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Outdoor Free Flight Forum => Peanut Scale => Topic started by: Tyrannt on December 08, 2015, 03:32:21 PM



Title: SR-71 Blackbird
Post by: Tyrannt on December 08, 2015, 03:32:21 PM
Hello everyone.

I decided to post my blackbird.  I admit to being scared to do this because of the excellent work by everyone else. I haven't build a free-flight model in years. (Mostly scratch builds, with comets and sterling kits thrown in.)

I drew the plans using a ruler and a circle template.  They are what I call working plans. Good enough to build on but not complete.  There is some mistakes in the plans, that I haven't fixed yet. The not completed parts, are parts I haven't quite figured out yet.

The model.  I am building it like the moon bat.  Flat on the building board. One Problem is that 3/4 of the blackbird is on top.  When doing the engines you can't just cut the circles in half, they are now at 3/4 circles.  This changes where the keel goes.  I admit to doing them five times. I saved the engine exhaught pipes for the end, so I could get them centered.  Getting the set up and the notches right was the hard part.  I did one engine first, then the fuselage, then the other engine. Then i built the wings into the fuselage and engines.

I included two shots with my 12" ruler for size comparison.

Main info:

Wingspan 13"
Fuselage 25"
Fuselage height 1 1/2"
Wing area approximately 54" to 56". ( I used, that looks like a square and divided it in half for the triangle's.)
Engines are 1 1/2" in diameter and ten inches long. Not including the nose cones.
Wings are cracked ribs. Main spars runs in the fuselage and into the engines.
Pusher prop with the rubber running through the fuselage.  Prop size unknown. I have a six inch red prop I am considering.
I also enlarged the rudders.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on December 08, 2015, 03:40:22 PM
A few more random photos


Title: Re: SR-71 Blackbird
Post by: Tyrannt on December 08, 2015, 03:44:06 PM
A few more.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on December 08, 2015, 03:54:49 PM
The two rudders. The weight right now is 17 grams. I am worried about the weight. Still have the bottom and the tissue to go.


Title: Re: SR-71 Blackbird
Post by: faif2d on December 08, 2015, 04:27:11 PM
I have absolutely no idea why you were being shy about your build!  I think it looks wonderful, both the plans and the construction.  Thanks for sharing with us!!!


Title: Re: SR-71 Blackbird
Post by: Wout Moerman on December 08, 2015, 04:31:36 PM
That is a ambitious project, and it really looks great! About the weight, I have no idea how much lift the body will generate. It might work out OK. At least you won't be needing nose weight, I guess! Do you have an idea where the center of gravity has to be placed on a free flight Blackbird?

I noticed that the wing has a normal airfoil without elevator. This might be a problem resulting in very little stability. For flying wings often a reflex airfoil is used, in which the rear of the profile is bent upwards.

I think the rudders will be stronger when the spars are one long part and the ribs are in smaller parts. But I think this is OK because they have little chance of being damaged.

Keep up the good work!

Wout


Title: Re: SR-71 Blackbird
Post by: Crabby on December 08, 2015, 04:38:18 PM
FWIW remember this thing is a supersonic jet designed to fly fast. Remember to wind up and throw it like a baseball.


Title: Re: SR-71 Blackbird
Post by: DavidJP on December 08, 2015, 05:26:27 PM
That is rather exciting and congratulations on the workmanship and the whole choice of project.

I think it is one of those models which will need quite a bit of experimentation but will be quite fun. Possibly you could make the construction a bit lighter but there is a very good chance that it will have to fly quite quickly anyway so your flights might be a little short but impressive?

Await more please!


Title: Re: SR-71 Blackbird
Post by: Sky9pilot on December 08, 2015, 06:47:24 PM
WoW... I love this model!  I've got quite a lot of pictures of the real bird when I lived in Sacramento and traveled up to Beale AFB their home base!  This is a great project.  I'll look forward to following this build!
Sky9pilot


Title: Re: SR-71 Blackbird
Post by: Don McLellan on December 08, 2015, 08:44:30 PM
What Sky9pilot said!  This is a great project and am also looking forward to more pics of your progress.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on December 08, 2015, 08:50:10 PM
Thank you everyone for the kind words. I am my own worst critic.

Thanks for the heads up on the elevator. I will probably be adding small plastic trim tabs for elevator. Been out to long on this and totally forgot about them.

For the center of gravity. I don't really know.  My plan is to cut out a flat piece of cardboard, the size of the model. Add the rudders and fly it untell I get a good glide. Then start from there on the model.

One of the reasons for posting is I am going to need some help. Start thinking of a good propellor and rubber size.  This is one area I have always struggled at.  I have learned a lot from this website.

My son said he would teach me how to throw a baseball again. He throws over the top, and I'm a sidewinder.

I have loved this plane since I was little.  Their is just something about it.  I really love the story behind this plane. What the engineers did to solve all the problems, just amaze me.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on December 08, 2015, 09:12:18 PM
Forgot to add. From prop hook to nose hook is 20".  I haven't bought any rubber yet, but plan on it soon.

Also the best way for the engine cones. Balsa build up, and hollow out. Foam. Or tissue, soaked in CA.


Title: Re: SR-71 Blackbird
Post by: Wout Moerman on December 09, 2015, 02:17:16 AM
Any idea how you will hold the plane when launching?


