3 different importers have reported in separate occasions that the bolt tensile used by the DUC Helices company was not of the appropriate grade for aviation use: The NZ importer for Xenon gyrocopters, the NZ importer for CZAW, the NZ importer and licensed repair centre for Rotax. Colin Alexandre, licensed aircraft engineer and importer for Rotax in NZ states: “They are grade 12.9 socket head cap screws. It is common knowledge in aviation that this grade of material can lead to premature failure on propellers and engine mounts as well as places subject to fatigue through harmonics. They are simply too brittle. A grade 10.8 or 8.8 is most desirable as you will already be aware that aviation bolts are definitely not 12.9”
We subsequently referred the matter to the DUC Helices Company and asked them to supply the propellers with bolts and nuts of aviation grade. Each time, DUC Helices dismissed our request by simply answering that if the customers weren’t using the supplied bolts and nuts the structural guarantee would be void. On that topic, Colin Alexandre said: “...This change is as a result of experience and in fact I have failed bolts in my possession. It is my understanding that in an application where the bolt is not designed to stretch, if you torque a bolt clamping two surfaces together ata certain torque value; the clamping force will be identical regardless of the grade of bolt and therefore should not have any influence on the warranty of the prop. I am interested in your reply.”
The DUC Helices company answered: “Toutes nos vis qui maintiennent les moyeux sur les porte-hélices sont de classe 12.9. C'est la classe qui offre la meilleure résistance. Toute une campagne d'essais avait été réalisée pour définir la classe la plus adaptée à notre application. Il en est ressorti que c'est la classe 12.9. Toutes ces vis ont un revêtement dacromet : c'est le seul revêtement qui n'abîme pas la dureté de la vis, comme peut le faire un revêtement zinguage ou bi-chromatage.
Ces 6 vis qui maintiennent l'hélice sur le porte-hélice travaillent en cisaillement. Par contre, les 6 vis du pourtour du moyeu sont en classe 8.8 et celles-ci peuvent être zinguées ou bi-chromatées (elles ne travaillent pas en cisaillement mais uniquement en traction). Cette classe est donc suffisante"
This didn’t resolve the case for our customers as the use of 12.9 grade bolts is not allowed by their Aviation Authority. Therefore customers couldn’t use the bolts and nuts supplied by the DUC Helices Company. Subsequently, the matter was referred to the NZ Aviation Authority who answered:
“Re 12.9 Bolts
Attached is a general comment re aircraft bolts (the article from EAA about bolts and nuts was attached as a PDF. A transcription is available on our website in the knowledge category. Read the article in a new page)
Further to this;

Note: Rotax specify grade 10.9 bolts for engine mounts, equivalent of an aircraft AN bolt.  Most European sport aircraft use 8.8 bolts for propeller assembly and mount.
Regards
Tony Hansen
Inspector, Sport & Rec”
Conclusion: If you intend to buy a DUC propeller, we advise that you check with your Aviation Authority if 12.9 grade bolts and nuts are allowed for propeller attachment. If not, you’ll find yourself between a rock and a hard place: either you use the bolts and nuts supplied by the DUC Helices company, and then you breach your Aviation Authority requirements, or you use other bolts and nuts and you void the guarantee of your propeller.

Many customers around the world have reported delaminating of the inconel leading edge. In some cases, the delaminating has lead to forced landings. These delaminating have always occurred before the 800h life limit of the blades but after the 6 months structural guarantee. Note: if you are a customer of Love4aviation, your structural guarantee is 6 years from date of purchase.

Quote: "In reference to the propeller that was bought on the 04 May 2009 and shipped to us on the 22 May 2009. I would like to point out that the manufacturer’s terms and conditions of trade was giving us a 6 year structural guarantee, we now have the stainless insert delaminating on two blades……pictures attached. Furthermore this prop is well inside the 6 year period of your guarantee so I expect your company will send out replacement blades seeing that you have international standards in place and I have a 6 year guarantee. What we found was a serious flight safety hazard in a pre-flight that would have lead very easily to an in-flight separation of the stainless steel leading edges forcing a pilot to carry out an emergency landing with all the risks associated. It is our duty as a professional flight training organization to report these issues to the Civil Aviation Authority and also to RA-Aus the body that regulates Light Sport Aircraft in Australia. Because of this unforeseeable issue our aircraft is now grounded and it now results in financial prejudice as we have had to cancel business until further notice. Unless you can supply us 3 replacement blades ASAP we will have to consider legal action against the manufacturer to recover the loss, in any case we will wait to see what the manufacturer is going to do about it before deciding if it is appropriate to send a warning message to the Australian industry about the risk associated with dealing with this manufacturer that claims International Standards. We have informed Fly Synthesis the importer about this, and we are waiting an explanation from Fly Synthesis as to how on earth they have certified this propeller to be used on their range of aircraft. We will keep away from the media for the next 14 days awaiting reply."

