AMA’s New Beta Model Airplane — Improve Its Performance by Making a Few Modifications

If you look closely at the propeller in the photo above, you may notice a Peck silver propeller, which is not what the AMA Beta comes with. Instead, the Beta’s prop is a 7”diameter black paddle and it’s almost identical to the Sig Manufacturing 7” red propeller. Unfortunately, the black Beta propeller just didn’t produce much thrust, so the climb performance was poor. I gave Bill a 7” Peck prop and a reverse “S” hook to see if we could improve the Beta’s climb performance.

Right away we noticed a marked improvement in the Beta’s climb rate and altitude gain using the same 3/16” by 23” long rubber motor that was used with the Beta’s original black prop. Also, the reverse “S” hook eliminated the problem of the rubber knots getting caught on the motor stick due to the original square shaped prop hook.

I had noticed that the Beta tended to spiral dive to the left for the first two circles, then the model would suddenly climb rapidly, indicating a torque roll problem.  Bill had already adjusted the aileron trim tabs with the left wing’s tab down and the right wing’s tab up, and he reduced the amount of left rudder trim tab.  These adjustments helped reduce the model’s tendency to spiral dive to the left, but it did not completely eliminate it.  I suggested to Bill that he try launching the model with a slight right bank and with the motor stick parallel with the ground and this made a huge difference in the Beta’s climb performance.

Bill let me launch the Beta for what would be its last flight of the day, and what a fantastic flight it was.  I launched the Beta with about a 35 to 40 degree right bank angle and the model climbed out at a very steep angle of around 45 degrees and continued to do so until it was well over 250 feet above the ground.  I told Bill that I would buy him a new AMA Beta if it flew away.  I believe the model had hit some light lift, even though it was a cold, overcast and intermittently rainy day.  After the power stopped, the model made a couple of huge circles over the field while slowly descending and landing on the field.  The glide was about as perfect as you could want, and we would have lost the model had the lift been any stronger.

The Beta’s black prop is almost identical to Sig Maufacturing’s 7” red prop shown at left. The recommended Peck 7” prop is shown above at right..

Anyway, if you decide to buy a Beta, replace that lousy black propeller with a Peck 7” prop and use a reverse “S” hook made from 0.039” diameter music wire.  It should be noted that making a reverse “S” hook from 0.039” wire is not easy to do, so an alternative is to make a standard round prop hook, cleaning the hook with lacquer thinner or acetone, adding some J-B Kwik to the round portion of the hook and shaping the J-B Kwik before it fully cures as shown in the illustration below into a kind of “Bowtie” sort of a shape.

J-B Kwikweld shown below can be purchased at most stores. Ace Hardware’s price is $7.59. Lowes has it for $5.38, Home Depot at $5.27 and Walmart comes in at $4.84. Prices taken via the Internet 3/23/2021.

I have used J-B Kwikweld modified round prop hooks on several rubber powered model airplanes with 100 percent success, so I highly recommend this as an alternative to the rather difficult task of bending a reverse “S” hook.

J-B Kwikweld is a 2-part epoxy adhesive that has the viscosity of putty when mixed, so it can be readily shaped as shown.

If the J-B Kwikweld cures before you have finished shaping it, you can peel it off and start all over again with a new batch of it. Or, you can simply blob the J-B Kwikweld onto the round portion of the hook, allow it to fully cure, then carefully carve, sand and/or file the excess J-B Kwikweld to a sort of “Bow Tie” shape shown in the illustration.

After the rubber motor has been wound, the O-ring centers itself on the J-B Kwikweld modified “Bow Tie” shaped prop hook as shown in the photo below:

The Propeller Shafts and the 7″ Silver Peck Prop(s) can all be purchased on the Easy Built Models website. This is the link to their Model Building Supplies Page on their site where they can be found.

Scroll a fourth of the way down on the page and you will see the propellers on the left. Choose the 7” Silver Peck Prop. Order the quantity you think you will need. Scroll down a little further and you will come to the Propeller Shafts with a green background. Choose the Small Shaft, 1 5/8” which is sold as a 6 pack. The diameter of these are 1.0mm which is equivalent to .039 inches. This size will work nicely in the prop shaft holes that the 7” Peck propellers have.

The 3/8″ OD O-Rings shown above can be found at Ace Hardware in the plumbing Dept. Ask an associate where you can find them. Alternatively, see if your model buddies have any spares they are willing to let you have.

An alternate solution to O-Rings can be found if you scroll down slightly until you get to what they call a Rubber Hook. They should work as well as the O-rings as mentioned above and may be just as convent for you to just add a package of these in lieu of searching for the O-rings.

Hint: You can use your finger nails or a staple puller to aid in getting the wires apart in order to put the rubber motor inside the larger loop.

Webmaster’s note:
David Higgins is a regular contributing editor
to our KCFreeFlight.org website.
We appreciate his input.
Kudos Dave!