Mar 28, 2012, 09:22 AM
was geht , müssen unten kommen
Keenan smith's Avatar
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Mar 28, 2012, 10:13 AM
Capt. Z
falcon5's Avatar
oh snap!!! well no way to move the rod at this point without destroying the stab, but I could just go with elevators and blow off the flying stab all together.

Man from the pictures it sure looked like it went in the middle. I looked at the Fiorenzi pic and two full size T-38 pics and would have bet it was a middle mount.

I am reading now that I guess most r/c guys put the pivot point at about 20% MAC ...Hmmm what to do..
Mar 28, 2012, 11:01 AM
was geht , müssen unten kommen
Keenan smith's Avatar
just add a shedload of wieght to the front of the stab and it should do fine!
Mar 28, 2012, 11:02 AM
was geht , müssen unten kommen
Keenan smith's Avatar
looks like the middle to me too!
Mar 28, 2012, 11:27 AM
deltas are cool
AIR SALLY's Avatar
i think it is forward of middle ,thats how the F-20 is .....yeah more weight to biggy
Mar 28, 2012, 11:31 AM
Registered User
I would consider bearing at around 25% MAC. Then balance. This is closer to the subsonic aerodynamic center. But if it worked for Fiorenzi then what the hell!

Edit: The leading edge has a pretty good sweep angle. Have you located the MAC? 25% MAC might be pretty close to halfway back at the root. Post your root chord, tip chord, tail 1/2 span and the pivot point location back from the leading edge and I'll draw a picture if you want. Or, just balance it like Fiorenzi and it should work!
Last edited by flyingfitz737; Mar 28, 2012 at 11:51 AM.
Mar 28, 2012, 11:33 AM
Official Boat Bum
Eddie P's Avatar
I don't want to add any additional confusion over the stabilizer issue but I thought I'd add a link that might be able to back up where your aerodynamic CG is on your stabs.

Place your dimensions in there as precise as you can, select your desired CG (%MAC) and it will show graphically where your stab CG should be. I did this to back up my most recent F-100 that uses a similar pivot point arrangement. All flying stabs are great as long as they are precisely controlled, for that we need a balanced stab and also enough torque, right?!! So to back those premises up I ended up adding ballast to the stabs to balance them at 18 percent MAC. Flying wings are typically 15 to 20 percent MAC so I thought my "flying wing" of a stabilizer should be about in the middle. My pivot point is slightly ahead of the 18 percent CG - looks like the design of the model places the pivot point right at 12-15 percent MAC of the stab based on my calculations (that can create flutter issues with the pivot point being too far forward).

A pivot point being too far back on the other hand, seems to me to be possibly setting up an aerodynamic control "snatch" hard-over control input, not easily returned to neutral due to aerodynamic forces above a certain speed, or servo strip/linkage/structure failure scenario above a certain loading. You have some mighty good servos going in, so the weakest link would be the linkage, servo mounts, and the pivot point hardware and mounts (if the problem even exists). Also think about what happens under heavy G loading - if the mass of the stab is forward of the pivot, the stab will tend to load up and increase into an additional control input that would add G loading further. That would be for positive and negative g loading, both cases. This could add to some subtle negative static/dynamic stability under load. OK, I'm getting too much into my old "aerodynamics" courses in college, I'll stop now.

If it get's to the point of having to pull the pin out of the stabs to re-position, the way I see it you will not have to destroy the stabs. Since you added no formers you are in luck. Simply cut into the foam in the pattern of your stab pin and pull it. cut a new pattern in the proper place. Put ply formers on the bottom and top of the new stab pin pattern all the way to the glass surface, extend the formers beyond a little to act as a carry through spar and cap the stab also to help secure it all in as well as hold the pin in a central location. Add some carbon fiber mat, wet layup and vaccum bagged if you can on the center section of the top and bottom of the stab. Use a little bit of filler to glaze the transition. Yes it will be noticeable but it will be very nearly "un-noticeable" and will look planned/normal if you do it cleanly.

Just my .02
Last edited by Eddie P; Mar 28, 2012 at 11:47 AM.
Mar 28, 2012, 11:37 AM
Registered User
Not on the build but T-38 related.

Had a great experience last night. I took my son to hear Astronaut Story Musgrave speak. He is an avid photographer and has carried a personal camera with him his entire career. He has accumulated some 10,000 pictures. He is a huge fan of the T-38 and has logged crazy amounts of time in the jet. He praised the jet for its simplicity, forum and function. During his presentation he showed some of the most amazing T-38 photos that I have ever seen. He mentioned a book that will contain many of his photos. This will be a "must see" for any T-38 enthusiast.
Mar 28, 2012, 01:08 PM
Corporate Jet Mech
Halownr's Avatar

Gotta do it

Originally Posted by falcon5 View Post
A couple pics from the front. OK nuf playing around, time to get back to work
Not that building a giant sexy T-38 isnt enough gotta put it together every now and then for a glimpse into the finished project.

This thing is so bitchin. It is just an awesome size.... So jealous right now!!!!!

Mar 28, 2012, 03:23 PM
Capt. Z
falcon5's Avatar
Originally Posted by krypto71 View Post
Can I request an outdoor picture next to something like a car, to get some perspective of the size?
Here ya go kripto, took it outside for the first time. Not quite sooo masive as it looks in the house.
Mar 28, 2012, 03:29 PM
Capt. Z
falcon5's Avatar
Well in the interest of "doing it right" I better make sure the pivot point is in the right place, I wanted to see if I could carve out a new stab by hand..I am matching Nuts airfoil as best I can and think I am getting it pretty close.

I hate to not use Nuts hard work on hot wiring the stab but I would rather destroy it this way then in a flutter structual failier.

I will plot the rod location and use formers this time. The new stab took me about 45 minuets to carv out so far..not a bad investment to get it right.
Last edited by falcon5; Mar 28, 2012 at 03:51 PM.
Mar 28, 2012, 03:55 PM
RC Fanatic
Reco's Avatar
Dang it Falcon there goes my tourretts again....
Mar 28, 2012, 04:02 PM
Capt. Z
falcon5's Avatar
Originally Posted by Reco View Post
Dang it Falcon there goes my tourretts again....
Yeah well I am out in the yard makeing airplane noises again...I think the little old lady next door caught me too... Worst possible time I think I was in the middle of a full burner climb and spit was flying everywere..
Mar 28, 2012, 04:12 PM
Registered User
skyracer068's Avatar
Originally Posted by falcon5 View Post
Yeah well I am out in the yard makeing airplane noises again...I think the little old lady next door caught me too... Worst possible time I think I was in the middle of a full burner climb and spit was flying everywere..
......would of been worse if you were imitating 2 radials from a B-25....your chin and the front of your shirt would have been soaked! I don't know how I know this.

Absouletly beautiful!!!

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