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Old Apr 24, 2006, 02:42 PM
Park Jet Guru
jetset44's Avatar
Seattle, WA
Joined Jun 2002
5,589 Posts
Build Log
X-31 EDF Park Jet with Thrust Vectoring System

Hereís the latest project from the Jetset44 Skunk Works. Itís a model of NASAís X-31 Enhanced Fighter Maneuverability Demonstrator, which flew in the early 1990ís. The X-31 was equipped with a thrust vectoring system and was famous for being able to execute extreme post-stall maneuvers and sustained 70 degree high alpha flight. This model also features a working thrust vectoring system--which works even better than I hoped! Itís amazing to just hold this model in your hands, spool the fan up to about 50% power, and then feel the thrust vectoring system pitch and yaw the model VERY strongly. Iíve got 8 flights on this model so far (4 without the thrust vectoring system installed and 4 with it), so Iíve still got a lot to learn about how to use the thrust vectoring in flight.

This model features very simple foam construction similar to my other pusher prop park jets and is very quick to build. I built the prototype in only a week and a half, working mostly in the evenings. Here are the specs:

Wing area: 144 sq in
Span: 20.5Ē
Weight RTF: 13.5 oz as shown (with paint and thrust vectoring system)
Wing loading: 14 oz/ft2
Motor: Hyperion Y22S 5000 kV
Fan: Wemotec Microfan
Battery: Thunder Power 11.1V 1320 mAh Lipo
Current draw: 20.0 amps static
Power input: 200 watts
Power loading: 240 watts/lb
Electronics: Hitec Electron 6 Rx, Phoenix 25 ESC, 5 GWS Pico servos
Flight controls: Elevons, canard, rudder, pitch control vane, yaw control vane (5 servos total)

The overall handling qualities of this model are very good. It is VERY quick on the controls at medium to high speed as expected, but because of the thrust vectoring system itís also quick on the controls at low speeds. Thatís something that takes getting used to with a jet, though itís not at all unlike a foamie 3D ship. Itís also very aerobatic, with blindingly-fast rolls and easy loops.

The Microfan/Hyperion Y22S combo provides GOBS of power on this ship. I havenít directly measured the thrust, but it appears to be in the 11-12 oz range since the 13.5 oz model can almost climb vertical. From a high speed pass, though, it will climb vertical out of sight. Hand launch is very easy and the model cruises around easily at Ĺ throttle and does big loops from level flight. Top speed seems to be in the neighborhood of 60-70 mph, but thatís tough to gauge by eye since this model is so small. However, with 20 amp current draw static, this setup is definitely pushing my TP 1320 PL batteries to the limit. The batteries are very hot after the flight and my flight times have averaged only about 5 to 6 minutes. Gotta be very sparing with full throttle on this setup!

Below is a flying video that demonstrates all the capabilities of this model. This video is a little fuzzy at times, but it was very difficult for my cameraperson (my wife) to keep this fast and tiny model in the frame!

I still have some work to do to clean up the plans, but Iíll post them here in the next few days.

Steve

X-31 EDF Flight Demo (3 min 3 sec)
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Old Apr 24, 2006, 02:48 PM
Park Jet Guru
jetset44's Avatar
Seattle, WA
Joined Jun 2002
5,589 Posts
Thrust vectoring system

The thrust vectoring system on this model is different from the real X-31, both to make it simpler and more effective, and because unlike the real jet I didnít have to worry about keeping parts out of the hot jet exhaust! It uses two simple 1/16Ē plywood vanes that span across the exhaust, one for pitch and one for yaw. The yaw vane is slaved to the rudder, while the pitch vane uses a dedicated servo. The vanes are supported by simple carbon tubes, and pivot on 1/16Ē music wire. The thrust vectoring hardware weighs only 0.35 oz installed, so including the weight of the dedicated pitch control servo the entire system weighs only 0.55 oz.

