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power to weight

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wingsdown(at)comcast.net
Guest

Posted: Mon Apr 03, 2006 7:40 am Post subject: power to weight

There  has to be someone on the list smart enough to figure out what

each pound of weight does to performance. I guess what I mean is if an

engine weighs 50 pounds more but produces 50 HP more is is better or

worse than an engine that is 50 pounds lighter and make 50 HP less. You

know like a chart that has curves that show two lines that cross or

something. It would take the guess work out of engine selection

somewhat. I guess engine torque would have to be considered as well.

Would be nice to see don't you think?

 

Rick

john.marzulli(at)gmail.co
Guest

Posted: Mon Apr 03, 2006 8:48 am Post subject: power to weight

Rotax lists the power to weight ratio on their website.



http://www.rotaxservice.com/rotax_engines/rotax_912S.htm

On 4/3/06, wingsdown <wingsdown(at)comcast.net> wrote:

 	  Quote: 	
		  

 



 There  has to be someone on the list smart enough to figure out what

 each pound of weight does to performance. I guess what I mean is if an

 engine weighs 50 pounds more but produces 50 HP more is is better or

 worse than an engine that is 50 pounds lighter and make 50 HP less. You

 know like a chart that has curves that show two lines that cross or

 something. It would take the guess work out of engine selection

 somewhat. I guess engine torque would have to be considered as well.

 Would be nice to see don't you think?



 Rick

wingsdown(at)comcast.net
Guest

Posted: Mon Apr 03, 2006 8:54 am Post subject: power to weight

Well what I mean is what that weight is worth cost  in HP, or rather how

much HP does it take to carry a pound of weight over and above the

airframe weight. Kind of hard to express clearly.  



Rick



--

ruebd(at)skymail.csus.edu
Guest

Posted: Mon Apr 03, 2006 10:21 am Post subject: power to weight

Rick



	Unlike the other powered vehicles, such as cars, tractors,

boats, with aircraft the weight of anything that is part of the machine

is critical.  For a boat it can actually be advantageous to have heavy

engines for the ballast that they contribute.  Tractors benefit from

weight also, to a point.  Cars will sacrifice handling to a heavy

engine, but if they are judged more on acceleration, then it works.

Dragsters certainly attest to that; but their trip is short.   

	The first thing that a heavier, more powerful engine has to

carry in an airplane is itself, so the first effect is to reduce the

payload, or useful load.  A more powerful engine will also need a

larger, heavier propeller, more weight; not only does this offset the

benefit of having more power, it affects the balance, so now more weight

will be needed in the tail (assuming a conventional layout) to counter

the heavier engine and restore the balance.  So now the total weight has

increased even more than by just the heavier engine.  

	The airframe is what holds all of the major components together

and each of them acts to stress it under turbulent or any high 'G'

maneuvering.   The engine's mass is cantilevered out from the main

structure (fuselage) and is always acting to get away from the rest of

the machine by torque, thrust, and the mass that it involves when G

loading is a factor.  So here we go again, now you need to beef up the

thrust frame and fuselage to take the extra weight hanging out there, so

now we are stuck with still more total empty weight.   

	When the thrust developed at cruise power equals the drag

produced by the sum of lift drag and the parasitic drag, the airplane

finds its cruising speed.  Since a heavier engine adds weight, the lift

drag factor will be higher with it installed, and the parasitic drag may

also increase, due to a larger cowling or the cooling drag increase that

typically occurs.      

   	Drag reduction is the best way to increase an airplanes speed.

This is borne out time and again by the performance figures of very

clean designs with modest power.  On the other hand, airplanes with a

high drag coefficient, such as the Boeing Stearman will not cruise much

faster no matter what engine is doing the towing.

	A simple chart to illustrate all of this is just not practical.

You have to take cases and evaluate them as they are defined.  All

designs are nested tradeoffs, and this is especially true when they fly.

Small airplanes work best with reliable, not too heavy engines.  This

has always been best achieved by using fairly large displacement, low

rotational speed designs that can directly turn the propeller.   

	Remember the real purpose of that fan turning out front is to

cool the pilot, because when it quits doing that he (she) starts to

perspire almost immediately.  



Duane Rueb

 Message-----

From: owner-kitfox-list-server(at)matronics.com

[mailto:owner-kitfox-list-server(at)matronics.com] On Behalf Of wingsdown

Sent: Monday, April 03, 2006 8:40 AM

To: Kitfox

Subject: power to weight 






There  has to be someone on the list smart enough to figure out what

each pound of weight does to performance. I guess what I mean is if an

engine weighs 50 pounds more but produces 50 HP more is is better or

worse than an engine that is 50 pounds lighter and make 50 HP less. You

know like a chart that has curves that show two lines that cross or

something. It would take the guess work out of engine selection

somewhat. I guess engine torque would have to be considered as well.

Would be nice to see don't you think?