Title: Re: SR-71 Blackbird
Post by: DavidJP on December 09, 2015, 06:23:04 AM
A cross bow? ;)


Title: Re: SR-71 Blackbird
Post by: Bulldogger on December 09, 2015, 08:30:53 AM
Very cool.  Looking forward to following this build.  Thank-you for sharing it!
Bulldogger


Title: Re: SR-71 Blackbird
Post by: Wout Moerman on December 09, 2015, 09:09:27 AM
A cross bow? ;)
good one! I was thinking catapult.


Title: Re: SR-71 Blackbird
Post by: Copbait73 on December 09, 2015, 09:40:21 AM
Neat subject and excellent build.

Regarding your C/G, go to your scale side profile and locate it just forward of the main gear. Do a lot of glide testing without the prop and rubber to get this right. Make sure your evelon adjustment and C/G location give adequate pitch stability. Error to a forward position or you will have a lawn dart.

You will need evelons on your delta but your oversight will help you out. Adding clear tabs of adequate area will effectively give more wing area. Pure jets are sensitive trimming the elevens but your addition of a prop (large stabilizer) makes this much easier.

If you make this a pusher you will need noticeable nose weight. A practical solution is to place the prop at the nose. I find this unsightly and "cheating" however it is fully legal in FAC scale modeling competition.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on December 09, 2015, 11:42:10 AM
The mental image of me having a cross bow was great. Loved the idea. But, no I plan on launching it like a baseball fastball.  The plane is quite sturdy in front of the leading edge. So one hand on the leading edge the other holding on to the prop.

Thanks for the help on the center of gravity.  I still want to keep it a pusher.  That way it kinda disappears in flight.  Thought about painting the prop black for that reason

What's a good kind of plastic for the trim tabs?



Title: Re: SR-71 Blackbird
Post by: tom arnold on December 09, 2015, 12:10:17 PM
I would not put too much faith in the fastball launch. I ran into that problem with a ducted fan model I had in which needed a fast launch. The only problem was that the harder I launched it, the more my hand would roll like a baseball pitcher's and I succeeded in snap rolling it into the ground constantly. My solution eventually became an overhead launch like a thrown soccer ball but even that was a poor solution.


Title: Re: SR-71 Blackbird
Post by: Sky9pilot on December 09, 2015, 04:26:22 PM
Found this I think on RCgroups... it's a ball park location for CG.  Wishing you great luck with this project!
Sky9pilot


Title: Re: SR-71 Blackbird
Post by: Big Dave on December 09, 2015, 04:31:48 PM
A good fast launch Tom, takes practice, and guts.  Our arms were not designed to throw model airplanes the correct way, without a lot of training.  And a pusher would be even more difficult. 

This is an amazing project, I hope it flies like a dream.

Dave


Title: Re: SR-71 Blackbird
Post by: Crabby on December 09, 2015, 05:21:36 PM
I would not put too much faith in the fastball launch.

I would put nothing but faith in your launch its your best bet!


Title: Re: SR-71 Blackbird
Post by: jym6aw6 on December 10, 2015, 02:24:35 AM
Some years ago saw a FAC Nats video with Dennis Norman launching his B-52 scale glider using the hi-start catapult method. He had an assistant hold a tall pole upright. One end of a very long length of rubber strip was attached to the top of the pole and the other end was slipped over a hook on the model. The effect was like a gentle slingshot. Not sure that he had the model trimmed but the flights were of short duration.

Maybe someone with some hi-start launching experience can comment? Looks like it might have some potential with smaller jet models like the Blackbird.


Jim (6aw6)


Title: Re: SR-71 Blackbird
Post by: DavidJP on December 10, 2015, 05:08:16 AM
This becoming a very entertaining topic!


Title: Re: SR-71 Blackbird
Post by: Copbait73 on December 10, 2015, 07:11:49 AM
Don't know where all this concern regarding launch is coming from. Rubber powered models with their high static thrust are basically motor sticks at launch. This one even more so. It's ducted fan models of very low relative thrust that have these issues at launch.

 I found my  XB-70 - a long nosed delta - to be a baby to launch. Use typical two handed over head.


Title: Re: SR-71 Blackbird
Post by: Crabby on December 10, 2015, 08:14:11 AM
I talked about launch because my Mig 15 wouldn't fly unless I launched it at initial power-burst speed, after that it would cruise around really happily. But if I did a gentle push it would do any number of insulting things on its way into the dirt. Not a ducted fan model, just a simple prop tractor...I see the obvious differences in the two. I just wanted to raise some awareness.


Title: Re: SR-71 Blackbird
Post by: yagua on December 10, 2015, 10:11:38 AM
Really interesting!!! Have you contacted Tobgun? He build a Concord, but aparently didn´t last too long  :-\. Anyhow, he have experience with a prety similar type of plane (long fuselage, delta wing..) http://www.schauggspace.de/my_hangar.htm


Title: Re: SR-71 Blackbird
Post by: Maxout on December 10, 2015, 11:11:42 AM
Really interesting!!! Have you contacted Tobgun? He build a Concord, but aparently didn´t last too long  :-\. Anyhow, he have experience with a prety similar type of plane (long fuselage, delta wing..) http://www.schauggspace.de/my_hangar.htm

I miss his work. Very innovative.

He built two Concordes. The second one flew great and there's a video of it in there somewhere.

