R/C SR-71 Hobby lab

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Unfortunately, the four E15-P's are not in good shape. After some finagling under a bright lamp I could look inside the motor and saw that the slot grain had swollen shut. I tried to ignite the motor with a very good igniter, but that option failed. My next recourse is to use an Aerotech re-loadable E18-4W.


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I have some old E15s (1999 if I read the date codes right). I find that only the nozzle ends of the grains swell up. A 2-56 threaded rod opens them right up. Once you do that though, the c-slot has a lot of oxidation and may have a hard tile ignighting. I use the same 2-56 pushrods to scrub all 3 surfaces of the c-slot. I found that I have to scratch oxidation off the entire length of the slot, or I get a chaff-chaff-chaff-pfffffft-t-t-t kind I ignition.

Ari.
 
I wasn't going to mention this, but I did try using a small screw driver to open up the slot. I thought that I did open the front a little bit, but evidently that didn't work. Obviously, I will not discard these motors until I try your idea. I might have some push rods around here, but they might not be the same size that you are talking about.
 
Um... ObMotorJoke: It's unsafe for you to do this. Send these motor to me for safe disposal.

Ari.
 
I finally got around to flying my SR-71 at Hellfire-19. I did get control of it after boost, but towards the end of the glide I panicked and gave it nose-down elevator, when it should have been nose-up. I realized the mistake at the very end with nose-up, but it was too little, too late. I don't know if it can be repaired. Here are some photos of the boost.

UROC_0122sm.jpg UROC_0123sm.jpg
 
If anyone is looking for a hobbylab sr-71 a guy came to our meeting with a free flight version he was trying to find a home for, pm me if you are interested and I'll see if I can hook you up.
 
I finally got around to flying my SR-71 at Hellfire-19. I did get control of it after boost, but towards the end of the glide I panicked and gave it nose-down elevator, when it should have been nose-up. I realized the mistake at the very end with nose-up, but it was too little, too late. I don't know if it can be repaired. Here are some photos of the boost.

View attachment 180376 View attachment 180377

If you can, post a picture of the damage. I still have a few beta molded foam parts from way back of the SR-71 nose area only. With a new top and bottom nose part, I predict the repair woudl not be too hard.
 
If you can, post a picture of the damage. I still have a few beta molded foam parts from way back of the SR-71 nose area only. With a new top and bottom nose part, I predict the repair woudl not be too hard.

Not to jump on the band wagon here, but If you have enough, I have one that needs repair. I would be interested, as mine is just the nose, and cockpit area. If possible, just let me know how much.

Thanks
Mike Dickinson
shortckt4-at-cox-dot-neut
 
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I am not sure mine is salvageable. I just tested the R/C. The side-to-side or left/right elevons are there, but the up/down elevons do not work. I can hear the up/down servo's trying to do something, but there is no physical response. I don't think that my model is worth flying again without the up elevon. Photo's of the damage are attached.

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Looks repairable to me, but you may have to open it up more to get to the servos, and their "sled", as these used mechanical "mixing", and as I recall, the server that worked the up, and down, actually moved a "sled" that had a servo mounted to it, that works the side to side. If you decide not to fix it, please do not discard it, as I might me interested in parts, as so far my flying skills with mine has not been great.
Post 24 of this thread, shows the insides, and the servo mounts.
 
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Thanks, Mike,

I will look at my SR-71 some more. After moving the airframe parts around a little bit trying to imagine how things might be epoxied back together, the lower shell became loose enough that I took a long Xacto stryofoam knife and was able to split the remaining attached shell apart at the seam. Then I saw the sled with the roll servo attached that you are talking about. The servo in front of the sled probably moves the sled back and forth. This front servo has become debonded from its wood base. So, I am thinking that I need re-attach to its wood base. I will look at this some more.

It looks like I have the motor mount, elevon cables, and transmitter from my old SR-71 that crashed a decade ago, but I don't think that those are the parts that you need.

Bob
 
Thanks for looking but you are correct, I need to rebuild the nose on mine. Good luck on the repairs, I have spliced a new nose on one before, using thin fiber, and epoxy. I also ran some bambo skewers, down the inside, right where the top and bottom shell mate together, and a little past where the main nose flares into the wings, as that is where I spliced to.
 
Finally made it to the storage and dug out a set of beta molded parts. Thought I had several, but only found one.

Picture attached.

Production parts were one part for the top shell and one for the bottom shell. Took a while to find a company back in the 1990s that could handle vac formed extruded EPS sheet as large as the SR-71 model in one piece.

Having found them, I do not think I would fix Aerostadt's model by using them, after looking at the pictures, especially now that he has separated the shells. The best way forward would be to simply put the cracked parts back together carefully with a thin film of 5 minute epoxy, one part at a time. if the joint is carefully wiped with alcohol after joining, the repair will be nearly invisible. Any minor crumples can be filled with lightweight spackle and touch up painted with black acrylic craft paint.

