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Old Mar 24, 2008, 12:34 AM
Park Jet Guru
jetset44's Avatar
Seattle, WA
Joined Jun 2002
5,608 Posts
Build Log
Grumman X-29 Park Jet

Here's my 10th park jet design to share with the forum. The Grumman X-29 has always been a personal favorite of mine and has long been on my must-do list, and I finally got around to doing it. This model is sized similar to my other park jets and uses all the same construction methods. It is based on a scale outline of the X-29, but I took my usual scale liberties to make for a better-flying RC model—I increased the vertical tail area about 10% and also scaled the wing and canard up about 15% relative to the fuselage (since the real X-29 has a rather small wing). These changes paid off, since this model is smooth and solid in the air and can truly be called a park-capable flyer.

Here are the technical specs:

Wing area: 217 sq in
Span: 28.1”
Length: 46.4”
Weight RTF: 20 to 23 oz
Wing loading: 15 oz/sq ft
Motor: Littlescreamers Super Park Jet
Battery: Thunder Power 2100 mAh 11.1V Prolite
Prop: APC 7x5
Current: 19 amps
Watts: 185 watts
Power loading: 130 watts/lb
Speed control: Castle Creations Phoenix 25
Receiver: Berg 7P
Flight controls: Canard, aft strake flaps, ailerons, rudder (optional)

My model is powered by a Littlescreamers Super Park Jet motor, which provides fantastic performance--unlimited vertical and probably 70 mph top speed.

The first few flights of this model were quite challenging, and it took a half-dozen flights to get the optimum CG and control throws figured out. But now that that's done, I've had a blast flying this model. It's smooth and graceful in the air and looks absolutely unmistakable with that unique wing planform. While this model flies quite well, it does have a few quirks. First of all, the flight controls are very speed sensitive. At high speeds the model gets very pitch sensitive, but at low speeds the controls get very sluggish. All airplanes do this to some extent (especially park jets), but it's really exaggerated on this model and I had to resort to dual rates (in addition to exponential rates) to cure the problem. On all my other park jets, expo alone has been enough to provide good handling at both high and low speeds without having to flick a dual rate switch. I personally don't like having to use dual rates while flying, but it's not that big a deal. Just use high rates for takeoff, landing, and high alpha/slow speed maneuvering, and low rates for everything else. This model also has a mild spiral instability due to the forward wing sweep and no dihedral, but that's not uncommon and isn't a big deal. Bottom line is this isn't an airplane that will fly hands off, but then again the real thing requires multiple sensors and triple-redundant flight control computers to stay in the air, so even getting a scale X-29 model to handle satisfactorily with no computers and no gyros is an achievement!

As you can see in the pictures, my finished model is just bare unpainted foam (one of the nice things about using white Depron!). I did that mostly to save time but it also saves a little weight. The famous X-29 red, white, and blue paint scheme was all done with decals, which I created in my CAD program and printed on clear Avery label paper and just applied directly to the foam. It's not a top-quality finish, but it got the job done with minimum effort and I'm satisfied with the result.

Here's a video of the model in flight:

X-29 Park Jet (2 min 54 sec)
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Old Mar 24, 2008, 12:39 AM
Park Jet Guru
jetset44's Avatar
Seattle, WA
Joined Jun 2002
5,608 Posts
Construction Details

Here are some of the construction details of this model. If you've built any of my park jet designs before, you won't see anything new here.

The wing of this model features a special spar design to solve the inherent structural problems of forward-swept wings. Unlike aft swept wings which are structurally stable, forward swept wings are inherently unstable structurally. When a forward swept wing generates lift, the tips bend up slightly due to the load. But when the tips bend up, the wing also twists slightly such that the angle of incidence at the tip increases (i.e., the wing washes in). That increases lift, which increases the bending, which increases twist, and so on until the wing rips off the airplane! An unstable situation. To solve this problem, the wing must be built extremely strong and/or designed so that it resists bending in torsion. Both solutions tend to be very heavy, which is why you don't see many forward swept wings in the real world. On this model, I solved the problem using a little of both approaches. This wing features a double carbon tube spar that is triangulated to provide a very strong and stiff structure—both in bending and more importantly in torsion. Plus, I located the spar far forward chordwise in the outboard wing, which makes the wing tend to wash out at high angles of attack (i.e., the unsupported foam sheet twists trailing edge up) to naturally counter the inherent tendency to wash in. I also reduced the aileron span at the tip, leaving a fixed trailing edge segment at the tip that helps generate more wash out. All in all, this design seems to work well since I've been able to do high-speed high-g turns with this model with no problems. Aviation history buffs will note that the real X-29 also solves this problem the same way—a very strong composite wing structure that is aeroelastically tailored to resist twisting.

This model also features a unique control surface arrangement. In addition to the usual canard, ailerons, and rudder, it features scale working aft strake flaps that are mechanically slaved to the canard for pitch control. While this arrangement works fine for pitch control, I was able to improve controllability at low speeds further by slaving the wing flaperons to the canard. Thus, when you pull aft stick on the transmitter, all six control surfaces (two canards, two flaperons, and two aft strake flaps) move! It's very cool to watch and gets a fun reaction from bystanders. The flaperon mixing isn't required for this model to fly well, but it definitely helps and if you use individual servos for the ailerons like I do it's simply a matter of turning on a mix in the transmitter to get it.