I think the SR-71 and the Concorde are both excellent FF subjects if built light. One could probably set them up as twin pushers and get great performance and ridiculous bonus points at the same time. Not to mention the cool factor.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on December 10, 2015, 11:47:25 AM
Want to thank everyone for the help.  I have to say I am really excited about this.  I am a slow builder and the only time I can build is burning the midnight oil. Because of this I started to lose interest. You all have rekindled that spark. Thank you.

Last night after reading your comments. I had to find out where the center of gravity is right now. I put a small piece of tape to hold the nose cone in place. Found where my landind gear goes. And balance it.  Just about perfect balance at that point.  I would have never figured on having to add nose weight. I now know its going to need some. ( didn't have the rudders on.)

Next step for me is to use my dremel and sand I little out of each bulkhead in the engines.  I have the bulkheads for the engines cut and notched, along with the fuselage bulkheads.

I always planned on it being a pusher, but entertained the idea of a multi.  Three props. Two in front of the engines.  I also thought about turning the engines in to rubber powered duct fans.  I already am in over my head in this build, so decided to keep it simple for this one. One prop, pusher style.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on December 10, 2015, 03:58:46 PM
One of the other reasons I decided to just go only with a pusher prop, is that the two front propellers could only be 2 1/2" max.  I thought the weight vs. Usefulness about the same. Launching it would be a whole new set of circumstances.  If you look closely at the engines you will see that it was set up for multi propellers.

When I was a kid. I used a ten foot piece of rebar set in the ground. Had about ten feet of 1/8 rubber attached to the top. Used a paperclip for the hook. Models were around 10".  Flew for three or four seconds at a time. Hours of fun.

I realized that the two attachments with my ruler didn't upload so I am attaching them now.


Title: Re: SR-71 Blackbird
Post by: Crabby on December 12, 2015, 09:23:13 AM
Everything looks straight as a pin. Great craftsmanship going on here!


Title: Re: SR-71 Blackbird
Post by: Crabby on December 12, 2015, 09:25:44 AM
Really interesting!!! Have you contacted Tobgun? He build a Concord, but aparently didn´t last too long  :-\. Anyhow, he have experience with a prety similar type of plane (long fuselage, delta wing..) http://www.schauggspace.de/my_hangar.htm

 One could probably set them up as twin pushers and get great performance and ridiculous bonus points at the same time. Not to mention the cool factor.

Now I am getting turned on! a twin pusher would be wayy out cool!


Title: Re: SR-71 Blackbird
Post by: Maxout on December 14, 2015, 02:05:44 PM
Really interesting!!! Have you contacted Tobgun? He build a Concord, but aparently didn´t last too long  :-\. Anyhow, he have experience with a prety similar type of plane (long fuselage, delta wing..) http://www.schauggspace.de/my_hangar.htm

 One could probably set them up as twin pushers and get great performance and ridiculous bonus points at the same time. Not to mention the cool factor.

Now I am getting turned on! a twin pusher would be wayy out cool!


Ain't nuthin' like em. They always fly well, and they fly for a mighty long time, too.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on December 14, 2015, 03:11:51 PM
I want to give a special thanks to copbait73 and sky9pilot for the center of gravity on the blackbird.  That was a great big help.

Crabby, I would love to see a multi.  I would suggest using motor sticks.  The props need a little distance to clear the leading or trailing edges.  Other wise you have to use really small props and spin them really fast.


Title: Re: SR-71 Blackbird
Post by: Copbait73 on December 14, 2015, 07:06:33 PM
Thank you.
One more thing. Based on my experience with many jet type configurations I believe any rubber motor configuration other than a prop at the extreme nose will make your model too heavy to fly.


Title: Re: SR-71 Blackbird
Post by: dslusarc on December 27, 2015, 09:03:03 PM
I have flown a few RC SR71s. They are very sensitive to roll input. Very little aileron will make them roll very quickly so keep those adjustments small. The fuselage makes lots of lift but get the nose up a little too high and it will flip over itself. So my guess is a smaller prop with low pitch and a long loop of rubber may be a good way to go. The CG on the ones I had were more forward closer to the notch by the engines. One ballpark way on a jet CG is to look at the main gear in the extended position then make a 15 degree angle going forward, that will be a approximation of the CG. The reason being that they want the plane to rotate easily for takeoff. Not a hard fast rule but a good way to estimate when the model is complex in shape.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on January 05, 2016, 03:28:21 PM
I have question for everybody. Have you every had a model you are building and something keeps bugging you. You think about it but just can't figure out why.

This happened to me. Something kept bugging me and I finally figured it out. My cockpit was all wrong.  The window supports run up and down, not front to back. The cockpit also sits a little more forward then the rest of the body blending. I got it fixed and feel a lot better about it now.  It's all the time I have had to work on it though.

After rereading all the many posts.  I am getting a little concerned about having a flat wing,  I am putting on plastic tabs on the end of the delta wing for adjustments. ( still can't believe I missed them in the building). Do I slice and dice my outer wings and  put in a 1/4" of dehydral or rely on the plastic tabs.  Now is the time to fix this. I can still pin it down to the building board flat. I haven't started building the bottom stringers yet.


Title: Re: SR-71 Blackbird
Post by: Super64 on January 07, 2016, 11:12:22 AM
Hi Tyrannt,

I will give you my humble, very stale opinion, since I haven't built in ages.

I put together an Me262 and failed to properly build the wings, all she did was roll off to one side or the other.

The wings need sufficient dihedral so that the tips are above the thrust line.