So far Iíve used the thrust vectoring system for two cool new maneuvers. The first Iíll call a pitch pirouette, which causes the model to spin about the pitch axis (a 3D aerobatics pilot would call this a waterfall). Just take the model vertical, chop power, and just when it stops apply full power and full pitch control (either direction). The model will spin fast about the pitch axis as it falls. The second is the maneuver made famous by the real X-31, the Herbst maneuver. This is a maneuver that allows making a 180 degree turn very quickly. In cruise, chop the power, pull up sharply, and after the model bleeds off speed, apply a burst of power and some yaw control. The model will rapidly spin in yaw and will fly away in the reverse direction. This maneuver looks a lot like a hammerhead stall, but the difference is you pull up sharply from level flight to bleed off airspeed quickly. Both of this maneuvers are shown in the video.

The other key capability of the thrust vectoring system is low speed flight control. With most jet models, the flight controls get very sluggish at low airspeeds. The thrust vectoring system completely solves that, providing very good control in both pitch and roll/yaw at low speeds and at high alpha. It also provides working flight control after the wing is completely stalled, enabling post-stall maneuvering.

The thrust vectoring system is completely optional on this model, in fact, I made the first four flights without it (itís easy to install later). Without it, this model makes a great-flying sport jet and flies pretty much like any other EDF jet.

Steve
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Old Apr 24, 2006, 02:48 PM
diligentia vis celeritas
gunracer's Avatar
Corona, CA
Joined Feb 2006
3,547 Posts
very nice...
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Old Apr 24, 2006, 04:34 PM
Model Citizen
fatbutcher's Avatar
Northamptonshire, UK
Joined Sep 2004
96 Posts
i concur!
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Old Apr 24, 2006, 05:03 PM
Giddy up!
Sal C's Avatar
Woodridge, Illinois
Joined May 2000
4,478 Posts
You stole my paint scheme Steve! (j/k). I made good progress this weekend but I need to post some progress pics. Hope to be flying by the end of the week or the weekend...

Great job!
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Old Apr 24, 2006, 08:36 PM
That thing's operational!
birdlives1955's Avatar
New Orleans/Dallas
Joined Jan 2006
4,706 Posts
Steve,

You've outdone yourself again! The jet looks great! This is really too cool, I'm really excited about this one. Thrust vectoring, it's amazing that you were able to figure out to make that work on an R/C aircraft! The paint scheme looks great too, great job and thanks for sharing your planes with us! This definitely might be a fun one to try and build! Way to go!

The video looks really cool, it looks so scale in the air. I've never seen the real one fly, but those thrust vectoring maneuvers looked pretty authentic, it's really interesting how that system works. It looks a little bit harder to control than some of your other models, and it seems especailly fast. I really like the sound of that ducted fan, that Hyperion motor looks like it's doing its job nicely! Well, I'm looking forward to seeing who will be first to build it! I saw that someone recently completed an EDF tomcat, they posted a video and it looked really nice.

-Matt
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Old Apr 24, 2006, 08:46 PM
Giddy up!
Sal C's Avatar
Woodridge, Illinois
Joined May 2000
4,478 Posts
Steve,

I just watched the video and it's great! You flew it superbly. It hug those turns nice and tight and the TV loops were unbelievably tight. You're a natural jet jockey! I've got to get mine in the air asap but I've got so much going on during the week the weekends seem to be my only chance. Nice paint job too...
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Old Apr 24, 2006, 09:30 PM
Registered User
titaniumracingt's Avatar
United States, CA, Citrus Heights
Joined Apr 2004
117 Posts
Very cool model! Well I got bored and decided to figure out how to further complicate things by going with the scale 3 paddle system. Heres what I came up with.

Top Paddle-----------------------------------------Elevator Channel


Bottom left-------| |--------------------------Rudder Channel
Bottom Right-----Vee-tail mixer----------------------- Y'ed into the Elevator Channel

Then if you wanted to further complicate things, you could connect both the top elevator paddle servo and the elevator lead off the mixer for the bottom two paddles to another mixer, like at www.veetail.com (since its programable), and slave this to the throttle so the paddles can fold in or open up slightly to control eflux


Just a thought

PS I wrote this in a hurry so sorry for any mistakes


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Old Apr 24, 2006, 09:58 PM
EDF rules... :)
AirX's Avatar
Joined Nov 1999
13,506 Posts
Nice project there Steve...

