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E-PROPS : Carbon Spacers

In leisure aviation, there are not large series as in the automotive industry. Aircraft manufacturers are used to change somes details on their aircraft, and particularly engines covers. Sometimes the engines come outside the covers, and sometimes are inside. It depends on the versions, and it is difficult for propellers manufacturers to know all versions of all aircraft.

Usually propellers manufacturers propose aluminium spacers if the engine is inside the engine covers, in order to space the propellers from the engine fairings.
But aluminium spacers are heavy, expensive and difficult to assemble (with many screws and bolts).

E-PROPS has developed an exclusive system to replace the usual aluminium spacers : THE CARBON SPACERS.

Advantages :
✗  The E-PROPS spacers are ultra-light (13 times lighter than an aluminum spacer).
✗  The "E-PROPS spacer" option is free of charge, regardless of the chosen length.
✗  E-PROPS spacers are extremely easy to install (no unnecessary screws and bolts, thus avoiding vibrations).
✗  Orders are facilitated by the interactive drawings published by E-PROPS.

carbon aluminium spacers
E-PROPS Carbon Spacers / Standard Aluminium Spacers

There are 2 types of extended hubs, depending on the range of propellers concerned: V12 or V20.

1- Carbon Spacers V20 range
2- Extended hubs V12 range
3- Does your aircraft need an extended hub / spacer ?
4- Length of extended hubs / spacers : measures

1- Carbon Spacers V20 range

The hubs of the E-PROPS ground adjustable pitch propellers are simple and light.
They are in 3 parts:
✗  Two flat carbon parts in which the blade feet are positioned, called HHU1 and HHU2.
✗  A carbon spacer that allows the propeller to be fixed to the engine, called ESU, which has a variable length according to the customer's wishes.

the E-PROPS hub + spacer, an exclusive ultra-light system

The length of the E-PROPS spacer depends on the position of the engine cover and spinner. The interactive diagram below allows to visualize the solutions.
Please note: the measurements of E-Props spacers are not the same as those of other brands of propellers. Please take the measurements using the interactive diagrams and videos.

1 - Choose the spinner diameter (if desired) / 15 available diameters :

2 - Choose the length of the spacer / 38 available lengths :

3 -Choosing a drilling adapter :

NOTE: the spacer length selected does not keep into account the additional thickness of our drilling adaptors, might one of those be necessary to mount the propeller on your engine. Please remove the adaptor's thickness from the selected spacer's length in order to obtain the wished final distance between our spinner plate and the engine's cowling.

E-PROPS hubs
38 different lengths: from -20 to +170 mm in steps of 5 mm

the E-PROPS hub, an exclusive ultra-light system


✗  Mass gain
Mass in grams of the E-PROPS carbon spacer V20 range = only 1.5 g/mm, including screws and bolts
. This is to be compared to the 20 g/mm of an aluminium spacer with screws and bolts.
Example for the extension of a 120 mm on the Savannah ultralight :
- mass of the carbon spacer = 120 mm x 1.5 g/mm = 0.180 kg
- mass of an aluminium spacer = 120 mm x 20 g/mm = 2.4 kg
=> a gain of 2.2 kg only on the Savannah's extension function!

✗  Money saving
E-Props extended hubs are at the same price as standard hubs. So there is no need to buy an extra spacer.
For example, an aluminium spacer for Savannah (120 mm) can cost up to 300 EUR...
=> a nice money-saving for E-PROPS customers.

✗  Exist in 38 lengths
E-PROPS has developed an automatic machine that takes out the spacers at the desired length.
The E-PROPS V20 carbon spacer system is available in 38 lengths, from -20 to +170 mm, in 5 mm steps. This ensures that you will find exactly the right length for your assembly.

✗  Gerabox protection
If too much mass is attached to the gearbox unit, its service life is significantly reduced. Heavy propellers create a high risk of breakage of the gearbox unit.
Reducing the mass of the spacer limits this risk.
ROTAX does not recommend the use of propeller extensions longer than 120 mm.
This of course applies to aluminium spacers, as the weight of the spacer (more than 2 kg) would then be too high for the gearbox.
E-PROPS, with its ultra-light carbon spacers (example: the 170 mm spacer weighs only 255 g), allows solutions to keep the propeller away from the engine fairings up to 170 mm, without risk to the gearbox.

✗  Reduction of vibrations
The propeller is directly centred by the hub. This avoids spacer stacks and the various screws and pins, which often generate vibrations.
A simple and straightforward system like E-PROPS greatly reduces the risk of vibration.

✗  A reliable and durable system
E-PROPS hubs, whether standard or with spacer, are extremely strong.
Material: 100% carbon + high temperature epoxy resin
Injection according to the RTM (Resin Transfer Molding) process
Compact volume hub: for minimum drag and optimised engine cooling
MTBO 2,000 hours / Unlimited potential

✗  Simple assembly
The E-PROPS spacer allows quick and easy assembly, with the minimum number of parts. The centering pins, mandatory on ROTAX 9 series engines, are integrated in the carbon part, whereas they have to be added on the aluminum spacers (weight of the 6 Rotax pins = 125 g).

E-PROPS spacers
comparative : carbon spacer / aluminium spacer

click on the video to discover the E-PROPS V20 carbon hubs & spacers

2- Extended hubs V12 range

=> In January 2020, E-PROPS has stopped manufacturing V12 hubs. They have been replaced by the V20 hubs (evolution of the range).

