flyboy122 wrote:Somebody smarter than me can probably verify (or invalidate) this, but isn't an early 172 just a 170 with a squared off tail and a training wheel? Mechanically are their any other differences? Flying wise are their any other differences? As long as the autopilot isn't expected to work on the ground, this one outta just be a pencil whip. I would argue minor change based on similarity and push the paperwork through.
DEM
Easy answer. Appearances aside,... Are the two airplanes on the same Type Design Certificate?
No?
.... looks like a separate certification is required for a
Supplemental Type Certificate, ...Heh?
John, the 172 Century autopilot places a servo-box (which holds the clutches and pilot-cables that grab the airframe's flight control cables) in a location which does not match the 170/170A and some 170B models. That means the servo box has to be located differently for the 170 series and despite "similar" flight characteristics requires the entire series of flight tests to be done all over again to insure that cable tensions and applied-forces are not exceeded yet are adequate to control the aircraft.
There are numerous flight control "feedback" issues with the many different model variants over the years. Fly a 1956 thru 1960s 172 and compare that to any of the 1970s model or any of the later, higher horsepower models and you will easily see that flight control forces and feedback are quite different. (Why,...there's not likely a single autopilot model that can be installed into that long-range of various 172s under the same process due to those differences. (Remember a "172" is not a single airplane nor is a Century IV autopilot a single autopilot...there are numerous variations necessary in each to meet the different needs/certifications.) An electro-mechanical autopilot device must be able to be adapted/adjusted to each difference. This makes it uneconomical to develop a new-design autopilot for an older airframe. (And, exceptionally-few of the airplanes were ever equipped with autopilots
when they were new. How many would be logical candidates for a newly certified autopilot that cost even more (due to modernity) and would be required to work in symphony with the incredibly-wide range of obsolete-thru-recent avionics which comprises the 170-fleet?
I.E., Let's cut to the chase in this discussion:
How many of you are willing to place your airplane into a shop you don't know out in California for an autopilot-installation which requires them to remove your interior and dig into your instrument panel for the experimental installation after-which that shops pilot will fly your airplane through a series of flights which stress your airframe to the limits of its original design in low and high-speed, high-G manuevers (the particular brand and model autopilot not yet known) for $11,000 bucks....after which your airplane MAY be allowed to keep the autopilot installed?... or not...?
....and did I mention that your airplane will FIRST be very closely inspected and maybe flown by FAA authorities or their designees BEFORE the work begins to determine it meets the original design completely? OK now... How Many?
As for the "minor alteration" suggestion: As anyone who's flown a 170B and a 172 can tell you, the rudder-control pressures are quite different between the two aircraft. The 170B feels "light" while the 172 feels "heavy" due to the centering-cam/bungee arrangement in the nosewheel which keeps the nosewheel centered in-flight regardless of pilot input. Further, the idea a 172 is just a 170B is simplisitic. There are 172s, 172As, Bs, Cs,.... all the way thru the 172S, and those do not include the TGs, RGs, and XLs or any of the Reims (French built) aircraft.
Don't get mad at the messenger.
