Nitroplanes X-29 build thread - Page 16 - RC Groups
Thread Tools
Apr 28, 2009, 04:40 PM
Done it all

I have been sitting at the edge of my seat waiting for the results, but, being a business man, I like your decision making. You did the right thing. No rush to jusgement, or even to please us, we are just the peanut gallery.

When you feel that the plane is ready, we are ready to cheer you on.

However, since some of us have construction in process, or are comtemplating our own similar project, we respect your caution as you are in a positon to save the rest of us aggravation and expense.

Good going

Sign up now
to remove ads between posts
Apr 28, 2009, 09:30 PM
Registered User
The suspense continues with Bob's maiden. Hope not too much damage caused by the adaptor. Totally agree with Scalefan, & I know Bob will not be rushed but will go only when he is ready.

Apr 28, 2009, 09:50 PM
Registered User
As a filler I'm attaching a few pix of my build I took today.

Note the fan shroud low point wud have been blocked by the original former if not ground down. Also kit in mind that with fan axis now about parallel to plane axis, the inlet air path is upward into fan after the intake.

Finally, note the tailpipe is about 1/8 smaller than the 4.28" OD of the fan shroud. It is constrained by the tailpipe cutout in former #6, which obviously needs to be enlarged. Formers #7 & #8 have large enuf cutouts. I also have to replace the #8 former in the kit I received as this former obviously moved during fabrication & got cured at about 15 to 20deg off vertical plane

I'll have pix of my full flying canard mods next.

Apr 28, 2009, 10:23 PM
Registered User
Perhaps I've been too presumptous in posting my build in Bob's thread. Before I proceed any farther, I really shud ask Bob's permission, or opinion if I shud post my build in a new thread. But I'm also concerned that a separate thread may not be as continuously organized without repeating some items.

Last edited by PhilLin; Apr 29, 2009 at 10:26 PM.
Apr 28, 2009, 10:25 PM
EDF all the way!
bruff's Avatar
Go for it. This is about Nitro Models X-29. We all can learn for the various people who build and fly them!
Apr 28, 2009, 10:37 PM
Registered User
Thanks, Bob!

I've been contemplating shortening the ailerons & making the tip portion fixed. It seems to me that a forward sweep wing (FSW) can have a unique reaction shud the wing tips begin to stall. This will move the center of lift aft, increasing a nose down tendency, compared to a sweepback wing which moves the center tof lift forward. I'm wondering if this is a plausible explanation for tendency of FSW planes to tumble out of control? Making the tip bays fixed shud therefore help to delay wing tip stalls. Any feedback?

Apr 28, 2009, 11:11 PM
"Marcy" VF-A
wekenav8r's Avatar
Phil, I thought the wing stalled at the root first, rather than the tip on a FSW?

Apr 29, 2009, 12:19 AM
Done it all
WOW, the dialog and expertice among this thread's participants is really impressive. I, for one, am really enjoying it. If we aren't carefull we might learn something.

Phil, obviously living in Oshkosh and being close to the once a year experimental event has allowed you to both share and learn some tricks of the trade.

By the way, almost all build threads contain multiple builds, however, did you notice that no two builds are alike. That's what makes participation so neat.

There is an on-line version of the CG calculator for Canard type planes. One of the entries allows for swept wings. I suspect that with this X-29 the sweep measurement would be entered as a negative number as it is swept forward. If someone wants to get a head ache they might try it out. Thats it, I'm not saying another word about CG.

Last edited by SCALEFAN; Apr 29, 2009 at 12:26 AM.
Apr 29, 2009, 11:57 AM
Registered User
Thanks for the kind words, Scalefan. I'm just a wanna be airplane expert. Yes, the spirit of aviation can rub off being close to the EAA.

I do want to see your CG calc program if you have a link for it. d_wcrash was suppose to sent his .xls program but had some problem with sending it thru the net. Perhaps he can activate the list formula function & just sent those as text; designating the cells that goes with them, of course.

Apr 29, 2009, 12:02 PM
Registered User
Originally Posted by wekenav8r
Phil, I thought the wing stalled at the root first, rather than the tip on a FSW?

Tim, you cud be correct about the root stalling first in FSW. In which case the aerodynamic center shifts forward as more root section stalls. OTOH, the canard wud normally induce a downwash that lowers the angle of attack for the root portion. I'm not sure if on a high G turn or manuever, the tips might not reach stall first?

Good input.

Apr 29, 2009, 12:18 PM
Done it all

Phil, let me warn you, most hobbiests would rather use the "gut feel" method of CG determination.

I tried to introduce the normal CG calculator on another thread and I was nailed up, arrows were shot into me, then kindling was placed at the bottom and lit afire. To make matter worse, the author of the thread then proceeded to blast mathematics, science, aeronautical engineers, commercial pilots that use a program to determine CG for their passenger jets. They made fun of me for saying that a plane with a long fuse has a very wide safe area for flying. Sooooo, take your chances with the results. If everything is correct, the safe area for flying should fall somewhere between the 5% and 15% variable that is entered into the progarm.

