Original: Tired Old Man

Setting up a gas engine isn't really any more difficult than correctly setting up a glow engine. First order of business is never to build something while subscribing to the law of minimums, which so many of you do. In doing so you assure than the smallest thing can become the weakest link that can take down your plane. That may be battery type or capacity, hardware dimensionality, servo strength, whatever.

Next is to take the time to learn about the products you are using instead of accepting as gospel something you read on the Internet. It was on the Internet and therefore must be true, right? Yea, right. In learning about what you have, want, or plan to use you learn how to install and use it correctly. Learn about servo to throttle lever geometry. Learn about fasteners, connectors, and wire security. Learn about current consumption with the particular products intended for use. Size everything for a minimum of 25% greater than required. 30-50% is better.

For some reason many of you think glow engines are safe while gas engines are not, or that glow engines are safer than gas engines. I cannot understand that way of thinking. I can kill someone with a 1" blade pocket knife or a 16" blade butcher knife. A blade is a blade. People are reacting to gas engines out of fear. Apparently fear of the unknown, with the unknown being their lack of education and familiarity with the product. Others are responding to titillation from advertisers trying to make a buck...off of you.

The simpler the end result the more reliable it will be. Pretty basic thinking but it works. KISS is still a very functional method of doing things. In engineering if it doesn't break it hasn't been loaded enough or doesn't have enough features yet. It really does work that way but that doesn't mean it's right. Ignition kills fail and do so all the time. Failure to program your tx failsafe will bite you in the ***** long before a correctly set up engine will and that has been proven over and over. I've seen it too many times.

Buying more goodies to overcome a deficiency in knowledge and ability will not make anything safer. Just more expensive with a greater propensity for failure. Where is the problem in flying for 20 minutes to run out a gas tank? Worse, why did someone use such large gas tanks unless they originally intended to fly for that long? Didn't they bother to perform ground runs to see how long the tank would take to empty? Using too smAll of an ignition or receiver battery? Another area where the user wasn't very bright or was trying to cut cost corners. You read about them all the time in the 2.4 brown out/lost link threads. <span class="info"> </span>

Original:Tired Old Man 11-9-11 Selection of Gas Model Servos

A good servo is a good servo regardless of gear train composition. The use of metal geared servos is still only a relatively recent event. Say the last 7 years or so. Prior to that all the 35 and 40% planes were being flown at all the high dollar contests like the Tournament of Champions on nylon geared servos such at the JR 8411. Until about two years ago the Comp Arf manuals were still calling for the attachment of their servo arms to the nylon output wheels of high end servos. On a more personal level I generally make it a point to use JR 4711 servos for all my throttles. The 4711 is a nylon gear servo. One other point, many metal gear servos have a nylon idler gear to drive the output shaft from the servo motor, so they are not 100% metal gear.

Your selection of servos should not be based on price. If that is the qualifier for what servo you use in your aircraft you are betting the life of the plane and the safety of everything around when you are flying on the cheapest common denominator. You are effectively telling yourself you cannot afford to be flying the aircraft that you put the servos in. Speed, precision, accuracy, and durability are never found in the bottom dollar servos. My personal tests of the Power HD servos determined they would never find a home in my planes. The good stuff still costs more. Even your previous choice of the HS 645mg leaves a lot to be desired. They are strong enough for most small gassers but a lot of accuracy is left on the table. A lot. Ever wonder why your planes don't seem to the same things the same way every time?

So a good servo does not have to be metal geared but it does need to be accurate and dependable. As noted in the quote from Bliksem, correct set up is also extremely important. I've seen $130.00 servos destroyed on throttles because no attention was paid to linkage geometry. I've also seen servos literally burst into flames because of ganged servo bind. There have been servos that stripped the gears just from the weight of an aileron or elevator flexing during a semi hard landing. So pick a good servo and take the time to learn how to correctly set up linkage through proper geometry. A good nylon geared servo that is correctly set up will still work just fine if you did your job and installed things correctly. Learn to determine what speed and torque will be required in the worst case scenario and plan to meet that condition all the time. You would be surprised to learn how often that worst case condition is achieved and repeated.

