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Decalage - 5/19/2008 10:15:34 PM   
jashley1


 

Posts: 24
Joined: 12/9/2005
From: , TX, USA
Status: offline 		Ladies and gentlemen:

I think that is what the alignment of the stab and wing are to the lateral axis of the fuselage; not as nice as cleavage, but that is another subject. Anyway, I built a Midwest Esquire from Bill Northrop's Plan Service. I will fly it on rudder and an exhaust baffle throttled OS .15. I have a fear of launching it and seeing it climb, stall and crash. As the horizontal stabilizer and wing both have positive incidence, should I shim the stab for less incidence until I see how it behaves? Long grass for a test glide is kind of hard to find here in Central Texas. The stab is a symmetrical airfoilwhy have both the wing and the stab positive?

Thanks in advance,
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RE: Decalage - 5/19/2008 10:57:28 PM   
HighPlains


 

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From: Over da rainbow, KS, USA
Status: offline 		On a slightly more than calm day (windy in other parts of the country) just run with the model and see how it feels in the hand. At some point it might even be doing formation flight with your slightly opened hand. If it behaves there, have courage and give it a forward push level with the ground. If all is well it will find it's gliding speed and sink to the ground. Don't give it a big throw, since that may be faster than it wants to glide at, and it will climb and perhaps stall.

Then it's time to try power. If it is climbing and stalling, turn. The extra loss of lift due to the turn will keep it flying level and level to the ground is the goal. When you throttle down, the turn will need to be more shallow. The main thing is to either climb without stalling or maintain altitude until you slow down to glide speed.

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RE: Decalage - 5/20/2008 2:10:43 AM   
khodges


 

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From: newton, NC, USA
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quote:

ORIGINAL: jashley1

Ladies and gentlemen:

I think that is what the alignment of the stab and wing are to the lateral axis of the fuselage; not as nice as cleavage, but that is another subject. Anyway, I built a Midwest Esquire from Bill Northrop's Plan Service. I will fly it on rudder and an exhaust baffle throttled OS .15. I have a fear of launching it and seeing it climb, stall and crash. As the horizontal stabilizer and wing both have positive incidence, should I shim the stab for less incidence until I see how it behaves? Long grass for a test glide is kind of hard to find here in Central Texas. The stab is a symmetrical airfoilwhy have both the wing and the stab positive?

Thanks in advance,

I'm more into cleavage myself, but decalage is the angle difference between the wing and H stab. When they are both compared to a third reference, such as the longitudinal axis, it is called incidence.

So, if the wing is, say, +2 degrees incidence to the centerline of the fuse, and the tail is +1, then the decalage is +1. Decalage also refers to the difference in incidence between the two wings of a biplane.

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RE: Decalage - 5/20/2008 3:03:36 AM   
CoosBayLumber


 

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Joined: 1/20/2002
From: San Bernardino Calif
Status: offline 		Mr. A....

The Esquire was a climbing fool. If you use modern light weight radio gear, a new H-P motor it will climb once you toss it into the air. I also found this out on an old timer, for then had to do numerous series of Hold-em spirals to keep down, nearer the ground. Once I let up it automatically began climbing. Up, then spiral down, up, then spiral down, numerous times awaiting gas to run out.

I would thnk perhaps you could build as is, and the add in a bunch of ballast.

Wm.


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RE: Decalage - 5/26/2008 8:04:00 AM   
balsaworks



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Joined: 12/27/2004
From: Stockholm, SWEDEN
Status: offline
quote:

ORIGINAL: jashley1

...... Long grass for a test glide is kind of hard to find here in Central Texas. The stab is a symmetrical airfoilwhy have both the wing and the stab positive?



If the model is built as designed it should have the proper decalage.
I don´t have access to a plan of the Esquire, but presumably it has a flat bottom wing with a Clark Y airfoil? That airfoil has a LOT of lift.
The angle of attack for a Clark Y or similar airfoil isn´t measured along the flat bottom, but rather along a line that can be drawn from the tip of the rear end, and then through the very tip of the nose.
Since the nose is rounded the angle of attack may be 2-3 degrees more positive than the flat bottom, depending on the shape of the nose. The effective angle of attack may be even higher because of the high lift character of airfoil.
It would be very difficult to find the right trim without test gliding over tall grass.
The next step - powered flight is critical too. You need the right amount of downthrust to balance out the climbing effect of the positive decalage. A very good throttle and some tall grass will be helpful...
Or you you might add elevator control until you have sorted out the trim, and then go back to rudder only?