Please continue, this is fascinating.

-Joe  8)


Title: Re: SR-71 Blackbird
Post by: Tyrannt on January 07, 2016, 03:06:01 PM
Thanks super64.

I am going to put a 1/4" dehydral in the outer wings.  I was looking at it last night and realized that it wasn't as bad as I thought.  I just need to cut a small triangle out of two spars on each wing and push them up. Then add a 1/32" gusset to each side of the spars.  Maybe just the front spar.  I will leave the leading edge and trailing edge alone and just let it curve up with wing.

Made a little progress on the blackbird last night. Put most of the bulkheads and stringers on the bottom of the fuselage and the engine bays.  It really adds a lot to the look to see the bottoms on.

Still have to work on the tail end of the fuselage. Need some more thought on how I am going to do it. Haven't figured out how to bring the top and bottom together and leave enough room for the prop hook.

Thanks for all the kind words and help with this project. I have learned some much from everyone.



Title: Re: SR-71 Blackbird
Post by: Tyrannt on February 15, 2016, 06:55:57 PM
Hi everyone.  Sure have been enjoying everyone's builds lately.  I am amazed at all the great work and lessons I see here.  Haven't had much time for building lately, but, doesn't mean I can't watch everyone's else.  Thought I would give you all a quick update.   Progress has been made. It's moving forward now. More about that later.

The bottom stringers are on as I mentioned in my last post.  I broke off all the stringers I had left long for the tail ends on the fuse and engine bays.  I decided to do the engine exhaught ducts differently than originally planned.

I taped the nose on for the head on shots.  I saw where someone took a picture down the fuselage, I thought it was pretty cool, so I copied them.  The pictures didn't come out as well as I had hoped, but you get to see them anyway.

Oh no here it comes, why I went backwards.  The last picture is the weight.  I have never used a scale in building. I have to admit it's been an eye opener.  I kept watching the weight grow and grow.  The bottom stringers and their bulkheads add 4 grams of weight alone.  I was starting to freak out about the weight.  Thats when I figured out my weight problem.  I have been building this all out of 1/16" balsa, when I should have been using 1/32".  (Why do i, all of a sudden, start hearing laughter and "ROOKIE."). I decided to sand down all the stringers I could, instead of starting over.  After several hours of work with a disposable finger nail file, I have taken over 4 grams of weight out.  I sanded down the outside to where it needed to be, then carefully sanded the inside of all the stringers to around 1/32".  All ready started stripping some 1/32" to finish the rest of the plane.

Next up. Finishing the tail end of the fuselage and install the thrust button.  


Title: Re: SR-71 Blackbird
Post by: Tyrannt on February 15, 2016, 08:16:30 PM
Oops. I forgot to mention that is the weight before sanding. With the nose, plane and tail feathers it now weights 16 grams.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on August 03, 2016, 02:47:57 PM
Hi everyone.  Well life has been getting in the way of working on my blackbird. Some good, some bad,  some real bad, but we all just keep moving on.

I have been able to get some work done on it.  Couldn't sleep a couple of nights ago, so decided to mock up the plane.  This is one of the first times I have done this.  Building most of the plane on the building board hasn't really made for a need.  Thought y'all would like to see them.



Title: Re: SR-71 Blackbird
Post by: Tyrannt on August 03, 2016, 02:54:51 PM
Forgot to mention that I added some dihedral to the wings. The now are even with the trust line. It ended up about 3/8". 

Couple of more pictures.  I really like these ones. 


Title: Re: SR-71 Blackbird
Post by: Tyrannt on August 03, 2016, 03:07:27 PM
The engine noses cones are made of card stock.  Had fun trying to match the colors to a sample of balsa.  Wanted to match the balsa when I cover it in tissue.  I had a couple of problems making them. ( Posted some of my failed attempts.  There were a couple more in styrofoam.) Due to were they are at, I made them removable using a bamboo skewers.

Now the tail end.  I didn't like the trust button I had, but could not find a good one. So I installed it.  Later I found a good trust button.  When I went to take it out, and build a new one. I found I had glued it to the nose block.  I ripped out the bulkhead trying to get it out.  I am going to use the new trust button and the black propeller.  It was made as a pusher prop.

I am going to need nose weight to balance it.  It balances at the center of gravity with out the prop on.


Title: Re: SR-71 Blackbird
Post by: skyraider on August 03, 2016, 03:36:31 PM
This is one awesome build. Well done and I know you still have more
coming. Simply Stunning!!

Skyraider


Title: Re: SR-71 Blackbird
Post by: Tyrannt on August 03, 2016, 06:41:02 PM
Thanks skyraider.  This build has really been a challenge for me.

Somehow I missed a picture. I really like this one. Don't know why, but I do.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on November 24, 2016, 08:49:11 AM
Finally the moment of the reveal.  I have chosen the NASA #844 for my model.

I love it when the history of the plane is posted. (I really learn alot by the history.)  So now, I guess it's my turn.

Facts and time line. ( Just the NASA flights)
Lockhead SR-71A (61-7980/NASA 844)
Retired by air force in 1990.
Given to NASA on Feb 15, 1990.
Placed in storage untell 1992.
Flown by NASA from 1992 to 1999.
Final flight on Oct. 9, 1999.
Placed on static display on Sept. 14, 2002,  at Dryden Flight Research Center.
Flew 734 flights including 56 NASA flights.
Total flight time of 2353.6 flight hours.
Last one of the blackbird's to fly.