Your plane wil only fly as good as the person flying it and the equipment in it. A great pilot can overcome some equipment deficiencies but he will never be able to fly up to his potential. The plane will not let him. An average pilot flying good equipment that is correctly set up becomes a great pilot a lot easier, and faster, when he is not fighting equipment deficiencies. I won't tell you what you should buy because you know what you need better than anyone, but I will say choose wisely and don't use cost as the primary qualifier. Those that do lose more planes and replace a lot of equipment a lot more frequently. <span class="info"> </span>

Original: MTK


BTW- I took last year's tank apart in which I had installed PolyUrethane tubing (Tygothane special formulation for gasoline). on the clunk line, McMaster Carr part #5549K44

As supple and strong as the day of installation. It is a clear tubing but it may come in various colors, I have not checked. Black would be perfect for inside or outside the tank but isn't really a big deal either way

Tubing is 1/8"ID x 1/32" wall, dirt cheap at 30 cents per foot. It comes in 25 foot lengths min plus shipping.

I will fly the same piece of tubing inside the tank this season to see if it will continue to perform as I want

original: Tired Old Man

TWENTYFLIPSTOGETA POP?

20 flips to get a pop when an engine is choked tells me there are one or more things wrong with the set up. The first would be verification the choke plate is fully closed. The second would be the geometery of the throttle linkage arrangement. A third would be the positioning of the throttle stick and trim tab. That also takes things back to linkage. A fourth would be a leak in the plumbing, inside or outside of the tank. A fifth would be concerning the pulse port. Lastly would be the pump diaphragm and condition of the check valve flaps.

If the choke is fully closed with correct length linkage, with the linkage installed at the correct positions on the throttle servo and carb throttle lever, The throttle stick should fully close the throttle plate with the trim tab in the full closed position. Without moving the throttle stick, the trim tab should be able to open the throttle plate a good 1/8" open with only 1/2 to 3/4 rotation of the trim tab. If that's not happening the linkage set up is fooked up. The engine should be able to start and shut down using only the trim tab with the throttle stick at full close. If the throttle plate is not opening no fuel gets into the engine, ergo, a lot of flips to get a pop.

MOST people screw up the throttle linkage on a gas engine. I see it so often is grants me the ability to say "most". They relate linkage installation to what is done on a glow engine where a rod is slid into a throttle lever EZ connector, connect the other end to another EZ connector or clevis on the throttle servo, with the servo motion dialed back or forward to achieve rotational distances with travel adjust. Even a method similar to that assures absolutely horrid gas throttle response, along with lots of potential starting issues.

THROTTLELINKAGE

Linkage installation on a gas engine starts with the throttle stick and trim tab in their fully closed positions, the throttle servo and carb lever at their mid travel point positions, travel adjusts at 100%, and no other mixes or trims in that channel of the radio. From that point you establish linkage lengths based on attachment at the innermost point available at the servo, and outermost point available at the carb lever. You want maximum servo rotation to provide minimum lever movement, with minimal carb lever movement providing maximum travel motion. The carb end requires very little servo throw to achieve stop to stop travel so you dial down travel at the servo end by using inside attachment points. You do not dial down servo travel by using travel adjust when it can be avoided. That travel is your resolution, and without good resolution you have really bad throttle control. You see it all the time with people coming up with a multitude of ways to build throttle mixes to smooth out throttle response. That's too much work and takes too long to get right for me. The other side of that is seeing people with throttle servos that are binding up at both ends of travel.

It's quite acceptable to make new holes on the servo arm inside of those provided by the manufacturer. Those that do experience immediate benefits. <span class="info"> </span>

Original:Tired Old Man 8-24-11
Gasser Throttle Linkage Installation and Set Up

Servo selection:

Use a standard sized servo. That's the initial basis of a good throttle servo. If you want precision, speed, and accurate throttle position every time, use a good coreless or digital servo. If you don't care about a wandering throttle position or difficulty in establishing a consistent idle, an analog servo will do. Servo quality is predicated on the choice of manufacturer and price. The low end servos provide low end performance and a lot of frustration. They don't center well, if at all, and rarely hit the same position for the same stick input twice in a row. You will be the one to decide what you prefer. Servo torque should be a minimum of 48 ounce inches. There is no maximum but 48 to 50 oz. in. is plenty for any throttle servo. Micro servos are a very bad idea. The Hitec hs225mg is as small as I would ever consider for a throttle servo. Metal gears generally last longer than nylon gears, and carbonite gears are noted for breaking when used with a gas engine. Nothing lasts forever. That should be enough for you to make a servo decision.

