Two 144" long T-38's - Page 63 - RC Groups
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Mar 29, 2012, 12:31 PM
was geht , müssen unten kommen
Keenan smith's Avatar
Yourrrrrr welcome!
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Mar 29, 2012, 12:37 PM
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Here is a discussion thread that has some interesting ideas/info... "Most" turbine guys focus most on the rigidity of the servo to flying stab and flying stab to pivot set ups rather than balancing the stab. On my ducted fan Byron F16s I balanced the stabs on the one that had Byrons' half ring connection to the servo, but didn't balnce the stabs on the direct servo control version. Never had a flutter problem either way.
Mar 29, 2012, 03:05 PM
Official Boat Bum
Eddie P's Avatar
Originally Posted by gbmoore
Yeh ... it's fun
just finished an evening with the neighbor-kid (now 1st year masters in Aero at Univ. of Colorado) talking about pivot points.....
When CU did the DreamChaser for NASA, the pivot point was placed about 5% in front of MAC (which rang a bell from the thread I mentioned earlier).
When we took the stab from my (lamented) Tam's F-16, the pivot point was about 48% of the root, which calculated to about 20-21% of MAC.
He (of course) was talking about the Beta movements and the ??? factors, of which I only understood the Greek word "Beta"......
Soooo........looks like both of your stabs are in the ball park.
Keep up the PHENOMENAL work!
"Beta" is a generic term for negative.. it could mean angle of attack, or stability with pitching moments, etc depending on the context. I'd guess he was referencing static/dynamic stability of the stabilizer as it relates to MAC, center of lift / center of pressure... where the pivot point is, and how that plays out. This is a generic symmetrical subsonic airfoil so the variables are fewer, that helps.

Most model airplanes are built with massive servo torque relative to the control surface compared with a full scale. This is good enough to over come small build and engineering errors that are hard to really know exactly how to iron out without wind tunnel and extensive flight testing. Besides we need a strong structure to withstand transportation and abuse real planes don't get. So if we put in a "powerful enough" servo and very strong control support and linkage "for a little extra" we are good (experience shows what works in the past for some models of certain types). I think in this case even if there is some argument about where the actual pivot point should "mathematically" be, it's probably safe to say as long as you have a very strong flight control actuator and supporting structure you could probably get away with some considerable setup "deviations" and never really be the wiser.
Last edited by Eddie P; Mar 29, 2012 at 05:25 PM.
Mar 29, 2012, 03:34 PM
Capt. Z
falcon5's Avatar
[QUOTE=Eddie P;21178491as long as you have a very strong flight control actuator and supporting structure you could probably get away with some considerable setup "deviations" and never really be the wiser.[/QUOTE]

Well that's the plan anyway. Going to try and make it as tough and slop free as possible. Ball bearings, thrust bearings, aluminum servo arms, and steel rods and links. We will see,

I will be Johny test pilot on maiden day
Mar 29, 2012, 04:37 PM
corsair nut's Avatar
that will cover it!
Mar 29, 2012, 07:54 PM
Registered User


Sorry for mix-up. Flyingfitz was closer to correct answer. I made a mistake with my addition, as usual Attached was my sketch of your T-38 Stab, I almost erased just now.
Last edited by PhilLin; Mar 30, 2012 at 12:19 AM.
Mar 29, 2012, 08:08 PM
Registered User
Originally Posted by rcnats
I'm retired now but here are some pics of my "VIP" flight
That reminds me of the best part of a VIP flight brief. "If you hear me say 'EJECT, EJECT, EJECT' if you say 'What?'... you'll be talking to yourself!"
Mar 29, 2012, 08:57 PM
Bypass Ratio = Infinity
scatsob's Avatar
Originally Posted by corsair nut
that will cover it!
+1 I think you hit the nail on the head. If you have a slop free, strong linkage and spindle setup it will be fine. I am sure that is Avonds secret.
Mar 29, 2012, 09:49 PM
Capt. Z
falcon5's Avatar
The stab servos came today and they are pretty sweet. No slop in the gear train so that's good.

I got the flaps and ailerons hinged and mounted today, and just about servoed up and ready to go.

Hmmm ...I was kind of looking at what's left to do before it can techniqly go for a maiden and really there is not that much. The hard stuff is pretty much done. If I had fans I could darn near have it flying in a couple weeks, a month at most..

Main items to do yet is mount the vertical stab, install horizontal stab stuff, mount the fans, build a balancer,( I don't think I can put my fingers under this one) hack out a temporary foam canopy. A couple days of going over stuff, and taking care of the little things .. pre flight inspection..Go fly..
Mar 29, 2012, 09:54 PM
Endlesslag's Avatar
Sounds great! Painting it before maiden or not?
Mar 29, 2012, 10:05 PM
Capt. Z
falcon5's Avatar
Originally Posted by Endlesslag
Sounds great! Painting it before maiden or not?
Well it depends on fans. I f eveything is done and still no fans..then into the paint shop it goes.
Mar 29, 2012, 10:18 PM
Endlesslag's Avatar
Originally Posted by falcon5
Well it depends on fans. I f eveything is done and still no fans..then into the paint shop it goes.
Sounds great! this thing has made it so far from a few chunks of
Mar 30, 2012, 08:46 PM
Onward and upward.
Pilatuspc12's Avatar
Looks good. I'll be watching...........
Apr 02, 2012, 11:13 AM
Racquetball Lives!
Backwall's Avatar

Ground testing

After all is said and done, maybe you should build a wind tunnel before maiden! Or you might attach it to the roof of your F-150 and get up to about 120mph and see if the truck's front wheels lift off the ground. Make sure you have an emergency release for the T-38. You wouldn't want it to be smashed when you roll the truck!

Apr 03, 2012, 08:19 PM
Capt. Z
falcon5's Avatar
That's one spicy meatball

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