What do speed mods do to the yellow/ red arc / Vne?

[Joe G.]

Hello,

First post and new to the mooney world.

When speed mods are done to the pre Js allowing for faster speeds than the originals, what affect does this have on the recommended speeds? I understand the AC can now achieve better speeds but, do these speeds have a negative effect on the airframe, etc?

Thanks and thank you for all of the great information I've already picked up by lurking.

Joe

[DS1980]

Not sure of the question.

 

If asking about  the green, yellow and white arcs, these will remain the same.

 

Stall, flap and gear speeds will remain the same. I do not believe in maneuvering speed but this will not change either. These are INDICATED airspeeds.

 

Vne is a TRUE airspeed and will not change. It is based on the frequency magnitude (true) of air hitting the airframe rather than the mass (indicated).

 

The airplane doesn't care what speed mods it has on it. The mods must not interfere with flight characteristics or affect the structure of the airframe. 150 knots is 150 knots, whether or not you have modifications.

[Joe G.]

Not sure of the question.

 

If asking about  the green, yellow and white arcs, these will remain the same.

 

Stall, flap and gear speeds will remain the same. I do not believe in maneuvering speed but this will not change either. These are INDICATED airspeeds.

 

Vne is a TRUE airspeed and will not change. It is based on the frequency magnitude (true) of air hitting the airframe rather than the mass (indicated).

 

The airplane doesn't care what speed mods it has on it. The mods must not interfere with flight characteristics or affect the structure of the airframe. 150 knots is 150 knots, whether or not you have modifications.

I was working under the assumption the F has lower Vno, Vna and Vne than the M20J. This may be my first mistake.

Assuming the speeds are different for the different models; if making speed mods to an F ,thereby giving it closer to J speed capabilities, do the Vno, Vna and Vne remain the same as they would for an un moded F airframe?

I guess it's really the Vne I'm wondering about the most? Can speed mods on an F put the capabilities of the AC outside the Vne?

Hope this makes sense and isn't a foolish question.

[carusoam]

The difference is....

With speed mods, you will get to the red line sooner.

You will save some gas while getting to the red line.

The limitation is in the airframe.

By putting a few fairings on the AF, you haven't changed the structure...

If you want to fly faster, select the airframe with higher red lines and the power to achieve them.

Same discussion applies to maneuvering speeds.

Enjoy safely,

-a-

[Joe G.]

The difference is....

With speed mods, you will get to the red line sooner.

You will save some gas while getting to the red line.

The limitation is in the airframe.

By putting a few fairings on the AF, you haven't changed the structure...

If you want to fly faster, select the airframe with higher red lines and the power to achieve them.

Same discussion applies to maneuvering speeds.

Enjoy safely,

-a-

Thank you, this is exactly what I suspected and was wondering about.

[carusoam]

On the east coast...

Flying above 5k' is usually smooth air.

Red line VNE can be exceeded easily by descending at a high rate.

When your air frame is 50 years old, you may prefer it maintained and cared for like it was built recently.

The air worthiness testing (red lines set) was done on new airframes...

The good news... You can search for Mooney accidents. Very few will be by an air frame failure.

Unfortunately... The pilot is often the week link (T-storms and icing). Keep studying!

Continued training is good for you...

Best regards,

-a-

[DS1980]

I was working under the assumption the F has lower Vno, Vna and Vne than the M20J. This may be my first mistake.

 

He wasn't comparing models, just asking about pre-J. Simply asking what speed mods do to speed limitations, which is nothing.

[carusoam]

Darin,

I took some liberties.....

The older planes have lower speed limits and the F can be modded into a J.

So the follow up question would be...

If I buy an F, then later modify it to a J...

Do I get the higher speed limits and GMTWs that come with that???

Personally, I would lean towards get the O with all the attributes you want. Money is not going to be cheaper for decades to come... (But I kept that under my AOPA hat)

Best regards,

-a-

[rbridges]

 

 

Vne is a TRUE airspeed and will not change. It is based on the frequency magnitude (true) of air hitting the airframe rather than the mass (indicated).

 

 

well, I learned something.  I though Vne was IAS.  I figured less dense air meant less structural strain.  Never busted it either way, but my thinking was wrong.

[Joe G.]

He wasn't comparing models, just asking about pre-J. Simply asking what speed mods do to speed limitations, which is nothing.

Correct and as you pointed out, the mods don't raise the limits, they just get you there faster. (which was a great way to put it). Which brought me to, "why do the mods then if you can't take advantage of the ability to go faster". The answer seems to be; better fuel efficiency and the F allows for operation above the 145-150knt range ((in the yellow) which you can fly in when in smooth air.

