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Most economical cruse speed for a FireFly

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jbhart(at)onlyinternet.ne
Guest

Posted: Sun Feb 11, 2007 10:39 am Post subject: Most economical cruse speed for a FireFly

FireFlyers & Kolbers,



Due to snow and cold, I am house bound.  January passed and it was the first 

month the FireFly has not flown since its first flight.  It has given me 

some time to reflect and so I made some calculations using simple drag and 

horsepower equations to approximate FireFly performance.



Basically, it you want to stay up longer, fly further and reduce cost cruise 

slower.  For minimum time between two points, you have to consider refueling 

time.  Sometimes cruising slower gets you where you want to go in less time 

and at lower cost.  In general, the faster cruise eats up hp at a higher rate

than the increase in speed, so cost per mile increase dramatically.



If you would like to see the calculations, they can be seen at:



http://www.thirdshift.com/jack/firefly/firefly130.html



More snow is expected later on today and tomorrow.  Not as bad as western 

New York.  Sanding and finishing wood Wright Flyer wing ribs.  The EAA 

Chapter 373 is building a spare wing for Wilber Wright Museum.



Do not archive



Jack B. Hart FF004

Winchester, IN

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sun Feb 11, 2007 11:02 am Post subject: Most economical cruse speed for a FireFly

Sometimes cruising slower gets you where you want to go in less time

| and at lower cost.

|

| Jack B. Hart

Jack:



How about explaining the above statement.  Think my mind is cruising 

too slow to grasp.



Many times, faster cruise will get you there sooner and at less cost, 

based on speed and time in flight.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

jrsmith2(at)triad.rr.com
Guest

Posted: Sun Feb 11, 2007 11:32 am Post subject: Most economical cruse speed for a FireFly

stupid me.... it the removal of the 11-Man ballot   sorry





---

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sun Feb 11, 2007 11:43 am Post subject: Most economical cruse speed for a FireFly

| 

| 

| stupid me.... it the removal of the 11-Man ballot   sorry

 



HUH???



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

planecrazzzy
Guest

Posted: Sun Feb 11, 2007 2:38 pm Post subject: Re: Most economical cruse speed for a FireFly

You know John....The 11th man ballot...

.

..

    Gotta Fly...

Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Sun Feb 11, 2007 6:15 pm Post subject: Most economical cruse speed for a FireFly

Neat work Jack, got a question:

Does the math still work the same if you use different horsepower numbers, 

and different airspeeds? At least within the low speed spectrum that most of 

us fly at? For instance, could I plug in 65 horsepower and the math still 

work? Or change the airspeed up or down 10 or 20 mph?

I am slow at math, so pardon me if this is a dumb question.

Thanks.

Richard Pike

MKIII N420P (420ldPoops)

do not archive



---

_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

jbhart(at)onlyinternet.ne
Guest

Posted: Sun Feb 11, 2007 6:22 pm Post subject: Most economical cruse speed for a FireFly

At 01:02 PM 2/11/07 -0600, you wrote:

 	  Quote: 	
		  

  Sometimes cruising slower gets you where you want to go in less time

| and at lower cost.


	


John,



To keep things in context:



"Basically, it you want to stay up longer, fly further and reduce cost cruise 

slower.  For minimum time between two points, you have to consider refueling 

time.  Sometimes cruising slower gets you where you want to go in less time 

and at lower cost.  In general, the faster cruise eats up hp at a higher rate

than the increase in speed, so cost per mile increase dramatically."



As taken from the web page and modified:

----------------------------------

If you like to fly one hundred mile legs. Calculating flight times at 

various speeds will give the following results.



                  trip time  total fuel

.mph.................hr:min  used (gal) 

.40..................2:30     2.6

.45..................2:13     3.3

.50..................2:00     4.0

.55....1:49 + 0:30 = 2:19     4.7 (must refuel before or at 93 miles)

.60....1:40 + 0:30 = 2:10     5.8 (must refuel before or at 78 miles)

.65....1:32 + 0:30 = 2:02     6.7 (must refuel before or at 67 miles)



On the last three flights, one would have to stop for fuel and so 30 minutes 

was added to accommodate refueling. Assuming no head wind, this indicates a 

50 mph cruise would give the quickest time point to point. 

-----------------------------------



By not refueling and cruising at 50 mph, the 100 miles in two hours will 

burn 4 gallons of fuel.  The next best time is cruising at 65 mph with a 

fuel burn of 6.7 gallons.  From ferrying the FireFly from south east 

Missouri to Indiana, I discovered that it was very difficult to refuel and 

get back on the way in one half an hour.  People are drawn to the FireFly, 

and I had to ask them to get out of the way so I could start up and taxi 

away.



