Oleo Struts conversion for Mooney?

[Niko182]

2 minutes ago, ilovecornfields said:

You may have forgotten that this is an internet discussion - your extensive professional and personal experience on this exact subject is completely irrelevant. Everyone gets to express their opinion and demand to have it treated as fact.

Lol

[A64Pilot]

Sigh,

      Sure VG’s lower stall by a significant amount, which allows shorter takeoff distances, shorter landing distances and tighter turns, all of this would occur if stall speed was lowered.

That’s what all Ag planes have VG’s as well as all STOL airplanes and military fighter jets and of course all Aerobatic aircraft, right?

Surely all of those manufacturers and kit builders are fools, just by glueing on VG’s they can enhance performance significantly, but they don’t, because it would cost them thousands of dollars to Certify? Most manufacturers would name their first born after you if you could knock off 8% of stall speed for a insignificant cost and no increased weight, loss of useful load etc.

At high angles of attack in any aircraft, the airspeed indicator starts to be inaccurate, just as one posted his Cherokee was indicating zero when it stalled, he’s not wrong, it was probably approaching zero because of the angle of the pitot tube to the relative wind.

That is why in test flying we install an airspeed boom, that gets the pitot tube away from the wing, but more importantly it has a “bird” a dart looking thing that articulates so that it points into the relative wind regardless of aircraft attitude, that is how you get an accurate airspeed at high angles of attack.

I don’t doubt that maybe you guys are seeing 5 kts lower indicated airspeed, maybe. I’m doubting it’s actually five knots true. Just as I do not doubt the poster that said he saw zero

‘I never said VG’s don’t work, as I said you see them often on Commercial aircraft at places where there is an undesired airflow separation, they are good band aid just like flow fences are, but I’ve not seen them all across the wing of any modern aircraft, but I’ve not seen them all.

It’s not just Mooney that’s limited in gross weight by min stall speed, it’s pretty much any efficient / fast small aircraft, I bet a Cirrus SR-22 for instance is all over 61 kts stall too. It’s been a performance limit for a long time

 

Edited September 25, 2021 by A64Pilot

[aviatoreb]

43 minutes ago, A64Pilot said:

Sigh,

That is why in test flying we install an airspeed boom, that gets the pitot tube away from the wing, but more importantly it has a “bird” a dart looking thing that articulates so that it points into the relative wind regardless of aircraft attitude, that is how you get an accurate airspeed at high angles of attack.

I don’t doubt that maybe you guys are seeing 5 kts lower indicated airspeed, maybe. I’m doubting it’s actually five knots true. Just as I do not doubt the poster that said he saw zero

 

Sigh right back at ya.

Sure - instrument error may increase as angle of attack increases.  So what's your point.  If I am measuring 5 kts slower stall speed its actually 0.1?  Or is it really 4? 1?  sigh.  I can't make out your point.  How much instrument error makes the point absurd.  If its 4 or if its 5, its roughly the same thing in discussion terms claiming it works.  And, sigh, we didn't talk about weight.  Or human error when reading that number 5 which are both also likely well over 1kts.  So unless you are sighing over an order of magnitude error then I think your point is a red herring.

[ilovecornfields]

@aviatoreb is a pretty smart guy. I’m not just saying that because we went to the same college and he has a PhD in a subject that baffles me but because I’ve had several discussions with him and he has me convinced.

When all the backtracking and caveats start then maybe it’s time to let it go. It sounds like you’re admitting that they do something to stall speed and that “something” doesn’t increase speed. The only remaining option is that they decrease stall speed- let’s say by some number between 1-10 (an order of magnitude range is good enough, right?) Why don’t we just leave it and talk about something else that we can all have an intelligent discussion on? Like lean-of-peak touch-and-goes in a crosswind with no flaps?

[ArtVandelay]

‘I never said VG’s don’t work, as I said you see them often on Commercial aircraft at places where there is an undesired airflow separation, they are good band aid just like flow fences are, but I’ve not seen them all across the wing of any modern aircraft, but I’ve not seen them all.

For commercial aircraft I thought they were only in front of the ailerons, to improve control, like Learjets, who removed them and replaced the vanes with bumps, but same function.

