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Speed Mod - Engine Down Thrust Angle

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Discover

Joined: 26 Feb 2007
Posts: 429

Posted: Sun Mar 31, 2013 6:21 pm Post subject: Speed Mod - Engine Down Thrust Angle

Gary posted:

â€¢ Regardless of what the factory says about alignment, experience shows that a down thrust angle makes the plane more stable during power changes.  It also makes the plane faster.

Ned posts:

I'm interested in the experience that you mention. Is that from the WWII aircraft designs you mentioned a few years ago? Or have you actually flown your Tiger with 0 then 2 degrees down angle? That would be very interesting flight tests. If you haven't tried that I might do that sometime just to see what happens.



I've been racing my Tiger for several years now. One of the fun things about doing that is getting to hang out with all the other racers. Nobody ever mentions a speed advantage with anything but zero thrust angle. That is, they always say the same thing and that is you need to have zero thrust angle for maximum speed. Maybe they are all wrong?





 [quote][b]

teamgrumman(at)yahoo.com
Guest

Posted: Sun Mar 31, 2013 7:52 pm Post subject: Speed Mod - Engine Down Thrust Angle

I don't know about 2 degrees down.  2 Degrees is a lot.  One thick shim is worth about .5 degrees.

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

I double checked the AA1B mockup I'm using for pre-fitting the Jaguar cowling.  

Canopy rail:  Left at .9 degrees up.  

                  Right at 1.1 degrees up.

Engine:  Left at .8 degrees up.  i.e., .1 degrees down

            Right at .9 degrees up.   i.e., .2 degrees down

That means the mockup engine is somewhere around .1 to .2 degrees down.  So, worst case scenario, my cowling is, at most, .5 degree down.

Note:  I measured the engine in several different places and got different answers at each location.  Measuring  the cylinder bases, which, one would think, would be on the centerline, varied .1 degrees on each side.  That is, the front cylinder might show .2 down thrust and the rear .1 down or vice versa.  Measuring at the lifter body bosses yielded values not consistent with either.  

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

When I get the upper cowling on N28697 so I can open it, I'll double check it.

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

Down thrust:  I did a lot of reading regarding down thrust.  RC modelers use down thrust to make power changes less of a control issue.  Straight and level, when the power is pulled back, the plane doesn't sink as fast sink the engine is no longer pulling it down.  Likewise, when power is applied, there is less need for down elevator since the engine is pulling down.  

The T-28 has 5 degrees down thrust angle.

During WWII, it was found, mostly on big radials, that the plane was faster with the engine in a down thrust position.  This was due to reduced trim drag.  As you go faster, if you don't have to trim the nose down, there is less trim drag.  

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

Galloping Ghost:  The trim tab failed on Galloping Ghost causing an abrupt pitch up.  At those speeds, the trim is at the limit trying to keep the plane flying straight.  Why not point the nose down and shed all that trim requirement . . . or at least a large portion of it?

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

NACA 64-415 Mod.  That's our airfoil.  It's pretty close to a Clark Y (if you rotate the Clark Y on  it's axis 2.5 degrees.)  The Clark Y has best L/D at around 2 degrees down AoA.  Or, about where the -415 is when the Grumman is at 2.5 degrees down at the waterline.  

So, you want the plane to be nose down.  Why not let the engine pull it down, reduce trim drag, and put the airfoil at minimum L/D?  And, get less pitch change when changing power settings?

Gary

 

        From: 923TE <923te(at)att.net>

 To: "teamgrumman-list(at)matronics.com" <teamgrumman-list(at)matronics.com> 

 Sent: Sunday, March 31, 2013 7:20 PM

 Subject:  Speed Mod - Engine Down Thrust Angle

  

 

 Gary posted:

â€¢ Regardless of what the factory says about alignment, experience shows that a down thrust angle makes the plane more stable during power changes.  It also makes the plane faster.

Ned posts:

I'm interested in the experience that you mention. Is that from the WWII aircraft designs you mentioned a few years ago? Or have you actually flown your Tiger with 0 then 2 degrees down angle? That would be very interesting flight tests. If you haven't tried that I might do that sometime just to see what happens.



I've been racing my Tiger for several years now. One of the fun things about doing that is getting to hang out with all the other racers. Nobody ever mentions a speed advantage with anything but zero thrust angle. That is, they always say the same thing and that is you need to have zero thrust angle for maximum speed. Maybe they are all wrong?