Several of the missions for NASA were for sonic boom testing with other aircraft. F-16 xl, f-18, yo-3a.  Testing new electronic systems, and my favorite, the larse system. (Linear aerospike). (Imagine strapping a rocket motor to the tail of the blackbird.  Due to leaks in the oxygen system it was never truly fired off, and they got all the information they needed from the other tests.)

Still have several fiddly little bits to do.  I also am going to try and shrink up the tissue alot more.  This time with water and a hair dryer. First time was with just water, and I left it to air dry.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on November 24, 2016, 05:16:50 PM
For covering the blackbird I had a few Interesting problems to overcome.  I covered the bottom first.  It went on in eight pieces.  I first covered just were the rear of the fuselage were it starts to taper down to the tail.  Then both engines. Then the rest of the fuselage.  Both outer wings.  Last i did the inner wings.  

The top of the plane was the same except for the leading edge of the outer wing.  I forgot to put a glue joint in.  I ended up just glueing the tissue to tissue.  That ended up being a huge challenge for me.  

Accidentally poked a couple of holes in top. I just added a small piece of tissue and am calling it an access panel.

I covered it dry using white glue and water mix.  Using the hair dryer and more water alot of the wrinkles came out.  Still plenty left but I'm happy with it.

On the rudders, I covered them normally.  For the NASA logo, I cut a strip of copy paper a half inch wide.  I then kept copying the NASA logo untell I had it the way I wanted.  Then colored it in really dark.  I then cut another strip the same size and placed it over the top of the new template.  Then copied it with a red colored pencil.  Using a red colored pencil I copied it.  ( The S is still not right, but, I'm happy with it.) Then glue it in place with a glue stick and trimmed off the excess.

The white strips were made the same way.   The numbers were drawn out several times.  I placed a couple of pieces of copy paper between some newspaper.  Using a brand new knife I cut out the numbers I had drawn.  Then it was a matter of just picking out the best ones and glue them on.

For glueing on the rudders, I made  a jig out scrap foam board.  I traced the pattern off the plans then transfered it to the foam board.  Used two bamboo skewers to hold them in place.  Then glued both rudders in place at the same time.  Worked great.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on November 24, 2016, 05:19:33 PM
Not sure why the one picture went upside down.  Don't know how to flip it. Sorry.


Title: Re: SR-71 Blackbird
Post by: Sky9pilot on November 29, 2016, 10:13:45 PM
Nice job on the SR.... love this aircraft!  Hope to do one some day!  I look forward to your flight reports!
Tom


Title: Re: SR-71 Blackbird
Post by: Tyrannt on December 01, 2016, 10:45:36 PM
Flight report.   Well... ummm.  Right now she is resting in the hanger awaiting repairs.

After I got the fuselage covered and before the rudders went on, I started flight testing.  The balance was really close to the center of gravity.  The across the room flight on the bed went pretty well. So to I took her outside.  She can be a bit of a challenge to launch. Center of gravity is right at my hand holds.  She is just like to real thing. The faster she flies the better she flies.  When the speed drops off she does a nasty death roll to the left ending in a nose plant.

I put the rudders on and she is tail heavy, and I haven't put the propeller on the tail yet. Definitely going to need nose weight.  Still having the problem with the death roll to the left.  Then it hit me.  I balanced the plane front to back not left to right.  Need to add weight in the right wing tip.

Damage is not bad.  The first bulkhead behind the nose cone cracked from the nose plants.  I used 1/32" balsa for the stringers from front to back  on the bottom.  The first set of stringers behind the first bulkhead cracked or broke from the nose plants.  I have cut out the tissue And replaced the three bottom stringers with 1/16" square.  Picture is of broken bulkhead and stringers.

I thought about running some planking from the first bulkhead to the second on the bottom.  Is this a good idea or should I just leave the stringers.


Title: Re: SR-71 Blackbird
Post by: Copbait73 on December 02, 2016, 10:38:24 AM
Unfortunately if you chase reinforcement to survive the type of arrivals described you will have a SR-71 Blackbird shaped Jart. The best insurance is to never glide test without first accurately confirming C/G. Jets are easy, fabricate a wedge and check it out. Next, most of my "pointy nose" jets and especial my large XB-70 have a nose cone held on by magnets so it separates on arrival.


Title: Re: SR-71 Blackbird
Post by: fuzzywill on December 03, 2016, 03:37:20 PM
I've been following this project.  Gotta luv pushers.  Since you need nose weight, I don't see harm in planking.  I'm currently building a Henschel P-75 and I used 1/16 basswood solid formers for the 1st 2 bays and 1/32 for the rest.  By the way, if you live near Logan, UT, we need to get together.


Title: Re: SR-71 Blackbird
Post by: Sky9pilot on December 07, 2016, 10:35:09 PM
So sorry she "darted" on you.  Copbait73 is sooo right on the "finding the CG" before glide test.  Best of luck with the repairs and many happy landings in the near future!
Tom


Title: Re: SR-71 Blackbird
Post by: Tyrannt on December 08, 2016, 03:04:57 PM
Thanks everyone for the support in this project.  The kudos really mean alot to me. 

I was like a kid at the candy store when I finished covering the blackbird and went to fly her.  After crashing her I held my head in shame because I knew better than to try it.  A great lesson has been learned by me.  Check everything out before you fly.  I was just lucky the damage was so minor.

