Bruce,
I don't think that I will be pushing the NP that far back unless I really cantilever the tail surfaces back....
Where I am using a symmetrical airfoil for the tail planes I can adjusted the AOI of the stabilators as needed. (at least that is the hope)

I am gathering up the bits to try a smaller scale (1/4 the size of my original) EDF version for testing.

A friend forwarded me a copy of a recent story from issue of MAN, where someone had built a Turbine powered aircraft with vectored thrust. Now he had only up-down in the vectored thrust system and only used it after takeoff. It seemed to have limited throw as far as the vectoring system but it was a far more conventional airframe. I was wondering if anyone who has built or flown that airplane what the effect of the vectored thrust system was to them, and what type of deflection were set up for.

I have been thinking about how I am going to do my foam version, the other night I was thinking serious about the construction of this beast. To keep the weight down I need to make a mold and a plug. I will need to make both a full size and one that is minus 1/32 for sheathing. There will be no balsa skin on the small one only a fiberglass shell around a foam core.

All of this means that I will have cut two sets of everything, one set will me my positive the other my negative. One set will be the plug or interior the other the mold where I will cover with glass cloth resin then set the plug into cover with glass cloth and resin then put the top half of the mold on and weigh it down till it cures. Home brew version of vac form method without the vac. Anyhow this is for the flight surfaces and body only; I have to work out a couple of things with that yet. One thing I have to update on the sketches is that the rear flight surfaces are going to be cantilevered to the rear about three to five inches on this version. Which will equate to about a foot to 20 inches on the next one. I am going to be using the eppler 168 for that structure because it is fully symmetrical and with some work will be part of the tail and rudder system. I am going to have to come up with a way to make the tail group for building and service. But I have got to make up the body and wing so I can make up the internal layout (drawn and cut in the foam for the intake, duct, radio compartment and servos. I am also going to embed some structure to stiffen the wings and give me hard points for landing gear.

By building up my foam components out of separate pieces I will be able to take it apart after cutting the basic shapes to do all of what I mentioned above. That will also allow me to hollow out portions of the foam to make it lighter. I need to keep the weight of this thing as close to two pounds as I can. Hopefully I can take measurements of I how I cut and layout the structure internally, thereby giving me a way to do some more drawings to make up a better set of plans. It is easier for me to figure out what to do when I have something solid and three dimensional to lay out the plans with. I know that doesn’t make much sense but the only thing I can tell you is I have to build something sometimes in order to know how to do it. It’s that “yea, that looks about right�, type of thing.

Time for an update.

After some more experiments, observations and time spent thinking and sketching there have been even some more changes to the design.

First of all the strip type ailerons on the main wing are to be eliminated and spoilers shall be added for roll control. Keep in mind that these will still be augment via the tail surfaces as well as vectored thrust. The first reasons this change is being made made is this: the wing loading on this aircraft is very low, adding more lift into the is the last thing that I need to do. The second being that this type of roll control is reputed to be "yaw favorable" so that adverse yaw cause by the aileron is eliminated.

Next the the tail fins have been swept toward the rear by 6" on the foam version which translates to 24 inches on the large model. By moving the control surfaces further to the rear I am increasing the moment of elevator control. I have read that the reversed delta when used in a wig application has very good longitudinal stability inherently. Thinking that I wanted to improve the overall effectiveness of the elevator function. This aircraft's wing drag moment is neutral given that the wing shall be on the cg, but I shall a large amount of profile drag above the cg to the rear of the aircraft given the location and setup of the fins and stabilizer. Given that in the foam version that needed size of the intake for the ducted fan makes the most forward location of the ducted fan unit and motor right about on the MAC and well aft of the COG. In order to make the intake system and ducted fan unit as efficient as possible I may need to shift the unit further aft. That was why the "flying tail" approach to the overall aerodynamic design considerations has been on my mind from the start.

Given the shift in the shape and location of the rear fins I am going to have to do some more thinking about the aerodynamic portion of way control system. The sweep and size of the vertical fins have improved yaw stability on the glider. But that added a whole new wrinkle regarding the setup of the aerodynamic portion of the rudder control system.

As far as any physical progress I have just cut out the patterns for the main wing and fuselage sections.

Your plane has a very low aspect ratio so the apparent wing loading in flight will be higher than what you'd guess based on crunched numbers. Just something to keep in mind.

