I am fully aware that they claim to be using Part 23 as a guideline ( makes sense, since ASTM doesn't have any guidelines for demonstrating spin resistance at this time, as far as I know. So I would expect any company that's chooses spin resistance would use FAR23.221
But FAR 23.221 requires the spin resistance demonstration at no less that 50% power. Has this been demonstrated to the FAA? ( In the Icon spin resistance video, the pilot said: " power at idle")
In any case, how can spin resistance require 250 pounds?
Last edited by Bill Berson; 05-24-2013 at 04:36 PM. Reason: Correct FAR number
If you go back to post#134, there's an attachment containing Icon's responses to the FAA list of questions. kmhd1 took the time and effort to search and post it for all those interested enough to read it. It should answer your question if you care to open and seek out the appropriate sections and appendixs.
That attachment would not open for me yesterday, but it did open today.
Reading it today, I found where Icon said the tested power level was at 75%. So yes, it would comply with the Spin resistant criteria of FAR23 (as I read it).
But that doesn't prove spin resistance at 100% power. No doubt some pilots will stall at full power, and it may or may not be recoverable. And since no production airplane has ever met this criteria ( according to Icon statement), there is no data to show that meeting the current FAR 23 "spin resistance" criteria will result in fewer spin accidents.
Moving on to my remaining unanswered question: is there a document somewhere on this forum that explains why a 250 pound exemption is needed to create spin resistance?
In the past, during creation of the LSA rules, the FAA has repeatedly said that they will NOT regulate by exemption. Therefor I think, if a safety issue is shown to be in need of some relief with a weight increase, Icon should petition for a LSA rule change that would apply to all, not just them.
That would allow for public comment about these complex issues.
Most of the dicussion have been on the spin resistance itself. Let me shelf this question for now and move on: Icon never explained or gave a calculation to show that 250 lb was the weight increase required to obtain the benefit of spin resistance. Proof this: it will take 250 lb, not 2.5 lb, or 25 lb, or 2500 lb for an LSA to be spin resistant. Strangely FAA did not ask this quantitative question either. The modification for spin resistance is mainly in the wing. I would estimate the full weight of a conventional wing to be 130 lb for an LSA (someone on this forum should be able to provide an exact example). The modification for spin resistance propably adds another 40 lb given the structural efficiency of composite wing. To ask for 250 lb is totally out of proportion.
I'm also scratching my head on how they needed 250 pounds of additional structure to make the plane spin resistant.
Ryan Winslow
EAA 525529
Stinson 108-1 "Big Red", RV-7 under construction
250 pounds does seem like a lot. Although, none of us are building this particular plane so its all speculation - even if an informed one given that some of the folks on here are building or have built their own plane - which I would love to do some day...
I noticed your signature says you are building an RV-7 - sounds like a fun project! I wonder what other modifications you would have to make if suddenly your wings were 40 pounds heavier? If memory serves, in Icon's original documentation for the weight exemption request they discuss the domino effect of structural changes that are needed to support the spin resistant airframe and it included more than just the wings being heavier.
I don't disagree with you. Icon certainly made things far more challenging for themselves in that regard. In fact, I recall seeing an interview they did with Kirk Hawkins a while back where he talked about the decision to delay the production launch to incorporate the spin resistant design. At the time he figured it was going to extend things out 8 months just to nail down the design changes. However, I don't think he ever thought the FAA would take more than a year (and counting) to make a decision on the subsequent weight exemption request initiated by the spin resistant airframe changes they incorporated into their POC.
Last edited by kmhd1; 05-26-2013 at 06:03 PM.
Following is the paragraph in Icon's original petition explaining the weight increase:
While it is beyond the scope and intent of this document to fully explain a full FAR Part 23 spin-resistance solution, a simplified, layman’s explanation is that a large portion of the outer wing sections must be protected from ever stalling by, among other things, reducing maximum lift well below the wing’s capability. Given the maximum stall speed (45 knots) required by the LSA definition, this loss of maximum available lift requires significantly increased wing area. The increased wing area then in turn requires increased tail size for stability along with the corresponding increase in internal structure, as well as proportional accommodation factor weight – at a minimum. Further, the increased wing, tail, and specific spin-resistance elements also result in an increase in aerodynamic drag which requires increased engine size and additional fuel to compensate. The net result is that a Spin-Resistant Airframe requires increased vehicle weight over a similar S-LSA airplane that does not achieve spin resistance.
In my understanding, basically they are saying they need a bigger wing because the maximun lift cofficient is limited to prevent outer wing stall, and to keep the tail volumes constant for stability, now they need a bigger horizontal and a bigger vertical tail. The arguement on a bigger engine is not true since they use the Rotax 912s regardless of this spin-resistance feature.
There is no quantitative analysis in the petition. They intentionally avoided this discussion. The number, 250, came from nowhere. In fact, most of this increased weight are likely for the stuff like automatic wing folding and gear retraction.
Last edited by wantobe; 05-27-2013 at 03:06 AM.