REFLECTOR: Speeds

[Scott Derrick]

Richard,

I think your doing very well at 170 KTAS..

I haven't seen a Std RG any faster when comparing TAS.

I don't have much confidence when I hear somebody reporting faster 
speeds than that with an STD RG. The longwing STD's are 5-10 knots 
slower than the orig STD.

There are two main reasons for incorrect airspeed reporting in homebuilts.

1.) the pitot Static system has not been calibrated. Usually this is a 
result of a bad static reading. The only way I know of to check this is 
a very low(50 ft) pass over the runway at cruise speed. before the pass 
set your altimeter(on the ground) and verify the altitude on your 
altimeter, add 50 ft for comparison. During the low pass write down the 
altitude.  If it is off by more than then 50 ft, you probably should 
adjust your static port. If it reads higher than it should you have too 
much static pressure, if lower you have too little. I adjusted mine with 
a small piece of aluminum tape in front of my port, this reduced the 
pressure and now I read the correct altitude. Because the IAS instrument 
is a comparator, comparing the pitot pressure against the static 
pressure, if your static port is off your airspeed indicator will be too.

2.) The other reason is the confusion between GPS ground speed and TAS. 
Yes if you are in a no wind situation, very very rare, they are 
basically equal. but more often than not they are not and you will need 
to subtract a tailwind component or add a headwind component.

Scott

-------- Original Message --------
Subject: Re: REFLECTOR: Speeds
From: Richard J. Gentil <richard at naples-air-center.com>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Date: 06/06/2012 04:02 PM

> Hi Scott,
>
> I am talking true airspeed. I am taking the alt, barometer, and OAT and using the KIAS I calculated my KTAS. I flew a triangular course and compared the GPS Ground speed to what the E6B was showing.
>
> I pushed the mixture, prop, and throttle full foward and let the speed stabilize on the two EFIS screens and wrote down my numbers. I tested several altitudes from on the deck up to 6,500 feet.
>
> Richard
>
> Sent from my iPhone 4 Classic
>
> On Jun 6, 2012, at 5:12 PM, Scott Derrick<scott at tnstaafl.net>  wrote:
>
>> Talking speeds kind be very frustrating.
>>
>> The only speed I like to talk about is KTAS,  Thats Knots True Air Speed
>>
>> not statute miles nautical miles, not indicated airspeed true airspeed, and certainly not ground speed(GPS).
>>
>> My IAS indicator has a TAS window, you select what your pressure altitude in reference to the OAT(upper window) and YOUR TAS will be indicated in the lower left window.
>>
>>
>> <jfaeejhi.jpeg>
>>
>> You can also fly a triangular course, using the GPS ground speed ,  and compute a fairly accurate TAS from that.
>>
>> And of course some of the higher end glass cockpits can compute it for you.
>>
>> And if flying very near to sea level on a std day temperature wise and assuming your IAS indicator is close to cal, it will show TAS.
>>
>> So Richard when you say 170 kts, what kind of speed are you talking about and how are you measuring it?'
>>
>> Scott
>> --
>> Talk sense to a fool and he calls you foolish.
>> Euripides
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