ARC propellers and MOSAIC.. and Hello!
Thread Starter
Joined: Mar 2026
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From: Germany
You may want to readdress that plan. The individual owners of an S-LSA in the US will not be able to install your prop on their aircraft unless the manufacturer provides the acceptable data as it is considered a major alteration. Now if the owner elects to convert their S-LSA to an E-LSA in order to install your prop then it would not need the mfgr. data, however, they may run across a different problem similar to what an amateur-built (E/AB) owner would face installing your prop. And at the E/AB level a new prop install with no engine history behind it, will probably push the aircraft major change required Phase 1 flight testing beyond the typical 5 hours and possibly out to the 25-40 hour requirement. Something to think about.
We are ASTM approved (approved? certified? compliant? one of those words) for Rotax engines. As I understand it, under the new rules, a manufacturer can take a look at our data and decide that the propeller meets their airworthiness requirements, in which case no further testing is required. They may, however, as you said, wish to see performance data specific to their aircraft, in which case flight testing would have to be done. Full disclosure- I am the "marketing guy" here, and an American, and I am trying my best to understand what my very technically minded German colleagues are explaining to me (in German!), and then pass that along here.. there is bound to be something lost in translation, and for that I apologize in advance. I have also passed your question to our American partner (who has been in the aviation business for longer than I have been alive) and as soon as I hear back from him, I will hopefully have something smarter to say : )
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From: Ontario, Canada
In my certification work, I do not [yet] work with the ASTM nor MOSAIC standards. I'm not familiar with those standards, nor the standards applicable to non certified airplanes. But, I do know that physics don't change because of how the airplane has been authorized to fly. The Part 23, 33, & 35 certification standards are very well thought out, and the result of some painful and expensive lessons. If you need to "do it differently" from those standards, you really want to consider all of the implications.
While doing flight testing for propeller change STC approvals on GA airplanes, I have found a few things which were pretty important to understand, and could be an indicator of a reduction of safety, if not correctly compensated or mitigated. In my flight testing of a Bellanca Scout, I found that replacing the metal propeller with a composite propeller allowed airframe and in particular, horizontal stabilizer vibration which was worrisome. I researched this and found a report of similar observations with a composite propeller change to a Citabria in England in 1992. That could be an unsafe condition, as on those airframes, the metal propeller acted as a "harmonic balancer" for the whole airplane, and when it was taken away, undesirable vibrations were possible.
As I have mentioned, a propeller change can dramatically change the gliding characteristics of the plane. If the characteristics have been changed, this needs to be understood from results of good flight testing, so that pilots know what to expect, and how to handle the plane in the case of engine failure
Composite propellers (including wood) are generally not subject to installation limitations to engines the way metal propellers are, though having a good understanding of any vibration vulnerabilities is still important. There have been a lot of hard lessons learned, some over longer than obvious periods of time, in the realm of propeller vibration, so it's worth understanding well for the combination you propose.
While doing flight testing for propeller change STC approvals on GA airplanes, I have found a few things which were pretty important to understand, and could be an indicator of a reduction of safety, if not correctly compensated or mitigated. In my flight testing of a Bellanca Scout, I found that replacing the metal propeller with a composite propeller allowed airframe and in particular, horizontal stabilizer vibration which was worrisome. I researched this and found a report of similar observations with a composite propeller change to a Citabria in England in 1992. That could be an unsafe condition, as on those airframes, the metal propeller acted as a "harmonic balancer" for the whole airplane, and when it was taken away, undesirable vibrations were possible.
As I have mentioned, a propeller change can dramatically change the gliding characteristics of the plane. If the characteristics have been changed, this needs to be understood from results of good flight testing, so that pilots know what to expect, and how to handle the plane in the case of engine failure
Composite propellers (including wood) are generally not subject to installation limitations to engines the way metal propellers are, though having a good understanding of any vibration vulnerabilities is still important. There have been a lot of hard lessons learned, some over longer than obvious periods of time, in the realm of propeller vibration, so it's worth understanding well for the combination you propose.
Joined: Oct 2006
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From: USA
As I understand it, under the new rules, a manufacturer can take a look at our data and decide that the propeller meets their airworthiness requirements, in which case no further testing is required.
They may, however, as you said, wish to see performance data specific to their aircraft, in which case flight testing would have to be done.
Thread Starter
Joined: Mar 2026
Aviation Qualifications: PPL
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From: Germany
In my certification work, I do not [yet] work with the ASTM nor MOSAIC standards. I'm not familiar with those standards, nor the standards applicable to non certified airplanes. But, I do know that physics don't change because of how the airplane has been authorized to fly. The Part 23, 33, & 35 certification standards are very well thought out, and the result of some painful and expensive lessons. If you need to "do it differently" from those standards, you really want to consider all of the implications.
While doing flight testing for propeller change STC approvals on GA airplanes, I have found a few things which were pretty important to understand, and could be an indicator of a reduction of safety, if not correctly compensated or mitigated. In my flight testing of a Bellanca Scout, I found that replacing the metal propeller with a composite propeller allowed airframe and in particular, horizontal stabilizer vibration which was worrisome. I researched this and found a report of similar observations with a composite propeller change to a Citabria in England in 1992. That could be an unsafe condition, as on those airframes, the metal propeller acted as a "harmonic balancer" for the whole airplane, and when it was taken away, undesirable vibrations were possible.
