XF-108 Rapier RC rocket glider.

While working up my recent XB-70 rocket glider project, I revisited a related full scale project that was designed and reached a full scale mockup before being cancelled. The was the North American XF-108 Rapier, intended to be a long range Mach 3 escort fighter for the B-70. As it became clear the XB-70 would never be produced in quantity as a bomber, there was no need for the Rapier.

I had always wanted to do a profile electric pusher prop jet RC model of the attractive XF-108 Rapier and finally go around to doing it, with the added incentive of being able to launch it on reloadable E6 power. I found a suitable three view and tile printed it to the size needed.

I am on a planned run of five profile Depron RC rocket gliders and this is number four. After this one is complete, the last one of the batch will be the Boeing 2707-200 swing wing SST.

Here is a peek at the Rapier that I knocked up today. Size is based on Frank's well proven formula. I had cut the vertical tail and ventral fins last week. The wing and fuse were cut today and assembled this afternoon.

I think it has lots of promise to be an excellent performer with a lot of wing area and generous vertical surface area.

I like to use a flat 1mmx6mm carbon spar in a lot of my 6mm Depron RC models (and as a reinforcement in model foam RC models) as it is easier to install than a tube. Just slice the 6mm Depron wing parts where you need a spar and laminate the parts back together with the carbon strip in between.

Got a lot done today as it was fairly windy, our DARS launch/contest was cancelled and my normal RC field is under two feet of water.

It is ready for panel lines, vinyl markings and the radio gear.

Now have two and very soon three new RC rocket gliders to maiden... If we ever get to have a launch in a North Texas again!

I always thought that was a beautiful looking design. Too bad they never produced it. If memory serves me, A lot of the design ideas went into the A-5 Vigilante.
A quick story---Back in the day when I was but a young boy, we used to go down to the St Johns River area for fishing trips--couldn't tell you where now---anyway, the USN had a target range near there. We would sit and watch A-5's come through and pull up and over releasing their dummy nuclear bombs. The bombs would continue vertical for several thousand feet---we would loose sight of them---Every one of them would hit within tens of yards from the target !!! This was back in the 60's. That's a pretty close hit for a nuke !! Not trying to steal the show. That's a nice looking bird. Let us know how she flies, looks like you got some good wing area !! Very Nice 11 ---H

I always thought that was a beautiful looking design. Too bad they never produced it. If memory serves me, A lot of the design ideas went into the A-5 Vigilante.
A quick story---Back in the day when I was but a young boy, we used to go down to the St Johns River area for fishing trips--couldn't tell you where now---anyway, the USN had a target range near there. We would sit and watch A-5's come through and pull up and over releasing their dummy nuclear bombs. The bombs would continue vertical for several thousand feet---we would loose sight of them---Every one of them would hit within tens of yards from the target !!! This was back in the 60's. That's a pretty close hit for a nuke !! Not trying to steal the show. That's a nice looking bird. Let us know how she flies, looks like you got some good wing area !! Very Nice !! ---H

No doubt at all that a good bit of XF-108 DNA made its way into the A-5. The vertical tail, fuse and cockpit areas ar quite similar.

I always liked the look of the Vig. I have some sketches for a small scratch built RC EDF model of the A-5 for twin 40mm or 50mm fans.

I have already test glided the XF-108 as a free flight and it is a real floater.

Finally got to try the XF-108 at Hearne yesterday. Pre launch picture while on the pad is attached.

During the build I remember thinking that the fuse structure was a little light and the wing area was pretty large and perhaps I needed a bit more structure. I should have listened to that inner voice....

The first 100 feet or so of the boost was perfect. It responded well to a couple of minor control inputs. Then it experienced an brief airframe (not control surface) flutter event that broke the fuse and wing in half at about the 1/3 mark of the wing root. Ouch.
The front of the model did what you would expect and followed the weights on the nose to the ground in a very stable manner.

The rear of the model was more entertaining. It still had 4-5 seconds of burn left and it started a high speed nose down pitch and spun end over end at a high rate. Seemed to be making some lift as it was sort of hovering in place and not decending much. At burnout, the rear of the model did a nice safe tumble recovery to the ground.

I am going to repair it by inserting some new Depron where needed and transplanting a new nose section into place. Going to stiffen the curent fuse with a pair of 2mm or 3mm doublers in the area under the wing. Also going to add a thin carbon spar at that 1/3 root cord area which should make the front portion of the wing stiffer.

These mods should cure the slight lack of airframe stiffness that likely caused the flutter event.

It will fly again soon and this time my ace photographer buddy will be there to document the occasion!

Tom, sorry to hear that, but interesting to see where and how things fail so we can learn. I was worried about that on my sr71 so I doubled the top and bottom fuse pieces and added the styrene bottom reinforce. Still surprised it failed there, the fuse top is pretty shallow but the bottom seems thick enough..

The XF-108 Rapier is almost back together again. Complete except for the lower fuse doublers in 3mm Depron (one for each side) and new 6mm Depron on the first 6" of the nose.

Pictures to come.

Hope to re-maiden it on Aug 11 at the DARS launch.

tab28682 said:

The XF-108 Rapier is almost back together again. Complete except for the lower fuse doublers in 3mm Depron (one for each side) and new 6mm Depron on the first 6" of the nose.

Pictures to come.

Hope to re-maiden it on Aug 11 at the DARS launch.

Click to expand...

Looking forward to it. Re-maiden... interesting expression! :grin:

And here is the Re-maiden report....

Hard to believe that almost a year has passed since the first flight attempt on the XF-108.

however, I did finally get around to flying it again, up at a model aircraft event in Little Rock, AR, last Friday. This time, with a little bit of reinforcement, all went pretty well. I was still getting a small amount of odd flutter on the way up. Pretty sure it was not control surface induced, as I had carefully checked the linkage and hinging for slop and found none. However, the entire body and wing was oscillating a little, with the middle of the fuse out of phase with the nose and aft end. It did this from about 1-1.5 seconds into the burn, all the way to motor shutdown. Going to add some .5mm x6mm carbon strips to the wing leading edges before the next flight. The oscillation is probably a function of the large wing area, fairly small fuse and single carbon wing spar.

Transition and glide was just right. This guy has some nice hang time with the large amount of wing area. Handling was very nice.

Here are some pictures taken by Richard Ng showing the flight.

Launch reports and flight photos of the XB-70, X-15 and XAB-1 from this same event coming soon....

PS. added the three view that I based the aircraft on. It did have an odd error...the wing mounted ventral fins were not in the right place, so I moved them tot he right place.

That looks really nice tom, I like the head-on drooped wingtip look, menacing.....

Frank

Thanks, Frank.

Hope to add a little more carbon and fly it again this weekend at the DARS launch, possibly at Hearne in mid July and at NARAM in late July.