HI Paul,
I do not understand what you mean by the "apparent wing loading" regarding the low aspect ratio, could you help me out here?
The design goal for the test model is on the order of 5oz/ft based on the wing area to weight.
The deeper I get into this, the more I find I have to learn!
One thing I discovered last night crunching numbers is that I may have a problem regarding the tail volume, relative to the tail moment arm...
And now you have me worried about my wing loading....

I'm not trying to worry you about the wing loading. My point is that a low aspect ratio wing has a lower lift to drag ratio than a higher aspect ratio wing. If you had the same wing loading as a plane with a high aspect ratio then the higher aspect ratio would float longer. Low aspect ratio wings sink pretty fast when they don't have power. But you see deltas flying all the time so it's not a problem. I'm just saying don't look at only the wing loading and think that's the whole answer.

Thanks for pointing this out, I think I have a better understanding of what you meant now. I know that the induced drag is very high on this design, what I did not understand was that it will fly much heavier than I would have expected. Thanks for the heads up and getting me to ask some questions about it, I learned a bit more about what I am dealing with.

Running numbers last night I discovered that the tail group is way undersized because of the short tail-moment arm I have in this design. I am in a bit of a quandary of how to deal with this issue. While the glider performs well the numbers say I am way undersized regarding the horizontal stabilizer. Originally I had not even considered using a conventional tail group due to the vectored thrust but had added it when I started to think about dealing with a dead stick issue with minimal aerodynamic control surfaces. At that point it was more of a flying wing concept with just the two strip eleavons for control. Perhaps I am obsessing about this now, the original Idea was just to give me enough control to land the craft in the event of a power out situation were the vectored thrust was not available. Since the stabilator arrangement is just for power out and not for normal flight perhaps this is not as much of a concern as I think it is because of the math...

Well for now I am going to go with the tail group sized as originally planed.

Added an updated side view....

In order to improve the tail moment arm the stabilator surfaces are going to be swept to the rear. The span of the stabilators have also been increased a bit as well.
Given some more thought to the roll control I am thinking about returning to the use of ailerons. Given the MAC of the aircraft, and shape of the wing; I can use strip type of ailerons and have them pretty much centered on the MAC of the aircraft.

As an update....
Now that flying season is upon us the design and build process has slipped down a couple of notches in priority. Now more time is spend on repair and service of the flying fleet as opposed to the new builds. Add to that as field chairman a lot of time is spent on the upkeep of the flying site.
I have made some small progress on this design, I have made up some patterns and now in the process of building a wire cutting system for the foam. The control surface mechanics are in process enough to at least to the point that I have determined the total number of servos needed (12 total) for the electric, the glow version will need two more for mixture and throttle. Of the dozen servos, 5 that are used in the thrust vectoring system will be high torque. Two are required for the stabilators, two more for the ailerons, two more for the spoilerons and one for a speed brake. So needless to say I am also going to have to look at using two batteries one for control and the other for the motor. So now I am currently am working on the weight and balance issues for placement of all of the components to keep the COG within a target range.

I am not trying to bore you all with the details, but as I mentioned when I originally posted this I am trying to document the design of this beast.

Boy what a learning experience this has been thus far.

Well, I'm interested... Keep it coming!!

Bob

The lift on a normal stab is down. When you stall a normal plane the nose goes down because the weight of the nose overpowers the downward force of the stab. a plane starts to fly "tail heavy" when the space between the center of lift and the CG get to close and the tail force overpowers the noseweight easyer. Airfoiled stabs use the airfoils to augment the ballance not to lift.

Just wanted to tell you guys that I am still working on this.
But the control system and surfaces are going to be a real PITA and that is no lie....
But to be total honest I needed to make sure that my understanding of aerodynamics and controlled flight were close to being right. I also wanted to experiment with some construction methods and materials before I went any further with this design. To that end I have a thread going in the kit build forum of a Sig Somethin Extra titled: Yet another Sig Something Extra Build, it fairly high on the most recent post within the top 2 pages, if you care to look.
My time was limited this past summer, I am the field chairman at my club and that really cut into my time. Not to mention that real life keeps getting in the way of my "airplane time". Not to mention that we all like to get out there and fly sometimes, so to all that have been following this, as well as the B-17 build listed on http:www.airfieldmodels.com links I have not given up just shifted focus on certain aspects of the science and experiments involved for a bit.