Van's Air Force
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EAS? Anyone know how to calculate EAS: Equivalent Air
- Thread starter TLYNCH
- Start date
David Paule
Well Known Member
1001001
Well Known Member
The terminology r0 in your formula is read as "r sub zero."
"r" in this case substitutes for rho which is density. "r sub zero" is standard sea level density. "r" is the density at the measured conditions.
The "1/2" is indicating "to the one-half power" which is the same as the square root.
Equivalent airspeed is defined mathematically as the True Airspeed multiplied by the square root of the ratio of the measured air density to the density at standard conditions.
So
EAS = TAS * SQRT ( r/r0 )
"r" in this case substitutes for rho which is density. "r sub zero" is standard sea level density. "r" is the density at the measured conditions.
The "1/2" is indicating "to the one-half power" which is the same as the square root.
Equivalent airspeed is defined mathematically as the True Airspeed multiplied by the square root of the ratio of the measured air density to the density at standard conditions.
So
EAS = TAS * SQRT ( r/r0 )
rv7boy
Forum Peruser
Tim, the zero is called a "subscript" in math. You will notice that it is written slightly below the line. In this case it represents the density of air in standard conditions at sea level. So it is a reference value and when the ratio of (r/r0) is written it is the ratio of the air density (r) to the reference air density (r0). [You wrote it as r0/r but I'm thinking it should be r/r0, but I could be wrong.] The term r0 is pronounced "r sub zero."
Usually, in engineering texts, the Greek letter rho (looks kinda like a "p") is used to express air density rather than the letter "r."
You didn't ask about the 1/2 but in the equation you reference, the 1/2 is an exponent of the ratio within the parentheses. An exponent of 1/2 is another way to say "the square root of."
Tim, I hate to dampen your enthusiasm, but when you fly your RV-12, you will not think about EAS. You may run across it on an FAA exam, but there are more challenging things to learn when you become a pilot.
If you can play a violin, I believe you can fly an RV-12.
Usually, in engineering texts, the Greek letter rho (looks kinda like a "p") is used to express air density rather than the letter "r."
You didn't ask about the 1/2 but in the equation you reference, the 1/2 is an exponent of the ratio within the parentheses. An exponent of 1/2 is another way to say "the square root of."
Tim, I hate to dampen your enthusiasm, but when you fly your RV-12, you will not think about EAS. You may run across it on an FAA exam, but there are more challenging things to learn when you become a pilot.
If you can play a violin, I believe you can fly an RV-12.
EAS. Thank you!
Wow....thank you all....david, paul, r boy et. al.
I'm taking the practical test next and trying to anticipate the oral horror. One examiner gives 5 hour Orals.
And we have a Neil Armstrong graduate!!!
Thank you all for the good advice.....where else but Vans Air Force.
It was John Palese who cited the air density as rho.....though my study of atic Greek gave away the RHO r.
Tim
Wow....thank you all....david, paul, r boy et. al.
I'm taking the practical test next and trying to anticipate the oral horror. One examiner gives 5 hour Orals.
And we have a Neil Armstrong graduate!!!
Thank you all for the good advice.....where else but Vans Air Force.
It was John Palese who cited the air density as rho.....though my study of atic Greek gave away the RHO r.
Tim
Test.... EAS question
Don
We scheduled 3 dates for the practical test but bad weather. Just as well...will give more time to study for the oral, learn about obscure trick questions like adiabetic compression. ......and get more hours when the weather improves. We will try again in April. Thanks for asking Don.
Tim
Don
We scheduled 3 dates for the practical test but bad weather. Just as well...will give more time to study for the oral, learn about obscure trick questions like adiabetic compression. ......and get more hours when the weather improves. We will try again in April. Thanks for asking Don.
Tim
RFSchaller
Well Known Member
Why would anyone care about equivalent airspeed for the RV-12 envelope? For that matter, why care about anything but indicated airspeed when you're in the air in an RV-12?
EAS IAS TAS .... All virtually the same ?
Good question Rich. Reason is I was warned that one of the examiners up here gives an oral for the practical test 5 hrs. long. At my age, 70.... I can't afford to fail....
I've wondered as you suggest about using anything but IAS ....especially since CAS & IAS are identical per the POH for the RV12.
Maybe the only real concern would be TAS adjusted for varying altitude/temp ?
