throttle muffler on a baby bee

[sebastian]

Heloo everybody. I´m new here.
I have a baby bee, and want to make a throttle muffler, like the dragonlfy, so i can have a 1/2A trainer, with throttle control instead of all the way until the gas goes down.

The data that i´ll need is the area of the hole that i have to make on the engine at full throttle. From there on, i more or less know what should i do.

The muffler that i currently have is the one that came on the baby bees with the U/C EZ flyers, it deviates all the exhaust to a little hole on the right side. I guess that enlarging the hole will do the work. Then I´ll make a little metal piece to cover that hole in a progressive movement done with the servo. Well, maybe i explained it too complicated. In fact it´s very simple, i just need to know the size of the hole!

Although i have to mention that i´m from argentina, and as you know situation here is pretty shaken. That´s why o don´t buy another engine, and ai try to do the best from mine.

Thanks in advance, any input will be helpful!!

Sebastian, from Buenos Aires, Argentina

[Dave Robelen]

Hello sebastian,
The good news is that the opening for full throttle is not critical at all. The most effective 1/2A throttles have an opening that is tapered toward the rear. A slot is cut in the exhaust stack, and the servo is set up to move a thin blade of metal in the slot. The reason for the taper is to give a more proportional throttle effect. Almost all of the change in RPM comes from a very small change in the nearly closed opening. Another effective method is to bend a sheet metal strap around the cylinder, with tabs facing each other. This is set up to rotate around the exhaust port area. A small slot in the metal that overlaps the exhaust port serves the throttle action nicely.
Take care, dave

[sebastian]

Thenk you Dave for answering my question!

i´m a little confused. Do you mean that i make a triangular slot on the wall of the muffler? I´m sending you a drawing (pretty basic) of the muffler that i have, and please, could you draw there the shape of the slot?

I understand by taper a triangular slot, but i´m not sure if you mean the same thing that i understand.

And another question. Which is better, the hole on the muffler or the metal sheet bended around the cylinder, with the slots cutted on it?

And what do you think of the nick ziroli mini sukhoi (I can get the plans and then make it from scratch) with this engine? is too much plane? should i do some modification on the plane to make it adequate for this plane? I´m looking for a semi aerobatic trainer for 1/2 A that have also a slow speed landing.

If not, can you recommend me something?

Thank you Dave!!
Sebastian

[Dave Robelen]

Hello Sebastian,
Personally, I am fond of the strap that wraps around the ports with a tapered slot for throttling. These are easy to make, and if you do not like the way it is working, try another. That question about the Mini Sukhoi is a tough one. I believe the model would be a bit "hot" to be classed as an advanced trainer. There is a design of mine called the Mini Kaos that Model Airplane News sells plans for. This is a 4-channel low wing 1/2A with a tricycle landing gear. With your engine it would be plenty gentle, yet resonsive enough for fun. Unfortunately, there are fewer choices with the 1/2A models, because not many have been published in recent times.
Take care, dave