Copbait73 I like the idea of a wedge.  Wish I had thought about that years ago.  I just used my finger tips to do it.  To easy to cheat that way and get a bad balance.  It's what I did on the blackbird. 

I also like the idea of magnets.  I think I may change the engine inlet cones to magnets.  They are starting to get wiggly. 

I decided to plank just the bottom between the first and second bulkheads.  I realized they take alot of stress.  I have never done that before and was surprised by how fast and easy it was.  I was also surprised by how much strength it added.

Next on my list is recover the bottom front.  Make some wedges for balancing it and check it front to back and left to right.  Do the windshield and the red stripe down the fuselage.  Oh yah, put the propeller on.  (That might be a good idea.)

Fuzzywill that would be great. I live in the Salt Lake valley.



Title: Re: SR-71 Blackbird
Post by: fuzzywill on December 19, 2016, 12:44:10 PM
I have to be in Salt Lake on January 11 and 12.  Perhaps, that could be a good time to get together?


Title: Re: SR-71 Blackbird
Post by: Tyrannt on April 23, 2018, 03:15:41 PM
Just a quick update on things here.  I have finished the blackbird. 
  I got my red stripes on.  It was actually kinda scary for me.  Stripes don't usually turn out well.  This time I used a glue stick on some red tissue and folded it in half.  Then I used a steel straight edge with a brand new blade in my knife and I cut out several strips out 1/8" wide.  Then cut to size and glued using the same glue stick.  It went really fast and worked great.
   I then worked on the windows.  Since this is not for competition, I wanted mirrored windows.  Long ago I saw a picture of the blackbird coming in for an air to air refueling.  The sun was glinting off the windows in gold.  One of my favorite pictures.  To get that look, I used the lens out of a pair of busted sunglasses.  The four windows installed can be covered up by a dime.
  The propeller is a six inch pusher prop from a old model I had. (I think it was called the joy.  Foam wings and balsa body.). I am using a 21" loop of 3/16" rubber.
  Flight report.  First real throws showed the plane wants to fly.  Death roll to the left was fixed by putting some balsa in the right wing tip untill balanced.  With the new propeller in the balance point moved back a ways.  The plane then nosed dived in to the grass.  It flew about 20' before crashing in.  ( I did get a four second video of it.  Only one second of it flying.) I tried 200 and 300 turns.  It only flew about 30' then nosed dived in.  When the speed drops off, the wieght in the nose causes it to nose dive.  I did add some clear plastic to the trailing edge for adjustment.  Even with them almost straight up, they could not over come the nose wieght.  By this time I had crushed the nose in to the first bulkhead.  Have to rebuild the nose, and reduce the nose weight.
  I will post some pictures later showing the strips and windows.


Title: Re: SR-71 Blackbird
Post by: piecost on April 23, 2018, 04:04:16 PM
That is a cool model of one of my favourite aeroplanes. Please keep us updated about progress. I would love to see a photo of it flying.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on April 23, 2018, 10:09:41 PM
Pictures that I promised.  Flying pictures to come later.  Need to fix the nose first and take out some of the nose weight.

I am also considering of making a new 7" prop.  Even with 300 winds I don't feel like I'm getting enough thrust.  The current prop is adding thrust but not much.  I know I can get alot more winds in with this loop.  It just feels small.


Title: Re: SR-71 Blackbird
Post by: flydean1 on April 24, 2018, 09:36:56 AM
Don't know the weight, but with that nose, I question the need for any nose weight.  Also, peanuts are hard to trim with big props.  Suggest a 5 inch max for starters; 4 would be better.  Easier to start small and add more diameter later.  If it takes 3/16 rubber, it's too heavy.  That airplane is very difficult to build light though.  Lots of shapes.


Title: Re: SR-71 Blackbird
Post by: Crabby on April 24, 2018, 09:58:53 AM
Great post. I would love to see this thing fly. I don't understand why it lawn darts when the power runs out if the glide is good. Next time you fly please post a vid, no matter what happens. I have a very finicky prop powered Mig-15 that when its good its very good but when its bad it flat out sucks! ::)


Title: Re: SR-71 Blackbird
Post by: yagua on April 24, 2018, 10:38:44 AM
just a "monkey thought".. maybe at low rpm the prop acts as a "rear air brake", causing the dive by leverage  ??? ???


Title: Re: SR-71 Blackbird
Post by: flydean1 on April 24, 2018, 10:38:56 AM
Just had a thought after reading Crabby's post.  It may lawn dart when it runs out of power and the prop fails to free-wheel.  Acts like a drogue chute.  Definitely post a video for Crabby to look at.  He is a proper authority on these matters, having learned from a true expert.  Thee Old Man.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on April 25, 2018, 03:02:03 PM
I wanted to get a weight before posting but I discovered that my scale is broke.  My guess on weight is about 30 grams.  The frame came in at 20 grams.  And I think I remember that covered was around 25 grams.

The reason for the bigger rubber is about weight and wing area.  The wing area is around 56 square inches not including the engines or fuselage.  When you add that in it pushes it up to over 70 square inches.  With this in mind I am treating it more like an embro class airplane.

