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Another video..

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ces308

Joined: 03 Nov 2008
Posts: 317
Location: houghton lake ,mi

Posted: Fri Oct 22, 2010 11:26 am Post subject: Another video..

Hello...



went for gas today and shot this....landscape is about the same ,but there is engine data video with the new prop.....

...Hey ! is free !http://www.youtube.com/watch?v=qdxkjmG83fM  lol



chris ambrose

M3X/Jabiru    153.0 hrs

N327CS

ces308

Joined: 03 Nov 2008
Posts: 317
Location: houghton lake ,mi

Posted: Fri Oct 22, 2010 12:52 pm Post subject: Re: Another video..

http://www.youtube.com/watch?v=qdxkjmG83fM



sorry...shouldn't have to copy and paste now...



chris ambrose

Thom Riddle

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

Posted: Sat Oct 23, 2010 4:19 am Post subject: Re: Another video..

Chris,



If your ASI is accurate, your airspeeds and rpm are almost exactly the same as my SS. 



A mystery as to why/how that could be. I'm beginning to think I'm losing a good bit of speed due to the thrust line angle. As I've stated on a recent post, mine is pointing up several degrees when it should be pointing down about 4-6 degrees relative to the wing bottom chord.



Can you tell me what your thrust line angle is relative to the bottom chord of your wing?

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

ces308

Joined: 03 Nov 2008
Posts: 317
Location: houghton lake ,mi

Posted: Sun Oct 24, 2010 11:56 am Post subject: Re: Another video..

Thom,



The engine is level with the factory engine mount....hopefully a picture is worth a thousand words...let me know if there is anything else I can help you with,....



chris ambrose

M3X/Jabiru  A-2200

N327CS

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Thom Riddle

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

Posted: Sun Oct 24, 2010 1:49 pm Post subject: Re: Another video..

Chris,



Thanks for the photos which shows the engine with its thrust line parallel to the ground. It is apparent from the photos that if you extend the centerline of the engine forward and the bottom of the wing forward that these two would intersect. I'm looking for this angle between them. On my SS, this angle DIVERGES instead of coming together and there is lies the problem, I believe. I'd like to get it close to right on the first attempt to adjust this angle.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

mdnanwelch7(at)hotmail.co
Guest

Posted: Sun Oct 24, 2010 2:15 pm Post subject: Another video..

 	  Quote: 	
		   On my SS, this angle DIVERGES instead of coming together > --------

 Thom Riddle


	


 Thom,

  

   As an interested reader to your description, I can't picture that your wing's incidence

 and the engine's thrustline diverge.

   This just seems very difficult to comprehend.

  

   Can you share a picture (similar to what Chris did)?  I am interested in knowing more

 about this subject.

  

 Thanks,

 Mike Welch

 MkIIICX

 		 	   		    [quote][b]

Thom Riddle

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

Posted: Sun Oct 24, 2010 2:46 pm Post subject: Re: Another video..

Mike,



The only photo I have of the SS directly from the side is a relatively low res photo, which I've attached. It does not show very well but here is the measured data.



With the airplane sitting in 3-point stance....



Tail Boom = 5 degrees (front higher)

Horizontal Stabilizer  = 5 deg. (front higher) parallel to boom

Wing Bottom = 12 degrees

Engine Thrust Line = 15.5 degrees



Therefore, relative to the Horizontal Stabilizer....

Wing Bottom has a 7 degrees incidence (12 - 5)

Engine Thrust line has 10.5 degrees incidence (15.5 -5)



The engine thrust line points higher (in front) than the wing bottom by 3.5 degrees!

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_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

ces308

Joined: 03 Nov 2008
Posts: 317
Location: houghton lake ,mi

Posted: Sun Oct 24, 2010 3:21 pm Post subject: Re: Another video..

Thom,



I see what you mean ...your thrust line and wing incidence are about parallel if you draw a line down the center of the crank and the bottom of the wing...



chris ambrose

M3X/Jabiru  A-2200

N327CS

ces308

Joined: 03 Nov 2008
Posts: 317
Location: houghton lake ,mi

Posted: Sun Oct 24, 2010 3:39 pm Post subject: Re: Another video..

Thom....It's like your engine is fighting the airframe....Like they say a aft CG makes the airplane fly faster,cause you're not trying to hold the nose up... and yours is trying to push the nose over...thats what it sounds like your's is doing....???  is that what you're thinking??



chris ambrose

Thom Riddle

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

Posted: Sun Oct 24, 2010 3:54 pm Post subject: Re: Another video..

Although it may look parallel, the angle actually diverges by 3.5 degrees, which is hard to see. I don't claim to understand what this is doing aerodynamically, but intuitively it seems reasonable for the thrust line to be parallel to the relative wind. If the AOA of the wing at cruise is about six degrees or thereabouts, then the thrust line should be about six degrees less than the bottom of the wing, but in my case it is 3.5 degrees greater. In other words it is about 9.5 degrees too high! At least that is how I see it.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

Richard Pike

Joined: 09 Jan 2006
Posts: 1670
Location: Blountville, Tennessee

Posted: Sun Oct 24, 2010 7:06 pm Post subject: Re: Another video..

Thom, if I were you, I would start stacking washers under the rear motor mounts and then go and test fly...



Richard Pike

MKIII N420P (420ldPoops)

Thom Riddle

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

Posted: Mon Oct 25, 2010 4:11 am Post subject: Re: Another video..

Richard,



I wish it were that simple. The Jab motor mount attaches to the standard Kolb motor mount plates with matching plates which would require beveled shims under the front and rear mounts to be done right, as well as the correct length AN bolts. I'd like to get close to the right answer the first try so I don't have to fabricate several different angle/thickness shims and purchase several different length AN bolts.



I think I'll just assume that the correct angle for the thrust line is parallel to the horizontal stabilizer and go with that. That angle has got to be better than what it is now.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

jbhart(at)onlyinternet.ne
Guest

Posted: Mon Oct 25, 2010 5:53 am Post subject: Another video..

Thom,



I agree with Richard Pike.  If one assumes the wing aoa is six degrees and 

your engine is set 3.5 degrees on top of that, and using the cosine of 9.5 

degree, it indicates that 98.6 % of your thrust is pushing in the direction 

of the relative wind. The other right angle thrust component is being used 

to help hold up the plane.  Agreed 1.5% loss is not very much and your plane 

should climb better than if the thrust vector was set in the direction of 

the relative wind.  By reseting the engine, you should gain some cruise 

speed, and reduce cruise power factor and fuel flow with less trim. 

The question is, is it worth the effort to capture a couple of horsepower?



Jack B. Hart FF004

Winchester, IN

Thom Riddle

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

Posted: Mon Oct 25, 2010 6:15 am Post subject: Re: Another video..

Jack,

I did the math too and that is the reason I've not been in a hurry to do the work, but think I will eventually get around to it. 



The other problem with this that Chris alluded to is that the point and angle at which the thrust is acting is so far aft of the CG that it results in a significant nose down pitching moment when adding power, more so I believe than if the thrust was parallel to relative wind. The net result of this torque about the CG is an effectively heavier wing (at CG) requiring more tail down force to counter. So the loss in direct thrust is only part of the net negative effect. Relieving the wing of the extra thrust angle induced load and the extra HS loading is worthwhile also. Perhaps I am visualizing this all wrong, so if you would like to correct me with your excellent vector diagrams, I'm all ears and eyes. Or if I am correct, your confirmation is welcome too .



When I get around to doing it, I'll report the qualitative and quantitive results, if any.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

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