REFLECTOR: Speeds

Thu Jun 7 07:48:21 CDT 2012

Here are some cruising true airspeeds we've verified for our turbo XL-RG
over the years at 2300 RPM, 28" MAP, 13.3 gph, LOP, which for our TNIO 550N
is a 60% power setting (186 hp). These are for an aircraft flying weight of
3000 lb:

6000' MSL 170 KTAS
12,000' MSL 180 KTAS
18,000' MSL 190 KTAS
24,000' MSL 200 KTAS

What we've worked the most on over the past couple of years is achieving
these steady state cruising conditions with the CHTs at or below 380
degrees. It gets increasingly harder with the thinner air at altitude, even
though the OAT is much lower. One thing that helps a lot (besides good
cooling airflow and tight plenums) is the 'over square' MAPs. 

We used to run 2" over square LOP (25" MAP for the 2300 RPM power setting
above), but found that 28" or 29" produced much lower still CHTs. It doesn't
add any more power (that's determined by the 13.3 gph fuel flow), just more
air for increased cooling -- sort of like the way you add extra fuel ROP for
cooling on WOT climb-outs. And the engine doesn't complain with balanced
injectors and dual Lightspeed electronic ignitions. We haven't had any
detonation issues.

One disappointment is that we were hoping for bigger TAS increases with
altitude than those above. Using the 2% per 1000' rule of thumb, we were
expecting better than 230 KTAS at 24,000' (with 170 KTAS at 6000'), but are
getting only 200 KTAS at the 60% power setting above. Changing to a four
bladed prop didn't help much, though we do run a lot smoother. Apparently
it's due to the increased induced drag due to the slightly higher AOA
required in the thinner air to provide equivalent lift. Still, we're pleased
with the performance we're getting!

Anyone else have a better explanation?

Bob Jackson
N2XF - 650 hrs

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Richard J. Gentil
Sent: Thursday, June 07, 2012 1:39 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Speeds

Hey Scott,

On the deck I was indicating 165-168 kts KIAS

At 6,500 feet I was indicating 150-151 kts KIAS figure temp around 56F and
altimeter around 30.03 if memory serves. 

As for the altitudes between 1,000 feet and 6,500 feet I do not exactly
remember but they trued out around 170 kts KTAS. 

Richard 

Sent from my iPhone 4 Classic

On Jun 6, 2012, at 10:11 PM, Scott Derrick <scott at tnstaafl.net> wrote:

> So, you do that in the air at 170 KIAS?
> 
> -------- 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 06:10 PM
> 
>> Scott,
>> 
>> I own a 145 repair station with an avionics department. I had my avionics
pump up with Velo with the test equipment while I set the calibrating
information in both EFIS systems. Altimeter and airspeed are calibrated from
-1,000 feet to 25,000 feet.
>> 
>> Richard
>> 
>> Sent from my iPhone 4 Classic
>> 
>> On Jun 6, 2012, at 7:48 PM, Scott Derrick<scott at tnstaafl.net>  wrote:
>> 
>>> 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
>>> 
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