Eric B.
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Old Apr 24, 2006, 10:55 PM
Park Jet Guru
jetset44's Avatar
Seattle, WA
Joined Jun 2002
5,589 Posts
Thanks for the compliments, guys. This has been a very fun and rewarding project. The inspiration for this model came from an X-31 flight sim model I downloaded for Aerofly Pro Deluxe last month. The physics of this model and the thrust vectoring system in particular are very realistic, which allowed me to get lots of good practice before flying the real thing. This particular flight sim model has been my #1 favorite model ever since I got it, since it's capable of screaming 200 mph passes at the high end and can actually hover at the low end under complete control! A lot of fun to fly. If you have AFPD, I HIGHLY recommend downloading this free model (www.rc-sim.de). I've attached a screenshot below to show what it looks like.

Steve
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Old Apr 24, 2006, 10:59 PM
Park Jet Guru
jetset44's Avatar
Seattle, WA
Joined Jun 2002
5,589 Posts
Quote:
Originally Posted by titaniumracingt
Very cool model! Well I got bored and decided to figure out how to further complicate things by going with the scale 3 paddle system. Heres what I came up with.
Yes, I originally thought about doing something just like this but decided it would be heavier and wouldn't be as effective as the full span vanes. That because it requires 3 dedicated servos instead of just one, and because paddles won't work as well on an EDF ship since the exhaust velocity is much lower than on a real jet engine and the paddles don't deflect much of the airflow. The full span vanes deflect MUCH more airflow and are thus much more effective.

Steve
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Old Apr 24, 2006, 11:02 PM
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Racine, WI AMA# 809291
Joined Nov 2003
5,856 Posts
She's a Beauty Steve!!
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Old Apr 24, 2006, 11:04 PM
Registered User
titaniumracingt's Avatar
United States, CA, Citrus Heights
Joined Apr 2004
117 Posts
Quote:
Originally Posted by jetset44
Yes, I originally thought about doing something just like this but decided it would be heavier and wouldn't be as effective as the full span vanes. That because it requires 3 dedicated servos instead of just one, and because paddles won't work as well on an EDF ship since the exhaust velocity is much lower than on a real jet engine and the paddles don't deflect much of the airflow. The full span vanes deflect MUCH more airflow and are thus much more effective.

Steve
Yeah it would be heavy. It would be kind of fun for a Midi or a regular DF model
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Old Apr 24, 2006, 11:13 PM
Park Jet Guru
jetset44's Avatar
Seattle, WA
Joined Jun 2002
5,589 Posts
Quote:
Originally Posted by RCParkflyer
She's a Beauty Steve!!
Thanks, Tom. By the way, once I get the plans done I'm planning to modify them to create a pusher prop version of this jet as well. It should make a great-flying pusher jet and will be easier to build without the complications of the fan and ducting installation. The pusher jet version won't have thrust vectoring, of course (at least I can't think of any practical way to do that), but it should be a great-flying sport model regardless.

Steve
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Old Apr 25, 2006, 12:28 AM
Renegade Fun Forever!!
rvincent's Avatar
Fontana, California, United States
Joined Jul 2004
27,242 Posts
Oh Man Steve, what are you trying to do to me?!?!? I just bought a new JR 9303 because my 8103 (which I loved) only had a 10 model memory! The 9303 has 30 I'm not even done with GGRN's A-4, your F-14, and That F-104!! And I already have 16 models in the new Radio! Now you throw this one at me! I saw the real x-31 in a demo at Edwards about 15 years ago and have never forgoten it Your probably right it would absolutely RIP with a LS PJ motor on it, but dang! It is too cool with all the thrust vectoring on it
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