After reading your posts, I hadn't thought about the prop acting like an air brakes or drag chute.  It makes alot of sense to me. Lots of thinking to do now.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on June 03, 2018, 10:10:41 PM
Well... Last weekend, I took the blackbird out to fly.  I just new it was going to fly and get that dream flight I always wanted.  Took her out to a local soccer field for the flight.  I was a little enthusiastic about the flight and launched her hard.  She flew about seven feet and noses darted in the field.  The pictures are what happened after the third flight.  Second flight did most of the damage. Just had to try again. Been licking my wounds since.

A little history since my last report.  I sent Crabby an message.  A big thank you for the help.  He suggested that it was way too nose heavy, and possible tail weight.  He also suggested bigger strips on the tail for adjustments, and an adjustable prop.

What I did. 
Step 1.  Rebuilt the nose and took out the nose weight I had added.  4 grams of nose weight.  Big surprise. Wow.  I did not add any tail weight after I had removed the nose weight. Mistake #1.

I did not make a new prop. Mistake #2.  Been scared to make a prop.  Never had any luck building a props, but I see the wisdom now and now have a 2 liter bottle for one.

Mistake #3.  Trying to fly alone.  Going to fly next time with someone much better qualified.  Never been able to fly well. Bad part of being self taught.

Mistake #4 forgot to add bigger and more tabs on the tail for adjustments.

Oh a little extra knowledge.  Got my scale to work. Contrast display was all the way down.  Total weight after removal of nose weight.  Total 45 grams.  Ouch.  Plane 37 grams. Prop assembly 2 grams.  Rubber 5 grams.

Do you think it's too heavy to really fly?  Is it worth rebuilding?


Title: Re: SR-71 Blackbird
Post by: Prosper on June 04, 2018, 03:09:02 AM
Sorry to see that Tyrannt. No, I wouldn't guess it's too heavy to fly at all. It'll just be a trimming 'journey' I should think. I would surely repair it and yes if there's someone who might have more instinct than you about how it needs to be set up for flight, take 'em along.

Stephen.


Title: Re: SR-71 Blackbird
Post by: yagua on June 04, 2018, 08:38:43 AM
 :'( :'(


Title: Re: SR-71 Blackbird
Post by: dputt7 on June 04, 2018, 09:07:42 AM
  That was bad luck, I keep hoping to see a flight video but good to see you haven't  given up.   I agree with Stephen, it should fly at that weight probably just not for a long time.   I may have missed it but I don't see any where that you have done any test glides.  I think this is important in an unconventional model, once the glide is sorted( CofG and elevator) then you can gradually work up the power and thrust angles. Start with your small prop and increase the rubber size until it starts to extend the glide and you are on your way.  Try to find some soft grass at least for the test glides.

             Good luck with your testing


Title: Re: SR-71 Blackbird
Post by: Crabby on June 04, 2018, 09:28:04 AM
Tyrant, keep up with the Blackbird, I would strongly suggest that you install elevons at the trailing edges of the wings, and also build a profile test model from sheet, and get your glide tests straight. I have seen an indoor version of this plane at Johnson City TN, it was a no-cal and it was mesmerizing to watch. The weight? well it was a piece of goose down.


Title: Re: SR-71 Blackbird
Post by: BG on June 04, 2018, 09:47:56 AM
Hi All,
this is an interesting project and would be a challenge even for those of us who have been flying free flight scale all our lives. I will throw my hat in the ring here, please disregard anything that repeats what other sages have already offered.

What I would do:
1.Find a field with some long grass. Getting ff models to fly is always a bit of a thrilling challenge and this is especially true of an unusual subject. You need to have a chance to make errors and deal with the unexpected arrivals. Long grass that gently captures your missile will give you the chance to make adjustments and learn. Soccer field are always inviting but they are actually pretty poor ff fields because the grass is kept short and the substrate is packed hard so that it holds up to the efforts of the cleated footballers. Soccer field are ok for well-trimmed reliable performers but not for an untrimmed tricky prototype.

2. Now at your new grassy field (it can even be a smallish field) on a calm morning or evening, spend some time figuring the CG out. I would remove the prop and balance the model roughly where it does when you have prop and rubber installed. Make sure the model is warp free with neutral rudders and elevators. Now with a blob of clay handy I would start test gliding the model. You are looking for a smooth steady glide with a slight turn. If the nose is up and the model rocks from side to side I would add some nose weight (just a bit at a time). If the model continues to rock it may need more rudder area (just add some rudder extensions with paper or tape). If the model glides but the slows and dives quickly it is probably stalling (I can imaging that this design would have a vicious stall...though I could be wrong) .... more nose weight. Given the weight I could see this ship gliding straight and fast for a fairly short distance.If you can get it to this point you are probably ready for the next step. Video would definitely help us to diagnose any issues.  Note: as you add or remove clay DO NOT mess with the rudders or elevators etc. One change at a time so that you know what your clay is doing.

3. Prop in place, lubricated rubber installed, CG set to the exact spot you found using your glide tests. Now you can start winding her up; start with 300 turns and launch with some authority (pushers need a good shove to get air flowing over the wings). Hopefully your glide testing will pay off resulting in an extended powered glide. If something weird happens it should be there result of torque or thrust line issues, because this is the only variable that you have altered. I think I will leave things here re. trimming ... please report your results back to us.

4. From what I read you are a more or less novice ffer. As much as I would enjoy following your progress with this exciting design I fear it will prove to be a frustrating experience for you. I would therefore suggest possibly shelving this ship until you have built a few more conventional designs and gotten them to fly well (at that long grass field). With more experience and success under your belt you could revisit this bird in the future. Crabby's idea of building a profile ship is a good one. It could even be built out of deperon foam .... this would help you figure out what is needed to get the built-up model to fly.

my two cents.

