Matronics Email Lists :: View topic

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

Thrust...Overrated?

Matronics Email Lists Forum Index -> Kitfox-List

View previous topic :: View next topic

Author Message

Clem Nichols

Joined: 10 Jan 2006
Posts: 88
Location: Munfordville, Ky

Posted: Tue May 09, 2006 5:55 pm Post subject: Thrust...Overrated?

This is a little apart from the question of thrust, but of parallel =

interest in the sense that it has to do with airplane performance.  I =

gather that most Kitfoxers use 3-bladed props just as I do, but it's my =

understanding (perhaps incorrectly) that the more blades a prop has the =

less efficient it is.  I know that Randy Schlitter who manufactures the =

Rans S6S, a plane much like the Kitfox, provides a 2-blade wooden prop =

with his kits, and states in his literature that (in his opinion, at =

least) he's never seen a 3-blade prop that works better than a 2-blade =

one.  (I hope I haven't misquoted him on this.  I couldn't find the =

brochure to check against my memory).  I realize the 3-blade by virtue =

of being shorter in diameter is less likely to strike the ground in a =

botched tail-dragger landing.  I was just wondering if anyone in the =

group is using a 2-blader, and if so, what their opinion is of it.



Kurt, your message on thrust was most enlightening.



Clem Nichols

smokey_bear_40220(at)yaho
Guest

Posted: Wed May 10, 2006 10:16 pm Post subject: Thrust...Overrated?

Hi Clem,



I would really like to see more prop testing on our

planes too.  There are a lot of considerations with

the different engines and Fox models, but we have so

many opportunities.



What engine is he running the wood prop on the Rans? 

Maybe someone with the same engine here would benefit.

 Generally speaking, the 2 blade should be the best

compromise.



Someone who really knows what they are doing with prop

aerodynamics would probably make the best blades out

of composit, due to the ability to form it better.



Kurt S.



__________________________________________________

Rex Hefferan

Joined: 10 Jan 2006
Posts: 147
Location: Olney Springs, Colorado USA "NOT a Kitpig"

Posted: Thu May 11, 2006 5:07 am Post subject: Thrust...Overrated?

I was out motorcycle riding with some friends last weekend and saw one 

of these airboats with the newer propeller drives. The one I saw had a 

counter rotating system with 2 sets of 4 blade propellers for a total of 

16 blades! This was all new stuff to me. I wonder if there may be some 

way to adapt some simple version for kit planes? Interesting stuff.

http://www.classicairboats.com/pages/props.html



Rex

Florida



kurt schrader wrote:



 	  Quote: 	
		  



Hi Clem,



I would really like to see more prop testing on our

planes too.  There are a lot of considerations with

the different engines and Fox models, but we have so

many opportunities.



What engine is he running the wood prop on the Rans? 

Maybe someone with the same engine here would benefit.

 Generally speaking, the 2 blade should be the best

compromise.



Someone who really knows what they are doing with prop

aerodynamics would probably make the best blades out

of composit, due to the ability to form it better.



Kurt S.



__________________________________________________

 

 

 





  




	


-- 

Karla and Rex Hefferan

Gypsy Bee Innkeepers

719-651-5198 or 719-651-9192

_________________
Rex
N740GP - M2/582
Colorado

Clem Nichols

Joined: 10 Jan 2006
Posts: 88
Location: Munfordville, Ky

Posted: Thu May 11, 2006 5:49 am Post subject: Thrust...Overrated?

Kurt:



Standard engine on the Rans S6S is a Rotax 912S.



Do Not Archive

---

smokey_bear_40220(at)yaho
Guest

Posted: Thu May 11, 2006 8:24 am Post subject: Thrust...Overrated?

Hey Rex,



Gald to see you getting out.



The Russian Bear Bomber was very fast with

counter-rotating props.  Fastest big prop plane I know

of.



Those props you saw though are for low speed only. 

Someone has to make a high speed version or you will

have a fantastic takeoff and climb, but a 65 mph top

speed.



Prop weight has to be considered....   



Glider tow?  Heck, at low speed you could pull a

manure spreader with that prop.  Lot's a low end

power.



