Wicked powered SR-71 - Page 45 - RC Groups
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Nov 09, 2011, 04:14 PM
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sanman55's Avatar
Yes, it covers nicely and the contrast is nice...and when the bright sun hits it the gloss reflects nicely..Testors spray enamel #1214 gloss yellow @ Michels craft store..I think I will be able to see this if I can take off
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Nov 12, 2011, 07:34 AM
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sanman55's Avatar
I am having a terrible time stearing this bird....I need a lot of speed to take off and as I get close to the speed and need to turn the bird to keep it straight it leans over and scrapes the nose and wings..That is what happened in my crash...I had scrubbed off so much speed that when it lifted off it stalled right away..
I am beefing up the nose wheel and trying to make it tight but its tuff...
someone suggested to use the right stick too...that is worth a try..trying to keep the wings level..I just put some wire looped skids on the wing tips in hope that this too will help..have not tryed these out yet..
Any one else have any ideas on how to keep this bird straight.??
I had no problems on my first 2 flights but since the crash have not been able to take off
Nov 13, 2011, 08:39 AM
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sanman55's Avatar
My nav lites and strobe came in and boy are they BRIGHT...I was very impressed with the kit..comes with a lot of options for installing...They are the brightest I have seen and thats what they said on their add...I put the green and red on the verticles
I know not to scale but I want to see them...Put the strobe behind the top canopy....
100_0156.MOV (0 min 39 sec)

Going to paint the wires and that should help hide them...thats about all I can do except get new eyes
Nov 14, 2011, 06:19 AM
I always find software bugs!
Hi guys.

I was doing some thinking tonight about how everyone says this plane is unstable, etc., so I got out the old pencil and paper and did some armchair calculations. I was intrigued by what I found. Keep in mind, I am NOT an aeronautical engineer, I know NOTHING about delta winged planes (especially the SR-71), and I HAVE NOT flown my model yet... so please take the following with a grain of salt!

Anyway, I whipped up some CG calculations (using the geometric method on a top down photograph of the model that was edge detected in software) and compared them to the diagram in my manual. I was surprised that my CG calculations for the DELTA WING PORTION ONLY, were spot on with what the manual has for the ENTIRE PLANE. Like I said, I am NOT an engineer, but assuming the chines on the forward fuselage supply aerodynamic lift (which I believe they must... like a canard or a lifting body) then the aerodynamic center (AC) of the entire plane should be forward of what my diagram shows (which again, is the AC of only the delta wing). If the AC of the entire aircraft is more forward, then the CG should be too. This is not taking into account the aerodynamic properties of the engine nacelles, which are just measured as part of the wing lifting surface in my diagram and could add or subtract from the actual lift component.

My understanding is that that the aircraft CG has to be ahead of a 'neutral point' (which I believe is the center of the sum of the lifting surfaces) by 5 - 15% (called the static margin). If it isn't, it creates flight conditions much like described in this forum. I don't have the mathematical abilities to calculate how much +/- lift the chine surface area is generating (or how much the nacelles might be contributing), but assuming a positive lift from the nose, it would seem that moving the CG to just behind the leading edge of the intakes would be a good place to start. It is also my understanding that a delta becomes more pitch stable with a forward CG due to the increase in wing area behind the CG (for an extreme example, think of a dart).

Anyway, based on my assumptions (unless someone explains otherwise), I think I am going to ignore the manual and put my CG just behind the leading edge of the intakes and see what happens. If successful, I may go forward from there. It may also help with the light nose wheel steering issue.

Anyone have any experience with this, or thoughts on my ramblings?


P.S. Sanman, I just went with normal shipping on the gear. I'll post pics of the installation when they get here.
Nov 14, 2011, 09:13 AM
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sanman55's Avatar
Interesting but I understand nothing about figureing cg but just how it flys...to me thats the test...at least with your caluations at worst it will be nose heavy...having said that...
I would go with the manual to start.. It has been my experience that MOST of the time the factory cg is nose heavy...
Mine is a the back end of the receiver compartment and thats seems just right..True I have had only 2 flights but it flew fine, when I could see it....
It landed fine, though fast.
If you move the cg that much forward it will really land fast....and if you try to flair it will drop like a rock...I usually like to have my planes a LITTLE tail heavy...it makes a nice flair and seems to float more...with nose heavy it seems to just want to drop fast....and if you make it heavy like mine it will really land fast..and if you try to slow it down to land you could end up in a bad stall or nose up and over..

This baby really needs speed on landing...just use the throttle and not the elevator to bring her in on a nice glide path...IMO
On my first flight I lost it and flew too slow and she just nose dived to the ground, but I recovered.
It might help with stearing but not lifting off..
I have to go a long ways for lift off, even with the cg where it is on mine.
I just think this plane is funky and has an attitude, It does not fly nicely atvery slow speeds.....