 

Rick

skyflyte(at)comcast.net
Guest

Posted: Mon Apr 03, 2006 1:10 pm Post subject: power to weight

All good points!  One more is that the bigger, heavier, more powerful engine will suck more gas, requiring bigger fuel tanks for the same kind of range performance.  Light weight, low drag aircraft perform the best.

-------------- Original message -------------- 

From: "Rueb, Duane" <ruebd(at)skymail.csus.edu> 



 	  Quote: 	
		   

 

 Rick 

 

 Unlike the other powered vehicles, such as cars, tractors, 

 boats, with aircraft the weight of anything that is part of the machine 

 is critical. For a boat it can actually be advantageous to have heavy 

 engines for the ballast that they contribute. Tractors benefit from 

 weight also, to a point. Cars will sacrifice handling to a heavy 

 engine, but if they are judged more on acceleration, then it works. 

 Dragsters certainly attest to that; but their trip is short. 

 The first thing that a heavier, more powerful engine has to 

 carry in an airplane is itself, so the first effect is to reduce the 

 payload, or useful load. A more powerful engine will also need a 

 larger, heavier propeller, more weight; not only does this offset the 

 benefit of having more power, it affects the balance, so now more weight 

 will be needed in the tail (assuming a conventional layout) to counter 

 the heavier engine and restore the balance. So now the total weight has 

 increased even more than by just the heavier engine. 


	


All good points! One more is that the bigger, heavier, more powerful engine will suck more gas, requiring bigger fuel tanks for the same kind of range performance. Light weight, low drag aircraft perform the best.

-------------- Original message -------------- 

From: "Rueb, Duane" ruebd(at)skymail.csus.edu 



 -- Kitfox-List message posted by: "Rueb, Duane" <RUEBD(at)SKYMAIL.CSUS.EDU>

 

 Rick 

 

 Unlike the other powered vehicles, such as cars, tractors, 

 boats, with aircraft the weight of anything that is part of the machine 

 is critical. For a boat it can actually be advantageous to have heavy 

 engines for the ballast that they contribute. Tractors benefit from 

 weight also, to a point. Cars will sacrifice handling to a heavy 

 engine, but if they are judged more on acceleration, then it works. 

 Dragsters certainly attest to that; but their trip is short. 

 The first thing that a heavier, more powerful engine has to 

 carry in an airplane is itself, so the first effect is to reduce the 

&g

 t; payload, or useful load. A more powerful engine will also need a 

 larger, heavier propeller, more weight; not only does this offset the 

 benefit of having more power, it affects the balance, so now more weight 

 will be needed in the tail (assuming a conventional layout) to counter 

 the heavier engine and restore the balance. So now the total weight has 

 increased even more than by just the heavier engine.

rjdaugh(at)rapidnet.com
Guest

Posted: Mon Apr 03, 2006 2:14 pm Post subject: power to weight

Duane,

I agree with almost all you said and you said it better than I could, but

there is one statement that I feel is wrong:



"This

has always been best achieved by using fairly large displacement, low

rotational speed designs that can directly turn the propeller."  



I suspect that other 912S drivers may disagree too.  There is a point where

that large displacement comes at weight cost.  You are better off getting

more horsepower out of the engine using RPM.  Compare an O-200 and the 912S.



Randy



.           

--

lcfitt(at)sbcglobal.net
Guest

Posted: Mon Apr 03, 2006 3:15 pm Post subject: power to weight

While we are on the subject of weight and power, it should be remembered 

that our designs are configured around the typical weights of the Rotax 

series engines.  The heavier engines will most certainly bring on W&B issues 

and in many cases larger heavier batteries or other essential equipment or 

even dead weight lead is used to bring the W&B into limits, further adding 

to the weight penalty.



This is, I believe, one of the reasons an engine reported to be just a few 

pounds heavier than the 912, for example, will result in an airplane 

significantly heavier than expected, given the engine weight differential.



Lowell

---

wingsdown(at)comcast.net
Guest

Posted: Mon Apr 03, 2006 3:29 pm Post subject: power to weight

Excellent  points on the auxiliary equipment needed for a particular

engine. That would be an interesting line as well. I think it will be

awhile before any manufacturer experimental or otherwise will publish

that real number. Kind of like performance figures. So the total weight

of the engine and support equipment required to run it should also be

weighed. To really understand an engines value to the airframe one must

consider all the weight, even extra fuel for equivalent range as

mentioned earlier. Then, if aircraft A is equal to B, essentially the

same aircraft, how much HP does it take to move a pound of additional

engine weight?



Rick



--

smokey_bear_40220(at)yaho
Guest

Posted: Mon Apr 03, 2006 6:57 pm Post subject: power to weight

This has been one of the reversals for turboprops

lately.  They are much lighter than piston engines for

the HP, but burn so much more fuel that there is some

movement to convert turboprop airplanes back to

pistons.  The decision has to include TBO costs, fuel

costs, normal loads carried, and length of a normal

flight for the plane.