Jack B. Hart FF004

Winchester, IN

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sun Feb 11, 2007 7:08 pm Post subject: Most economical cruse speed for a FireFly

Thanks for your explanation Jack.



Glad I carry that extra 20 gals of fuel.  Not so much to save time as 

to have it when the situation dictates that I need it to survive.



John W got me into the habit of topping off the tank every time I 

land, when flying cross country.  Never fails, when I don't do that, 

that the weather/wind changes drastically, gets nasty, and makes me 

wish I had all the fuel I could hold to handle the situation.



Refuel delays caused by strap hangers is a frequent happening. 

Normally, I enjoy it when folks take a sincere interest in my bird, 

where we have been, and where we are going.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

jbhart(at)onlyinternet.ne
Guest

Posted: Mon Feb 12, 2007 6:15 am Post subject: Most economical cruse speed for a FireFly

At 09:14 PM 2/11/07 -0500, you wrote:

 	  Quote: 	
		  


	


 	  Quote: 	
		  Does the math still work the same if you use different horsepower numbers, 

and different airspeeds? At least within the low speed spectrum that most of 

us fly at? For instance, could I plug in 65 horsepower and the math still 

work? Or change the airspeed up or down 10 or 20 mph?


	


Richard,



Yes, you can adapt it to suit your own aircraft.



To find the drag coefficient c, use your top speed and maximum engine hp.  

This will let you calculate the drag and hp columns.  The specific fuel 

consumption is a little tougher.  When I looked at the hp values and saw 20 

hp at 50 mph, I realized that 0.1 would be a good choice for me because the 

FireFly typically cruises at 2.0 or less at 50 mph.  



In your case, surely you have flown your plane enough to know with some 

accuracy the gph rate at your favorite cruise speed.  Compute the hp 

required to fly at that speed.  Then divide your gph by the hp you computed 

to get your specific fuel rate.  Using this number multiply it against all 

of the other hps to fill in the gph column.



For the range column, identify your useable fuel volume.  Divide this volume 

by gph and multiply by the air speed to find the range.  Mpg is the range 

divided by useable fuel volume.  Endurance is the maximum useable fuel 

divided by the gph.



This kept me busy for one cold afternoon.  I wish I had done it much 

earlier.  There have been times when I had to turn around because the gps 

and my cruise fuel burn rate said I could not get there.  If I had backed 

off the throttle, I could have.  This is just the opposite of sailplaning.  

When you are low, your first thought is to keep it in the air, but if you 

are going to make distance, you must let the stick go forward to gain speed. 

 Neither of these two cases intuitive.  Some how you want to fly faster to 

get there quicker to keep from running out of fuel.  And when you are with 

out power it is natural to want hold back on the stick to hold the plane up 

in the air and still make the distance.



I hope this helps you out.  The snow has been delayed until tomorrow and 

they are predicting up to 10 inches.  It is a balmy 20+ degrees this 

morning.



Jack B. Hart FF004 



do not archive

Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Mon Feb 12, 2007 7:24 am Post subject: Most economical cruse speed for a FireFly

Thanks.

Richard Pike

MKIII N420P (420ldPoops)

do not archive

---

_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

captainron1(at)cox.net
Guest

Posted: Mon Feb 12, 2007 9:01 am Post subject: Most economical cruse speed for a FireFly

Well jack I think you need to ad the caveat that saving gas at a          slower cruise speed only works with a 0 head wind or some small          fraction of it. I think we need to consider this caution lest someone          will try that method and run out of fuel in some inhospitable area.              

         To make it clear, here is a scenario; if I take off and I have a 30          mph head wind and I am only flying 30 mph to save gas I may have saved          gas on an hourly basis but 0 gas in terms of distance covered. If I          chose a higher fuel burn for higher speed 60 miles per hr, at the end          of one hour I'd be 30 miles ahead of the fellow that is trying to save          fuel but is really not moving an inch. Of course if someone wants just          stick time and doesn't care if he stays right above the strip where he          started than that will work. So if I wanna save fuel I will keep a          very close eye on the GPS ground speed / fuel burn. If it looks like I          am moving slower than I should based on the power I got, then more          power to increase speed.              

         If we have a spread sheet wizard we can figure out when to dial more          power and when to lay off it. With a tail wind          throttle back, with a head wind throttle forward can be a rule of          thumb. Say for a M3X its 8 mph and for a          Firefly its 4 mph or whatever figure works for the machine. In the          Sierra its about 10 kt or so. Below 10 kt I can stay at (my usual)          lower setting and above 10 kt I need to add power if I want to save          fuel.              