Extended hubs V12 range were made of 1 piece integrated with the hub.
Here is a presentation of these hubs:

presentation video


- Weight reduction
weight of the V12 spacer (carbon extended hub) = 3.5 gram * Se in mm (including screws)
it means 3.5 gr/mm
To be compare with 20 gr/mm of a usual aluminium spacer (with screws)
Example for the spacer of a Savannah ultralight :
- weight of an E-PROPS extended carbon hub, length 120 mm (including screws) = 0,42 kg
- weight of an usual aluminium spacer, length 120 mm (including screws) = 2,4 kg
it means a reduction of 2 kg !

- Less weight on the gear box
A too big weight hanged to the gear box is reducing its lifetime.
The heavy propellers generate a significant risk of breakage of the gear box.
Reducing the weight of the spacer allows to limit this risk.

- Lower cost
The extended hubs are at the same price as the standard hubs.
No need to buy a spacer in addition. Considerable savings !

- Less vibrations
With an extended hub, the propeller centering is direct. No need of spacers and screws stacks, which can generate vibrations.
A very simple system strongly reduces vibrations risks.

- A reliable and durable system
The E-PROPS hubs, standard or extended, are extremely strong.
Material : 100% carbon + epoxy resin high T°
Injection with RTM process (Resin Transfer Molding)
Compact hub for minimum drag and to optimize engine's cooling.
No life limitation. Recommended major periodic inspection : 2.000 hrs

- Simple assembly and reduction of the parts number

E-PROPS hubs

A : 6 Screws + 1 central nut (for the central screw of the hub)
B : 7 Nord-Lock washers
C : Flange in anodized aluminium
D : Upper Half Hub
E : Lower extended Half Hub
F : Option : 5mm counterplate to adjust the length of the hub (a 5 mm step)
G : Reducer flange (part of the engine)
H : 6 Rotax drive lugs (threaded)

3-blade propeller with extended hub : 3 blades, 2 half hubs, 1 aluminium flange, 7 Nord-Lock washers, 6 screws, 1 nut
=> It means 20 parts
3-blade propeller with aluminium spacer : 3 blades, 2 half hubs, 1 aluminium flange, 7 washers, 6 screws, 1 nut , 1 aluminium spacer, 6 drive lugs for spacer, 6 washers, 6 nuts, 6 screws and 6 washers for spacer.
=> It means 51 parts
The "Extended Hub" solution allows to reduce of 61% the number of parts necessary for the propeller's assembly.

E-PROPS hubs
hub with integrated spacer 115 mm (for Savannah, for example)
and on the right with a 250 mm spinner

E-PROPS hubs
extended hub on a ROTAX's reducer with a spinner

Lengths available : from 0 to 115 mm, on 5 mm increments

E-PROPS hubs
some examples of E-Props extended hubs

3- Does your aircraft need an extended hub ?

Sometimes it is necessary to have a spacer between the propeller and the reducer flange, whan the engine is far inside the engine cover.

It exists 3 configurations :

A) the gearbox flange is outside the engine cover
=> you don't need any spacer. Please indicate He = 0 in your order.

B) the gearbox flange is just at the edge of the engine cover
=> you don't need any spacer. A 5 mm spacer or 5 mm more on the ESU is usually enough to space the propeller from the engine cover.
Pictures of your present propeller assembly, taken above the engine and from the side, could help the E-PROPS team to see if a 5 mm spacer is necessary.

C) the gearbox flange is inside the engine cover
=> you need a spacer. An extended hub or a spacer as proposed by E-PROPS are very good solution : light, strong and cheap.
To know which length you need, please see § 4.

4- Length of extended hub and spinners : measures

If the gearbox flange is inside the engine cover and if you need a spacer :
the measurement of the desired spacer length [He] is very simple.

Measure M as shown in the picture below: between the gearbox flange (on which the propeller will be mounted) and the outer edge of the engine fairing.
Then add 5 to 10 mm to this measurement M to define the spacer length required for your aircraft (called He).
5 mm or 10 mm: it depends on whether you prefer to have the propeller close to the fairing or a little further away.
Be careful to see if it also passes at the lower fairing and plan for the removal of the fairings.

[He] = measure M + 5 or 10 mm

E-PROPS spacer measure

E-PROPS hubs

In case of mistake on the measure : we can change the extended part of the hub.
Please indicate the length you want.
- on range V20, we send the good spacer
- on range V12, we change the extended hub, and we balance the propeller again with the new extended hub (please send the whole propeller back to us)

NEVER cut an E-PROPS extended hub.

The extended hubs are designed and manufactured for a defined length. Cut them is similar to destroy the mechanical strength of the hub. This would be very dangereous.
It is absolutely FORBIDDEN to fly with an E-PROPS extended hub which would have been cutted.

If you do not have the right spacer length, please contact our team to find a solution.

E-PROPS hubs
V20 spacer - length 40 mm

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E-PROPS 712 Photos
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195, Route de l'Aviation
ZI Aérodrome de Sisteron
04200 VAUMEILH - France
Phone : +33 4 92 34 00 00
Phone reception opened from Monday to Friday
From 10 to 12 a.m and 2 to 4 p.m
The best way to reach us is by email :