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Aircraft performance (was Antennas)

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Gilles.Thesee(at)ac-greno
Guest

Posted: Mon May 22, 2006 5:45 am Post subject: Aircraft performance (was Antennas)

Cher George Mc. Jetpilot,



Thank you for replying.

Hope the group won't mind this conversation. After all, the initial 

topic was about hiding or not hiding antennas.

 	  Quote: 	
		     In the US we have large expanse of land and REMOTE 

 radio outlets. To get ATC for radar, Flight Watch for 

 weather or Flight Service to open / close flight plans, 

 a clear powerful radio is so so important. Also we 

 have many class B and C air spaces that require a 

 good radio.

   

Would 100  NAUTICAL miles at 2000 ft AMSL, or 140 NM when above 5000 ft 
	


fill your requirements ? I'm quite satisfied with that performance.

By the way, in the old continent, towers are more closely spaced than 

that, and we seldom have to contact anyone that far. Except for the fun 

of testing actual range.

 	  Quote: 	
		     

    

   This is what my hidden antenna friends heard all the time:

    

   AIRCRAFT  CALLING WASHINGTON CENTER YOU ARE 

 WEAK AND SCRATCHY,

   

Hmm, maybe they would benefit from the Aeroelcectric List...
	


By the way, my radio is loud and clear.

 	  Quote: 	
		      

 ....

> industry doesn't believe in the existence of drag. Especially 

> in the land of cheap gas and big engines.

>     

   What land and engineers are we talking about, monsieur.

   American engineers? pardonnez-moi

   


	


Very few light aircraft engineers anywhere are concerned with cooling 

drag, internal flow mechanics or drag reduction.

Those who really do their homework design faster airplanes.

 	  Quote: 	
		      

   Land of cheap gas and big engines? America?

   


	


Ever bought gas in Europe ? Then you'll understand what I mean 



 	  Quote: 	
		      

   I would say a long EZ, even with 160HP  is way more efficient 

   than a MCR 4S 


	


Two of our 5 hangar mates happen to fly Long EZ, and I'm not much 

impressed by their performance. And believe me, when taking off or 

landing on our less-than 2000 ft grass strip with no wind, they have 

their hands full.



 	  Quote: 	
		   ...I also say a RV-9A is more efficient than 

   your MCR 4S. Looking at the RV-9A with 115HP it has 10kt 

   faster speed (150kts).


	


Hey, that's cheat !

You're confusing TOP speed (100% power) and CRUISE speed (75%). The 

RV-9A numbers on their website are phony. We all know that 75 % power 

speed is 91 % of top speed, that's elementary flight mechanics.

So the RV-9A should either cruise at 136 kt, or peak at 159.

As very few people will minimize their top speed, I'd say that the 

little bird tops at 150 kt, and their 75% power cruise is nearer to 90%...



And our bird tops at 155 kt true on 100 hp only.

Oh, and by the way, that's with four on board and 4 hr fuel...

 	  Quote: 	
		    Not sure what engine you have 80 or 

   115 hp. 

   

115 hp takeoff, 100 hp top speed, 75 hp cruise at 140 kt true.
	


838 lbs empty, 1100-1200 ft/min (at) gross weight.



 	  Quote: 	
		   Want to race my big engined 

 RV-7 with O360 190HP? 

    

   

Why not race with a two-seater ?
	


The MCR 01 top speed is 168 kt on 80 hp. If you really want to cling 

behind at 80 hp, you better remove those antennas...



Regards,

Gilles

Grenoble, France

http://contrails.free.fr

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khorton01(at)rogers.com
Guest

Posted: Mon May 22, 2006 7:22 am Post subject: Aircraft performance (was Antennas)

On 22 May 2006, at 09:40, Gilles Thesee wrote:



 	  Quote: 	
		   

 <Gilles.Thesee(at)ac-grenoble.fr>



 Hey, that's cheat !

 You're confusing TOP speed (100% power) and CRUISE speed (75%). The

 RV-9A numbers on their website are phony. We all know that 75 % power

 speed is 91 % of top speed, that's elementary flight mechanics.

 So the RV-9A should either cruise at 136 kt, or peak at 159.

 As very few people will minimize their top speed, I'd say that the

 little bird tops at 150 kt, and their 75% power cruise is nearer to  

 90%...




