TAS or IAS in aircraft specs

[jgf]

I know the difference in TAS and IAS (and CAS, EAS, etc.).  But is there an understood or implied standard for aircraft specs when listing stall speed, cruise speed, and top speed?  Most I read merely state x mph or x kts for each.

[PhrogPhlyer]

Many aircraft, perhaps even most, use IAS.

This is due to the fact that your airspeed indicator is what you are using while flying.

The POH state if using IAS, and will provide any conversion charts/graph that may apply.

[lnuss]

5 hours ago, jgf said:

listing stall speed, cruise speed, and top speed?

Stall speed is generally stated as IAS (properly CAS, or Calibrated AirSpeed), while cruise and top speed are usually listed as TAS. In addition, Vne (Never Exceed) is IAS (CAS), as are gear and flap extension speeds, etc. So it depends. The speeds that are related to flying the aircraft are generally IAS while the speeds for advertising and navigation are generally TAS.

 

The ones listed in IAS (generally) are that way because they will be the same regardless of density altitude (that is, of the ambient air pressure, temperature, etc.) and affect aircraft safety, etc. and using TAS in those cases would be misleading, at best, accurate only under one set of conditions (usually standard atmosphere).

[jgf]

Thanks. 

 

I've always used IAS in FS, but this was instigated by some rather unbelievable top speeds listed for real aircraft;  for example a military prop plane with a top speed 450mph at 30k ft, if this is IAS it is going about mach 0.9 ...there are some jets that don't do that, especially at 30k. So off I go reading, and find: 

 

"The IAS is typically used for low speeds and low altitudes. For example, the IAS can be referenced for altitudes below 10,000 ft (3,000 m) and 250 knots (460 kph). .... As the altitude increases, the air pressure decreases, and the TAS becomes more significant than the IAS."

 

"...use true airspeed in knots (KTAS) for performance measurements and flight planning."

 

"True Airspeed & GS is used in flight planning."

 

"The maximum cruise speed is a True Airspeed value and is based on the highest TAS achieved with the engines operating at the maximum cruise power rating"

 

"IAS is an operational number (what you fly) vs TAS which is performance/planning number."

 

Another article, after lengthy discussions of converting speeds between the different references, stated that stall speed is IAS but cruise and max speed are TAS.  Yet elsewhere I read "you only need IAS for flying, unless you're in a B-52".

 

 

[lnuss]

8 hours ago, jgf said:

"The IAS is typically used for low speeds and low altitudes. For example, the IAS can be referenced for altitudes below 10,000 ft (3,000 m) and 250 knots (460 kph). .... As the altitude increases, the air pressure decreases, and the TAS becomes more significant than the IAS."

For some things that is true, such as never exceed speed, but TAS is useless for stall speed, best rate of climb Vy, and the like, regardless of altitude.

 

8 hours ago, jgf said:

...use true airspeed in knots (KTAS) for performance measurements and flight planning."

Use TAS is correct, but it doesn't have to be in knots, though that tends to be the international standard these days.

 

8 hours ago, jgf said:

Yet elsewhere I read "you only need IAS for flying, unless you're in a B-52".

Which is completely false if taken literally, but in the sense they meant it's sometimes true. What that really means is that IAS (CAS) is all that is needed to keep the aircraft flying safely (avoid stalls, use Vy and Vx, flap extension, etc., etc. You still need TAS and GS for navigation purposes, among other things, and when you get into the higher altitudes and speeds mach becomes significant.

 

So "it all depends" is the answer, since all of the various measurement types have their uses, and are significant for at least one purpose. Don't try to lock in on a single item. Most things in aviation are not intuitive, and "depend...".

 

Addendum: I should have mentioned that mach is a function of TAS, though its value changes with temperature (therefore altitude), and becomes important for structural safety at higher speeds and altitudes.

[PhrogPhlyer]

The main point to take away from this thread is to read the specific aircrafts POH.

For a simple example, the C-152, here are the airspeed types found in that manual:

Airspeeds on charts are listed with both KIAS and KCAS. 

Several airspeeds do not have any qualifications (CAS, IAS, TAS) listed.

However, the following information is provided for the airspeed indicator,

One of the best parts of flight simming is learning the detail for each aircraft flown.

Even on the C-152. there really in not a simple answer to your initial question.

[lnuss]

35 minutes ago, PhrogPhlyer said:

The main point to take away from this thread is to read the specific aircrafts POH.

This, of course, is the ultimate answer for each aircraft, but for many older aircraft such as the Schweizer 2-32 and the Piper J-3 Cub the POH isn't exactly what they've made standard for newer aircraft, and lacks a lot of the information. In fact the 2-32's manual is labeled:

 

            THE 2-32 SAILPLANE

FLIGHT  -  ERECTION  -  MAINTENANCE

                     MANUAL

It gives some quite detailed information regarding speed vs altitude vs rate of climb/sink vs distance, etc. in the form of graphs and tables but also gives information in normal text for liftoff speed, minimum towing speed and some other things. The 2-33 manual gives even less information, though in the same forms.

