combatpigg

My Feedback: (3)

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".

funkworks

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.

Lomcevak Duck

My Feedback: (14)

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.

vicman

My Feedback: (10)

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.

funkworks

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...

Lomcevak Duck

My Feedback: (14)

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.

vicman

My Feedback: (10)

AW Man...CP. You are way behind on this one right out of the gate

combatpigg

My Feedback: (3)

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.

funkworks

...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.

combatpigg

My Feedback: (3)

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.

funkworks

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..

LADDIE

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.

Lomcevak Duck

My Feedback: (14)

LADISLAY: I love the M-12 Cover scheme in the bottom photo. It just need a rocket powered D-21 drone riding piggy back.

combatpigg

My Feedback: (3)

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.

bob27s

My Feedback: (19)

Coming along nicely......

funkworks

...here is the latest pic.

The forward section is now sheeted.

I'm considering some sort of landing gear. Im not real sure how safe it will be to be holding the model between two screaming engines during launch. Im considering a launch dolly of some sort of light weight gear.

vicman

My Feedback: (10)

That is very cool.

combatpigg

My Feedback: (3)

Looks fantastic, FW! You must be a cabinet maker?
About launching pushers, in your mind go frame by frame in slow motion of a straight overhand toss. Visualize it from the side view. If you follow through with your motion, there is no way those props will get there before your hand is out of the way. You're only trying to clear a 4 inch radius. A launch dolly is in direct violation of the KISS rule.
I have been thinking about building this plane without gear, but I wonder what will happen if that long nose catches a clump of grass upon touchdown? The ability to flare and land at a low speed is something that I will be looking at. I'm still thinking about using two .061s or two .15s.

funkworks

CP...you are probably right. Ive only hand launched once in my life, and that was a sig kadet senorita just for fun... I was a little worried since I need to grab the model just ahead of the GoG. The problem is that the CoG will have two motors at max rpm on either side. Id hate to get tagged by one of them. [X(] For now, hand launch will still be my pick. The long pointy nose can be a problem in shorter grass. My field is surrounded by long chest high grass so Im not that concerned about it as I am hitting the paved runway with the long nose.

cncswiss1

use Piano wire gear that falls out after takeoff.

combatpigg

My Feedback: (3)

With 2 .25s running full blast, it should be more of a release than it is a launch. How do you land on pavement without gear? Kevlar belly?

funkworks

That's what Im hoping for. Im hoping the thing just flies outta my hand. Landing will be just laying the model down in the tall grass that surounds our runway. We are lucky to have a huge wide open area of nothing but tall grass surrounding a super long paved runway. Our flying field is a radar test site so its a huge wide open area with lots of tall grass... If I do have trouble tossing the thing, I will build wire gear that drops away after takeoff.

combatpigg

My Feedback: (3)

FW, I'll bet the .25s can turn 7x6 props well enough to give a good launch and decent speed after you get the plane checked out with a more conservative prop. I wonder how well a pair of .32s would run on open exhaust and 7x7 or 7x8 props on this thing? Ditching the mufflers saves a quarter pound or so, then just pressure tap the crankcases. Sounds like more R&D backlog for Vicman, he is about due for a build thread? Hurry up and get this sucker built before Lockheed finds out, it's no fun being followed everywhere by those flat black helocopters.

funkworks

you're probably right CP. I should get some more work done. The weather here is terrible so there isnt much else to do. I took off work today so I'll prob post some more pics soon...

funkworks

Here are some more pics... Ive got the rudders and linkages to run then off of one servo installed. I have not yet installed the elevons. I will do that after i finish sheeting the top. So far, the airframe weighs about 15oz so Im pretty sure Im going to come in under my initial weight estimate. Im using a pair of Thunder Tiger GP .25's that weight about 9.5oz with the muffler each. Im using two standard BB servos for the elevons, two mini servos for throttle control, and one standard servo to drive the twin rudders. I'll prob put the battery near the nose to help balance the model...