Note that with the CG shown on the plans, the neutral position of the canard should be set at 2 degrees incidence (leading edge up) relative to the wing. For reference, that puts the canard trailing edge about 5/8" up from the bottom of the fuselage, or puts the entire canard roughly parallel with the bottom of the fuselage directly underneath the canard.
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Last edited by jetset44; Mar 24, 2008 at 12:46 AM.
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Old Mar 24, 2008, 12:42 AM
Park Jet Guru
jetset44's Avatar
Seattle, WA
Joined Jun 2002
5,608 Posts
Plans

Plans for this model are posted below in the usual tiled and untiled formats. Remember, the rule is—if you build it, you gotta post pictures!

If you build this model, be forewarned of one thing—just about every time you take it to the flying field, some wisecrack will yell, "Hey WAIT, you've got the wing on BACKWARDS!". It's funny how many times that has happened to me in the short time I've been flying this model…

Steve

Edit: A PDF file of the decals I created for this model are posted here:

http://www.rcgroups.com/forums/showp...0&postcount=70
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Old Mar 24, 2008, 12:53 AM
Cant you feel the freedom
NuttyPro67's Avatar
USA, OR, Beaverton
Joined Jan 2007
345 Posts
Looking AWSOME!! How well do the wings react to the forward swept design? Did you have to do anything extra to the wings that you normally don't do to make them handle that or did they react just fine?
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Old Mar 24, 2008, 01:04 AM
Park Jet Guru
jetset44's Avatar
Seattle, WA
Joined Jun 2002
5,608 Posts
Well, aerodynamically forward-swept wings are great. They virtually eliminate tip stall and generally have excellent controllability at high angles of attack. The only problem with them is the structural instability I described above. So as long as you make them strong enough, they work very well.

Attached below for kicks is a photo of a gas-powered forward swept wing model I flew back in the late 80's called the FSW-3 (built from RC Modeler plans). It was great fun to fly and had excellent handling qualities. I flew this model regularly for years and have been a big fan of forward swept wings ever since.

Steve
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Last edited by jetset44; Mar 24, 2008 at 01:11 AM.
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Old Mar 24, 2008, 01:27 AM
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United States, TX, Sherman
Joined Apr 2006
224 Posts
Very nice. Good job, Steve!
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Old Mar 25, 2008, 03:09 AM
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RCParkflyer's Avatar
Racine, WI AMA# 809291
Joined Nov 2003
5,856 Posts
She looks Great Steve!!

Now on the Parkjets website
http://www.parkjets.com/X-29-jetset44.html
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Last edited by RCParkflyer; Mar 25, 2008 at 11:26 PM.
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Old Mar 25, 2008, 05:40 AM
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simonslim's Avatar
geordie land,uk
Joined Nov 2005
894 Posts
I'm gonna have to get me somemore foam. Yet another fantastic creation Steve, well done.

Simon.
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Old Mar 25, 2008, 01:28 PM
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United States, FL, Sebring
Joined Feb 2006
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Great job! this is a must have......
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Old Mar 25, 2008, 04:01 PM
Registered User
Türkiye
Joined Jun 2007
203 Posts
You got the wing backwards
Here is my concept FSW which I built in a couple of evenings without any plans or drawings or any calculations. I just cut depron and glued in a shape I like. It had absolutely zero engineering in it


And its maiden.
Untitled (0 min 32 sec)


I had only elevon control. Poor model never saw paint.

Not even comparable to your beautiful x-29 I just wanted to share.
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Old Mar 25, 2008, 11:02 PM
Park Jet Guru
jetset44's Avatar
Seattle, WA
Joined Jun 2002
5,608 Posts
Thanks for the compliments. This has been a long project since I've had so little hobby time lately. I started building this bird in early October and didn't fly it until late February...

I'm eager to see the results if anyone else builds one of these. Any takers?
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Old Mar 25, 2008, 11:44 PM
That thing's operational!
birdlives1955's Avatar
New Orleans/Dallas
Joined Jan 2006
4,706 Posts
Steve,

That's totally sweet! Wow! Man, that looks so nice. Way to go. From the short flight vid you posted it looks like a smooth flyer too. Way to go!
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Old Mar 26, 2008, 02:00 PM
Park Jet Guru
jetset44's Avatar
Seattle, WA
Joined Jun 2002
5,608 Posts
Hey, thanks for the new page on parkjets.com, Tom! Your website is an invaluable resource to us.

Steve
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Old Mar 26, 2008, 03:36 PM
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Nadim's Avatar
Linköping Sweden
Joined Nov 2006
960 Posts
Very nice looking model Steve! I really like that family photo, how can you decide which plane to fly?

What kind of mixing are you using I’m guessing flaperons and elevator to flap mix right? Or did you program an own mix to get all the surfaces moving at the same time for pitch control?

Thanks for sharing I’m looking forward to see another video.

Now why couldn’t you have posted these plans 2 weeks ago, I did build another F/A-18 of yours, I would have loved to be the first one to build this awesome plane. But then again I’m having a blast with my new F/A-18.

Nadim
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Last edited by Nadim; Mar 26, 2008 at 03:53 PM.
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Old Mar 26, 2008, 05:05 PM
Into the Wild Blue Wonder
Jasta_66's Avatar
ATL
Joined Jan 2007
1,018 Posts
I'll give her a go. Ive been wanting to try a working canard plane. I might have to KF that wing, though.

pics beginning tonite.

Thanks, Steve

Jasta
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