As I have mentioned, a propeller change can dramatically change the gliding characteristics of the plane. If the characteristics have been changed, this needs to be understood from results of good flight testing, so that pilots know what to expect, and how to handle the plane in the case of engine failure
Composite propellers (including wood) are generally not subject to installation limitations to engines the way metal propellers are, though having a good understanding of any vibration vulnerabilities is still important. There have been a lot of hard lessons learned, some over longer than obvious periods of time, in the realm of propeller vibration, so it's worth understanding well for the combination you propose.
While doing flight testing for propeller change STC approvals on GA airplanes, I have found a few things which were pretty important to understand, and could be an indicator of a reduction of safety, if not correctly compensated or mitigated. In my flight testing of a Bellanca Scout, I found that replacing the metal propeller with a composite propeller allowed airframe and in particular, horizontal stabilizer vibration which was worrisome. I researched this and found a report of similar observations with a composite propeller change to a Citabria in England in 1992. That could be an unsafe condition, as on those airframes, the metal propeller acted as a "harmonic balancer" for the whole airplane, and when it was taken away, undesirable vibrations were possible.
As I have mentioned, a propeller change can dramatically change the gliding characteristics of the plane. If the characteristics have been changed, this needs to be understood from results of good flight testing, so that pilots know what to expect, and how to handle the plane in the case of engine failure
Composite propellers (including wood) are generally not subject to installation limitations to engines the way metal propellers are, though having a good understanding of any vibration vulnerabilities is still important. There have been a lot of hard lessons learned, some over longer than obvious periods of time, in the realm of propeller vibration, so it's worth understanding well for the combination you propose.
Thread Starter
Joined: Mar 2026
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From: Germany
In general, what word used depends on the aircraft category and whether it falls under a Standard AWC or Special AWC. For an S-LSA, it would need to be compliant to an FAA accepted ASTM standard. However, that level of compliance is determined at the aircraft level under their Letter of Compliance to the FAA.
They do that now under the current rules. My point is you stated your plan was to approach the individual owner before the manufacturers. However, without the OEMs acceptance first, the owners cannot install your prop per the old or new rules without additional requirements or authorizations.
Not quite. You are intermixing requirements between different aircraft categories. Perhaps research the different requirements between an S-LSA, and E-LSA, and an experimental amateur-built (E/AB) aircraft, or discuss this with your American partner. All have unique requirements to use your new props.
They do that now under the current rules. My point is you stated your plan was to approach the individual owner before the manufacturers. However, without the OEMs acceptance first, the owners cannot install your prop per the old or new rules without additional requirements or authorizations.
Not quite. You are intermixing requirements between different aircraft categories. Perhaps research the different requirements between an S-LSA, and E-LSA, and an experimental amateur-built (E/AB) aircraft, or discuss this with your American partner. All have unique requirements to use your new props.
Thread Starter
Joined: Mar 2026
Aviation Qualifications: PPL
Posts: 13
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From: Germany
In general, what word used depends on the aircraft category and whether it falls under a Standard AWC or Special AWC. For an S-LSA, it would need to be compliant to an FAA accepted ASTM standard. However, that level of compliance is determined at the aircraft level under their Letter of Compliance to the FAA.
They do that now under the current rules. My point is you stated your plan was to approach the individual owner before the manufacturers. However, without the OEMs acceptance first, the owners cannot install your prop per the old or new rules without additional requirements or authorizations.
Not quite. You are intermixing requirements between different aircraft categories. Perhaps research the different requirements between an S-LSA, and E-LSA, and an experimental amateur-built (E/AB) aircraft, or discuss this with your American partner. All have unique requirements to use your new props.
They do that now under the current rules. My point is you stated your plan was to approach the individual owner before the manufacturers. However, without the OEMs acceptance first, the owners cannot install your prop per the old or new rules without additional requirements or authorizations.
Not quite. You are intermixing requirements between different aircraft categories. Perhaps research the different requirements between an S-LSA, and E-LSA, and an experimental amateur-built (E/AB) aircraft, or discuss this with your American partner. All have unique requirements to use your new props.
Many apologies for the delayed response- I needed to make sure it was ok with Bill before I mentioned him by name.
Joined: Oct 2006
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From: USA
Thread Starter
Joined: Mar 2026
Aviation Qualifications: PPL
Posts: 13
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From: Germany
Then perhaps sit down with Bill and educate yourself on the requirements to install your prop on US based LSA and amateur-built aircraft. MOSAIC has the potential to reverse the decline in the Part 91 sector here plus provide an opportunity for EU based LSA centric companies like yourself to expand here as well. However, you only get one chance to make a 1st impression and some of your comments in this thread, and on other websites as I understand, may "tarnish" that impression. Regardless, best of luck with your endeavor.
Let me know if you'd like to test out the propeller (no promises- but maybe we can set something up), or just want to talk about our current performance test results.
Joined: Oct 2006
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From: USA