I appreciate the information/ educations so let me know if my thinking is all wrong.

[OR75]

the mods should be spelled out in the STC and the impact should be spelled out clearly in the STC.

 

It may become very complicated when you start mixing STCs 

[podair]

I don't think you need to worry too much , the mods won't add that much relative to where the yellow arc is on an M20F.

the yellow arc on my 1967 starts at 175mph so waay above my normal cruise speeds.

I did some training on an M20C and there the yellow arc was lower and you would routinely go into it in cruise. 

 

Mine is completely stock , except for a 3 blade Hartzell prop.

I rarely achieve more than 145-150mph IAS, at my normal 65% power settings, but at my usual 9000-10000ft that is already routinely 142 to 145 kt TAS at 8gph, which is pretty good already and my optimum altitude.

If I really push it, I can sometimes get 155mph at lower altitudes but 10gph or so.

I doubt the mods achieve more than 10mph, maybe 15 max which would theoretically put you in M20J territory at 150-160ktas.

 

I am thinking at some point of putting a M20J windshield mod, and maybe a Powerflow, but I expect no more than 10mph out of both, combined. Maybe more if I put the LoPresti cowl, but not worth the expense. Looks cool though. The cowl closure seems to help with CHTs , not really an issue with mine but might do it regardless.

[DS1980]

well, I learned something.  I though Vne was IAS.  I figured less dense air meant less structural strain.  Never busted it either way, but my thinking was wrong.

I was in the same boat, and thought exactly how you did. Blew my mind when I read about it. But when I think about it in terms of flutter other than structural load, it makes sense, as Vne is a function of when the air frequency hitting the plane matches the internal resonance of the airframe.

 

So when you hear about people cruising high in the yellow or "bringing her all the way to the red radial line," they might be beyond Vne. The only thing that saves them is the margin of safety built into the calculations and airframes. I guess it helps having a plane with a spar 11 inches thick.

[mooniac15u]

Not sure of the question.

 

If asking about  the green, yellow and white arcs, these will remain the same.

 

Stall, flap and gear speeds will remain the same. I do not believe in maneuvering speed but this will not change either. These are INDICATED airspeeds.

 

Vne is a TRUE airspeed and will not change. It is based on the frequency magnitude (true) of air hitting the airframe rather than the mass (indicated).

 

The airplane doesn't care what speed mods it has on it. The mods must not interfere with flight characteristics or affect the structure of the airframe. 150 knots is 150 knots, whether or not you have modifications.

 

Vne is definitely IAS.  All markings on the airspeed indicator are required to be in IAS per the FARs:

 

Sec. 23.1545 Airspeed indicator.

(a) Each airspeed indicator must be marked as specified in paragraph (b ) of this section, with the marks located at the corresponding indicated airspeeds.

(b ) The following markings must be made:

(1) For the never-exceed speed VNE, a radial red line.

 

 

The rules for calculating Vne are detailed in 23.1505 if you are interested. 

[Mooneymite]

Vne is definitely IAS.  All markings on the airspeed indicator are required to be in IAS per the FARs:

 

. 

 

The subject of Vne is a little confusing, but aircraft that operate where there is a big split between IAS and TAS are usually equipped with "Barber Poles", or moving Vne indicators.  Carrying a chart around to define Vne at various altitudes would be cumbersome.

 

The concept of "coffin corner" is due to the fact that the wing needs IAS to fly, but the airframe is limited by TAS (or, more precisely, Mach).  

 

However, if you think that Vne is a convoluted subject, read up on the whole subject of maneuvering speed (Va)!  The Airbus engineers never clearly communicated their concept of Va to the pilots, so an American pilot, doing as he was trained, broke the vertical stabilizer off.  (AA587)  

 

This stuff can have consequences!

[DS1980]

Vne is definitely IAS.  All markings on the airspeed indicator are required to be in IAS per the FARs:

 

Sec. 23.1545 Airspeed indicator.

(a) Each airspeed indicator must be marked as specified in paragraph (b ) of this section, with the marks located at the corresponding indicated airspeeds.

(b ) The following markings must be made:

(1) For the never-exceed speed VNE, a radial red line.

 

 

The rules for calculating Vne are detailed in 23.1505 if you are interested. 

Yes, it's marked on the dial to show what it would be at standard atmosphere at service ceiling. When is the only time your fuel gauges have to be accurate? Not very helpful are they.

