Wing loading.

Main method to do this is set an airfoil with a higher stall angle on the wingtips. Most of the wing stalls; descent angle brings the tail to a high AoA so the nose won't come up any further, and keeps lift equal on the wingtips to keep it from rolling over.

Seems like the cuff does two things:

The most noticeable feature is that the edge is extended forward a few inches, allowing the leading edge to be shaped into a drooped shape similar to a glider.

This is a series of small folded pieces of sheet metal that are inserted under the wing skin, in front of the ailerons. This reduces high pressure air from leaking up through the gap of the ailerons and creating drag at high speed or rendering your aileron ineffective when you are at slow speeds

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Drooping increases the camber, raising the stall AoA; sealing the gap reduces drag and increases effectiveness.

The majority of the wing still stalls, it just is less likely to drop one side and spin.

We have found that our plane now stalls at between 10 and 15 knots slower than the figure published in the operation manual, depending on the flap setting. It now also has a TAS equaling that published, which it did not achieve before modification.

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I'd be surprised if these mods do not negatively impact high speed cruise.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

It's unlikely he did any Vh flights before and after, with identical power, altitude, weight, CG, etc. conditions for comparison. So I wouldn't accept the claim "no increase in drag". Maybe the STC holders of these kits had to do that, but they might not feel the need to tell you.

The other stuff may be reasonable though maybe exaggerated or oversimplified. The new tips might have some wash-out that points them several degrees lower than the rest of the wing. Tips still in flow, with inner portions stalled out. Are the ailerons extended too?

It help me to separate "stability" from "control" as concepts as I think about them. The Cessna may have more stability (especially in roll) with the extensions. Having no change to the elevator, the pilot has the same or less control authority than before. The "same" because the elevator is the same, OR "less authority" when the surface area of the elevator is compared to the increased surface area of the wing. About the ailerons, maybe the same question applies - depends on if they extended the ailerons on the extended wingtip or not. I kind-of hope they didn't. I flew a 172 during pilot training. There seemed to be enough authority in the ailerons of the 172 without needing to extend them.

Forward velocity is not zero when a pitot-static airspeed indicator reads zero. The vertical speed indicator might have been accurate, though.

Leave your BS meter switched on. GA Pilots do pick up a lot of marketing material designed to blind them with "science".

yeah, as others ... BS !

It sounds like he's developed a "deep stall" ... ask the crew of AF447 about this.

If he likes to fly with a VS of -400 ft/min then it'll be a short flight, or "flight".

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

Sounds like a lot of BS. Suggest you don’t fly with this guy.

...He really wants me to go flying. lol.

He doesn't realize he's acting as a test pilot and doesn't understand that these STC kits developed 30+ years ago aren't exactly the pinnacle of engineering... Pretty sure these were approved because they didn't kill the test pilot flying the airplane they put in experimental long enough to get a field approval, then back when the MIDO would actually pick up the phone issue an STC.

Sounds like most of you agree there has to be a downside... I'd agree Vh would be a likely suspect. I mean how can you add 3 feet to each wing and not have a drag increase? Likewise how can you change the nose profile, increase camber, sounds like effectively decrease AoA and not create more drag?

But really my main question still stands:
More lift=more drag=more stress... that's just the way it is right?
I know an IA signing off the installation of such things is supposed to investigate other STCs installed for compatibility... but really how is an IA supposed to make that determinization... because plenty have... as an engineer, having worked with Textron, I don't think anyone really knows. My opinion is I think stacking STCs up like that is dangerous. Thoughts?

BTW... hope this make sense...

Every individual modification by STC has to be approved for affect to structures, systems, areo-performance, etc.

NOW the question has to be asked... about mod1, mod2, mod3... up-to... modX. Individually these mods are 'STC OK'... but... does this mean that...

mod1+ mod2+ mod3+... up-to... modX... are by definition 'OK' all-interactive-together [risk = 0?]...

or...

mod1+ mod2+ mod3+... up-to... modX... = pose unknown-safety risk(s) from them [one-or-all] interactive-together [risk = unknown????]?


Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

LOL probably hit enter at the same time. WKTaylor at least we're on the same page.

yeah, a US STC ? probably a field approval. It does seem odd, very odd, that these wing tips change the stall performance (so much).

What stall protection does a 172 have ? any ?? How can a mod that impacts (seemingly) the stall performance so much get approved ??

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

Sure is. As soon as I find out what the tips STC is I'll post it up.

SA04657NY

how interesting ...

"stall speeds (with STC) are approximately the same as the basic aircraft" ... !?

landing distance is increased with wing tips (maybe max landing weight is increased ?)

