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Prop. for Direct Drive Engines

E-PROPS : Carbon ESU 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 very heavy (20 g/mm - for example a spacer length 120 mm weights 2,4 kg), difficult to assemble (with many screws and bolts), and expensive.

E-PROPS has developed an exclusive system to replace the usual aluminium spacers : THE CARBON ESU SPACERS :
✗  The E-PROPS ESU spacers are ultra-light (13 times lighter : 1,5 g/mm instead of 20 g/mm for an aluminum spacer).
✗  The "E-PROPS ESU spacer" option is free of charge, regardless of the chosen length.
✗  E-PROPS ESU spacers are a part of the hub, 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 (1,5 g/mm)   /   Standard Aluminium Spacers (20 g /mm)
E-PROPS spacer : 13 times lighter !

1- ESU Spacers V20 range
2- Does your aircraft need a ESU spacer ?
3- Spacer Length : measure to take
4- You want to change of ESU Spacer ?
5- The advantages of carbon ESU spacers
6- Extended hubs V12 range (2012-2019 / no more produced)

1- 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

Please note: The length of the E-PROPS spacer depends on the position of the engine cover and spinner.
The measurement of the E-Props spacers are not the same as the aluminum spacers on other brands of propellers.
The position of the spinner is also different.
Therefore it is necessary to take the measurements as indicated by E-PROPS.

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

E-Props spacer mounted on the Rotax gearbox flange

2- Does your aircraft need a spacer ?

Depending on the aircraft, there are 3 configurations:

A) The gearbox flange reaches the edge of the engine cover
=> you don't need a spacer. To facilitate the assembly and disassembly of the covers, 5 mm can be added to the spacer. See the interactive diagram in the following paragraph.

the flange of the Rotax gearbox is at the edge of the engine cover

B) The gearbox flange is inside the engine cover
=> a spacer is essential. An extended hub or E-PROPS spacer is an excellent solution: lightweight, very strong and economical.
To know which length to choose, see the interactive diagram in the following paragraph

the gearbox flange is inside the engine cover

C) The gearbox flange comes out of the engine cover
=> you don't need any spacer
If your gearbox flange comes out from the engine cover a lot, the E-Props system allows you to shift the spinner backwards, up tto 20 mm. See the interactive diagram in the next paragraph.

the flange of the Rotax gearbox comes out of the engine cover by 20 mm - the cover can go back

3- Spacer Length : measure to take

=> WARNING : please take the measure using the INTERACTIVE DIAGRAM and the VIDEO.
        Taking the good length of the spacer when ordering avoids having to make an exchange.
        Of course it is possible to exchange the spacer once the propeller is received, but this takes time and is expensive.
        See here : ESU EXCHANGE / E-Props V20 Carbon Spacer


1 - Choose the diameter of your spinner :

2 - Choose the length of your spacer :

3 -Choose a drilling adapter :


tutorial to measure propeller spacer & spinner
Measure spacer & spinner, it's easy !


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

E-PROPS mesure

E-PROPS mesure

4- You want to change your ESU Spacer ?

It's easy. Two solutions :
1- Order a new ESU Spacer. Cliquez ici : Carbon ESU Spacer
2- Exchange your Carbon ESU Spacer. Cliquez ici : Exchange : Carbon ESU Spacer

E-PROPS mesure        E-PROPS mesure

5- The advantages of carbon ESU spacers


✗  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.

✗  Gearbox 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
TBO 2,000 hours

✗  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 integrated drive lugs
E-Props integrated drive lugs

E-PROPS spacers
comparative : carbon spacer / aluminium spacer

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

NEVER cut an E-PROPS ESU Spacer.
The ESU spacer are designed and manufactured for a defined length. Cut them is similar to destroy the mechanical strength of the ESU spacer. This would be very dangereous.
It is absolutely FORBIDDEN to fly with an E-PROPS ESU spacer which would have been cutted.

E-PROPS hubs
V20 spacer - length 40 mm

6- Extended Hubs V12 range (2012-2019 / no more produced)

=> In December 2019, E-PROPS has stopped manufacturing V12 hubs.
They have been replaced by the V20 hubs. We have no more V12 hubs in stock.
It is an evolution of the range. The V20 hub is faster to manufacture, allows a pitch adjustment easier to realize, and makes the propeller gain 500g.

=> Description here : EXTENDED HUBS V12 range

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