To start a linkage installation, set both the throttle servo and the carb lever to 50% positions. So the carb is opened up half way and the servo is at midpoint. Use a clamp or other means to secure the carb lever in position. Remove and discard the idle stop screw that may be installed on the carb when new. That's used for yard equipment that are normally operated at two speeds, idle and wide open throttle. Hopefully you use a wider range of throttle positions than just those

DO NOT remove or disconnect the throttle return spring. It's on there for several reasons, all of them good for what you want to use the carb for. If you are using a servo of a size suitable to be a throttle servo you will never have a problem because of that spring. If you are using a servo unsuitable for a throttle servo all the problems you will have were self-induced. You know how to fix that. Get a more appropriate servo.

Before going any further determine that travel adjust for the throttle servo is set at 100% both directions, no trims have been input, idle trim tab on the transmitter is fully closed, no mixes are in the radio, no rates have been set, and use the shortest servo arm that came with the servo. You will use the innermost hole on the arm. You may find you will want to make a hole inside of that one for best resolution. You will want maximum servo throw to provide minimal linkage travel. That doesn't make sense now but it will later.

Measure the distance between the servo arm and the carb lever hole. That's your beginning linkage length. Make the linkage and install using your favorite and safe attachment method at both ends. I'll suggest that at least one end be a bolt on ball link, that no pinned clevises be used, and if a pinned clevis is used it will be a metal pin with a secondary method of securing the clevis. 4-40 ball links can be a pain because of size and screw heads. Dubro makes a 2-56 bolt on ball link for 4-40 threaded rod. I'll let you look up the part number No metal to metal contact is ever allowed, although it's perfectly acceptable to use a metal or carbon throttle rod as long as it's electrically isolated from any metal levers or servo arms with something like a ball link. Zee bends in a metal rod connected to the carb lever will be a disaster. Don't do that.

Hopefully the carb lever is at least 1" long. you may have to change or modify the throttle lever at the carb. There are bolt on products available to complete that task. It's better if it's 1-1/4" or so because you want use an outer hole (farther from the throttle plate rod center) to obtain maximum throw at the carb end. You want an installation where the servo moves a lot to move the throttle plate a little, with the total rotation of the servo being enough to obtain full range of motion at the carb. The short servo arm with the long carb arm helps you do that. That's resolution of the finest kind since it does not require mixing and expos. Starting to make a little sense now?

If using a decent servo you can check the amount of throw from one end to the other and how that impacts the carb lever without powering up the radio. You should be pretty close and need only to increase or decrease servo travel a few percentage points to go from full closed to full open. If it requires that you adjust travels more than about 15% in either direction move the attachment point at the carb lever in or out on the lever to determine the effects. The linkage may still be a little too long or short. Also work with adjusting the ball link/clevis in or out a little bit. This is where making a new hole on the inside of the servo arm becomes helpful.

Ultimately you want the throttle plate to achieve a fully closed position with the throttle stick full back and the trim tab full down. THIS is the absolutely correct throttle stop/engine shut off position of the carb throttle plate because it provides full control of the throttle for idle trim and engine shut down. It also makes establishing your idle positin extremely easy. Closing the plate will cut the engine every time. The trim tab will be what you will use to set idle throttle position. You can play with transmitter multiple idle positions later for those that like the idea of high and low idles. I don't but some do. if you let the engine warm up before setting the idle it will likely be the same when you land as it did when you took off. That's another subject of its own.

You do not want the servo or the carb level to EVER hit a hard stop at either end. The carb will be providing the engine the ability to make 100% power long befere the throttle plate is fully open. The throttle plate does little for power/RPM after it passes somewhere between 75% and 80% open. That has to do with the plate and rod dimensions/geometry and it's impact on throttle fraction area. Don't worry about this because I'm certainly not going to write all that is required to define it all.

If your servo is moving a little and the carb lever is moving a lot, the linkage geometery and installion is totally wrong. You will always have trouble with throttle sensitivity when things work that way. You want a little servo travel to make a little carb lever motion, and to be able to use 100% of the servo travel to achieve 95%-100% of the carb lever movement without hitting stops. It's ok to use 100% or a little more or less of the servo travel, but it is never ok to introduce so much travel or linkage so long that any bind will be present. That kills servos in a big hurry, and drains flight batteries.

Hopefully the above will get you off to a good start and make throttle linkage on a gasser a bit easier for you to set up. Copy and past this post into a Word or text document on your computer for future reference. I did <span class="info">