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RoarkS said:

More lift=more drag=more stress... that's just the way it is right?

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Bear mind F=ma. Sum of forces.
So if you believe the claim "more lift" and you interpret that as "more lift force" then there is a greater acceleration of the aircraft's mass upward. Until of course the pilot desires a level flight attitude and eases off the stick, reducing the angle of attack a bit. Then once again Lift = Weight and acceleration returns to zero. Note that this pilot is bragging about performance in descent, not level nor climb. Now what does he think he means by "more lift"? There's really no point thinking about it.

People say things, but they DON'T say what the mean. Engineering is a profession based on science. When we express terms in engineering language, we are trying to be factual and accurate.

People NEVER say in casual conversation "tendency to maintain constantly increasing slope of the lift coefficient curve at higher angles of attack than the original profile could achieve" but they do say "makes more lift" and somehow assume that they know what the #$%@ they are talking about.

RoarkS said:

I think stacking STCs up like that is dangerous.

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This might be a good time for me to play devil's advocate and ask you: why do you think so?

PS
I nitpicked you on the wording (that you shouldn't be repeating) but didn't circle back to what I think you might have thought you meant but didn't actually say, since you didn't use the term "spanwise distribution of lift" or similar, to set the context of your question about wing stress. Does that help? The whole problem I'm trying to get at is one of making clear (pedantic) statements that clarify exactly what you mean. The stuff your professors got on your case about. I think you know all this stuff because your instincts are telling you the right things, so being methodical with how you ask the questions will probably unlock it all.

Oh jeez they offer GW increases, too. You're on to something about more stress at the wing root.

Don't Cessna 172s have humongous struts?

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

you have more lift at the same incidence ... well likely ... on the DHC8 they did a wing extension when they did the heavier S300. In flight test they found that these extensions actually produce -ve lift.

anways ... more wing area means more "available" lift. In practice the plane will fly straight and level at a slightly lower incidence.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

SW...

I presume that a stock-vanilla older C-172 could benefit from some of the mods available from the company cited... for a whole bunch of positive reasons. After-all the 172 is not a highly refined thoroughbred and could 'stand being dolled-up' as long as empty/gross weight and cruise speed increases were modest... and structure was still in static and fatigue limits. Of course in this case 'money-$$ is likely NOT a problem'. I guess he loves this bird.

Stacking STC-Mods on the same aircraft, from the SAME company, would likely be acceptable if each has approved/tested each separately... then analyzed/tested various 'smart/anticipated' combinations of he STC-Mods for safe/effective/harmonious interactions... and if the STC-mods in combo received a full shake-down mini-flight test protocol by a company test pilot.... who then thoroughly 'checked-out' the owner over several hours of ground/flight instruction. I would be very wary of installing mods form more than one source... they may not 'play-well together'.

Personally, I would view wing/stabilizer/engine mods that change leading-edges/span/controls/control-surfaces/performance/mass with a 'hard-eye'... simply from the structural and aero-interactions... but smart analysis and thorough testing... to the edges of the flight envelope... should be enough.

NOTE1. Older 'CESSNA spam cans' were poured out of the factories by the thousands and workmanship and corrosion protection was often 'barely OK'.

NOTE2. In the early 1980s, I was the USAF lead engineer for the T-41A... MIL versions of the C-172 for primary pilot training. These were built under contract to rigid standards of QA... and many in the early 1980s were past 15,000-flight-training hours... and still going strong. When we disassembled sample-size of the fleet aircraft for a 'mid-life' inspection, I was impressed with the workmanship and applied corrosion protection... and lack of significant/major damage... mostly wear/tear, minor corrosion, a few rusty bolts, minor cracks, cracked wiring insulation, corroded-flight control cables, etc. A few parts replacements, and 'CPC'... and these aircraft were deemed suitable to fly for another 10,000-hours in training.

NOTE3. Subsequently... I've worked high performance MIL-Acft that are intended to carry XXXXX payloads when designed/tested... then the inevitable systems/structures/payload mod-cycle begins. It is remarkable how a 'simple change' can have unanticipated consequences. YEAH weird sh*t can happen.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

So from memory, if hes increased the wing span that much, hes going to be reducing the down wash angle from the wing, effecting reducing the AOA of the stab at max incidence, so probably simply can't pitch up sufficiently to stall the wing. Its a 172, its going to be gust load critical for wing bending, well if he is stacking up the STC's maybe his empty weight will increase sufficiently for it not to be an issue.

There was a good writeup of an accident a few years ago about someone who stack stc's (power, speed and gross weight ones) and broke up in flight, might have been in Flying (can't remember the airframe type).