Basic Aeronautics

[Celwin]

Servo speed is what sells them. When I first started flying, my transmitter came with Hitec HS 300's or HS 311's, I can't remember. They gave 3kg of torque and took 0.19 seconds to travel throw to throw. They were a good servo and were used in all models up to 1/4 scale. Nobody complained about them being too slow, as they were industry standard. Mind you, there was no such thing as flying 3D...

A few years ago I reused some of them. I did notice a hesitant elevator on an Extra 300 but only because I was flying other models with newer servos.

On a trainer and older sport models (Scanners included), most would unlikely notice the difference between a high-spec digital and $12 cheap analog servo. The power of a digital is nice, but something breaks when they hit the ground. Old analog servos lived forever no matter how you land.

My biggest question is, which servo should I buy for a 55 size sport model? Do I invest in a name-brand or go with something cheap from Hobbyking? There wasn't much choice 15 years ago...

[KENNYGLIDE]

Marcel , the Hitech servos with the Karbonite Gears are worth checking out. Around 20 to 30 dollars at last look.....they seem to survive some fairly severe conditions. .....I had HS-485HB ...rudder and elevator....HS-322HD throttle and not sure which ones are in the wings.....could be 422s or something like that...won't know till I take them out of the wings ...I have purchased 12 of these Karbonite geared servos and they all still work.... never had a problem with twitching or stripping and have never noticed them being too slow.

[gbar7217]

Hi Ken, you do give the Hi-Tec servos a good workout, the servos you described are all analog, if you look on your transmitter when you bind it should tell you what rate you are binding to. 11ms or 22ms it can prove fateful if you are using the wrong ms.

[Brian Clarey]

Hi Guys.....Hitec HS 82 MG (metal gear) digital servo`s and similar models have only the output shaft ie. the splined one ....that is metal!! The remainder are constructed plastic . All metal geared units are a lot more expensive than these economy models. I for one was misled until I damaged a servo and disassembled it for examination. Keep this in mind !! I guess the old rule is, you pay for what you get, applies !! Brian C

[Celwin]

I've only ever stripped Hitec nylon gears following a vertical arrival. I have however, stripped nylon gears in mini digital servos (HS82 size) when a control surface has jammed for one reason or another. I've also had Tower Pro digital servos simply stop working on models with petrol engines (throttle servo).

Putting a set of 5 or 6 HS422 or HS485's or better into a model is a fairly sizable investment now, when your hobby is on a strict and monitored budget (monitored by the financial controller and her 4 minions!). It's something I don't look forward to anymore.

[gbar7217]

Hi Guys,
I have been using Tower Pro 966mgs (genuine) for quite a while now with only 1 out of 10 units failing. Digitals are only used at 11ms and analogs at 22ms. I believe the Savox servos are really great but once you get into the top end, you can spend up-to $250 a servo. Spektrum put out a range of 20kg servos(digital) for under $70.
Say for instance you spend $500 on a RTF kit and another $400 on a 20cc petrol motor,then another $200 on servos, then $60 on a receiver, what's the weakest link??

[Celwin]

... my wallet?...

[Brian Clarey]

I thought it might of interest to mention a new topic "Glow Plugs and Fuel". There are more glow plugs available, than the weekend flyer might realise. The subject is interesting, but too lengthy to reprint here. So just an overview will have suffice at this point. Glow plugs come in numerous heat ranges...each one for a specific set of conditions.....Namely fuel type (ie; nitro methane content, compression ratio, ambient temperature etc.) they come in short reach, long reach, idle bar. A range of configurations for individual engine designs ,including spark ignition. It is really worth reading information from websites like One Stop Rc hobbies, is comprehensive for selection and application.
Fuel is a story within itself. Methanol based fuel has the advantage of producing more power and running cooler than motor spirit but at a consumption rate of approximately twice that of petrol. While petrol is more economical for a given fuel allowance in competition, it runs hotter and has a much noisier exhaust note....can be a problem in noise sensitive areas. A lot modelers developed their own brews , subsequently banned because it was considered to be carcinogenic. I know one control line speed enthusiast whose finger nails and cuticles were disfigured due to these bug juices of his own formulas. It came to pass that an extra allowance of fuel was permitted if club fuel was used jn some events.
Brian C

[Celwin]

Dennis and I were talking about glow plugs on the day you posted this Brian. We were talking about how today's plugs don't last like they did 20 years ago. Back then, plugs still worked even if they had been in a model for so long, carbon/gloomp would build up around the plug and surround the hole where the element is. I experience it myself. During the last Scanner race, I was blowing a plug (OS #8 and some Wolf ones) at the conclusion of almost every round. I would land and then the engine would stop. I'd try to re-start for the next race (or to check tuning, as it was off-song due to dying bearings so I was trying to squeeze the most RPM's out of it) and it wouldn't start. Dead plug. The instructions call for A3 plugs or #6 to be used in the 46AX, but a plug is a plug right? Obviously, the 46AX's are a bit particular on plugs.
I found it weird that the plug would blow at low revs or idle every time and not at full throttle. Spark plugs fail at high temperatures, compression and high rpm's from my experience with motorcycles.

We had heard (Dennis and I) that plugs nowadays are only coated in platinum, not solid like they used to be. The Enya plugs are apparently still made of solid platinum, so if you're having problems like me, either use the plug that is recommended or try an Enya.

Brian Winch once wrote about converting glow engines to spark ignition using petrol as the fuel. He claimed that there was little or no difference in power. That was something that I would disagree with (rare occurrence with his articles), as a tinkerer at my last club converted several engines, both small and fuel-guzzling larger Super Tigers. He said that anything under 15cc wasn't worth converting due to the power loss and increased weight.

I wonder if your deformed bug juice friend is still around Brian. Serious affects on the body like that are rarely localised as we reach our senior years.

Thanks for writing this sort of stuff Brian. It is appreciated.

[Brian Clarey]

Propellers.....A silent assassin. This seemingly harmless item is just that ,until it is rotating at around 8 to 10,000 rpm. Any unforeseen flaws within the prop can show up with devastating results. Anyone who has witnessed a prop explode will never forget it !! It happens so fast and without warning. Props should be removed and checked with magnifying glass on a regular basis , especially if it is older and has had a difficult life..... All materials have a finite lifespan . A common practice that I see regularly is for bystanders to stand beside or in front of an aircraft being started and run up. This .action would appear innocent enough till an injury or a death occurs. Another situation that I have witnessed was a four stroke that would backfire on startup or in flight and spit the prop off. I don`t remember the reason now ,as it was many years ago . Brian C