[A64Pilot]

1 hour ago, ilovecornfields said:

@aviatoreb is a pretty smart guy. I’m not just saying that because we went to the same college and he has a PhD in a subject that baffles me but because I’ve had several discussions with him and he has me convinced.

When all the backtracking and caveats start then maybe it’s time to let it go. It sounds like you’re admitting that they do something to stall speed and that “something” doesn’t increase speed. The only remaining option is that they decrease stall speed- let’s say by some number between 1-10 (an order of magnitude range is good enough, right?) Why don’t we just leave it and talk about something else that we can all have an intelligent discussion on? Like lean-of-peak touch-and-goes in a crosswind with no flaps?

From my testing on admittedly one aircraft it was a couple of kts max, depending on gross weight, that was with a airspeed boom.

They do work, I had them added to the Type Certificate of an S2R H-80, but their effect on stall speed is minimal, there did seem to be an effect of the spray pattern though that was quite substantial, we were validating that in Tx with Annie’s help, but unfortunately there was an accident and that testing was never completed, I do think the added energy in the airflow caused the spray to be more evenly mixed

From a seat of the pants observation on my Maule, I could hang it on the prop at near zero indicated airspeed, which of course it wasn’t. Maule has done their testing and as the GA aircraft that has the greatest difference between stall speed and cruise when airspeed is a %, they would kill to get a few kts. 

I am not a multi engine guy, but I’m nearly certain that at least on some of those VG kits due likely to them being on the tail reduces single engine airspeed, that’s evidenced by the FAA requiring the airspeed indicator to be remarked with the new lower airspeed. If you change airspeed significantly, the FAA will make you have the indicator remarked, which isn’t very expensive, but you don’t change V Speeds on a Certified aircraft and not document it.

They way they work is by adding energy to the airflow, this energized airflow will tend to stay attached longer at higher angles of attack than unenergized air, however with the wing loading most GA aircraft have stall angle of attack is pretty high, but it’s not linear, the slower you go requires an ever increasing amount of attack to get there, think of it like adding Power, you can increase power by 50%, but you don’t get a 50% increase in speed. So to get 5 kts it’s going to take a whole lot of angle of attack increase.

I just don’t think your getting anywhere near 5 kts.

Edited September 25, 2021 by A64Pilot

[A64Pilot]

16 minutes ago, ArtVandelay said:

For commercial aircraft I thought they were only in front of the ailerons, to improve control, like Learjets, who removed them and replaced the vanes with bumps, but same function.

You will see them near the engines on some aircraft on the fuselage and other places, wherever the airflow detaches and VG’s will keep it attached, not just on wings, some aircraft will have them on the leading edge of the wing, but under the slats, so that in normal flight they are covered and only uncovered on slat extension. Even if they only add a tiny bit there it’s worth it as they are covered in flight.

My Maule needed them in front of the ailerons as if hanging on the prop they became pretty much ineffective, if a wing dropped only the rudder would raise it.

Maule fixed that in later models by changing to a Horner tip from a droop tip. the different tip allowed for 6” more aileron without reducing flap length or adding wing length. if they extended the wing the FAA would make them re-pull the wing, and it’s likely it woudn’t pass, and they aren’t about to shorten flaps.

 

But to get back to the point of a gross weight improvement of the later model big motor Mooney’s.

Its going to take a lot more than replacing rubber donuts with Oleo struts in my opinion as I suspicion the big Mooney’s are probably crowding 61 kts pretty hard. I am not saying it can’t be done, but it’s not going to be easy, it’s going to be hard, take quite a long time and be very expensive, and in my opinion not likely to be retrofitted at least without a whole lot of money, because I think the landing gear are but one obstacle, and they may be the easiest to overcome.

‘I don’t know anything really about Mooney’s financial situation, but I suspect as someone already posted it’s not likely they have the $$$ to realistically take on such a project

[toto]

3 hours ago, A64Pilot said:

just as one posted his Cherokee was indicating zero when it stalled

I’m mostly just sitting here eating popcorn, but as a part-time Piper flyer, I’ll note that a Super Cub and a Cherokee are very different aircraft

[aviatoreb]

2 hours ago, ilovecornfields said:

@aviatoreb is a pretty smart guy. I’m not just saying that because we went to the same college and he has a PhD in a subject that baffles me but because I’ve had several discussions with him and he has me convinced.

