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A servo that is strong on paper can still buzz, overheat or lose a control surface if the linkage between it and the hinge line is sloppy. The servo gets the blame, and the horn screw that was never tightened gets away with it.
This page is built from manufacturer spec sheets, product pages and manuals, checked in October 2026. It is not based on our own bench work, so there are no "this servo survived" stories. Torque and speed numbers are the makers' claims. Where a model was found to be discontinued, the page says so.
The Control Chain
Every surface is moved by the same chain: servo, servo arm, pushrod, control horn, hinge line, surface. Torque is lost or wasted at every link. A flexing pushrod, a loose clevis, a horn mounted on soft foam or a hinge with play all reduce control and can add flutter. Extreme Flight puts the stakes bluntly in its Extra 300 manual: it does not warrant its aircraft against flutter, and it says proper servo selection and linkage setup is essential, because inadequate servos or improper linkages may result in flutter and possibly the complete destruction of the aircraft.
That is the reason to read this page in order: servo first, then everything that connects it to the surface.
Torque: A Sanity Check, Not a Recipe
The torque a servo must supply at the horn is the aerodynamic force on the surface times the horn's distance from the hinge line. Force in ounces times distance in inches gives ounce-inches (oz-in), the unit Hitec and Futaba use. Savox publishes kilogram-centimeters, and one kg-cm is about 13.9 oz-in, so Savox's 3.9 kg-cm at 6V is about 54 oz-in and its 20 kg-cm is about 278 oz-in.
Moving a pushrod to a hole farther from the hinge line raises the torque the servo must supply for the same air load. That is the reason horn position matters as much as the servo choice.
The hard part is the aerodynamic force, which depends on airspeed and surface area, and makers do not publish one number for "a 2 m plane". So this guide does not offer a torque table. The reliable approach is to match what the maker of your model installed:
| Model | Maker's servo choice |
|---|---|
| E-flite Carbon-Z Cessna 150T 2.1m | Six metal-geared servos; the manual lists 26g servos (EFLR7145) on ailerons, rudder and elevator |
| Hangar 9 J-3 Cub 10cc EP PNP | Four metal-geared digital Spektrum A6380 servos |
| Hangar 9 Valiant 20cc EP PNP | Six A6380 servos |
| E-flite Carbon-Z T-28 Trojan 2.0m | Seven metal-geared servos |
| Dynam warbirds (Spitfire, Bf-109, FW-190) | Six 9g micro servos |
| Extreme Flight 78" Extra 300 | Five full-size metal-gear, high-torque servos such as the Savox 1270, plus a throttle servo for gas |
| Seagull Giant P-47 | 10 servos, with a 6 to 9 channel radio |
If you are replacing a servo, start with the original's torque, speed, size and gear type, then step up one class when the surface is large, the plane is fast, or the model flies aggressively.
Servos With Maker Specs
Specs are from Horizon, Futaba and Savox pages, and stock status was checked at the same time.
| Servo | Type | Gear | Torque | Speed (per 60°) | Weight | Status |
|---|---|---|---|---|---|---|
| Hitec HS-65HB | Analog | Karbonite | 22 oz-in at 4.8V, 26 at 6V | 0.16 s / 0.13 s | 11.2 g | In stock |
| Hitec HS-65MG | Analog | Metal | 25 oz-in at 4.8V, about 31 at 6V | 0.14 s / 0.11 s | 11.9 g | In stock |
| Hitec HS-5065MG | Digital | Metal | 25 oz-in at 4.8V, 31 at 6V | 0.14 s / 0.11 s | 11.9 g | In stock |
| Savox SH-0255MG+ | Digital, core motor | Metal | 3.1 kg-cm at 4.8V, 3.9 at 6V | 0.16 s / 0.13 s | 15.8 g | In stock |
| Hitec HS-5245MG | Digital | Metal | 61 oz-in at 4.8V, 76 at 6V | 0.15 s / 0.12 s | 32.0 g | In stock |
| E-flite 26g Digital MG Mini | Digital | Metal | 65 oz-in at 4.8V, 78 at 6V | not listed | 1.09 oz | Backorder |
| Futaba S-U300 | Digital, S.Bus2 capable | Plastic | 44.4 oz-in at 4.8V, 56.9 at 6V | 0.23 s / 0.19 s | 1.26 oz | In stock |
| Hitec HS-645MG | per Horizon | Metal | 107 oz-in at 4.8V, 133 at 6V | 0.24 s / 0.20 s | 55.2 g | In stock |
| Savox SA-1231SG | Digital, coreless | Steel | 28.0 kg-cm at 4.8V, 32.0 at 6V | 0.18 s / 0.14 s | 79.0 g | In stock |
| Savox SA-1256TG+ | Digital, coreless | Titanium | 16.0 kg-cm at 4.8V, 20.0 at 6V | 0.18 s / 0.15 s | 64 g | In stock |
Changes from older recommendations
- Futaba S3003. The long-time standard analog servo is discontinued per Futaba USA. Futaba names the S-U300 as the direct-fit replacement with the same speed and torque figures: 44.4 oz-in at 4.8V and 56.9 oz-in at 6.0V.