Now if we had a counter rotating, 100 knot, 20 lb Warp

drive.... No torque to fight on takeoff either.



Kurt S.



--- Rex <gypsybee(at)copper.net> wrote:



 	  Quote: 	
		   I was out motorcycle riding with some friends last

 weekend and saw one 

 of these airboats with the newer propeller drives.

 The one I saw had a 

 counter rotating system with 2 sets of 4 blade

 propellers for a total of 

 16 blades! This was all new stuff to me. I wonder if

 there may be some 

 way to adapt some simple version for kit planes?

 Interesting stuff.

 http://www.classicairboats.com/pages/props.html

 

 Rex

 Florida


	


__________________________________________________

smokey_bear_40220(at)yaho
Guest

Posted: Thu May 11, 2006 8:24 am Post subject: Thrust...Overrated?

So a Fox with a 912S could try their prop....  Any

takers?



Kurt S.



--- Clem Nichols <cnichols(at)scrtc.com> wrote:



 	  Quote: 	
		   Kurt:

 

 Standard engine on the Rans S6S is a Rotax 912S.


	


__________________________________________________

Rex Hefferan

Joined: 10 Jan 2006
Posts: 147
Location: Olney Springs, Colorado USA "NOT a Kitpig"

Posted: Thu May 11, 2006 9:26 am Post subject: Thrust...Overrated?

Hey Kurt, They claim they can get 100mph+ on ice, but they're using a 

500hp Chevy big block or some such engine. 

Yeah I knew it was not really workable except maybe to win some STOL 

competetions. Did you see that they have a 6 blade hub?

Rex



kurt schrader wrote:



 	  Quote: 	
		  



Hey Rex,



Gald to see you getting out.



The Russian Bear Bomber was very fast with

counter-rotating props.  Fastest big prop plane I know

of.



Those props you saw though are for low speed only. 

Someone has to make a high speed version or you will

have a fantastic takeoff and climb, but a 65 mph top

speed.



Prop weight has to be considered....   



Glider tow?  Heck, at low speed you could pull a

manure spreader with that prop.  Lot's a low end

power.



Now if we had a counter rotating, 100 knot, 20 lb Warp

drive.... No torque to fight on takeoff either.



Kurt S.

_________________
Rex
N740GP - M2/582
Colorado

morid(at)northland.lib.mi
Guest

Posted: Thu May 11, 2006 9:53 am Post subject: Thrust...Overrated?

Rex, at close examination of the web page it appears to me that those props

aren't counter rotating.  Take a look at the through prop bolts.  Or am I

missing something?

Deke



---

smokey_bear_40220(at)yaho
Guest

Posted: Thu May 11, 2006 10:10 am Post subject: Thrust...Overrated?

Rex,



With 500 HP, you could get a John Deere up to 100 MPH

on ice.



I think with that arrangement they have a heck of an

air powered dragster up to maybe 60.  After that, they

have too much prop.  100 mph is probably where the

engine just over revs without enough prop pitch.



That Russian Bear Bomber made a lot of noise.  Pilots

who flew intercept said that its prop noise dround out

their own jets.  I doubt that the Russians worried

about that though.



I saw the hub.  Getting near a piston powered fan jet.



Kurt S.



Do not archive



--- Rex <gypsybee(at)copper.net> wrote:



 	  Quote: 	
		   Hey Kurt, They claim they can get 100mph+ on ice,

 but they're using a 

 500hp Chevy big block or some such engine. 

 Yeah I knew it was not really workable except maybe

 to win some STOL 

 competetions. Did you see that they have a 6 blade

 hub?

 Rex


	


__________________________________________________

Rex Hefferan

Joined: 10 Jan 2006
Posts: 147
Location: Olney Springs, Colorado USA "NOT a Kitpig"

Posted: Thu May 11, 2006 11:10 am Post subject: Thrust...Overrated?

Deke, Yes you are correct and I appologize that I didn't make it clear 

that the link was not going to display the version I observed. Here is a 

link from the company that makes the counter rotation drive. In 

Australia no less.

http://www.airboatindustries.com.au/counter_rotating_prop.html



Check out this photo! (only a 12 blade configuration)

http://www.airboatindustries.com.au/images/whatis/propeller2.jpg



Rex

Florida



Fox5flyer wrote:



 	  Quote: 	
		  



Rex, at close examination of the web page it appears to me that those props

aren't counter rotating.  Take a look at the through prop bolts.  Or am I

missing something?