When all the backtracking and caveats start then maybe it’s time to let it go. It sounds like you’re admitting that they do something to stall speed and that “something” doesn’t increase speed. The only remaining option is that they decrease stall speed- let’s say by some number between 1-10 (an order of magnitude range is good enough, right?) Why don’t we just leave it and talk about something else that we can all have an intelligent discussion on? Like lean-of-peak touch-and-goes in a crosswind with no flaps?

Thank you ilovecornfields.  (BTW - isn't that like a really bad avatar name for a pilot?!) (I love runways!). You are very kind - and we did go to the same school - go on you BEARS!

lean of peak is too complicated for me as I think there is quantum mechanics and cold fusion involved.

E

 

[aviatoreb]

1 hour ago, A64Pilot said:

From my testing on admittedly one aircraft it was a couple of kts max, depending on gross weight, that was with a airspeed boom.

They do work, I had them added to the Type Certificate of an S2R H-80, but their effect on stall speed is minimal, there did seem to be an effect of the spray pattern though that was quite substantial, we were validating that in Tx with Annie’s help, but unfortunately there was an accident and that testing was never completed, I do think the added energy in the airflow caused the spray to be more evenly mixed

From a seat of the pants observation on my Maule, I could hang it on the prop at near zero indicated airspeed, which of course it wasn’t. Maule has done their testing and as the GA aircraft that has the greatest difference between stall speed and cruise when airspeed is a %, they would kill to get a few kts. 

I am not a multi engine guy, but I’m nearly certain that at least on some of those VG kits due likely to them being on the tail reduces single engine airspeed, that’s evidenced by the FAA requiring the airspeed indicator to be remarked with the new lower airspeed. If you change airspeed significantly, the FAA will make you have the indicator remarked, which isn’t very expensive, but you don’t change V Speeds on a Certified aircraft and not document it.

They way they work is by adding energy to the airflow, this energized airflow will tend to stay attached longer at higher angles of attack than unenergized air, however with the wing loading most GA aircraft have stall angle of attack is pretty high, but it’s not linear, the slower you go requires an ever increasing amount of attack to get there, think of it like adding Power, you can increase power by 50%, but you don’t get a 50% increase in speed. So to get 5 kts it’s going to take a whole lot of angle of attack increase.

I just don’t think your getting anywhere near 5 kts.

I will say this - and I work closely with science and engineering experimentalists a lot.  every every every experimental measurement has error.  Some more than others.  No sensor is perfect.  A pitot tube has a nice mostly linear response over a certain range and then the response so it seems goes nonlinear with the absurd value of 0 you clearly called out while the airplane is still flying.  I wouldn't be surprised if a negative number were possible with some kind of back pressure arrangement.  An impeller on an airspeed boom can be better, as you call out.  So a much better instrument when flight test engineering, but it is far from a perfect instrument.  You simply don't see impellers in a more controlled environment like a wind tunnel because it is a crude instrument in comparison to other methods.  It has error.  lasers and piv methods I believe are the standard fare for decent quality measurements there.  Lasers also have a place in experimental in field aircraft flying.  But no measurement/no instrument/ is perfect no matter how fantastic it may seem or how expensive or how respected. Ask Heisenberg.

For the gross measurements I call out - 5kts, I will be the first to tell you that likely the largest error is me - the human - trying to read off a marked dial quickly during a dynamic event.  On set of stall while I am simultaneously trying to fly the airplane, keep it coordinated and watch the nose out the window with one eye and watch the airspeed indicator with the other eye.  Making up error bars out of my imperial hat, I will say plus or minus 2 knots is my ability to read AIS at the moment of stall.  

So you say, no where near 5kts.  Sure, I'm fine with that.  So call out a number.  Be bold.  Is that 4? 3?  Or are you saying its 0.5 or 0.1 knots slowed stall speed.  Be bold.

Supporting evidence that it is lowered appreciably, my roll out is shorter agreeably with a noticeably slower stall speed.  But I am afraid to call out how much shorter because, it is hard for the human to measure the exact moment of touch down and the exact moment of stop while piloting an airplane.  And even if I could, I would need to decide if I should use a tape measure to measure the distance (like measuring if 10 yds are made in a football game with the referees chains!), or a laser and time the light returning from a mirror placed at the opposite spot of measurement, or maybe by sonar, or I could use gps (and gps is used to measure distance in experiments all the time when accuracy is otherwise hard - like say in volcanoes and how the mountain bows as pressure builds), but then it is important to not bother measuring one part of the experiment with more precision than the rest of the experiment, e.g. if you cannot identify to microns where touch down occurred, then why measure the distance to stop in microns.