- Hitec HS-65HB. Horizon lists 26 oz-in at 6V, lower than the 31 oz-in some older roundups quote. The HS-65MG and HS-5065MG are the 31 oz-in options.
- Savox SA-1256TG. The current version is the SA-1256TG+, with titanium gears, a coreless motor and a 25T spline. Savox says the SA series has minimized backlash for flying surfaces, and the "Plus" series adds Soft Start and Sanwa SSR compatibility.
- E-flite S60 and S75. Both micro servos are discontinued.
Search for the Hitec HS-5245MG on Amazon
Search for the Savox SA-1256TG on Amazon
Search for the Futaba S-U300 on Amazon
Analog and Digital: What the Makers Say
Hitec describes its digital servos as using a digital programmable circuit for greater holding power, resolution and centering, and its listings show tighter deadband numbers: 2 microseconds on the HS-5065MG and 4 microseconds on the HS-5245MG, against 5 microseconds on the analog HS-65HB. A digital servo is not automatically a better choice for a trainer, because a slow foam plane may not need the extra holding power, but fast, large or aerobatic models can benefit from it.
Currents also differ, which matters for the receiver pack or BEC:
| Servo | Idle current | Stall or blocking current |
|---|---|---|
| Hitec HS-65HB (analog) | 7.7 mA | 1,200 mA |
| Hitec HS-5245MG (digital) | 3 mA | 1,200 mA |
| Hitec HS-645MG | 9.1 mA | 2,500 mA |
| Savox SH-0255MG+ | 5 mA | 1400 mA |
| Savox SA-1256TG+ | 5 mA | 5000 mA |
| Savox SA-1231SG | 5 mA | 5300 mA |
With several large servos on one receiver pack, the stall figures add up quickly, and a binding linkage can push a servo toward its stall current. The LiPo battery guide and the motors guide cover the power side, and the flight controller guide explains how stabilized receivers share servo outputs.
On gears, Horizon's HS-65HB listing describes Karbonite gears, which suit light loads, while the metal-gear servos in the table add durability under shock. The Futaba S-U300 is listed with plastic gearing.
Arms, Horns and Throw
Two choices control how a servo feels on the surface: the hole on the servo arm and the hole on the control horn. Use the manual's throw chart as the target, then pick a combination that delivers it mechanically at 100% servo travel.
E-flite's Cessna 150T manual does exactly that: the transmitter chart sets servo travel to 100% and gives deflections in millimeters, measured at the widest point and the root.
| Surface | High rate | Low rate |
|---|---|---|
| Aileron | 30 mm up and down | 25 mm |
| Elevator | 35 mm | 25 mm |
| Rudder | 55 mm | 40 mm |
| Flaps | Half 25 mm, full 50 mm | n/a |
The manual also specifies a flap-to-elevator mix of 14% down elevator at half flap and 24% at full flap, and warns that failing to use it may result in loss of control or a crash.
The Extreme Flight data sheet for its 78" Extra 300 shows the other end of the range: 1.5 in single servo arms on ailerons and elevators and a 3 in double-sided arm on the rudder, with a low rate for aileron of 15-20 degrees and 3D rates of 45-50 degrees on the elevator. Extreme Flight pairs those rates with 15-20% and 60-65% expo respectively, which the dual rates and expo guide explains in more detail.
Reducing travel electronically spreads fewer servo steps over the motion, so set the mechanical geometry first and treat dual rates as the final adjustment.