Deke

_________________
Rex
N740GP - M2/582
Colorado

smokey_bear_40220(at)yaho
Guest

Posted: Thu May 11, 2006 8:56 pm Post subject: Thrust...Overrated?

Neat idea.  Glad someone is studying it, but I wonder

about their claims.  Most props are better than 80%

efficient.  Even the first flight was done with props

over 80%.  So how can you get a 25% improvement?



I think they are measuring static thrust and, as we

discussed earlier, that is, ahhhh "Overrated" as a

factor.  But prop efficiency is usually low

statically, so there they could make the claim.



The other problem is that counter rotation means

cautious rotation.  Props flex in flight.  You could

be risking a prop collision if doing acro with this. 

The props would gyroscopic precess in opposite

directions and bend opposite.  Spacing between hubs is

important.



Lots to consider, but if we could really make it

better, I am all for it.



Kurt S.  S-5



--- Rex <gypsybee(at)copper.net> wrote:

 

 	  Quote: 	
		   Deke, Yes you are correct and I appologize that I

 didn't make it clear 

 that the link was not going to display the version I

 observed. Here is a 

 link from the company that makes the counter

 rotation drive. In 

 Australia no less.



http://www.airboatindustries.com.au/counter_rotating_prop.html
	


 	  Quote: 	
		   

 Check out this photo! (only a 12 blade

 configuration)



http://www.airboatindustries.com.au/images/whatis/propeller2.jpg
	


 	  Quote: 	
		   

 Rex

 Florida


	


__________________________________________________

Rex Hefferan

Joined: 10 Jan 2006
Posts: 147
Location: Olney Springs, Colorado USA "NOT a Kitpig"

Posted: Fri May 12, 2006 3:29 am Post subject: Thrust...Overrated?

There's your clue - Marketing language being what it is I suspect it's 

25% more than something, but not the 80%+ of most props best numbers. 

Picking the best numbers regardless of what they really mean in the real 

world is of course more Marketing Hype. I hadn't thought about the flex 

and they're using composite blades which usually mean omni-directional 

flex properties. I guess they could have some special design with 

uni-directional properties.



 Anyway, speculation can be fun plus it's different and looks kinda 

cool. Some people will buy stuff that looks cool regardless of it's 

practical purpose. Just look at 22" rims and tires for a Hummer.  

Rex (contemplating the round bump cowl on my M2)



kurt schrader wrote:



 	  Quote: 	
		  



Neat idea.  Glad someone is studying it, but I wonder

about their claims.  Most props are better than 80%

efficient.  Even the first flight was done with props

over 80%.  So how can you get a 25% improvement?



I think they are measuring static thrust and, as we

discussed earlier, that is, ahhhh "Overrated" as a

factor.  But prop efficiency is usually low

statically, so there they could make the claim.



The other problem is that counter rotation means

cautious rotation.  Props flex in flight.  You could

be risking a prop collision if doing acro with this. 

The props would gyroscopic precess in opposite

directions and bend opposite.  Spacing between hubs is

important.



Lots to consider, but if we could really make it

better, I am all for it.



Kurt S.  S-5

_________________
Rex
N740GP - M2/582
Colorado

wingsdown(at)comcast.net
Guest

Posted: Fri May 12, 2006 5:23 am Post subject: Thrust...Overrated?

Exactly. Static thrust only gives that relationship to other props at

that static RPM. It does not tell you what the overall efficiency will

be at a dynamic  airspeed and RPM. Even the Wright Brothers used a wind

tunnel. Without some real number thought the RPM and airspeed range no

one can know except by careful trials and testing on their own aircraft.

Even then the numbers may be skewed for a bunch of reasons. This list

most likely provides more real un-hyped numbers than any company will

ever supply particular to the aircraft we fly. 22s on a Hummer. That

gives me a great idea. Spinners for aircraft rims...I think they are 100

percent efficient and minimal flex under static loads. 