The above is pretty much true even for older Cessnas and such, though they tend to be closer to today's manual style. On the Piper Super Cub, the performance section of the 1977 manual contains exactly one graph (see below) and many of the performance parameters are embedded in the text, such as shown below.

 

So 1970s and before may have quite a variation of layouts and information. So it's far from "one size fits all..."

 

[jgf]

4 hours ago, PhrogPhlyer said:

One of the best parts of flight simming is learning the detail for each aircraft flown.

 

An aspect I've been pursuing since my return to FS.

 

As for speeds, I guess the questionable ones will have to be considered with a bit of common sense (an attribute with which I've never been overly endowed).  That 450mph top speed is reasonable if TAS, but since IAS is almost universally used it was perplexing.

 

Manuals are nice when available, but there's a Catch-22;  easily available manuals are mostly for modern GA aircraft, so similar you can make an educated guess for flying them (especially in FS);  but for aircraft from the twenties through forties, with much more variation, there is little info.  And military aircraft are even more problematic;  I found a site with many manuals for military planes, mostly forties and fifties ...if you care to pay $15-$60 each for pdf copies.  So I read all I can find for a particular aircraft and hope for the best;  I do have one advantage - RL doesn't have a reset button.

 

Thanks for all the input, I keep learning.

[PhrogPhlyer]

10 minutes ago, jgf said:

I found a site with many manuals for military planes, mostly forties and fifties ...if you care to pay $15-$60 each for pdf copies.

I have hundreds of pdf files of NATOPS Manuals, and other aircraft handbooks/POHs.

Internet Archive https://catalogd.archive.org/ is a good source.

My go to search phrase online is NATOPS, POH, Flight Manual or other term with PDF.

"NATOPS PDF" or "Flight Manual PDF: etc.

Also, once you enter your search, switch to images. Helps at times to find manuals.

If you have a couple specific manuals you are looking for, send me an personal message and I'll see if I have, or can find.

Free is a great thing!

 

[lnuss]

3 hours ago, jgf said:

Manuals are nice when available, but there's a Catch-22;  easily available manuals are mostly for modern GA aircraft, so similar you can make an educated guess for flying them (especially in FS);  but for aircraft from the twenties through forties, with much more variation, there is little info.

With a search on the web for "Piper J-3 manual" I had no trouble downloading one. Same thing for the Aeronca 11AC Chief.

 

I've also gotten the following online, so far:

Aeronca Champ_7AC_POH.pdf                                                 
Aeronca__11ac_chief.pdf                                                   
Aeroprakt a22 flight manual.pdf                                           
Beechcraft A36 POH I-IV General-Limitations-Emergency Proc-Normal Proc.pdf
Beechcraft Bonanza F33A Pilots Operating Handbook.pdf                     
Beechcraft Bonanza_AFM.pdf                                                
Beechcraft-Bonanza-A36-AFM.pdf                                            
Bellanca 8KCAB N215RV Flight Manual.pdf                                   
Bellanca 8KCAB N215RV Owner Manual.pdf                                    
Cessna 172S Skyhawk Information Manual Searchable.pdf                     
Cessna 180k_poh.pdf                                                       
Cessna C170 Owners Manual.pdf                                             
Cessna C182S_POH.pdf                                                      
Cirrus-SR22 POH.pdf                                                       
Corvalis-350-G1000_poh.pdf                                                
Diamond DA202-C1-Rev-28.pdf                                               
Diamond DA62 70125e-r4-complete.pdf                                       
Douglas C-47 Manual pfoi.pdf                                              
Husky-A1B-POH.pdf                                                         
J-3C Cub owners manual.pdf                                                
j3c65.pdf                                                                 
Kodiak100_POH.pdf                                                         
Lake-Owners-Manual-Original.pdf                                           
manuel_tecnam_p2002_jf.pdf                                                
Meyers Interceptor 200DOwner's Manual.pdf                                 
Mooney M20R oe-kgg_m20r_ovation_poh.pdf                                   
P-51D-manual-5april44.pdf                                                 
PA-24 ComancheN5448P_POH.pdf                                              
PA-28-161 Warrior II.pdf                                                  
pa32 Saratoga II  POH.pdf                                                 
Partenavia P68R_AFM_NOR10.707-30C REV27.pdf                               
Piper Super Cub ownersmanual.PDF                                          
Piper-PA-30-C-FCDI.pdf                                                    
Piper_PA-28-180E.pdf                                                      
POH VL-3B-3 sn VL-3-71.pdf                                                
SC POH-1-1-21_SkyView LSA.pdf                                             
Starship Airplane Flight Manual.pdf                                       
Super Cub ownersmanual.PDF                                                
T-34B_NATOPS_Flt_Man_NAVAIR_01-90KDB-1.1981Mar01-Change2.pdf              

 

 

 

 

3 hours ago, jgf said:

That 450mph top speed is reasonable if TAS, but since IAS is almost universally used it was perplexing.

Once again, top speed is always TAS, not IAS. IAS is NOT "almost universally used" for many things, though it is universal for such things as stall speed, Vy, max flap speed, etc. Get used to it not being IAS for everything. And I did offer additional explanations that you can try for other cases...