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Old Apr 04, 2007, 01:43 AM
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Park Jet Guru
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Seattle, WA
Joined Jun 2002
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Thrust Vectoring System

This model uses the same thrust vectoring system as my F/A-22 Raptor park jet, just with two of them instead of one. The design is based on 3/8" square hardwood sticks with 1/8" plywood brackets that swing around a small bolt, driven by Hitec HS-85MG servos. A strong metal-geared servo is required for this application, and the HS-85MGs have worked flawlessly in my model.

The F/A-22 has single-axis (pitch) TV, but using two motors together allows full 3-axis TV (pitch, roll, and yaw). Both motors gimbal up/down together for pitch, opposite for roll, and differential throttle provides yaw. The TV servos are electronically slaved to the stabilators to match their pitch/roll inputs, and the two ESCs are plugged into separate channels in the receiver to allow differential throttles (which are mixed to the rudder channel).

For those that haven't already seen it, here's a quick video showing a demo of the 3-axis TV system on my work bench:

Thrust Vectoring Demo

My model uses separate servos for the tailerons (Futaba S3110s) and the thrust vectoring, for 4 servos total. This allows me to turn the TV system on and off at will (via a switch on the Tx) and also allows adjusting the trims and rates of the TV system separately from the stabilators. To me, this setup provides the maximum fun factor. However, this model was also designed so that you could eliminate the two stabilator servos and just slave the stabilators and TV together mechanically. That eliminates the cost and weight of the extra pair of servos and also greatly simplifies the transmitter programming. To do this, just use the HS-85MGs, run a pushrod from the servo to the stabilator control horn (note the control must be installed pointing down instead of up as shown on the plans), and then run a second pushrod from the control horn to the TV mechanism. There are already two holes shown in the control horn template to allow this. Note this setup will require a lot of adjustments in the linkages to ensure the stabs and TV are properly aligned, especially once the airplane is trimmed. With the setup I used, all adjusting can be done easily just using the transmitter, which is very convenient.

In my experience with this model so far, 90% of the value of the thrust vectoring system comes from pitch. That's what allows the tight turns, flips, and low speed/high alpha control. Roll and yaw are also fun to play with, but I've found them to be useful only for post-stall maneuvering and tumbling maneuvers. Part of the reason for this is that the pitch TV responds instantly due to it's long control arm, but roll and yaw respond rather sluggishly due to their short control arms. This opinion could change though as I get more experience flying this ship and learn to use the TV better. I'm also eager to hear what some of you fellow modelers learn once you build this ship!
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Last edited by jetset44; Apr 04, 2007 at 02:01 AM.
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