         

         ---- "Jack B. Hart" <jbhart(at)onlyinternet.net> wrote:



 =============

--> Kolb-List message posted by: "Jack B. Hart"          <jbhart(at)onlyinternet.net>



At 09:14 PM 2/11/07 -0500, you          wrote:

 	  Quote: 	
		  --> Kolb-List message posted by: "Richard Pike"          <richard(at)bcchapel.org>


	


 	  Quote: 	
		  Does the math still work the same          if you use different horsepower numbers,

and different airspeeds?          At least within the low speed spectrum that most of

us fly at? For          instance, could I plug in 65 horsepower and the math still

work?          Or change the airspeed up or down 10 or 20 mph?


	


Richard,



         Yes, you can adapt it to suit your own aircraft.



To find the          drag coefficient c, use your top speed and maximum engine hp.

This          will let you calculate the drag and hp columns. The specific fuel

         consumption is a little tougher. When I looked at the hp values and          saw 20

hp at 50 mph, I realized that 0.1 would be a good choice for          me because the

FireFly typically cruises at 2.0 or less at 50 mph.



 In your case, surely you have flown your plane enough to know with some

         accuracy the gph rate at your favorite cruise speed. Compute the hp

         required to fly at that speed. Then divide your gph by the hp you          computed

to get your specific fuel rate. Using this number multiply          it against all

of the other hps to fill in the gph column.



         For the range column, identify your useable fuel volume. Divide this          volume

by gph and multiply by the air speed to find the range. Mpg          is the range

divided by useable fuel volume. Endurance is the          maximum useable fuel

divided by the gph.



This kept me busy          for one cold afternoon. I wish I had done it much

earlier. There          have been times when I had to turn around because the gps

and my          cruise fuel burn rate said I could not get there. If I had backed

         off the throttle, I could have. This is just the opposite of          sailplaning.

When you are low, your first thought is to keep it in          the air, but if you

are going to make distance, you must let the          stick go forward to gain speed.

Neither of these two cases          intuitive. Some how you want to fly faster to

get there quicker to          keep from running out of fuel. And when you are with

out power it          is natural to want hold back on the stick to hold the plane up

in          the air and still make the distance.



I hope this helps you out.          The snow has been delayed until tomorrow and

they are predicting up          to 10 inches. It is a balmy 20+ degrees this

morning.



Jack          B. Hart FF004



do not archive

         http://www.matronics.com/Navigator?Kolb-List

            

      [quote][b]

jbhart(at)onlyinternet.ne
Guest

Posted: Mon Feb 12, 2007 2:54 pm Post subject: Most economical cruse speed for a FireFly

 	  Quote: 	
		   Well jack I think you need to ad the caveat that saving gas at a slower 

cruise speed only works with a 0 head wind or some small fraction of it. I 

think we need to consider this caution lest someone will try that method and 

run out of fuel in some inhospitable area. 


	


Arizona Man,



Yes you are correct, the calculations were all done without considering head 

or tail winds.  This can easily be accommodated by using ground speed during 

the calculations for range.  Endurance will not change.  Just change the air 

speed to ground speed in the following:



"For the range column, identify your useable fuel volume. Divide this volume

by gph and multiply by the air speed to find the range. Mpg is the range

divided by useable fuel volume." 



If you fly with a gps that pin points your intended landing site and an in 

flight timer, it is very easy to determine if you can make it to your 

intended landing site.  Just as soon as you get to altitude and at cruise 

speed, check the expected time of arrival on the gps.  If the expected time 

of arrival plus the time on the flight timer add up to more than the 

endurance time at that cruise speed, you will not be able to make it.  Next 

reduce cruise by five miles per hour and again check the gps expected time 

of arrival and add it to the flight timer reading.  If it adds up to less 

than the endurance time for the new cruise speed, you can make it.  If not 

keep trying.  If the head wind is too strong, you will have to change your 

flight plan or cancel out.   All of this can be decided in the first fifteen 

minutes of the flight.



Flying a FireFly cross country is no different than any other aircraft.  We 

just get to stop a little more often.



Jack B. Hart FF004

Winchester, IN

jbhart(at)onlyinternet.ne
Guest

Posted: Tue Feb 13, 2007 2:23 pm Post subject: Most economical cruse speed for a FireFly

FireFlyers,



Reworked the page for range estimation to include the effect of head winds.  

It can be seen on the bottom of: 



http://www.thirdshift.com/jack/firefly/firefly130.html



House/snow bound again.  Difficult to tell how much snow we are getting as 

it is all passing by in the horizontal plane.  Some good drifts just outside 

the garage door and around the barn.



Jack B. Hart FF004

Winchester, IN



Do not archive

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