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Firefly at High Altitude

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ka5biw(at)swcp.com
Guest

Posted: Sun Oct 06, 2013 11:31 am Post subject: Firefly at High Altitude

Hello,



I am new to the list.  I am considering a legal 103 ultralight Firefly 

with a 40hp engine.  The bad news is that I live at 7171 ft ASL.  Other 

near by fields are still above 6000 ft ASL.  Will a 40hp Firefly be able 

to fly at these kinds of altitudes.



Thank you for any information.



Best Regards,

Paul

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ThermalHunter

Joined: 13 Dec 2012
Posts: 9
Location: Cleveland, TN

Posted: Sun Oct 06, 2013 4:03 pm Post subject: Firefly at High Altitude

Kolb Firestar II (at) 11,000' w/ Rotax 503...no performance problems.

 



    

From: Paul Littleton <ka5biw(at)swcp.com>

To: kolb-list(at)matronics.com 

Sent: Sunday, October 6, 2013 3:31 PM

Subject: Firefly at High Altitude



 

--> Kolb-List message posted by: Paul Littleton <ka5biw(at)swcp.com (ka5biw(at)swcp.com)>



Hello,



I am new to the list.  I am considering a legal 103 ultralight Firefly with a 40hp engine.  The bad news is that I live at 7171 ft ASL.  Other near by fields are still above 6000 ft ASL.  Will a 40hp Firefly be able to fly at these kinds of altitudes.



Thank you for any information.



Best =  --> bsp;                 -Matt Dralle, ===========



 [quote][b]

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_________________
Robert G

beauford173(at)tampabay.r
Guest

Posted: Sun Oct 06, 2013 5:13 pm Post subject: Firefly at High Altitude

Brother Littleton:

Welcome to the List, sir.



I do not presume to offer myself as an expert in this matter, never having

operated a Firefly at the altitudes you mention, rather having only run one

down at sea level for a while. 



I do have some limited experience with higher altitude operations, however.

I flew my 'ol Stinson off Meadowlake airport at Colorado Springs for three

years... That field is at about 6,800 feet.  Here are a few things I

learned, some of which may help with your question:

- In the summertime it was common to see density altitudes on the airport at

or near the service ceilings of many small airplanes and the scattered small

remains of past kinetic events in the weeds off the higher north end of the

asphalt strip bore testament to that fact.. About four months of the year,

my 165 hp bird would become a 120 hp clunker which I never dared fuel at

more than half capacity and which became incapable of carrying an average

adult in the back seat.  I don't know what the "service ceiling" of a

FireFly might be, but I once took a fit and coaxed mine to eight K feet. It

clearly wasn't a happy participant in that particular experiment once it

"climbed" past 7K with my flabby butt perched in the front.  I am certain

the longer wing of a Firestar would have performed much better.



- Rules of thumb can be dangerous, but here are a couple anyway: Subtract

3.5 to 4 percent from the rated horsepower of the engine for every thousand

feet above S.L.  Add about 12 percent to the takeoff roll for every thousand

feet of altitude, then add 12 percent more to the above numbers for every 15

degrees F above the standard 59F SL value for your altitude (which is 38F).

Do the math. Weigh yourself. You didn't mention your weight, but that would

likely be a significant factor, one way or another on a 6K ft. elev.

airfield with a 31 hp. machine.  My Fly never actually groans out loud when

it sees my 208 lbs coming, but I know what the little buggar is thinking,

even here at 20 feet MSL.  I would suppose that if you are near my weight,

you would need a pretty good airfield and some very well balanced wheels and

tires.  If you are heavier than me, I suspect you may well need Rand McNally

and some reliable street directions.



Hope this may help a little.  I don't know your level of aviation experience

and I trust my free advice hasn't insulted you should you prove to be a

retired Delta 747 captain who just lost his medical and retired to Colorado.



Worth what ye paid fer it...



Good luck.



beauford

FF-076, N173BW

Brandon, FL

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WhiskeyVictor36(at)aol.co
Guest

Posted: Sun Oct 06, 2013 8:39 pm Post subject: Firefly at High Altitude

Hi Brother Beauford,

  

 I was having a poorly executed day today.  Things were just  not going very well at all and I was feeling rather down in the dumps.   That is, until I opened your response to Brother Littleton with your advice  on high altitude flying in the FireFly.  Immediately my attitude improved  and by the end of your response I was LOL.  Thanks for keeping  humor in the list.

  

 Bill Varnes

 Kolb FireStar

 Audubon, NJ - elevation 120' msl

Do not archive

  

  In a message dated 10/6/2013 9:13:25 P.M. Eastern Daylight Time,  beauford173(at)tampabay.rr.com writes:

  	  Quote: 	
		  Brother    Littleton:

Welcome to the List, sir.



I do not presume to offer    myself as an expert in this matter, never having

operated a Firefly at the    altitudes you mention, rather having only run one

down at sea level for a    while. 



	


 [quote][b]

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Mon Oct 07, 2013 4:27 am Post subject: Re: Firefly at High Altitude

I have a spreadsheet that was written by some aeronautical engineer and published either on EAA's website or CAFE website (can't remember after so many years) that predicts performance of a light aircraft when plugging in specific physical attributes of the airplane.



I plugged in the known values for the 40 hp Rotax powered Firefly and this spreadsheet predicts a service ceiling(where climb degrades to 100 fpm) of about 12,010' density altitude at gross wt of 550 lb. These numbers seem reasonable to me. 



As Beauford said,  the longer wing Firestar, though a bit heavier, should have a bit higher ceiling. With same engine and an extra 100 lb of airframe the spreadsheet predicts a service ceiling of about 13,300' DA. Having owned a 35 hp Firestar and also a 40 hp Firestar, these figures seem reasonable too, though I never flew either Firestar over about 8,000' DA.

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Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Mon Oct 07, 2013 5:36 am Post subject: Re: Firefly at High Altitude

In case anyone is interested in the spreadsheet I mentioned in my previous post, here is a link to it on Google Docs. You should be able to down load it and modify it for your own use.



https://docs.google.com/spreadsheet/ccc?key=0Ap6b4DzV2dGZdGVsWGxrdHJFRzBfT3V1N0dLWGp3N0E&usp=sharing



The YELLOW fields are for the user to fill in. The BLUE fields are calculated estimates for various parameters. The numbers in the spreadsheet now are for the 40 hp Firestar I used to fly.

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Thom Riddle
Buffalo, NY (9G0)

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