Most pilots know much more about aerodynamics and airplanes than the FAA. I could explain to you why Vne is not an indicated airspeed, but  Mr. Krueger will do it much better.

 

Please read attached article.

Vne-and-hp_limts.pdf

[carusoam]

Things I learned after I bought my Mooney...

Fly in smooth air... 5k' AGL usually does the trick...

Slow down if you can't... Calculate the maneuvering speed for the weight of the plane...

Avoid exceeding VNE...

Maintain your plane to like new condition...

Avoid ice and thunderstorms. Planes can get bent or the lift can be robbed...

Keep bank angle under 30d in the TP. Stall speed increases and can exceed the current airspeed...

If anything seems funny, plan to go around. If the funnyness continues, go around anyway....

Wind direction can change 180d since you took off, clearly see the wind sock before landing...

Go get a Mooney,

-a-

[carusoam]

The free lunch theory...

Nice detail Darin!

-a-

[DS1980]

Gracious. But thank Krueger. A well written article.

[mooniac15u]

Yes, it's marked on the dial to show what it would be at standard atmosphere at sea level. When is the only time your fuel gauges have to be accurate? Not very helpful are they.

Most pilots know much more about aerodynamics and airplanes than the FAA. I could explain to you why Vne is not an indicated airspeed, but  Mr. Krueger will do it much better.

 

Please read attached article.

 

That whole article is related to flutter speeds in experimental aircraft.  In a certificated aircraft like our Mooneys there is no way to know what the flutter speed is.  The Vne on our airspeed indicators is absolutely in IAS and is effectively a placarded limitation.  In some certificated aircraft it may be related to flutter speeds and in others it may not.  If you stay within the flight envelope defined by the certification limitations the indicated Vne will always keep you in a safe operating range.  In some conditions (e.g. higher altitude) you will be closer to the edge of the envelope when you are near Vne.

 

The problem here is that you are considering the Vne of a certificated aircraft to be based upon actual aerodynamic factors.  That is not necessarily a good assumption.  Vne in a certificated aircraft is a legal statement not a performance limitation.

 

The fact that the M20F has a different Vne than the M20J is really the only evidence you need that Vne is not an actual aerodynamic limitation for our aircraft.  Flutter speeds in these aircraft would be nearly identical since they are the same airframe.

[mooniac15u]

From the Krueger article:

 

"Vne can be established based on a number of factors.

One consideration is the speed at which the airframe design

limit will not be exceeded when encountering a sharp

edge vertical gust of 25 fps. Another is the maximum

safe speed at which the airplane can be flown without encountering

aerodynamic flutter. The RV-9A Vne was set

based on flutter considerations. But in cruising flight, gust

loads are the limiting factor. If an engine capable of producing

75% power speeds of over 180 mph is used, design

strength could be exceeded."

[DS1980]

I'm not speaking of any plane in particular. I'm speaking of what Vne is. It's a true airspeed. Most airplanes will flutter before structural failure.

 

0:50-1:05

 

Call Mooney. I'm sure an engineer or test pilot will tell you exactly when the Mooney flutters. Maybe they won't.

 

 

[PTK]

Speed mods do not (must not) change the envelope of the airframe.

All speeds on the ASI are based on IAS with the exception of Vne (Red line.)

This is because it takes into account service ceiling and protects against exceeding it in a descent from altitude. (If Vne was based on IAS it would have to be lower as we approach the service ceiling.)

The difference between TAS from IAS is altitude dependent.

We can easily exceed Vne if in a descent from altitude.

Incidentally the beauty of flying a certificated airplane is exactly this. Stay within its envelope and all is good!

[mooniac15u]

Vne is IAS per the FARs. Aerodynamic flutter is related to the TAS. The two are not necessarily related.

On a certificated aircraft the Vne is an arbitrary fixed value.

If you believe that something bad happens aerodynamically to the M20J above the published Vne please tell me how the M20K and the Missile/Rocket conversions are able to operate above that airspeed with the same airframe.

The bottom line is that Vne is a regulatory requirement not a speed at which something has necessarily been shown to fail. It is an IAS and it builds in a safety margin to account for the fact that their are bad aerodynamic effects related to certain TAS.

[mooniac15u]

If you need more evidence that Vne is not necessarily an aerodynamic issue (i.e. Not Flutter) take a look at this Mooney SB:

http://www.mooney.com/wp-content/themes/mooney2014/force-download.php?file=http://www.mooney.com/wp-content/uploads/2014/03/sbm20-198.pdf

Just modify the prop and Vne went up 25 mph.