I did offer them to Aerostadt first. If he passes, I would be willing to sell them to mickeyd if he thinks they would work for his repairs. I was thinking 10 bucks plus shipping would be fair......

Should be easy enough to re-attach the elevator servo to the mixing tray assembly. However, I would strongly consider a modification to the radio installation.

A near fatal flaw on the production R/C SR-71 was the use of simple mechanical mixing and stock control horns and servo arms that, as shipped, gave far too much roll control for a new or beginner R/C pilot. When I left HobbyLab after the free flight model was being shipped, the plan for the R/C version was to use an adjustable on board electronic mixer with the inexpensive Hitec 3 channel radio system to give less roll authority and good pitch authority, so the average guy MIGHT be able to handle it. (kind of a pipe dream, I know.) The R/C guy involved after I left ended up using a simple sliding servo tray instead to get the needed elevon mixing, due to price point pressure. The R/C model as shipped is pretty tough to fly well, even for an experienced pilot.

If you happen to have a modern TX with elevon mixing and dual rates and an associated RX, the best fix would be to ditch the sliding tray and simply have one servo hooked up to each elevon. Mix as needed and set the rates to a small amount of roll and a moderate amount of pitch.

If you must use the stock TX that came with the SR-71, play around with the aileron servo arms to reduce the roll throws to make the model easier to fly with the simple TX and sliding servo tray.

The stock R/C SR-71 was a little overbuilt and overweight for 24mm motors, but we flew early production prototypes a number of times on F25W motors, which was pretty exciting. Right at the edge of foam flutter. I never tried it on a G40, but the guys after me did and thy reported to me that it typically reached the "speed of foam" and fluttered apart during boost. They also flew production models on F25 motors with few issues.

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Thanks, for checking. I still have one of each in the box, so am hoping I can make a make a mold from it, and maybe make a lightweight fiberglass copy.
 
Tab28682, it is interesting to hear your experience on designing and building of the HobbyLab's SR-71. Thanks for all the information. I am going to try to fix my SR-71 with the parts that I have. So, Mikeyd can order whatever he needs. I wish that I could use something even faster than 5 minute epoxy, but maybe that is the way I will have to go. I am posting some photos of the two servo's. It looks familiar to posts #24 & #25 of R&R Model Aircraft. I will go with the mechanical mixer, if I can get it to work. One can see the sliding roll servo on the aluminum sled and tray in the photo's. The forward servo actually slides the tray that the roll servo is on.

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5 minute epoxy is about the best and fastest way. Foam safe CA embrittles the foam next to the joint, most other adhesives take too long for my taste. Gorilla glue is ok, but can be hard to keep the joint looking good as it foams up and takes longer to cure.

As the extruded EPS foam sheet/Depron ages, it becomes more and more brittle. Bumps that would leave a minor dent or wrinkle 15 years ago can cause a large crack now.

Do consider adjusting control throws to tame the roll rate when using a non computer radio.

Best of luck with the repair.
 
Even though my epoxy is curing fast I did not want to hold the broken pieces together by hand for 5 or 10 minutes, so I used masking tape, which worked pretty good. I did get some shiny spots of epoxy and I was not able to wipe with alcohol, because of all the tape. Actually where the tape was located there was not shiny epoxy. If I had known that I would have used more tape.

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After repairing the crack shown above I epoxied the forward servo in place to give up/down pitch. This worked and up/down elevon has been restored as shown in the video. The aft servo has roll left/right, which can be seen in the video, if you look closely. So, mechanical mixing has been restored completely.

[video=youtube;zZdh2FlrdIU]https://www.youtube.com/watch?v=zZdh2FlrdIU&feature=youtu.be[/video]
 
I know of at least one Hobby Labs RC SR-71 that will be flying at Airfest in a couple of weeks. I suspect the motor of choice will be an E-6.
 
An E6 might not be the best choice, as the SR-71 is heavier than the typical S8E glider. Also, not as much wing area for lift in an ascent off of vertical. Just a guess, as I never tried the E6.

Anyone out there who has tried an E6 in the SR-71?

All test flights except for a few 29 mm F and G motors were on AT E15-Ps and the old Estes E15 motors that were discontinued in the 1990s.
 
An E6 might not be the best choice, as the SR-71 is heavier than the typical S8E glider. Also, not as much wing area for lift in an ascent off of vertical. Just a guess, as I never tried the E6.

Anyone out there who has tried an E6 in the SR-71?

All test flights except for a few 29 mm F and G motors were on AT E15-Ps and the old Estes E15 motors that were discontinued in the 1990s.

I concur. The OP states that his SR-71 is 14.5oz. An E6 has only about 16 oz. of thrust after the initial peak. It would be a marginal flight at best and more than likely an very non-vertical flight. We like to keep the S8 birds to at least a 1.5:1 TWR, and they have large control surfaces capable of controlling low speed flight.

An E12, E15, or E16 would be better (either BP or APCP).
 