I've wondered about other calculations like isogonic lines with similar interest....what difference do isogonics make anyway? ...we live in Wisconsin, a virtual AGONIC location. Plus 1 or 2 around here means lpassing an airport on the left vs. right side of the plane!
Sure hope I pass this exam. Any suggestions welcome.
Tim
Good question Rich. Reason is I was warned that one of the examiners up here gives an oral for the practical test 5 hrs. long. At my age, 70.... I can't afford to fail....
I've wondered as you suggest about using anything but IAS ....especially since CAS & IAS are identical per the POH for the RV12.
Maybe the only real concern would be TAS adjusted for varying altitude/temp ?
I've wondered about other calculations like isogonic lines with similar interest....what difference do isogonics make anyway? ...we live in Wisconsin, a virtual AGONIC location. Plus 1 or 2 around here means lpassing an airport on the left vs. right side of the plane!
Sure hope I pass this exam. Any suggestions welcome.
Tim
RFSchaller
Well Known Member
Tim,
I'm a CFI. When I look for a DPE to work with I pass on ones that give check rides that don't reflect the PTS elements. There are some that seem overly impressed with themselves, and there are some that genuinely want to be sure the pilot they license is competent to deal with expected situations. You might want to shop around for another DPE.
Rich
I'm a CFI. When I look for a DPE to work with I pass on ones that give check rides that don't reflect the PTS elements. There are some that seem overly impressed with themselves, and there are some that genuinely want to be sure the pilot they license is competent to deal with expected situations. You might want to shop around for another DPE.
Rich
It's probably good to have an idea of the difference between ias and cas for your airplane and tas is useful for dead reckoning for those that don't have a gps..is there anyone without a gps?? Eas is used for engineering calculations and has no practical purpose for a pilot that I can see.
For isogonics, you can't assume that you will always fly only in wisconsin!
RFSchaller
Well Known Member
A good thumb rule for quick calculation of TAS is to add 2% of IAS for each 1000 feet above MSL. Seems to work pretty well at the altitudes the 12 flies at.
If you fly roughly the same altitude and power settings you can usually come up with an average cruise speed that will consistently put you within 5 or 6 minutes block to block on a two hour flight. For example a 300 NM flight in my Cherokee will consistently take 3 hours so I use 100 KTS GS for flight planning. Unless the wind is doing something really radical it works. Maybe not as accurate as getting out the E6B, but as they say: close enough for govrnment work.
Obviously you would want a more detailed calc if you know the wind is howling or, you're going IMC or your fuel state may be close to minimum at your destination. But for $100 hamburger trip on a CAVU day this approximation is completely adequate.
If you fly roughly the same altitude and power settings you can usually come up with an average cruise speed that will consistently put you within 5 or 6 minutes block to block on a two hour flight. For example a 300 NM flight in my Cherokee will consistently take 3 hours so I use 100 KTS GS for flight planning. Unless the wind is doing something really radical it works. Maybe not as accurate as getting out the E6B, but as they say: close enough for govrnment work.
Obviously you would want a more detailed calc if you know the wind is howling or, you're going IMC or your fuel state may be close to minimum at your destination. But for $100 hamburger trip on a CAVU day this approximation is completely adequate.
RFSchaller
Well Known Member
If they are ELSA or SLSA they are glass. I think the discussion was mainly oriented toward preflight planning. Once in the air HAL will tell yo the right answer!.
"Shop, Shop Around"
1. Rich (and the Miracles) offer good advice when it comes to a DPE:
My mama told me
you better shop around
2. A reasonable person won't expect you to know all the answers; rather, you should know where to find (some of) the answers.
(See Doug Reeves' gouge on prepping for his instrument exam:
http://www.vansairforce.net/articles/myIFRCheckride/my_ifr_checkride.htm
3. I passed the private written; you can too!
1. Rich (and the Miracles) offer good advice when it comes to a DPE:
My mama told me
you better shop around
2. A reasonable person won't expect you to know all the answers; rather, you should know where to find (some of) the answers.
(See Doug Reeves' gouge on prepping for his instrument exam:
http://www.vansairforce.net/articles/myIFRCheckride/my_ifr_checkride.htm
3. I passed the private written; you can too!
RFSchaller
Well Known Member
Paul,
I'll always remember ICET (ice tea) somewhere in my past a CFI beat that into my hard head!
Rich
I'll always remember ICET (ice tea) somewhere in my past a CFI beat that into my hard head!
Rich