 [quote][b]

Discover

Joined: 26 Feb 2007
Posts: 429

Posted: Sun Mar 31, 2013 10:41 pm Post subject: Speed Mod - Engine Down Thrust Angle

Gary posts:



The T-28 has 5 degrees down thrust angle.

This was due to reduced trim drag.  As you go faster, if you don't have to trim the nose down, there is less trim drag.  



So, you want the plane to be nose down.  Why not let the engine pull it down, reduce trim drag, and put the airfoil at minimum L/D?  And, get less pitch change when changing power settings?



Ned posts:



Ok, I'll buy that.



My tiger flies with neutral trim at its maximum speed. The horizontal stab is aligned with the elevator which is aligned with the trim.

So it has no drag due to trim while racing. 

Also, it has the engine thrust pulling straight ahead. So I lose no thrust due to a downward component.



Now I understand better why you say you need to fly the tail on your plane. That is, you don't have the horizontal stab aligned with the elevator aligned with the trim. Your plane has to have some pull up to counter the engine pulling it down.......???



Like you I reflex the flaps to lower the nose for a little bit more speed. The amount of reflex is dependent upon how much fuel, (weight) I have on board. I find best speed is when flap reflex gives about 1 to 1.5 degree nose down as indicated by the canopy rail.



See:

Trim Wheel Neutral (Small).jpg

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33.83 KB

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4472 Time(s)

Left Stab Alignment (Small).jpg

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4472 Time(s)

Last edited by Discover on Sun Mar 31, 2013 10:58 pm; edited 1 time in total

teamgrumman(at)yahoo.com
Guest

Posted: Mon Apr 01, 2013 11:23 am Post subject: Speed Mod - Engine Down Thrust Angle

No message

        From: 923TE <923te(at)att.net>

 To: "teamgrumman-list(at)matronics.com" <teamgrumman-list(at)matronics.com> 

 Sent: Sunday, March 31, 2013 11:40 PM

 Subject: Re: Speed Mod - Engine Down Thrust Angle

  

 

 

 

  

 [quote][b]

Discover

Joined: 26 Feb 2007
Posts: 429

Posted: Mon Apr 01, 2013 2:21 pm Post subject: Re: Speed Mod - Engine Down Thrust Angle

Wouldn't it be great if the Tiger Factory could provide a jig to determine where the engine thrust line is supposed to be adjusted to?

They could do it by starting with a standard lower cowl, beef it up and make it compactable so it could be shipped and reassembled true....



That'd be the only to know 4sure. Same as with the the flight control jigs

n76lima(at)mindspring.com
Guest

Posted: Mon Apr 01, 2013 2:48 pm Post subject: Speed Mod - Engine Down Thrust Angle

If they'd just publish the data, we could measure it ourselves.

--Bob



discover <923te(at)att.net> wrote:



 	  Quote: 	
		  



Wouldn't it be great if the Tiger Factory could provide a jig to determine where the engine thrust line is supposed to be adjusted to?

They could do it by starting with a standard lower cowl, beef it up and make it compactable so it could be shipped and reassembled true....



That'd be the only to know 4sure. Same as with the the flight control jigs





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=397583#397583

aa5_driver(at)yahoo.com
Guest

Posted: Mon Apr 01, 2013 3:17 pm Post subject: Speed Mod - Engine Down Thrust Angle

Has anyone asked Kevin at true flight?  Maybe he would provide the info.



Kevin



On Apr 1, 2013, at 5:45 PM, Bob Steward <n76lima(at)mindspring.com> wrote:



 	  Quote: 	
		   

 

 If they'd just publish the data, we could measure it ourselves.

 --Bob

 

 discover <923te(at)att.net> wrote:

 

> 

> 

> Wouldn't it be great if the Tiger Factory could provide a jig to determine where the engine thrust line is supposed to be adjusted to?

> They could do it by starting with a standard lower cowl, beef it up and make it compactable so it could be shipped and reassembled true....

> 

> That'd be the only to know 4sure. Same as with the the flight control jigs

> 

> 

> 

> 

> Read this topic online here:

> 

> http://forums.matronics.com/viewtopic.php?p=397583#397583

> 

> 

> 

> 

> 

> 

> 

> 

> 

>

flying-nut(at)cfl.rr.com
Guest

Posted: Mon Apr 01, 2013 3:45 pm Post subject: Speed Mod - Engine Down Thrust Angle

Just a gut feeling, but I'm betting the differences in the thrust line 

(without shims) are normal 'manufacturing tolerances' when the firewall 

and engine mount fittings are glued in.  I think the thrust line issue 

suffers from the same problem the rigging has ....

