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-   -   Internal setup for AMA 424 racer (https://www.rcuniverse.com/forum/q-500-racing-149/8942406-internal-setup-ama-424-racer.html)

twitte1 07-17-2009 08:30 PM

Internal setup for AMA 424 racer
I am about start the construction of several airframes that I am going to fly in the AMA 424 class. I am currently flying Club 40 and Q-25 here in NC and surrounding areas. After talking to several very experienced flyers around here, looking around these forums and seeing several pictures that are posted, I see that there is many different ways to set up a plane. I would like to hear and see pictures of your setups in regards to AMA 424.

Forward mounted fuel tank or CG tank?

Throttle placement/orientation and pushrod type and connectors?

Switch placement?

I have been told and realize that as the plane go faster proper set up is essential. Any help in this area would be greatly appreciated.

Thank you in advance!


blindfaithnogod 07-17-2009 11:03 PM

RE: Internal setup for AMA 424 racer
mount the tank as close to the CG as possible. a little forward is ok.

for the throttle, the servo will probably have to be behind the cg. for balance. a standard 2-56 pushrod is what i use. clevis at the engine end and z-bend at the servo. drill a hole straight through firewall and mount. make hole in mount 1/4" so clevis can slide through for engine change.

mount the switch internally, attach a string, with one end out one side and the other out the other side.

rbg 07-17-2009 11:17 PM

RE: Internal setup for AMA 424 racer
Been doing this for years. Put your servos behind the trailing edge. That means 3 servos and a switch. THe string is for vibration. If you use a pc of wire to turn switch on it could cause other big issues.

Trael on all is Elevator 5/32 up 3/32 down. Aileron up 7/32 down 5/32. Rudder as much as you like. 1/4 inch is usually used.

Make sure you go to nmpra websitte so that motor is set up right to shut off on command. We can tell you how in an other thread.

daven 07-18-2009 07:17 AM

RE: Internal setup for AMA 424 racer
Depending on the plane will determine where things need to go to cg properly. Many of the newer planes fly with a cg around 3" so its pretty common to see 3 servos and a switch just behind the wing, accessed by a hatch.

For throttle, I've always used the sullivan braided cable in the yellow tube (not the flexible). Solder a threaded coupler on the engine side and install a ball link to the throttle and use an ez connector at the servo that the cable goes through. About the middle of the wing, I rough up the yellow tube and CA it to the side of the fuse for support. I've started drilling holes in my backplate mounts where the hole is just large enough for the ball link to go through. If you make a template of the location of this hole, and drill all your backplates and firewalls the same, it will help with interchangability down the road if your swapping motors around.

I place the center of my tank about 1/2"- 1" forward of the CG. I still believe that the force of the plane going forward pushes the fuel to the back end of the tank during flight as it empties. At this spot I do not notice any elevator trim change during the course of the flight, so it must be close.

paysonhobbies 07-31-2009 12:48 AM

RE: Internal setup for AMA 424 racer
Most of all of the tanks in the 424 and 428 airplanes go right in the nose of the plane with a bladder tank from jett.

Most of us put the 3 servos right behind the trailing edge of the wing. Depending on your class and the size of your wallet you can put futaba, hitec, jr or your favorite. Your looking for the 225 225mg hitec's, 5245 digital hitec, 3002 futaba's, 3421 Jr's. It depends on how much consistancy on centering you want. Most of these servos have the same amount of torque but centering is what you are going to pay for. You will also see a slight difference in the speed of the servos. Most people use 3421's and 3002's.

Switches can be put in with the servo tray behind the wing. You can turn them off with a metal wire as long as the piece of the switch it is going into is plastic. Most people use metal on the 424 and 428 and then switch to the string on the 422's.

Let me know if you need an pictures for ideas.

twitte1 07-31-2009 07:09 AM

RE: Internal setup for AMA 424 racer
Thank you all for the responses. Pictures would be great. My fuses are almost complete. I will be working on the setups soon.

I have seen and heard of several throttle pushrod types, music wire & cable. Which is best? Does one or the other reduce the vibration from the engine to the servo?


HighPlains 07-31-2009 07:57 AM

RE: Internal setup for AMA 424 racer
1 Attachment(s)
Put a mechanical filter in the throttle link if you are worried about vibration to the servo. All this consists of is a weight about an inch ahead of the servo. In this case a wheel collar connecting the short piece of music wire to the cable that goes to the engine. Do the forward end as Daven said.

Here is a photo as used on all my models. Throttle servo is lower left.

paysonhobbies 08-05-2009 06:21 PM

RE: Internal setup for AMA 424 racer
If you use the plastic celvis from dubro on your engine or the plastic ball cup for the nelson, you wont have any vibration back to the servo. I have used wire that is a little smaller then 2/56 and the cable from dubro and either seem to work just fine.

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