I think the same goes for our engine choices.  Weight

isn't the only factor.  Initial engine cost, TBO,

reliability, parts costs, etc cause us to chose

different engines that fit our particular missions.



There is a 100 HO turboprop available for us that

weighs around 100 lbs, but it burns 11 gal/hr at idle!

 I am sure that is why many have chosen the "heavy"

rotax 912's over the turboprop.  Right???  



Kurt S.



Do not archive



--- skyflyte(at)comcast.net wrote:



 	  Quote: 	
		   All good points!  One more is that the bigger,

 heavier, more powerful engine will suck more gas,

 requiring bigger fuel tanks for the same kind of

 range performance.  Light weight, low drag aircraft

 perform the best.

avidsid(at)yahoo.com
Guest

Posted: Mon Apr 03, 2006 7:21 pm Post subject: power to weight

Kurt, 

  where is the link to the 100hp turbo..........?

  Sid

  --------------          just curious

   

  



kurt schrader <smokey_bear_40220(at)yahoo.com> wrote:

  



This has been one of the reversals for turboprops

lately. They are much lighter than piston engines for

the HP, but burn so much more fuel that there is some

movement to convert turboprop airplanes back to

pistons. The decision has to include TBO costs, fuel

costs, normal loads carried, and length of a normal

flight for the plane.



I think the same goes for our engine choices. Weight

isn't the only factor. Initial engine cost, TBO,

reliability, parts costs, etc cause us to chose

different engines that fit our particular missions.



There is a 100 HO turboprop available for us that

weighs around 100 lbs, but it burns 11 gal/hr at idle!

I am sure that is why many have chosen the "heavy"

rotax 912's over the turboprop. Right??? 



Kurt S.



Do not archive



--- skyflyte(at)comcast.net wrote:



 	  Quote: 	
		   All good points! One more is that the bigger,

 heavier, more powerful engine will suck more gas,

 requiring bigger fuel tanks for the same kind of

 range performance. Light weight, low drag aircraft

 perform the best.


	




"Why can't we all just get along?"

		

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

markL

Joined: 04 Apr 2006
Posts: 3

Posted: Tue Apr 04, 2006 1:34 pm Post subject: Re: power to weight

The company at Osh promoting lightweight turbine engines was Innodyn WWW.inndodyn.com  And I dont believe they burn 11gph at idle, their website says the following:



How much fuel do the Turbines burn?



On development turbines our fuel flow, tested by measuring the amount of fuel used in the tanks, was comparable to, but slightly higher than internal combustion engines. Measured in all phases of operation with the RV4 and SuperCub, we found in general, our fuel usage to be approximately 7 gallons per 100 hp per hour. This is internal historical data and has not been independently tested or verified. We continue our efforts to gather additional fuel usage data from independent testing and evaluation. Until we have completed this detailed testing on our first full production engines, we cannot provide precise fuel flow rates. We will be conducting detailed integrated testing on fuel flow and associated hp ratings in the near future. Please check back frequently as we will make this further defined information available as soon as testing is completed. 



Definitely seems like the future of experimental will be turbine. Especially since they can burn Diesel, Bio-Diesel, Jet A or kerosene.

markL

Joined: 04 Apr 2006
Posts: 3

Posted: Tue Apr 04, 2006 1:40 pm Post subject: Re: power to weight

ooops typed in the web address wrong its:



http://www.innodyn.com/



Mark

smokey_bear_40220(at)yaho
Guest

Posted: Tue Apr 04, 2006 7:40 pm Post subject: power to weight

The company I talked to used the Solar T-62 engine. 

Garrett also makes a small one.  If you Google the

Solar T-62, you will find a lot of talk about it.



The company I spoke to said theirs burned from 11-17

GPH for up to 100 hp.  Not what I wanted witht he

short range it had.  I think they gave up too much to

save weight.



The engine is capable of up to 150 hp and weighs less

than 60 lbs without a GB, but the GB's applied can add

up to 100 lbs more though, depending on who is

building what.



I think the BD-5 used a T-62 as a pure jet.



Here are a couple of sites that talk about

applications for small turbos as examples:



http://www.zenithair.com/misc/turbine-power.html



http://www.auctionaz.com/092305aircraft1947.htm



Rotaway is also testing a 150 hp turbine, last I

heard.



Kurt S.  S-5



--- markL <mloos(at)pilbal.com> wrote:



 	  Quote: 	
		   The company at Osh promoting lightweight turbine

 engines was Innodyn WWW.inndodyn.com  And I dont

 believe they burn 11gph at idle, their website says

 the following:........

wingnut

Joined: 11 Jan 2006
Posts: 356

Posted: Wed Apr 05, 2006 5:41 am Post subject: Re: power to weight

 	  Quote: 	
		  Measured in all phases of operation 	




I take this to mean that they averaged out cruise with taxi and landing ops. So how long did they have to sit on the tarmac at idle to get these numbers? Sneaky bastards.

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