Conclusion: The design or manufacturing process of the DUC propellers is questionable. We recommend you check very often the condition of the inconel leading edge. If a delaminating appears, the aircraft should not fly as an in-flight breakage of the propeller is likely to occur soon after.

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A customer has reported a partial delaminating of a blade tip probably due to a manufacturing flaw (air bubble in the resin).
Quote: “Please find attached photos of the prop as delivered with a small hole in the tip then a photo after 8.5 hour running with the tip partially delaminated. There is no damage to the props second blade, nor any impact marks from debris. I fly from sealed airstrips.”
Conclusion:This can be extremely dangerous on the ground as the flying part of the wrenched tip is a serious hazard for people around the aircraft. It is also jeopardizing flight safety as an in-flight blade delaminating would conduct to a forced landing. It must be noted that the propeller was delivered with a small hole in the tip, which resulted in a partial delaminating. Therefore, we can only conclude that there is no quality assessment at the end of the production chain of Duc goods. Consequently, all customers purchasing a Duc propeller must thoroughly inspect the goods received and reject any goods deemed un-airworthy, especially blades showing holes in the composite.

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A licensed aircraft engineer has detected a design flaw in Duc propellers.
Quote:”The aluminium retainer collar is starting to crack/corrode at the outer edge. This crack is approx 10mm now. The issue with the DUC collar is the aluminium next to carbon. They could do a fibreglass wrap or maybe a stainless collar. Doesn’t seem that difficult. There must be some reputable manufacturers who stand by their products – somewhere?”
This design flaw has also been reported on a French internet forum. Quote: "Ce type d'hélice qui mélange allègrement carbone et aluminium (pied de pale) est une bombe à retardement. Les 2 font mauvais ménage, il y a des risques de corrosion. Il faudrait être également certain que la température du moyeu d'hélice qui, par le plus grand des hasards est parfois aussi l'extrémité du vilebrequin, n'altère pas la qualité de l'époxy....
C'est un peu de la roulette russe avec plus d'une seule balle dans le barillet."
Go to the Forum ULM-ELA-LSA about the polemic on DUC propellers: http://www.forum-ulm-ela-lsa.net/viewtopic.php?f=88&t=821&sid=14bbf14482b9260bb2aeb8ebc7088f6b
Conclusion:This propeller was purchased in March 2008 but we have no indication that this design flaw has been fixed. Consequently, we advise all operators using a Duc propeller to thoroughly inspect at regular intervals the blade collar of the blades for corrosion.

Crack 1	Crack 2
Crack 3	Crack 4

A licensed aircraft engineer has reported a manufacturing flam with Duc/Jabiru propeller shafts. In total, this problem has been reported to us on 3 separate occasions.
Quotes: “I have also attached a photo of the prop adaptor as supplied. I must say I was surprised at the very second-hand , corroded and cracked unit supplied [...] On inspection the gold coating on the spacer seems to have had a bubble during treatment and a section inside hub isn’t treated. This area is untreated steel and will corrode badly Id expect [...] Regarding the Chromate coating on the prop adapter, I would still prefer to exchange if the offer were still open. To correct this now is very easy, after assembly it’s very difficult. It is also near impossible to inspect once installed. To be honest I’m a little disappointed with the Duc QA process which let this component through, despite the problem being minor in nature. [...] received the adapter, and the new one has the same issue, so No, not really satisfied. I may be mistaken but the new unit appears to have surface corrosion beginning too. I’m not satisfied corrosion treatment is applied at this portion either, as far as I can tell its bare steel.[...] I have had some parts we produce treated in similar way. Firstly is electroplated Zinc layer, then washed and acid primed and gold (dichromate) finish is next process. Whilst it is often considered cosmetic it adds dramatically to corrosion resistance OF THE ZINC coating which in turn protects the steel underneath. In these untreated areas I cannot see base zinc coating at all and parts have been in same position for dichromate coating also, looks like a bubble in both processes, or perhaps Zinc didn’t reach there so gold treatment wont adhere to steel I don’t think.”
Conclusion:We can only conclude that there is no quality assessment at the end of the production chain of Duc goods. Consequently, all customers purchasing a Duc/Jabiru propeller shaft must thoroughly inspect the goods received and reject any goods deemed un-airworthy, especially adapters showing incorrect coating as this will result in corrosion, which will occur in an area impossible to inspect during pre-flight, and probably after the 6 months structural guarantee will have lapsed.