Linn



On 4/1/2013 6:21 PM, discover wrote:

 	  Quote: 	
		   



 Wouldn't it be great if the Tiger Factory could provide a jig to determine where the engine thrust line is supposed to be adjusted to?

 They could do it by starting with a standard lower cowl, beef it up and make it compactable so it could be shipped and reassembled true....



 That'd be the only to know 4sure. Same as with the the flight control jigs





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=397583#397583





 -----

 No virus found in this message.

 Checked by AVG - www.avg.com

teamgrumman(at)yahoo.com
Guest

Posted: Mon Apr 01, 2013 7:20 pm Post subject: Speed Mod - Engine Down Thrust Angle

Obviously, engine trust angle is not that critical.  I've seen engines as much as 1/2 inch off center in all directions and the pilot doesn't notice or care.

        From: discover <923te(at)att.net>

 To: teamgrumman-list(at)matronics.com 

 Sent: Monday, April 1, 2013 3:21 PM

 Subject: TeamGrumman-List: Re: Speed Mod - Engine Down Thrust Angle

 --> TeamGrumman-List message posted by: "discover" <923te(at)att.net (923te(at)att.net)>

Wouldn't it be great if the Tiger Factory could provide a jig to determine where the engine thrust line is supposed to be adjusted to?

They could do it by starting with a standard lower cowl, beef it up and make it compactable so it could be shipped and reassembled true....

That'd be the only to know 4sure. Same as with the the flight control jigs

Read this topic online here:

http://forums.matronics.com/viewtop= Archive Search & Download, 7-Day Browse, -========================                     &nbs===================

 [quote][b]

Discover

Joined: 26 Feb 2007
Posts: 429

Posted: Mon Apr 01, 2013 7:32 pm Post subject: Speed Mod - Engine Down Thrust Angle

All I can say is that I have found a lot of speed in the tail.....



On Apr 1, 2013, at 10:18 PM, Gary L Vogt <teamgrumman(at)yahoo.com (teamgrumman(at)yahoo.com)> wrote:

Obviously, engine trust angle is not that critical.  I've seen engines as much as 1/2 inch off center in all directions and the pilot doesn't notice or care.



   

 [quote][b]

teamgrumman(at)yahoo.com
Guest

Posted: Mon Apr 01, 2013 8:12 pm Post subject: Speed Mod - Engine Down Thrust Angle

On a Cheetah, the engine can be installed with "NO" shims.  

On a Tiger, you need at least one shim on the lower left.

Let's just say, for shits-and-grins, the factory set up the engine mount with at least one shim in the lower left.  I doubt it of course, but let's just say.  Given that, the engine mount would  be asymmetric. 

Adding a shim to the bottom on the right should move the engine up and to the left.  This would make the engine not align with the cowling.  

So far, all of the planes I've worked on also have a shim on the lower right.  Most have one on each top mount.  Where is it supposed to be, and how much does it  matter?

Story:  I aligned the engine to a cowling on a 78 Tiger about 8 years ago.  The owner didn't ask, I just did it.  After the annual, the owner brought the plane back and said the plane required too much rudder to correct for yaw.  He claimed it flew perfectly before the annual.  I told him I shimmed the engine to align it.  He wanted the shim out.  I removed it.  It's still out.  The engine is not aligned to the cowling and he is still happy with the way it flies.

        From: Linn <flying-nut(at)cfl.rr.com>

 To: teamgrumman-list(at)matronics.com 

 Sent: Monday, April 1, 2013 4:42 PM

 Subject: Re: TeamGrumman-List: Re: Speed Mod - Engine Down Thrust Angle

  

 

 --> TeamGrumman-List message posted by: Linn <flying-nut(at)cfl.rr.com (flying-nut(at)cfl.rr.com)>



Just a gut feeling, but I'm betting the differences in the thrust line 

(without shims) are normal 'manufacturing tolerances' when the firewall 

and engine mount fittings are glued in.  I think the thrust line issue 

suffers from the same problem the rigging has ....

Linn



On 4/1/2013 6:21 PM, discover wrote:

[quote] --> TeamGrumman-List message posted by: "discover" <923te(at)att.net (923te(at)att.net)>



 Wouldn't it be great if the Tiger Factory could provide a jig to determine where the engine thrust line is supposed to be adjusted to?

 They could do it by starting with a standard lower cowl, beef it up and make it compactable so it could be shipped and reassembled true....



  That'd be the only to know 4sure. Same as with the the flight control jigs





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=397583#397583





 -----

 No virus found in this message.

 Checked by AVG - www.========================

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