It seems to me that instead of flaming me, perhaps all that was needed was to double check my entries into the program, as I measured the plane while it was sitting on the floor un-assembled. Accurate measurements are a must, and with a swept wing plane it's easy to make mistakes. From what I learned, a tapered wing is not a swept wing, but, that has nothing to do with this plane.

Last edited by SCALEFAN; Apr 29, 2009 at 12:51 PM.
Apr 29, 2009, 01:33 PM
Registered User
Originally Posted by SCALEFAN

Phil, let me warn you, most hobbiests would rather use the "gut feel" method of CG determination.

Thx, Al! Much appreciated. I've seen this link before, but with my poor skill on searching the net, just wud not be able to find it on my own.

"Different strokes for different folks", as they say. Some just don't want to be bothered with the math I'm more of a sucker for working things out. One thing I've learned from the experimental builders: "measure 3-5 times & cut once" if one does not want to waste too much materials.

I've copied the input page so I can fill in all the required figures, then I'll try make a run of the CG program. Then maybe we can compare results. If this drags on till Airventure 09, I might even try asking Barnaby Wainfan for help

I've been doing CG same way as Darryl has; ie. using the CAD method. My track record? I tried it first time when I modifed the EJF F-18 by building mine with a much large LERX of the F version. Then I checked CG on my JHH F-4 & set it 1" forward where kit plan said it shud be. Then there was my KeeCat conversion where my CG was IIRC some 2.5" ahead of the kit manual. Tried moving these after maiden but all went back close to where my calcs determined. Guess it is beginners luck. But it shows my propensity for double checking.

BTW, I did go back to the NASA site last night & printed some 92 titles of technical reports on their X-29 work. Have marked some 15 for going back to read their abstracts when time permits; but did not see anything specific to CG. Perhaps most of the NASA folks take it for granted everyone there know how to work it out?

Apr 29, 2009, 01:50 PM
Done it all
I'm sure you know and I know that CG is an absolute location based on the weight and balance computations. However, theory says that if the CG is within the safe range, it's OK to fly. I tried to say this, and again I was blasted into the black hole of the universe.

I really thought my comments would agree with the gut feel guys who adjust the CG location to suit their comfort zone for flying. I merely wanted to point out that CG can be moved and the plane will still fly good. The nitro and gas guys know that, they know that CG changes as fuel is burned or the landing gear is dropped.

Us electric guys need to learn that CG changes as the volts run out of the batteries or when parts fall off the plane in mid air. LOL

Apr 29, 2009, 05:00 PM
Carbon fiber is our friend
Steve C's Avatar
Al, that's a nice cg tool you have there. I have a very old Model Aviation mag that had the math for canard cg. Whenever I've done canards, I've had to dig it out. Having a web based one is nice.

Guessing is ok if you have the knack for it, but there's a lot more comfort when your guess gets backed up by some math! Airfoils and fuse shape can affect proper cg by quite a bit and then it gets really tricky.

BTW, cg ranges get bigger with wider wing chord. The fuse length only helps by putting the tail section further back. A larger or high aspect ratio tail does the same. For a canard, I'm sure it helps to have the surfaces further apart as well, which is hurting the X-29.

That plane sure looks like it could use some inlet ducts.

Good luck you guys!

Steve C
Apr 29, 2009, 05:22 PM
Lithium Member
Herb's Avatar
A few years ago I scratch-built a small proto X-29 for edf (MF480 sized).

Yesterday I re-computed the CG on your china arf, based on the pictures posted here before.

I found it can't be behind where the wing fairing attaches to the fuse...

Then a small paper model gives exactly the same result as my calculation, the plane goes wildly unstable with a CG behind the red dot.

With a CG at or ahead of the red dot, mine glides just fine

Good luck with it ... btw selling larger edfs without ducts should be considered a crime in 2009.

Last edited by Herb; Apr 29, 2009 at 05:30 PM.

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Northrop X-4 Bantam Build thread Robert May Electric Ducted Fan Jet Talk 232 Dec 14, 2009 03:45 AM
Pocketcam X Build Thread....It begins! ZRX Doug Aerial Photography 98 Nov 17, 2007 12:57 AM
Discussion Another X-29 Thread- This time alittle smaller Cautrell05 Scale Kit/Scratch Built 8 Dec 12, 2006 08:18 PM
RBC A-4 Skyhawk build thread X.X Willmsy Electric Ducted Fan Jet Talk 6 Nov 22, 2005 11:01 PM
X-29 Building Thread Arbo Electric Ducted Fan Jet Talk 66 Apr 07, 2003 07:01 PM