Control Horns
Du-Bro's T-style nylon horns are 1 1/8 in long with 5 adjustment positions and include self-threading nut plates and 2-56 x 5/8 in screws. A Super Strength T-style horn of the same size is made from a stronger material for sport, scale and high-performance models. Heavy Duty horns and dual horn systems exist for large aircraft.
Mounting matters more than horn choice. The screws pull out of unsupported foam, so use a hard point, and mount the horn directly over the hinge line. Extreme Flight's manual recommends medium CA on high-stress areas such as servo mounting trays, which is a good habit for any build. For a full builder's workflow, see the build from scratch guide.
Search for Du-Bro T-style nylon control horns on Amazon
Pushrods and Connectors
- Threaded rods and Kwik-Links. Du-Bro sells 4-40 threaded rods in a 12 in (305 mm) 6-pack, with 3/4 in (19 mm) of threading on one end, and 2-56 and 2mm rods. Nylon Kwik-Links thread directly onto a 2-56 rod, weigh about 0.5 grams each, and connect to horns or servo arms.
- E/Z connectors. The standard #121 and #605 connectors suit .072 in (2-56) pushrods and include 4-40 x 1/8 in slotted screws, black snap washers and push-on steel washers. Heavy Duty #489 and #490 versions use 4-40 x 3/16 in socket head cap screws.
- Ball links. Du-Bro's E/Z Adjust ball links have a tension screw that sets how tight or free the joint feels.
- Dual arms and pull-pull. Full Dual and Long Dual servo arms exist for cable systems on large aircraft.
Keep pushrods straight and any bends gentle, and use threadlock on connectors that can loosen. The Du-Bro Control Over-Ride Servo Saver is a spring-loaded assembly that absorbs sudden impacts and binding for throttle linkage, nose-wheel steering or control rods, and it comes with light-duty and heavy-duty springs.
Search for Du-Bro E/Z connectors on Amazon
Hinges
Du-Bro's nylon hinges have a locked-in pin and six holes on each side for glue to flow through, in standard and mini sizes. Heavy Duty nylon hinges measure 3/4 in (19 mm) wide by 1-3/8 in (35 mm) long by .040 in (1 mm) thick with a removable 3/64 in (1.2 mm) cotter pin, and Du-Bro targets them at large and high-performance airplanes. The Kwik-Hinge Slotter #216 has 3 slotting blades and 3 snap-on jig guides for cutting hinge slots, and the larger #660 kit has more options.
A loose hinge is a flutter risk, so check hinge play along with horn screws before each session.
Mounting the Servo
Use the grommets, eyelets and screws that came with the servo, and keep the servo from rocking in its tray. Du-Bro sells socket head servo mounting screws (#2 x 7/16 in) and a small servo mounting hardware set. Route pushrods in a straight line from arm to horn at neutral, avoid sharp bends in wire rods, and check full travel for binding before the first flight.
Common Problems
- Soft mounting. Horns on unreinforced foam pull out under load.
- Wrong servo class. Extreme Flight's flutter warning applies to any model, not just aerobatic ones.
- Loose connectors. E/Z connectors and clevises loosen, so use threadlock and check them regularly.
- Binding. A servo pushing against a stuck linkage draws high current, which is why blocking currents in the table matter.
- Electronic throw as the primary adjustment. Set geometry first.
- Skipping the mix. E-flite's flap-elevator mix is not optional on the Cessna 150T.
FAQ
Q: Do trainers need digital servos?
Not necessarily. Many models ship with the servos they need, so a first plane rarely calls for a swap (the best RC planes for beginners guide lists what each model includes). Digital servos add holding power and resolution, which matters more on fast or large aircraft.
Q: Is the Futaba S3003 still available?
Futaba USA lists it as discontinued and names the S-U300 as the direct-fit replacement with the same torque and speed figures.
Q: How much torque is enough?
Start with the maker's installed servo, then size up for larger surfaces or faster flying. The maker's torque figure is for the servo, and the horn position changes how much of it reaches the surface.
Q: How often should linkages be checked?
Before each flight session is a sensible habit, given Extreme Flight's flutter warning: check horn screws, connector tightness, hinge play and pushrod straightness, and look for binding through full travel.