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RE: Decalage - 5/26/2008 12:49:47 PM   
Michaelj2k



Posts: 309
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From: Newark, DE, USA
Status: offline 		In days of olde, most designers first recommended that power off hand glides be performed to observe for any stalling or nose heavy conditions, warps, etc.. Shift weight, add or subtract weight as necessary to get a long distance glide of at least 50 to 100 feet. Then perform the first flights with reduced power until the trim changes (if necessary) were figured out. No doubt, at full power your Esquire will be a climbing fool. Good luck!

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RE: Decalage - 5/28/2008 1:49:55 PM   
rainedave



Posts: 5175
Joined: 7/21/2005
From: Greensboro, NC, USA
Status: online 		Trimming these planes has a lot in common with Free Flight. I agree that test gliding is necessary to sort out the CG and incidences. Once that's optimized, then, you can adjust downthrust to help it fly closer to level at mid throttle. It's still going to climb at full power and glide (lose altitiute) at idle. That's just the nature of the design. At any rate, get the glide sorted out first.

David

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RE: Decalage - 5/28/2008 2:00:22 PM   
jashley1


 

Posts: 24
Joined: 12/9/2005
From: , TX, USA
Status: offline 		Thanks for all the help so far, but how do I know how whether to shim the stab or the wing?

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RE: Decalage - 5/28/2008 2:58:13 PM   
rainedave



Posts: 5175
Joined: 7/21/2005
From: Greensboro, NC, USA
Status: online 		One way to do this is to keep the decalage as it's shown on the plans and adjust the balance until you have a good power-off glide.

David

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RE: Decalage - 5/28/2008 3:43:08 PM   
jashley1


 

Posts: 24
Joined: 12/9/2005
From: , TX, USA
Status: offline 		ThanksI built it per the plans which incidentally show 2 different options for the stab incidence1 has more incidence I believe is for a heavier radio than the other. I built it according to what I believe was intended for the lighter receiver.

As an aside, I ran the OS .15 with the exhaust baffle. It is very loud at full throttle, but it is a screamer with an 8x4 Master Airscrew blue prop. I didn't checck rpm yet with a tach. I ended up using an OS type F four-stroke glow plug with 2 washers as it didn't want to idle with the K&B 1L I wonder if an idle bar plug would have worked better? I'll try that if the type F burns out. I hope to teach my 5yo daughter to fly it if I can keep her interested. I won't fly it at the established field due to muffler rules-most likely it will be flown in the country and probably just above idle at that.

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RE: Decalage - 5/28/2008 3:53:47 PM   
rainedave



Posts: 5175
Joined: 7/21/2005
From: Greensboro, NC, USA
Status: online 		Just be certain to use fuel with lots of castor oil. I have been running my old baffle-piston OS's on Sig Champion with 5% nitro and A3 plugs. The Enya #3 is another good choice.

David

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RE: Decalage - 5/28/2008 4:00:10 PM   
Michaelj2k



Posts: 309
Joined: 9/15/2006
From: Newark, DE, USA
Status: offline
quote:

ORIGINAL: jashley1

Thanks for all the help so far, but how do I know how whether to shim the stab or the wing?


Test glide on a calm evening over reasonably tall grass when winds will not be a factor. Then, experiment to see what works best. You will find that it is a balance of the two angles of attack of the wing and stab to find the best power off glide. Once you add power, things will change. BTW, some guys will trim with the prop removed to prevent breakage.

quote:


As an aside, I ran the OS .15 with the exhaust baffle. It is very loud at full throttle, but it is a screamer with an 8x4 Master Airscrew blue prop. I didn't check rpm yet with a tach. I ended up using an OS type F four-stroke glow plug with 2 washers as it didn't want to idle with the K&B 1L I wonder if an idle bar plug would have worked better? I won't fly it at the established field due to muffler rules-most likely it will be flown in the country and probably just above idle at that.


The OS .15 has been around for a long time. The idle bar plug should work ok, I've used them in the .19. Another trick to slow down the rpm is to use a larger diameter prop. As far as OS .15 mufflers are concerned, they can be found on our favorite auction site. Look for an OS 702 (I think). Once you have mastered rudder only, show the guys at the field how it was done 40 years ago.

< Message edited by Michaelj2k -- 5/28/2008 4:02:55 PM >

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