You can fine tune it later but for now I think the factory cg is good to start..It is definitely not tail heavy at factory cg...
You make this baby real nose heary and you will be saying LAWN DART..
I hope I am not over critical..I want you to have a good experience with this baby..
Just my thoughts on the matter...look forward of seeing those new gear..

PS.. Just got back from my dog walk and thought about this...I have increased the original weight of this plane by 70%....over its design parimeters...that alone would probably cause a host of problems, speed of plane, take off distance and landing and stability??
Anytime, and thats most of the time, we monkey around with weight,power and batterys , unknowns crop up..my battery alones weighs almost a pound...my brain hurts
Last edited by sanman55; Nov 14, 2011 at 11:30 AM.
Nov 14, 2011, 11:49 AM
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Joe 1320's Avatar
The problem that I uncovered flying it tail heavy was the stall and subsequent flat spin. If you are maybe 4 mistakes high, you might save it. At least nose heavy when it snaps to the side, the nose drops and recovery is a little easier. With the whale tail mod, nose heavy is not as much of an issue as there is much more elevator authority and you don't stall the wing tips. Combine that with the forward fuse is designed to aid in lift, nose heavy is a little more desired. A few minor mods and it will perform well with the CG more forward.
Nov 14, 2011, 12:33 PM
Shameful Warbirdaholic.
Aros.MotionRC's Avatar
Kennamer that's an interesting analysis. At least for me personally that would make sense as the recommended CG on my last bird sure acted grossly tail heavy hence the utter lack of control on the final two hand toss attempts. Especially knowing that my hand tosses where spot on level with the proper AOA. I never did get a chance to move the CG forward like your diagram illustrates.

Knowing me I will probably torture myself further and buy a 7th airframe down the road (lucky #7??). I just can't seem to quit her no matter how hard I try. I've flown high wing load composite large scale warbirds without anywhere near the trouble the 70mm foam Habu gave me!
Nov 14, 2011, 01:28 PM
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Joe 1320's Avatar
Go ahead, get it...... you already know you want it. Put those afterburnerz on the proper airframe. LOL!

Do the proper modifications and you won't be disappointed. Mine 1st one flew brilliantly until my own dumb thumbs destroyed it.
Nov 14, 2011, 04:55 PM
I always find software bugs!
I thought about you yesterday Aros when Nitroplanes had that 11% off coupon. The SR-71 was only $51 plus shipping. Came to $66 total for me. I thought about posting on here, but I didn't see it until late last night. I almost bought one for myself, then passed (because then I could get a second one for just $55 more... And a third...). You might want to wait until Black Friday and see what happens.

I am definitely going to add the inboard elevons. I think that is a necessity. I was reading the real (declassified) SR-71 flight manual the other day, and it has a matrix that shows the actual percentage of deflection of the flight control surfaces at various speeds. Was pretty interesting. The up elevator deflection is quite a bit more than the down (I think it was 25 up and 10 down at slow speeds). I have the link on my other computer if anyone is interested.


P.S. Aros, you keep mentioning 70mm in your posts. My Blackbird has twin 64mm fans, so what are you referring to? Do we have different versions or are you talking about something else. Did you fit 70mm units in yours?
Nov 14, 2011, 05:14 PM
Shameful Warbirdaholic.
Aros.MotionRC's Avatar
Oh I keep getting 70mm stuck in my head. That's right, the airframe is 64mm. The last three airframes have been modded out to include the 69mm motors I've put in her. Maybe it's my punishment for not running Don's wicked power.
Nov 14, 2011, 07:13 PM
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sanman55's Avatar
What ever works..I was just throwing ideas out there Some of you have a lot more flights than I do and have better knowledge on the cg..
Mine is nose heavy with the cg at the back of the receiver compartment..think I will leave it there for now...
I just hope I can see it now
Nov 16, 2011, 08:15 AM
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sanman55's Avatar
Originally Posted by Aros
Oh I keep getting 70mm stuck in my head. That's right, the airframe is 64mm. The last three airframes have been modded out to include the 69mm motors I've put in her. Maybe it's my punishment for not running Don's wicked power.
If you do break down and get another , make her for bungy launch...that will surely help at a critical time..launch..
Nov 16, 2011, 11:52 PM
Indoor Free Flight Modeler
If they put this on Black Friday sale at NP I think I will get one. I ususally dont go back and do a model a second time but my first one was a LX and these are Max Jet so different right ? Plus you guys keep posting and you are making me jealous
Nov 17, 2011, 08:41 AM
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sanman55's Avatar
Come on back, we miss you.....
Do you remember your flying weight,battery and all??
Nov 18, 2011, 06:11 AM
I always find software bugs!
I'll donate $20 towards helping Aros getting another airframe. Any other takers? We could have him on AF#7 in no time, with little out of pocket expense for him. I mean isn't $2000 enough already? Let's help a brother out!

I'm being serious BTW.


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