	


Top speed (100% power) will be achieved at sea level, as the power  

will be lower at higher altitudes (assuming a normally aspirated  

engine).  At sea level, the speed at 75% power should be about 91% of  

the speed at 100% power.  As you said.  But, at a given amount of  

power, the speed increases as the altitude increases.  So, the best  

speed at 75% power will be at the highest altitude at which the  

engine will produce this amount of power.  That is usually around  

8,000 ft for normally aspirated engines, and the speed at that  

altitude should only be a few percent slower than the speed with max  

power at sea level.



The CAFE Foundation tested Van's 160 hp RV-9A demo aircraft, and they  

found that the speed was higher than Van quotes on his web site (193  

mph at 8,500 ft density altitude, vs 188 mph claimed by Van's).   

Van's claimed 75% cruise number for a 118 hp engine falls pretty much  

where you would expect given the difference in power, so I have no  

reason to believe that it is phony.  I'd be interested in knowing  

what test data you have that contradicts the CAFE Foundation results.

Kevin Horton         RV-8 (finishing kit)

Ottawa, Canada

http://www.kilohotel.com/rv8

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Gilles.Thesee(at)ac-greno
Guest

Posted: Mon May 22, 2006 3:29 pm Post subject: Aircraft performance (was Antennas)

Kevin,

 	  Quote: 	
		    ... and the speed at that  

 altitude should only be a few percent slower than the speed with max  

 power at sea level.

   

You're right, we should take air density into account. But at lower 
	


altitudes, the angle of attack is less, and so is drag, so the effect 

you describe is somewhat compounded.

I just phoned a buddy aircraft engineer on that matter. A 75% cruise at 

only 3 % below top speed still seems rather close, but who knows ?



Please consider that we only talked about the RV-9A because George chose 

it for a comparison with our 4-seater. I was not criticizing any of the 

RV models.



 	  Quote: 	
		   The CAFE Foundation tested Van's 160 hp RV-9A demo aircraft, and they  

 found that the speed was higher than Van quotes on his web site (193  

 mph at 8,500 ft density altitude, vs 188 mph claimed by Van's).

How come ? 2 % more speed means 8 % more power. Please note I'm not 
	


questioning  the CAFE ability to test an aircraft.

 	  Quote: 	
		     

 Van's claimed 75% cruise number for a 118 hp engine falls pretty much  

 where you would expect given the difference in power,

118 hp to 160 hp yields a 10-11 % speed gain.  And here we have 14 %...
	


 	  Quote: 	
		    so I have no  

 reason to believe that it is phony.


	


Please pardon me for questioning those numbers,  but at first sight, 

they seemed strange to me.

I should have said that I always take published numbers with a grain of 

salt.

And there is that tendancy for homebuilts to lose airspeed once they've 

crossed the Atlantic ...



 	  Quote: 	
		     I'd be interested in knowing  

 what test data you have that contradicts the CAFE Foundation results.

   

Kevin, all I know is what you just told us, so why would I contradict ?
	


Hope I didn't ruffle too  many feathers.



Best regards,

Gilles Thesee

Grenoble, France

http://contrails.free.fr

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dave.thompson(at)verizon.
Guest

Posted: Tue May 23, 2006 9:07 pm Post subject: Aircraft performance (was Antennas)

You guys are talking about efficiency. 



 



Here=92s some real trivia! Way back in the early 80=92s there was an 

efficiency

race in Central California called the Caf=E9 250. One year, My Dad=92s 

Quickie

WON with only an 18HP engine. I don=92t know any other details except 

the

pilot was the late Col. Martin Fisher. Several months later, the Quickie 

had

a forced landing and was lost in the Arizona Desert en-rout to Oshkosh.

Nobody was hurt. I was told that the win really P=92d-off some of the 

=93big

guys=94.



 



Dave Thompson



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Speedy11(at)aol.com
Guest

Posted: Wed May 24, 2006 9:50 pm Post subject: Aircraft performance (was Antennas)

In a message dated 05/23/06 3:02:39 AM Eastern Daylight Time, 

aeroelectric-list(at)matronics.com writes:

Hope I didn't ruffle too  many feathers.

Gilles,

I doubt you ruffled any feathers.  Personally, I find your comments 

entertaining, so keep them coming.

I also admire anyone who builds an airplane in Europe.  The rules and 

restrcitions are much more severe than in the US - and the cost of fuel is almost 

prohibitive.  Not to mention the cost of avionics, paint, interior, etc.  All is 

more expensive in Europe and more difficult to obtain.

My hat's off to you.

Stan Sutterfield

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