My guess - just a guess, is that the pitot tube designed and spec'ed on my aircraft is able to measure 54 knots to reasonable accuracy even at the angle of attack near vg-enhanced stall, at least to a precision that is agreeable (comparably accurate/comparably inaccurate) with the error I already brought to the table by claiming I can read 54 knots while trying to pilot during the dynamic event of piloting and stalling and looking out the window and trying to keep my aircraft coordinated so it won't spin.

So I challenge you. Rather than just throw spit balls and sigh a lot, please be bold and call out what you think may be the actual likely stall speed reduction, in knots, a number - so if I say 5 - knowing full well it is an imperfect measurement - what do you say?
E

[A64Pilot]

Call out a number? I did I said in the aircraft that I test flew it was a kt or two, two max. I’ve not flown a Mooney with VG’s but I’ve flown Cessna’s and a Maule M6-235 and all I’d say were really about a kt or two.

Yes a SC and  Cherokee are different, I thought I saw PA 28-160, not PA 18. You would be surprised at how similar they are in a stall though, neither really stalls power off, they just mush very controllably.

‘But we get back to all the high performance aircraft that there are are out there that are pushing 61 kts pretty hard, if by adding one simple thing they could drop back to 56 kts, they would in a heart beat, because there are other things they woud love to do but can’t, because they are all over max stall speed as it is. 

I know you guys don’t want to believe that, and that’s fine believe what you want, that all or most anyway if the current aircraft manufacturers won’t improve their fleets performance and safety by adding VG’s, which no one has a patent on so it would be very simple for them to do.

I had Annie put her STC on because frankly for the price she would sell the kits to us it was a no brainer. I did it for sales, the same reason I incorporated the Air bag seat belt into the TC, and by the way I don’t think they do much either ,in fact I think them inferior to our stock belts because they are 1500 lb belts and the stock belts are 5,000 lb. 5 point harnesses, but some wanted them.

‘What surprises me is you guys think the FAA doesn’t mind a V speed being changed by 5 kts or 8% without even changing the operating manual 

Edited September 25, 2021 by A64Pilot

[aviatoreb]

4 minutes ago, A64Pilot said:

Call out a number? I did I said i’m the aircraft thstI test flew it was a kt or two, two max.

Fair enough.  So you assert it is 1 kt for Mooneys, maybe 2 max?  Is that your number for Mooneys?  I didn't catch if the aircraft you flew was a Mooney or if you say its also the same for our make and model.

Interestingly, the marketing material for the VG companies available for many GA planes call out numbers, but I think that is just advertising. I don't know the process but I bet the stc process not require them to demonstrate an accurate number or maybe even any number as to if it changes stall speed.  I bet they only need to demonstrate that it does not make the airplane flying characteristics worse and it still stalls at that magic 61 or better.  Other than those some twin models where they get to actually re-mark their AIS and also they get gross weight increases.

[A64Pilot]

33 minutes ago, aviatoreb said:

Fair enough.  So you assert it is 1 kt for Mooneys, maybe 2 max?  Is that your number for Mooneys?  I didn't catch if the aircraft you flew was a Mooney or if you say its also the same for our make and model.

Interestingly, the marketing material for the VG companies available for many GA planes call out numbers, but I think that is just advertising. I don't know the process but I bet the stc process not require them to demonstrate an accurate number or maybe even any number as to if it changes stall speed.  I bet they only need to demonstrate that it does not make the airplane flying characteristics worse and it still stalls at that magic 61 or better.  Other than those some twin models where they get to actually re-mark their AIS and also they get gross weight increases.

I have not flown a Mooney with VG’s. but have several other aircraft and they have all been I think about a kt or two actual, I would suspect a Mooney to not be any different, but that is supposition. My Maule it lost about a kt or two cruise and lost about the same in stall, seemed what it lost in cruise it also lost in stall.

What you say about the VG test flight at least the one Annie’s DER conducted on our aircraft is exactly correct, the test flight validates no significant change in flight qualities.

