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Author Topic: Guillows Spirit of Saint Louis  (Read 710 times)
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Vyper
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« on: June 04, 2018, 04:01:00 PM »

Hi,

I am somewhat new to the group and returning to the hobby after a 25+ year absence.  My wife purchased the Guillows Spirit of Saint Louis for me as a gift.  I'm a bit of a Lindbergh fan and I would like to see this model fly.  Studying the plans, Guillows calls for the free flight versions to to be built with a significant dihedral added to the wing.  I am curious if it may be possible to build in about 3 to 5 degrees of washout into the wing to achieve the required stability and still preserve the scale look of the original Spirit of Saint Louis? I have built balsa models in the past using this method and I found that building washout into the wing does improve stability.  I am curious if anyone else has tried this with this kit and what were the results?

Also, any other building tips would be appreciated.  Thanks in advance for your replies.

Best regards,
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Crabby
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« Reply #1 on: June 04, 2018, 04:17:53 PM »

Hi Vyper, I was all set to build this model, but got distracted by other projects. There are several plans on outerzone that you ought to look at, just for the sake of being well informed. I think that model will fly flat winged. The fun part is gonna be figuring out how to do that aluminum swirl cowling. I recently found a very lightweight silver compound called Rub & Buff at Michael’s. If you chuck up a small buffing wheel in your dremel you might be able to pull it off. I bought some pressure adhesive sheets that looked ok at first but the swirl is way out of scale. Whatever. Good Luck and I am gonna watch this thread!
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ZK-AUD
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« Reply #2 on: June 04, 2018, 04:55:54 PM »

Hi Vyper.  The answer to your question is yes but I think 3-5 degrees is excessive.  You also have to consider the effect on the average angle of attack of the wing.  I build a few scale models and usually go with the scale dihedral for high wing monoplanes.

Important thing is weight - build light and you can get away with murder.  Be especially careful with  Guillows as they have a reputation for putting Oak in their kits, so don't be afraid to use their parts as templates and cut your own wood.  Make sure the wings are particularly light and of equal weight - helps if you get a bit of pendulum effect
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billdennis747
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« Reply #3 on: June 04, 2018, 05:21:45 PM »

I built the diesel model by Ron Moulton. He said it was stable with a flat wing and it was; remarkably so (the small tail was a different matter).  I've seen plenty of similar models flying well with around one degree. I would build it flat and see what happens; modify only if necessary. Nor would I bother with washout.
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Vyper
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« Reply #4 on: June 04, 2018, 06:38:30 PM »

Thanks to everyone for the replies.  Somewhere in the deep recesses of my mind, I seem to recall that an aircraft with a high wing is equivalent to having 2 degrees of dihedral built in right from the start.  I could be wrong on this though, so take it with a grain of salt.  The idea of washout is just a thought that I happened to have.  I may just build two wings. One with washout and one without just to experiment.  I am thinking that I may need to increase the size of the tail surfaces slightly.  I am aware that Guillows wood is rather heavy.  I think I will be substituting a fair amount of this kit with lightweight material.  It's going to be an interesting build.  Thanks again!

Best regards,
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Vyper
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« Reply #5 on: June 04, 2018, 09:16:16 PM »

Hi Crabby,

"There are several plans on outerzone that you ought to look at, just for the sake of being well informed."

 I've been looking at the plans on outerzone.  They are interesting.  It seems that the designers of those models didn't worry about dihedral or washout at all.  The one thing I noted that I think is very good was the plans called for 1 degree down thrust and 2 degrees of right thrust at the prop.  I recall that was typically done on most models to counter the prop torque.  As for the swirl pattern on the nose, I have some ideas.  As I proceed into this model, I'll be experimenting with that also.  Thanks for the info.
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Vyper
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« Reply #6 on: June 04, 2018, 09:21:18 PM »

Hi ZK-AUD,

Now that you mention it, 3 to 5 degrees of washout is extreme.  If I do add the washout, I think it will be on the order of 1 degree to perhaps 2 degrees max.  I went over some notes that my dad made 45 years ago on the old Comet Stinson SR-7.  He added 1 degree of washout to the model he built.  That became a standard for us on later models.  Thanks again for the input.
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ZK-AUD
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« Reply #7 on: June 04, 2018, 09:55:10 PM »

Some people don't bother but I use washout on everything as a matter of course.   If my models stall under power they tend to mush and then resume flying rather than dropping a wing and spinning.

I think your Dad was right -  For a model with say 21" span and a chord of 3.5" I would chuck in about 1/16 which is roughly 1 degree. 

I think stability is easier to achieve if you build with a positive turn in mind.  If you make your SOSL go right and induce a positive turn you only need to worry about it dropping the right wing.  I'd go with differential washout  say a degree and a half on the left and a degree on the right,  then make it go right with rudder for the glide and right thrust for the power.  the differential washout will oppose the right turn and keep the right wing up.

https://www.facebook.com/Aveteknz/videos/  Check out this link of my Sommer Monoplane peanut.  It has next to no dihedral,  but it has washout.  Watch what happens when it hits its own wake turbulence and how it recovers
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Vyper
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« Reply #8 on: June 05, 2018, 11:45:05 AM »

Hi ZK-AUD

It's interesting.  The wing drops slightly and then the plane recovers and continues it's flight.  I would bet that if it had not had washout, it would have simply rolled into a spin and crashed.  Nice recovery.  Thanks!
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John Webster
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« Reply #9 on: June 10, 2018, 02:51:15 AM »

Full size aircraft with constant chord wings (Spirit of St. Louis) usually do not have washout. Planes with tapered wings (Hurricane) or elliptical wings (Spitfire) need washout. Spitfires have 3º at the tip rib.
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Vyper
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« Reply #10 on: June 11, 2018, 08:11:19 PM »

Hi John. Just curious why that is?
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John Webster
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« Reply #11 on: June 14, 2018, 05:03:34 AM »

http://www.dauntless-soft.com/PRODUCTS/Freebies/Library/books/FLT/Chapter17/WingPlanform.htm

The above is a one page explanation of stall distribution for various wing planforms.


The technical explanation has to do with Reynolds numbers. In the mathematical formula that shows what lift a wing will generate one of the numbers above the dividing line is the Reynolds number. The Reynolds number includes the wing chord; the longer the chord, the higher the Reynolds number. If the tip chord is half the root chord the tip will produce half the lift of the root (disregarding fuselage effects).
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A pilot starts out with a bag full of luck and an empty bag for experience. The object is to fill the bag of experience before you empty the bag of luck.
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