Snake Oil or will it actually work?

[farmrjohn]

I wonder if a website like snopes.com could answer this. I asked A.S. about documentation etc. and they answered the STC is included in the box (question and answer now on their web page). Since it's too hot to go outside it provided a good excuse to find the STC, and it actually exists: http://rgl.faa.gov/Regulatory_and_G...325C163795B2648086257DE00060EC62?OpenDocument or STC SP01222WI if the link doesn't work. Does this make it semi-legit? (Of course the FAA is the same organization involved with the approval of the 737Max)

 

[ElPaso Pilot]

I wonder if a website like snopes.com could answer this. I asked A.S. about documentation etc. and they answered the STC is included in the box (question and answer now on their web page). Since it's too hot to go outside it provided a good excuse to find the STC, and it actually exists: http://rgl.faa.gov/Regulatory_and_G...325C163795B2648086257DE00060EC62?OpenDocument or STC SP01222WI if the link doesn't work. Does this make it semi-legit? (Of course the FAA is the same organization involved with the approval of the 737Max)

There are tons of so called “speed mods” with FAA paperwork.

That has no bearing on whether or not it works, only that it doesn’t cause unforseen harm.

 

[Bell206]

Does this make it semi-legit?

Provided it applies to your prop that doc is all you need. Snopes not required.

 

[Capt. Geoffrey Thorpe]

Turbulators and vortex generators work (when they do work) by putting energy in the boundary layer which can help the boundary layer stay attached to the surface at higher angles of attacks where it would tend to separate towards the aft end of a foil and generate more drag. Same thing as dimples on a golf ball - the boundary layer stays attached longer leaving a smaller wake. Under conditions where there isn't a tendency to separate, turbulators, vortex generators, dimples, etc. just add drag. So, it is possible that on some props under some conditions, there could be a reduction in drag. It is also likely that on other props or under other conditions turbulator tape ain't gonna do nuthen - at best. And, likely, the difference may be hard to measure.

 

[mwagg737]

I own a Cessna 182. There literally hundreds of speed mods available for my airframe. I've installed them all.

My 182 cruises at 310 ktas.

I believe it! My '56 310 runs out at 425 ktas with all the speed mods!

Sent from my Pixel 2 XL using Tapatalk

 

[weirdjim]

I own a Cessna 182. There literally hundreds of speed mods available for my airframe. I've installed them all.

My 182 cruises at 310 ktas.

Only if you hung an IO-5000 onto it.

Jim

 

[bflynn]

All the while allegedly also making the engine RPM faster

So you still don't understand.

VGs provide reduced drag on the prop in addition to tightening the airflow and increasing airflow efficiency. These two means the prop is better - more aerodynamic with better air flow. The engine no longer has to overcome that part of the prop resistance. All else being equal, the prop is turning faster and, being stubbornly attached to the crankshaft, engine RPMs are going up too. Conservation of energy, for the same fuel burned, there is less friction, which means there must be more energy in the prop.

The prop turning faster will mean the aircraft is going to move forward faster, generating faster wing movement through the air and generating more lift.

I think your disconnect is that you're missing the prop efficiency increase and that the engine incurs less load.

 

[Tantalum]

So you still don't understand.

ok.

There are a lot of assumptions made in the premise. VGs have their applications but aren't a magic panacea to all things airfoil related. You don't see VGs on Mooney / Lancair / Cirrus / Gulfstream / Citation X / etc. wings.. You seem them on STOL equipped planes, and their primary job there is to aide in the slow and high AoA environments. They also aren't magically tightening the airflow, all they do is create a small vortex that goes down the "wing" - it takes energy to "spin" the air up like that.. that's got to come from somewhere. There's a big assumption to be made that the energy it takes to "charge up" the air like that does enough drag reduction to make the whole thing worth it

the whole thing with this prop VG is an assumption that it adds enough aerodynamic efficiency to gain 50 static RPM and an increase in cruise speed

The OP asked if we thought it was snake oil... I'm dubious of the overall idea that prop VGs are meaningful, primarily because, out of all the efficiency gains people seek out of their planes and advances we've seen in prop design, composites, etc., we don't see anyone doing this, and like the other poster said, they've been around for a long time