BG


Title: Re: SR-71 Blackbird
Post by: Crabby on June 04, 2018, 11:45:43 AM
Tyrant, I found the source of the indoor SR-71 I referred to a post or two back. It is in our plans section, and was designed by Dave Aronstein. I saw this thing fly at Johnson City. I am wrong about it being a no-cal. If you haven’t already, check this plan out


Title: Re: SR-71 Blackbird
Post by: BG on June 04, 2018, 11:56:07 AM
Crabby could you find a reference to a CG on this plan? I couldn't. I still think a simple profile version would be useful.
BG


Title: Re: SR-71 Blackbird
Post by: Crabby on June 04, 2018, 12:43:37 PM
Bernard, No I don't see anything, but check out Don S's reply#35, seems to make sense. Make and install a set of scale LG and then take a 15 degree angle and "X" marks the spot approx. I think most planes rotate on take off at or around the CG. Anyway that would get you in the ballpark. I am getting twitchy over a CLG model of this thing. Aronsteins SR-71 flew on the edge of stall, nose up like on a landing approach. His was only like 8"wingspan, but qualified as a peanut by means of fuselage length. He covered his with Gampi, I think. Whatever. It was almost lighter than air.


Title: Re: SR-71 Blackbird
Post by: strat-o on June 04, 2018, 02:33:23 PM
That's a good idea for finding the CG, Crabby, although, I might warn that sometimes it's not going to work, like the B-52. Tail draggers probably work if you reverse the 15%.  The main gear typically needs to be near the CG so that the plane can easily rotate, for the case of a tricycle geared aircraft, or, to easily get up onto the main gear in the case of conventional geared aircraft.  I don't think a B-52 rotates, I think it just magically levitates somehow.

Marlin


Title: Re: SR-71 Blackbird
Post by: Tyrannt on June 05, 2018, 01:11:43 AM
Thank you everyone for all the help and encouragement.  I have decided to rebuild the blackbird.  I can't just let this one go.

In reply #19 on this thread sky9pilot posted a plan with the CG location on it.  When I went to fly it it was just a little ahead of the one showing on the plan. I think that's why I tried to fly it.  Been thinking about the flights and I think it was a launch error and too much nose weight.  To toss the plane in the air you have to hold it I front of the CG.  It makes it a little tricky sometimes.  I had no winds in the rubber just a dead stick toss to check trim.

I haven't figured out yet, how to toss the plane, and hit record on the camera and keep it all in focus at the same time yet.  I have been flying by myself.  That's the big reason for no flight videos.  The couple of times I tried to take video, you get to see my grass or my shoes more than the blackbird.

So for now I think I will start rebuilding the blackbird.  Step #1 put the elevons on the plane before I forget again.  I also want to replace the strips on the tips of the wing and make them a little bit bigger.  Step #2 rebuild the nose and try to keep it light. Step #3 build a better prop.  Step #4 fly with someone that knows how to trim an airplane.  In a field with very long grass next time.  (Alfalfa fields are looking real good about now.)

I have to admit that I'm 100% a novice, a rookie, or greenhorn, or what ever you want to call it.  You don't know how much I appreciate all the help.  No way this would have been possible without out  all your help.  Thank you.

Crabby.  I did see that plan. Thank you.  I actually studies them before I drew up my own plans.  It's good to hear it flew well. Gives me hope.  Are you thinking of a catapult launched glider.  That would be cool.

BG.  Thanks for all the info on trimming going to try it.

The only one I know around where I live that flies free flight lives two hours away from me.  But I am learning that it's a trip well worth the time.


Title: Re: SR-71 Blackbird
Post by: Crabby on June 05, 2018, 09:38:55 AM
The thing about advice is, all of it is right. You just have to refine it and come up with this magical blend. Please build that all sheet model for chucking around and getting the feel before you got back into the sticks with a new build! I thing the reason for the shape of the fuse ahead of the wing is to gain some lift...surely there are other more profound reasons. There are cheap knock offs for the GO Pro that attach to a head band so you can video hands free. That launch must be critical!? :( >:( :D ;D


Title: Re: SR-71 Blackbird
Post by: dputt7 on June 06, 2018, 03:33:09 AM
  How about a nice soft bungee with a forward hook, just enough to get some flying speed.


Title: Re: SR-71 Blackbird
Post by: Tyrannt on June 06, 2018, 11:44:29 AM
I was actually thinking of building a launching pole.  Just a long pole with a piece of rubber attached to the top.  Then putting the new foam glider that Crabby suggested to test the design and practice trimming with.

 I'm going to build a foam glider that is full size.  I am going to get a new copy of the plans and put that on the foam.  Then just build right on top of that.


Title: Re: SR-71 Blackbird
Post by: Crabby on June 07, 2018, 09:44:24 AM
Check out the CLG Jet section here lots of good stuff going on there. Tross is proving that math flys models. Hate it that I do, he's right.


Title: Re: SR-71 Blackbird
Post by: Sky9pilot on June 22, 2018, 11:16:30 PM
Here's a link to the SR-71 plan Crabby was referring to:  Click Here for Sr-71 Plan  (http://www.hippocketaeronautics.com/hpa_plans/categories.php?cat_id=37&page=3)
Sky9pilot