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I agree the E-12 is probably the better motor for that RC casing in that model. I fly some of my depron gliders that are about the 14.6 oz weight on the E-6 but they too have large surfaces and large deflection, he'd probably get 3-400 feet at the most on the E-6. My own design SR which is a bit larger flies fine on E-6's but it has larger elevons and is about 9-10 oz rtf.

Frank
 
Guys,
Thank you for the advice on motor selection! I've been flying this particular SR-71 for about 8 years now (I have two) and have flown it on every reload available for the 24MM RC case as well as most of the 32MM reloads including the G-12.

You're right, the E-6 will not lift this plane straight up but it fly’s off of angled rods quite nicely and it's a hoot to fly under boost! The E-6 gives me just over 7 seconds to perfect my aerobatic routine before it turns back into a glider.

As far as altitude, in this case, it may or may not be your best friend. Notice the non-scale yellow stripes running down the bottom of the airframe. After a strong boost to higher altitudes, the two little vertical fins all but disappear making orientation difficult.

I now have just under 80 flights on this airframe and as you can tell there has been a lot of repair work done to it (both with very light fiberglass and plain old electrical tape). The sun baked dirt clods at our launch site are not conductive to keeping it in pristine condition. That and I've flown it in winds I probably shouldn't have!

Here's a few photos from two weeks ago. I really like the liftoff photo! That's the first time I've actually seen the flame coming out of the motor. Up until this point, I thought it only hissed! I'd like to thank Terry Smemo for taking these photos!
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G-12's in that model must be fun, but given it is a 4.5oz motor you you probably needed to add quite a bit of nose weight for CG, what sort of glide that get at about 20-21oz rtf?
 
Glad to hear the E6 motors do work. Given the weight of the model as mass produced, I would not have thought it would work so well. My favorite motor from all the test flying we did was the AT E15-P.

I still have a few unassembled and unpainted SR-71 foam shells that I have always wanted to put together with a minimal 1/16 balsa spine, very minimal other structure and modern micro radio gear to create a very light SR-71 that would perform well on the E6 reloads.

I like the occasional aerobatic flight with an SR-71 as well, but prefer to use my electric pusher conversion of the HobbyLab SR-71 for aerobatic sessions lasting longer than a few seconds....;). I also have one of the larger LX (sold by Banana Hobby a while back) electric ducted fan SR-71 models that is a lot of fun.
 
G-12's in that model must be fun, but given it is a 4.5oz motor you you probably needed to add quite a bit of nose weight for CG, what sort of glide that get at about 20-21oz rtf?

Frank,

I guess I never looked at the SR-71 as a glider but rather I see it as a rocket powered aircraft. I'm the worst guy for trying to give glide times as I never, ever, fly it to the maximum altitude achievable then transition into the best L/D glide speed trying to maximize flight times. With that said, I honestly can't tell you about it's glide performance. However, flying the G-12, I learned two important lessons. The first one is, play in the vertical plane rather than the horizontal. The G-12 has enough thrust for a long enough period of time which allows you to fly out far enough that radio reception becomes an issue. The other thing is, always stand upwind from the launch. The G-12 puts out enough smoke that you can lose the plane as it blows over you. It's not fun trying to reorient yourself while the place is heading straight down under thrust! Been there, don't want to do that again!
Guys, I love my SR-71! Spectators seem to like it as well. On a scale of 1 or 10 (with 10 being the best), as a glider it's probably a 4. (I can't imagine the full scale aircraft is much better!). If gliding is your thing, you probably ought to be looking elsewhere. However, this really nicely fits my need of blending two of my hobbies, rocketry and RC aircraft.

One last thing, I never launch these vertically! I stick three launch rods in the dirt at a 45 degree angle. The aircraft's launch lug slides down the center rod and the other two rods (Spaced about 3-4" to either side) keeps the wings level until flying speed is reached. I actively fly the aircraft both up and down. After all, that's half of my hobby interests.

Bob Brown
 
The other thing is, always stand upwind from the launch. The G-12 puts out enough smoke that you can lose the plane as it blows over you. It's not fun trying to reorient yourself while the plane is heading straight down under thrust! Been there, don't want to do that again!
Bob Brown
I'd say we almost lost her that day. But all your buddies will yell, "Pull up, pull up!!!" That was helpful, right. ;)

I can attest to the fact that Bob has become very adept at flying this model. It is fun to watch on a calm launch day.

--Lance.
 
This particular SR-71 for sale is a curious item. It sounds like the frequency of the receiver is not known. Also, the buyer is thinking that a previous owner modified the model by moving the servo's towards the aft end maybe about mid-section. Why would someone do that?
 
This particular SR-71 for sale is a curious item. It sounds like the frequency of the receiver is not known. Also, the buyer is thinking that a previous owner modified the model by moving the servo's towards the aft end maybe about mid-section. Why would someone do that?

He may be thinking that due to where the push rods exit, and not due to any dissassembly.
 
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