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Vic, I'll have to look that article up. Over the years, those designs of his that I've seen paraded out to the field fall into the category of, "looked better on the ground than in the air".
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CP- youre right about the electric set up option being better. However, I have no EP gear other than a charger. Id have to buy all the motors and esc and stuff like that plus I have as much experience with electrics as our Houston Texans do Super Bowl experience. I did price everything out an it would cost me too much to get 2 motors, esc's and batteries vs buying one .25 to match one I already have new in the box. I also feel like the larger bird will fly better so if I can get the little one to fly decent then I think I'll have a winner in the larger one. The mini blackbird will be a little more than half scale so I still should be able to get some good data from it and at least be able to practice getting used to the shape in the air.
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If you want to play around with a smaller chuck glider to better understand the effect of the chines, look for an SR-71 model rocket. I had one several years back (Estes maybe, don't recall) and if you removed the rocket motor and added a bit of clay in the nose it actually made a fair glider. It wasn't too far off of scale because it wasn't really meant to fly on the wing. I always thought it would make a neat electric pusher park flyer, but that was before brushless and lipos. I don't even know if it's still in production or not. I found out it made a good glider by mistake.
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I have several of those rockets and they do glide really cool. As mentioned if you change the amount of clay in the nose (ala CG) they go up for a short while and nose over under power and are flat awsome...a little scary too.
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I thought about using the estes glider too and I sort of based the shape of the model on it, but fudged the dimensions a little because the glider was designed for a much lighter wingloading. I basically wanna prove my new shape works and my ideas for mixing.
Here are some pics of what Ive got so far. I went nuts last night and this is basically the results of one nights work...
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You're doing a great job. Scratching out something like this looks quite difficult to draw out seeing how the Blackbird has so many complex curves and blended shapes, but it looks like you've done a pretty good job of preserving scale lines.
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Vic, I know it..... but FW looks like he is the right guy to show the way here. Beautiful work, but......
FW, you call THAT fudging on the areas? Holy frijoles! I don't think I could keep that sucker right side up or tell which end is up! Maybe I'm getting too old and should just shut up?
I would have to fudge the wing area about 100% from what looks like scale.
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...thats what I meant by fudging a little...haha.
I tried to increase the wing area a little bit. The two leading edges (inner and outter) are actually parrallel to each other. The nacelle helps break up the line to the eye and helps keep the thing looking like a delta.
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FW, after reading the RCM article, it doesn't look like a SR 71 model in the 450-500 sq inch size range will be any trouble to fly at all......the model in the article weighs less than 5 pounds. The length of the body and those nacelles really give the model an appearance that it could only stay in the air at 100 mph. The nacelles break up what the eye is tracking when looking at the wing area, which makes the wing look smaller. A pair of .15s would power the plane in the article nicely. Your model with a pair of .25s will be a show stopper.
< Message edited by combatpigg -- 8/12/2007 4:51:18 PM >
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Ive got the forward fuse sheeted now. I have to decide now about rudder control. I'd love to go without them to save even more weight but Im figuring I better put them in. I'll post some more pics tonight or tomorrow. The model is starting to really look cool. The airframe with vert fins before sheeting weighs about 8oz. Im using 1/16'' balsa to sheet the top of the fuse. The bottom is finished already. The nacelles will get 3/16'' balsa sides with the corners rounded off to keep the nacelles strong without looking "boxy". I expect the weight of the airframe to be about 13oz-16oz finished not including the weight of the motors and flight pack..
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Several years ago I built and re-built three SR-71. On all of them I kept scale outlines. My experience with them was mix. I placed C/G just in front of the main landing gear. The take offs and the flying was no problem. The model was rock steady. Only problem was doing the loops. Only large diameter loop would work. I the tight loop the model would stall. The biggest problem I encountered was during the landings. I damaged or destroyed the model when setting up for the landing. Here is what happened. Before I built SR-71 I designed built and flown many delta wing models. With these, any time when coming for the landing to slow it down, I would control descend with changing the pitch to create more or less drag. This did not work with SR-71. First time I tried this when coming in for the landing the nose shoot up, instantly stalling the model. I tried to move the C/G more forward. This action made the model next to impossible to rotate on take off. I am not aeronautical engineer so I can not give anyone proper explanation why it is happening. From reading the books and magazines, I think that when nose of the SR-71 is raised, the center of the pressure moves forward alongside of these wide chines and ahead of the C/G causing the model to stall. After several crashes I managed to make number of good landings by coming in at shallow angle. But this requires having the wide open space. Even then, one mistake and the model is goner. It would be nice to move the C/G forward when setting up for landing. If I am not mistaken, the full size SR-71 pumped the fuel around like crazy to cool the skin and change the C/G to some degree depending if the aircraft was taking off, in level flight or when landing. Personally, I saw only one model of SR-71 flying reliably, built by modeler here in Ontario. But his model was stand off-off version. From the distance it looked like the SR-71, but the shape of the wing, total length and mainly the width of the chins was not scale. But it flew great. Actually the drawings for his model were published in the RCM magazine. I am enclosing photos of my models from that time. The model in the top picture had the retracts. Good luck with your model. Laddie.
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Beautiful models! 100% scale sure is impressive to look at. Go back to the frying pan analogy. Any "lift" generated by that great big "handle" will cause a pitching force, likewise in yaw axis in a slight cross wind. You're going to get some fish tailing. Cheating on the scale outlines should tame some of the tendencies, but never totally eliminate handling quirks. Especially if you compare with a more conventional delta.
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All Forums >> RC Airplanes >> Extreme Speed Prop Planes >> RE: SR-71 prop jet project 
RE: SR-71 prop jet project - 
I did price everything out an it would cost me too much to get 2 motors, esc's and 
