you can increase the angle of attack without the model climbing as much. It makes it look like it has a much higher wing loading than it actually does.
It bleeds speed fairly quick in the flare but its pretty easy to fly it 50 feet or so down the runway to a nice landing. If you come in a little shallow, the flare to touchdown takes place much quicker, more like 20 feet. Its pretty easy to come in with a scale like approach, slowing near the flare point, then perform a scale flare like on the real videos. You can also keep the approach speed a little longer and extend the flare to touchdown more like a shuttle landing. Its pretty fun.
12/11/11
Videos! Yipee! The first one was from a few weeks back. The others are from this past weekend.
Here is a guide I was using to set it up. 
It flies best if you use the forward CG. You need to keep the speed up as you can see in the videos. If seems if you don’t carry speed into the final, it doesn’t have enough pitch authority to rotate. This is common in the dozens of Shuttles I have flown. The control throws are not as critical if you carry the speed. Its a little sensitive when fast but then you need the throw as it slows down. If I fly it anymore, I’ll play with rudder inputs more, feel out control throws at different speeds, and maybe move the CG around some more
Now to start on the X-37…