We even put VG’s on the underside of the horizontal, mostly because they look cool, but also because our aircraft even at max aft CG stalls like a Piper power off, meaning it doesn’t really stall, it runs out of elevator authority and just mushes, I wanted to see if the VG’s added elevator authority, then it might just push us to a real stall and it would be at slower air speeds of course, but it didn’t make any difference. I wanted it to, who doesn’t want to increase the performance of an aircraft they make?

If you want to install VG’s it’s best to strip the part of the wing they go on, the Loctite Depend adhesive they use is a very strong adhesive, it’s much stronger than the paint bond so if someone drags a fuel hose over your wing or whatever, most likely it’s the paint that will pop off when the VG is broken off, but if it’s glued directly to the metal I’ve seen them bent and still be attached, that glue is tough.

[GeeBee]

Let’s face it. We are talking at the most 3 knots here. Lot if ways to accomplish that but the point is if you’re any kind of engineer and you can’t find 3 knots your glutes are seeing a Brazilian wax specialist…regularly.

[A64Pilot]

I think three or four kts is not easy.

‘I know what I’d try first may not work but what would you try first?

[GeeBee]

In no particular order. 

Wing to fuselage fitting

Wing tip

spanwise flow

flap to wing area

[A64Pilot]

Those are very generic answers.

I can tell you from my own testing that wing tips do pretty much nothing on GA aircraft, Mooney is an excellent example the older Mooney’s have no tips and how much was gained from the tips on the J?  Other than maybe looking cool, I don’t think much was gained.

I’ve seen wing root fairings cause buffering in a stall, and an early false buffeting, but I’ve not seen them change speed by much.

By span wise flow, you mean fences? Maybe, but it would be butt ugly, look at almost all older Soviet designs, fences do work though.

By flap to wing area do you mean increasing flap size? Maybe if it doesn’t become pitch unstable, I suspect it might and simple flaps aren’t very efficient anyway.

 

I’d want to try Fowler flaps, one benefit for a Mooney speed freak is as they run in tracks, there are no hinges to hang down in the airflow, but again they may be destabilizing in pitch.

You can make a “poor mans” Fowler by dropping the hinges lower. the longer hinges of course cause the flaps to move rearward as they go down sort of emulating a Fowler. Look at an Aviat Husky to see what I mean 

However you might get there by drooping the ailerons with flap deployment like many large Commercial jets, Beavers and many STOL airplanes do, that’s maybe the least risky and I think drooped ailerons would get you the three or four kts.

I feel sure you could easily get there with slats, but that’s real $$$

On edit, as the stall speed test is conducted at max gross, and max fwd CG, moving max forward CG aft is another way, on many aircraft as the weight goes up, you’ll see the max allowable CG come aft, often that line represents 61 kt stall, but on many it also represents the nose wheel landing gear drop test too, so it can be either structural as well as aerodynamic limit.

Sometimes the max fwd CG limit is well past any reasonable loading so there is no harm in moving it aft. I have no idea about the bigger Mooney’s but suspect as they have those big heavy motors and ballast to accommodate them, that you can’t move the limit aft.

Edited September 26, 2021 by A64Pilot

[philip_g]

5 posts about struts. 2 pages on vortex generators. Jesus Christ guys.

[philiplane]

well, VG's would be part of the solution for increased gross weight, rather than new flaps. Keeping under the 61 knot stall limit makes the whole exercise a lot cheaper. VG's will do that. Oleo struts are not hard, just figure what weight you expect, CAD model them, prototype a set and install. Then the hard part begins. FMEA of the wing structure for the higher weight, flight testing of a VG equipped plane at the higher landing weight, and if the margin is insufficient, figure out how to get more flap travel or more flap area to stay within the desired landing stall speed. VG's would be the quickest and cheapest way to meet several goals.

[mike_elliott]

On 9/25/2021 at 6:10 PM, A64Pilot said:

I did I said in the aircraft that I test flew it was a kt or two, two max. I’ve not flown a Mooney with VG’s

Like Eric and Raul, I have flown and stalled a Mooney with VG's. It stalled at 52 kts. It was a Mooney M20V with TKS N242PT approx 200# under gross.

