Hi Everyone,

Been flying foamy RTF's for the past year. Into my first build, the Falcon 120. I am purchasing my servo's. Can anyone please explain the difference between the Servo J and the Servo U. Any help is much appreciated.

Thanks,

Umm... servo J? Servo U?
Please clarify. Who makes them? What are the servo model numbers?

Go to a website that sells servos (e.g. Tower Hobbies). Go to HiTek and search for the HS 225MG. You are offered that servo with two options: 1) Servo J and 2) Servo U. I'm pretty sure it has to do with the connection, and that Servo "U" stand for universal, but I'm not sure.

Thanks,

that would be the connector with out the futaba tab. CG I run across the driveway and flew my little park flyer for a few minutes. Only problem when when I landed I had to fight knee high snow to get to it. I have a 60 acre hay field at the end of the drive.

Folks are confusing this a bit. It's super simple.

"J" connectors are the type used by Futaba. "U" connectors are "universal," used by most everyone else. Js have a little plastic alignment tab on them. Us don't have the tab. Js can be made to fit most any receiver by cutting off the plastic tab. Us will work with most any receiver out of the box.

If you've got Futaba receivers, buy either the J or the U. Either will work well for you, and it's just your personal preference as to what you buy. If you have a receiver other than Futaba, I would suggest buying the U connectors. Why buy J connectors if you're just going to have to cut the tabs off of them?

I was thinking of going over to the local parking lot and giving the Diablo a try. I might do that if the wind isn't to bad. Only problem is that it does not have that much power, (thrust out of that ducted fan) and it may be hard to hand launch.

CGr.

w8ye hit it:

J=Futaba "J" Connector

U = Universal connector

That's a bit better description than your original post. I'll take a look and see what it is you are referring to.

CGr.

I'm not confusing anything, Mike. I've never heard of "servo J" and "servo U". But, live and learn.

CGr.

Give it that old college throw from left field to home plate. That sucker will fly. Good luck, let me know how it went. You are using the trainer setup?

From Tower Hobbies. Pretty much spells it out for THAT servo.

College throw? Ooooh kay!!!

And, yeah, I'm using the trainer setup. Mike is going to send me the dual motor setup, I have the "performance" wing setup still in the box. I don't think it has enough ummph to pull ( push??? ) that heavy thing around with the brushed motor it comes with. I gotta figure out how to swap out the motors. I have a brushless in-runner somewhere around here.

CGr

Oh I see, Mikey likes you better than me. Mom always did like Mikey better

Thanks everyone for the conformation on Servo "J" as opposed to Servo "U". I am going to purchase Futaba's new 10C transmitter, but who knows if it will ever break down so I think I'll go with the "U" version for the servo set-up on the Falcon 120. There are a couple of excellent build threads on the Falcon, but I figured I'd add my to the mix. Keep an eye out over the next few weeks. Still deciding on the prop jet set-up vs the turbine. Can't really afford the turbine for a few months (espescially in this economy), so trying to decide on an engine. I would imagine that for the Falcon 120, and limited prop length, a high RPM engine would be the best, something like the OS 91FX. It's only .9, but puts out 15,000 rpm at max. Any thoughts???
Thanks,

15,000 RPM on a 91FX? 'Fraid not. I have no idea what a Falcon 120 is, but you're not going to get that RPM out of that engine. If you want a .91 size 2-stroke that'll hit that sort of high RPM, be prepared to shell out for a Jett. Never take specs from mainstream manufacturers at face value. If you want to see some realistic, actual figures have a look at the Tachometer Readings forum.

Ok Mike, thanks. The Falcon 120 is a very popular ARF distributed by two companies (that I'm aware of); NitroPlanes and RaidenTec. The plane was designed as a prop jet, but has experienced a large interest in all types of power plants (Prop, EDF, and Turbine). It has become known throughout the industry as a great starter jet for those of us that are not too familiar with an aircraft capable of nearly all flight mechanisms (e.g. flaps, alerions, rudder, and elevator). It's even a great jet for experienced pilots. Check it out on YouTube. Thanks for you help.
Regards,
Steven

The specs for the OS .91 show:

SPECS: Displacement: 14.95cc (0.912 cu in)
RPM range: 2,000 - 16,000
Bore: 27.7mm (1.090")
Stroke: 24.8mm (0.976")
Compression Ratio: 10.1 : 1
Weight: 550g (19.42oz) 24.3oz w/muffler
Horsepower: 2.8 BHP at 15,000 RPM

This is a theoretical horsepower IF that engine reached that RPM. Attempts to reach that RPM with that engine will end up with a pile of aluminum and steel dust.

CGr.

Don't confuse peak torque rpm with peak horsepower. At 15K, 2.8 hp is most likely correct for the .91 (That is really not very much for a 2cycle engine).

However, you would never prop for 15K on the ground, because engines unload in the air. Depending on airframe drag, and the engine exhaust system you would target 13K as a proper load in a speed application.

But for sport models where vertical performance is also important, I find that going with the greatest diameter prop for a given pitch that will allow enough speed for good knife edge flight gives the best of both worlds.

Also as a practical matter, if you are turning a 13 inch diameter prop above 12,000 on the ground, you will have complaints about noise.