Rick  

--

wliles(at)bayou.com
Guest

Posted: Fri May 12, 2006 6:07 pm Post subject: Thrust...Overrated?

Well lets see.  A 25% improvement on an 80% efficient prop?  I suspect 

it would be 25% of  20% .  In other words maybe a whooping actual 5% 

improvement.  Not to be sneared at if true but hardly what the 

advertisement would have you believe.

Jerry Liles

Rex wrote:

 	  Quote: 	

There's your clue - Marketing language being what it is I suspect it's 

25% more than something, but not the 80%+ of most props best numbers. 

Picking the best numbers regardless of what they really mean in the real 

world is of course more Marketing Hype. I hadn't thought about the flex 

and they're using composite blades which usually mean omni-directional 

flex properties. I guess they could have some special design with 

uni-directional properties.

 Anyway, speculation can be fun plus it's different and looks kinda 

cool. Some people will buy stuff that looks cool regardless of it's 

practical purpose. Just look at 22" rims and tires for a Hummer.  

Rex (contemplating the round bump cowl on my M2)

kurt schrader wrote:

>

>

>Neat idea.  Glad someone is studying it, but I wonder

>about their claims.  Most props are better than 80%

>efficient.  Even the first flight was done with props

>over 80%.  So how can you get a 25% improvement?

>

>I think they are measuring static thrust and, as we

>discussed earlier, that is, ahhhh "Overrated" as a

>factor.  But prop efficiency is usually low

>statically, so there they could make the claim.

>

>The other problem is that counter rotation means

>cautious rotation.  Props flex in flight.  You could

>be risking a prop collision if doing acro with this. 

>The props would gyroscopic precess in opposite

>directions and bend opposite.  Spacing between hubs is

>important.

>

>Lots to consider, but if we could really make it

>better, I am all for it.

>

>Kurt S.  S-5

>

> 

>

>    

>

smokey_bear_40220(at)yaho
Guest

Posted: Fri May 12, 2006 8:46 pm Post subject: Thrust...Overrated?

Rick, Rex, Jerry and the list,

I was once in the operational testing branch of the

Marine Corps.  Our job was to be the "truth tellers"

for procurement decisions.  We took real Marines and

gave them the production articles and training

programs, then simulated the part of war they were to

operate the item in.  The test was to see what

actually happened "in the mud under fire".  I mostly

did aviation projects, but one of my projects was the

M-16A-2 rifle you may have heard about.

We would test all the candidates for a job and report

the results to Congress.  The idea was to pick the

best and tell what needed fixing before buying.  The

reality was, it depended upon who's district an item

came from and whether he was up for reelection,

whether the thing worked or not......

In the case of the M-16A-2, the manufacturer said it

was 50% more accurate at 100 yards than the old one. 

A 2" group instead of a 4" group from the bench mount,

as if we all fought from a bench.

We expected that it would mean something like a 12"

group instead of a 14" group in the hands of Marines,

a substantially smaller improvement.  (I created a

test that I am proud of for this gun too.  Interesting

results in many ways.)

The accuracy results were that if a Marine could hit

the target, the weapon mattered little.  Marines

either adjusted for inaccuracies, or they couldn't hit

a barn.

The job was a real education in what works, what was

said to work, and politics, which doesn't work.  Since

Federal $ are bottomless in some hands, the price was

really how many Marines lost per vote.

We are the truth tellers here.  We experiment and this

list is where we tell each other the truth as best as

we know it.  (I trust no one is up for election?)  If

we are wrong, we pay, so we are motivated to get it

right.

And now the right guy owns the company too!  

What a contrast.....

Kurt S.

Do not archive

--- Jerry Liles <wliles(at)bayou.com> wrote:

 	  Quote: 	
		   Well lets see.  A 25% improvement on an 80%

 efficient prop?  I suspect it would be 25% of 

 20% .  In other words maybe a whooping actual 5% 

 improvement.  Not to be sneared at if true but

 hardly what the advertisement would have you

 believe.

 Jerry Liles

 Rex wrote:

 >

 >There's your clue - Marketing language being what

 it is.......

__________________________________________________

Display posts from previous:

	Matronics Email Lists Forum Index -> Kitfox-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum