Re: 170A with the Sportsman STOL Kit?
Posted: Wed Apr 01, 2020 6:24 pm
This post may be viewed as “contradictory”... but please do not do so. That is NOT my intention.
Nor is it my intent to bring any denigration or disparity to anyone’s airplane or person. My intent in the following comment is solely for contemplation and consideration when selecting and/or modifying an airplane.
Whenever modifying (or considering for purchase a highly-modified airplane) I believe it wise to keep in mind that just because a modification is “approved”... does not make it worthwhile, valuable, or safe even.
In this discussion, it was apparently implied that the STC holder didn’t think it “profitable” to go thru the certification process of their mod to the A-model.
While that may be true, the conclusion one might “leap to” is that there’s no real reason their STOL mod is really any different on an A-model than it is on the B-model (which they clearly DID consider it to be profitable.).
The questions I believe which SHOULD be asked are:
1- Is the STC holder expecting end-users to accept that their only restriction to “profitability” is the smaller number of A-models to B-models..???
<OR>
Is the potential ADDED EXPENSE of getting their mod “Approved” by Certification Authorities the ACTUAL reason for less profit in that model?
2- Is the mod AS SAFE as it should or could be in that skipped A-model? (And does that also apply to the straight 170?
3- How will the mod affect my investment-value? Will my initial belief that a “mod” equates to “improvement” an Actual Fact? Or is it only Perceived?
If I were in the market for an all-metal 170, I would (and DID) add a slight value to the B-model MOSTLY because of it’s minor improvement in performance over the A-model with regard to field-length,... the direct result of it’s larger flaps.
The other reasons I considered the B-model in more favorable light was because it was the direct-ancestor of the hugely popular/numerous follow-on model, the C-172. This gives the B-model (especially the ‘53s and later) more commonality with that 172, and that equates to PARTS AVAILABILITY.
I believe it’s easy to recognize that the 170 airplanes were evolutionary models to the world’s most-numerous/popular airplane, the C-172 series.
I view earlier versions of the 170B to also be great airplanes that share many of the same wonderful/popular characteristics.
But WHY would the STOL/STC holder skip over what most people would consider a practical (if not virtual) TWIN to the B-model?
I suggest it’s because there is an oft-overlooked feature that not many recognize: The TAIL feathers!
The B-model required significant design change to it’s tail, especially the elevators, because of significant handling characteristic changes resulting from those large flaps. This has been cussed/discussed many times with regard to WARNings against slipping the B-model (and 172s) with full flaps deployed.
The STOL modification falls DIRECTLY into the regime of flight where full flaps are usually deployed in landing configuration.
The change in the leading edge of the wing results in a change in Center-of-Lift (C/L) during that portion of flight where the STOL features are most-utilized/most-influential. This leads to the question which will be asked of aerodynamicists: How does the change in wing-characteristics affect elevator effectivity and elevator stall-margins?
I suspect that experienced test pilots and aerodynamicists would require more extensive flight testing of the A-model than the expected sales of that STOL STC would support with regard to “profitability”.... and perhaps, Safety.
I was never an engineering test pilot... only a “production test” pilot... which is mostly a quality-control task, not a certification task.
But this STOL STC not having passed the scrutiny of a full flight-handling-test would concern me if I was considering purchase of airframe mods that have only had a “field approval” by a group of maintenance inspectors.
Just my thoughts. YMMV
Nor is it my intent to bring any denigration or disparity to anyone’s airplane or person. My intent in the following comment is solely for contemplation and consideration when selecting and/or modifying an airplane.
Whenever modifying (or considering for purchase a highly-modified airplane) I believe it wise to keep in mind that just because a modification is “approved”... does not make it worthwhile, valuable, or safe even.
In this discussion, it was apparently implied that the STC holder didn’t think it “profitable” to go thru the certification process of their mod to the A-model.
While that may be true, the conclusion one might “leap to” is that there’s no real reason their STOL mod is really any different on an A-model than it is on the B-model (which they clearly DID consider it to be profitable.).
The questions I believe which SHOULD be asked are:
1- Is the STC holder expecting end-users to accept that their only restriction to “profitability” is the smaller number of A-models to B-models..???
<OR>
Is the potential ADDED EXPENSE of getting their mod “Approved” by Certification Authorities the ACTUAL reason for less profit in that model?
2- Is the mod AS SAFE as it should or could be in that skipped A-model? (And does that also apply to the straight 170?
3- How will the mod affect my investment-value? Will my initial belief that a “mod” equates to “improvement” an Actual Fact? Or is it only Perceived?
If I were in the market for an all-metal 170, I would (and DID) add a slight value to the B-model MOSTLY because of it’s minor improvement in performance over the A-model with regard to field-length,... the direct result of it’s larger flaps.
The other reasons I considered the B-model in more favorable light was because it was the direct-ancestor of the hugely popular/numerous follow-on model, the C-172. This gives the B-model (especially the ‘53s and later) more commonality with that 172, and that equates to PARTS AVAILABILITY.
I believe it’s easy to recognize that the 170 airplanes were evolutionary models to the world’s most-numerous/popular airplane, the C-172 series.
I view earlier versions of the 170B to also be great airplanes that share many of the same wonderful/popular characteristics.
But WHY would the STOL/STC holder skip over what most people would consider a practical (if not virtual) TWIN to the B-model?
I suggest it’s because there is an oft-overlooked feature that not many recognize: The TAIL feathers!
The B-model required significant design change to it’s tail, especially the elevators, because of significant handling characteristic changes resulting from those large flaps. This has been cussed/discussed many times with regard to WARNings against slipping the B-model (and 172s) with full flaps deployed.
The STOL modification falls DIRECTLY into the regime of flight where full flaps are usually deployed in landing configuration.
The change in the leading edge of the wing results in a change in Center-of-Lift (C/L) during that portion of flight where the STOL features are most-utilized/most-influential. This leads to the question which will be asked of aerodynamicists: How does the change in wing-characteristics affect elevator effectivity and elevator stall-margins?
I suspect that experienced test pilots and aerodynamicists would require more extensive flight testing of the A-model than the expected sales of that STOL STC would support with regard to “profitability”.... and perhaps, Safety.
I was never an engineering test pilot... only a “production test” pilot... which is mostly a quality-control task, not a certification task.
But this STOL STC not having passed the scrutiny of a full flight-handling-test would concern me if I was considering purchase of airframe mods that have only had a “field approval” by a group of maintenance inspectors.
Just my thoughts. YMMV