[Shadrach]

9 hours ago, mike_elliott said:

Like Eric and Raul, I have flown and stalled a Mooney with VG's. It stalled at 52 kts. It was a Mooney M20V with TKS N242PT approx 200# under gross.

So that's 5kts below calculated stall speed at 3168lbs with the "standard" Mooney wing. 

 

I will echo the comments of others in saying, how foolish of Mooney for not pursuing this earlier.  This is not new tech. They've added 4 aircraft to the TCDS in the last 15 years.  All that work... If they had just added VGs, they'd have a 4000lb MGTOW airplane that could meet Part 23 requirements with extra margin.  It's a shame the smart folks on this board weren't running the company.  VGs add enough margin for an easy MGTOW increase of 650lbs.  Let's say the new oleo struts add 200lbs of weight.  Now add the new chute (which would be certifiable because of the new oleo strut gear) at 60lbs. This makes for a payload increase of 390lbs.  That's two good size people or one FAA standard Marauder "Lady".  Would make for a Cirrus killer for sure...that is...unless Cirrus management gets smart too...Then they'll add VGs and have a 4250lb airplane with 1800lbs of useful. Textron will likely follow with the Beech and Cessna lines.  It will be a revolution of slow stalling, seats full, GA aircraft that has been long over due. 

Edited September 27, 2021 by Shadrach

[carusoam]

Ross is a highly technical Mooniac…

But tonight… his technical Marketing skills are on FIRE!  

Going to want that Land Now feature too… the option of using a real airport… would be a nice added touch if able…

Best regards,

-a-

[Shadrach]

8 hours ago, carusoam said:

Ross is a highly technical Mooniac…

But tonight… his technical Marketing skills are on FIRE!  

Going to want that Land Now feature too… the option of using a real airport… would be a nice added touch if able…

Best regards,

-a-

Highly technical? I’ve always considered my strengths to be my charm and sweet disposition...

[A64Pilot]

On 9/27/2021 at 11:32 AM, Shadrach said:

So that's 5kts below calculated stall speed at 3168lbs with the "standard" Mooney wing. 

 

I will echo the comments of others in saying, how foolish of Mooney for not pursuing this earlier.  This is not new tech. They've added 4 aircraft to the TCDS in the last 15 years.  All that work... If they had just added VGs, they'd have a 4000lb MGTOW airplane that could meet Part 23 requirements with extra margin.  It's a shame the smart folks on this board weren't running the company.  VGs add enough margin for an easy MGTOW increase of 650lbs.  Let's say the new oleo struts add 200lbs of weight.  Now add the new chute (which would be certifiable because of the new oleo strut gear) at 60lbs. This makes for a payload increase of 390lbs.  That's two good size people or one FAA standard Marauder "Lady".  Would make for a Cirrus killer for sure...that is...unless Cirrus management gets smart too...Then they'll add VGs and have a 4250lb airplane with 1800lbs of useful. Textron will likely follow with the Beech and Cessna lines.  It will be a revolution of slow stalling, seats full, GA aircraft that has been long over due. 

You really believe that none of the major manufacturers have discovered the miracle attributes or VG’s? They are ALL stupid? What, nobody’s told them?

VG’s are so easy to get into a TC, call Annie, she shows show up with her DER test pilot, one day to install and conform the installation, one test flight and a couple of weeks and the STC is issued, and with permission of the STC holder, the STC is rolled into the TC, and she will give a manufacturer OEM pricing on the VG’s.

Of course you can roll your own too, there is no Patent.

Not much is easier in aviation, it was the easiest modification I ever did to the aircraft.

For instance leading edge lights used primarily as recognition lights got so stupid that I just gave up

 

I’ll repeat again, I am NOT saying you guys are not telling the truth about what you see on your airspeed indicator, or mistaken.

However any aircraft as it approaches stall angles of attack, the A/S indicator becomes unreliable , as some have seen some light STOL aircraft you can hang on the prop and indicate zero or near zero airspeed.

I’ll bow out of this conversation as I’m obviously not going to change any minds, However just as a general rule in life, question miracle mods that any manufacturer could adapt but doesn’t. like fuel line magnets or “intake vornado’s” or 100 MPG carburetors to name a few for cars during the energy crisis of the 70’s. 

Edited September 28, 2021 by A64Pilot

[PT20J]