*However, I am not part of an anti-prop VG lobby, and don't really care one way or the other. If people want to drop money on putting tape on the leading edge of their props more power to them


PS - the FIKI and non FIKI Cirrus don't have any different published cruising speeds (assume same conditions, etc.).. however the FIKI Cirrus has a fairly aggressive rubber liner going down the front first third of the blade with deep grooves in it for TKS channels. I would imagine if this was as sensitive of an airfoil area as it is claimed to be, we'd see different published performance figures for planes with and without the prop FIKI

 

[MauleSkinner]

*However, I am not part of an anti-prop VG lobby, and don't really care one way or the other. If people want to drop money on putting tape on the leading edge of their props more power to them

thats the object.

PS - the FIKI and non FIKI Cirrus don't have any different published cruising speeds (assume same conditions, etc.).. however the FIKI Cirrus has a fairly aggressive rubber liner going down the front first third of the blade with deep grooves in it for TKS channels. I would imagine if this was as sensitive of an airfoil area as it is claimed to be, we'd see different published performance figures for planes with and without the prop FIKI

In order to publish different performance figures, the manufacturer would have to go through the full flight test sequence to verify those numbers. Even if grooves had the same effect as the vortelator strips, the cost to build the data would probably not be worth it.

Most speed & performance mods don’t go through that expense.

 

[bflynn]

it takes energy to "spin" the air up like that.. that's got to come from somewhere. There's a big assumption to be made that the energy it takes to "charge up" the air like that does enough drag reduction to make the whole thing worth it.

And yet, that's what the aerodynamic tests showed, so it isn't an assumption.

It's drag reduction. There's nothing magical about that.

 

[Tantalum]

And yet, that's what the aerodynamic tests showed, so it isn't an assumption.

It's drag reduction. There's nothing magical about that.

Is there documentation for the aerodynamic tests somewhere? Other than the advertised claims, some "testimonials" (that don't write anything about changes in atmos conditions, etc.) and the ONLY review is by a guy in a Tri-Pacer who claims Citation speeds?

 

[bflynn]

Of course there is. The topic has been studied for decades.

Test Results Vortex Generator Propeller

 

[Tantalum]

Of course there is. The topic has been studied for decades.

Test Results Vortex Generator Propeller

thanks. I've actually never used Google and have no idea how to use the internet

We're talking about this specific application on sporty's website. Not the general conceptual aerodynamic principles behind vortex generators. OP asked about this specific product, not about to theoretics behind it. The testimonials appear to be fake, and don't offer anything beyond a regurgitation of what the sales pitch already says above, and the one apparently genuine review is obviously a joke. this is like any one of a dozen AutoZone products that apparently promise 5 to 10 horsepower

Cheers, I'm out

 

[bflynn]

If you don't want to understand the science, then its difficult to make the claim that it must be bogus. The company who makes the OP's product is a zombie company in a larger conglomerate, so they don't have a lot going. But the topic of vortex generators improving propellers is not new.

If you're legitimately interested in the topic, let me know. I have a cousin who is a former propeller engineer for McCauley, now a test pilot for Cessna. I'm sure he can help dig up some good stuff, but I suspect it's a heavy subject.

Bottom line, not snake oil.

 

[Tantalum]

If you don't want to understand the science, then its difficult to make the claim that it must be bogus.

I understand the science. I'm questioning if this specific product's claims are actually true, in any meaningful way

I feel like we're talking about two different points (aerodynamics and VGs, vs this propeller sticker product). Theoretically improving the airflow around the propeller will surely help. I'm just not sure if these stickers on the prop are going to achieve the advertised goals

Let's say we both bought them, put them on otherwise identical 172.. and both left San Diego and flew up to the Bay Area.. a long enough flight where small gains help.

I'd venture to guess that we'd land at about the same time, after having burnt roughly the same amount of gas

 

[MooneyDriver78]

And yet, that's what the aerodynamic tests showed, so it isn't an assumption.

It's drag reduction. There's nothing magical about that.

VGs only reduces drag with non laminar flow airfoils or at high angle of attack, that’s why we don’t see them (or shouldn’t) spanning entire wings or covering the entire fuselages...like dimples on a golf ball.


Tom