Coating 1

Coating 2

The importer and licensed aircraft engineer for ELA gyrocopters has received a propeller showing manufacturing flaws on the entire composite surface
Quote: "After waiting for almost 2 months, I recently took delivery of a new DUC Windspoon propeller to suit my ELA-08 gyroplane. The finish on all three blades is completely unacceptable and well below the standard I or ELA Australia’s Neil Sheather have seen on any other DUC propeller fitted to an ELA gyroplane. I have attempted to photograph some of the blemishes in the propeller but it is difficult to do so. One the concave surface of one of the blades, adjacent to both the leading and trailing edges, the texture of the matting is exposed for the length of the blade and there are several blemishes … lumps, holes, scratches (or cracks) on the other 2 blades. I can only assume that these 3 blades have been manufacturing rejects that have somehow been shipped by accident.
As a gyroplane instructor it is costly and inconvenient to have to wait for 2 months and now to have received an unusable propeller. I therefore request that a replacement propeller be shipped to me urgently. Hopefully you will also be prepared to cover the cost of the return freight from Australia to France."

Conclusion: This propeller is completely un-airworthy as each of these holes is a point of rupture; it is therefore jeopardizing flight safety as an in-flight breakage or delaminating could result if the propeller was to be used, conducting to a forced landing. A licensed aircraft engineer is working under delegation of his civil aviation authority, and therefore it is his responsibility on behalf of the CAA to assess the airworthiness of an equipment prior to installation. No licensed aircraft engineer will ever take the responsibility of installing or signing off an aircraft fitted with a propeller in such condition. It must be noted that the propeller was delivered brand new straight from the factory, after a 2 months lead time. Therefore we can only conclude that there is no quality assessment at the end of the production chain of Duc goods. Moreover the Duc company does not have any knowledge with regard to airworthiness standards and civil aviation practices. Consequently, all customers purchasing a Duc propeller must thoroughly inspect the goods received and reject any goods deemed un-airworthy, especially blades showing holes in the composite.

Duc-FC 1	Duc-FC 2
Duc-FC 3	Duc-FC 4
Duc-FC 5	Duc-FC 6

 

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Following an accident, the company DUC Helices has sent an email to inform that Jabiru engines shall use only 3 blade propellers and not 2 blade propellers anymore. If you purchased a DUC propeller before December 2009, you may be using a 2 blade propeller. This configuration may present a risk of in-flight breakage. Read the original email in French (Jpeg 67 Ko)

Translation of the email:

Mister,

I am really sorry. Following an accident on a Jabiru, mister Duqueine has just decided that only 3 blade Swirl or Swirl inconel will be sold for Jabiru and only with a 210mm 3 blade turbo spinner

I can’t follow up on your request for a 2 blade propeller.

We are going to design a new propeller which could be installed on Jabiru but for now, we advise the 3 blade propellers.

Best regards,
Marie-Lare Balian,

Commercial manager
texte in French:
Monsieur,
Je suis vraiment désolée. Suite à un incident survenu sur un Jabiru, Monsieur Duqueine vient de
décider que seules les tripales swirl ou swirl inconel seraient vendues sur Jabiru et obligatoirement
avec cône Turbo 210 Tripale.
Je ne peux donner suite à votre demande pour des hélices bipales .
Nous allons sortir une nouvelle hélice qui pourra être montée en bipale sur Jabiru mais pour le
moment, nous vous conseillons de monter des tripales .
Sincères salutations
Marie-Laure Balian
Assistante Commerciale