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Author Topic: Flat Iron Embryo  (Read 4102 times)
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mkirda
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« Reply #25 on: March 02, 2015, 06:53:02 PM »

Hey, I didn't write the "rule book".  "Should be" is an awfully subjective phrase.  Speculation can go on forever.  Different CDs, different interpretations.    If people really want to know what is "allowed" then ask Headquarters for a written clarification.  The OP asked for comment, so allow me to rephrase my opinion:  A built up tip plate will never be challenged, given the current rule book wording.

Maybe so, but given that the rules do not define structural requirements for tip plates, you'd have a really good argument that sheet tip plates would not be disqualified either.

i.e "Tail" means "stab" to me. So tip plate sheet rudders would pass unless tail is defined to include both stab and rudder.

If a CD were to challenge this it would be worth going up the chain to get things defined properly.
Just sayin'

This is a nice looking model, BTW. I'd guess I'd have it down at about 8 grams too.
(My latest is a 28"WS Rearwin Skyranger and it weighs less than 20 grams.)

Regards.
Mike Kirda
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calgoddard
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« Reply #26 on: March 03, 2015, 09:24:25 AM »

I will probably build a lighter Flat Iron Embryo some time in the future.  I am leaning toward solid tip plates.  Maybe I can get the model closer to 10 grams. I think 8 grams would be difficult but possible if I use a 6 inch Ikara prop.

On a different note, one of the problems I had with my Prairie Bird Embryo was the lack of space at the location of the motor peg.  The fuselage of the Prairie Bird is very narrow at that location.  See the attached picture of my blue tissue covered Prairie Bird Embryo fuselage.

You can see in the photograph of my Flat Iron Embryo that I enlarged this area quite a bit to facilitate insertion of the motor peg through the rubber motor, and use of a blast tube.  Yes, I actually use a blast tube when winding my Flat Iron Embryo. It consists of a length of carbon fiber arrow shaft with L-shaped notches for locking on to the motor peg which is made of 1/8 inch Aluminum tubing. I made a small extractor from .025 inch music wire to facilitate removal of the blast tube once the motor is wound. In one of my early winds of my Flat Iron, the rubber motor broke, and the blast tube probably saved my model from major damage.
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Re: Flat Iron Embryo
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calgoddard
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« Reply #27 on: March 13, 2015, 12:10:38 PM »

I added a 1/32" shim under the LE of the wing and got a better climb.  On one launch, my Flat Iron hit a curtain wall at about 22 - 23 feet, then dove, then recovered, and then landed on its landing gear.  I am getting near one minute now. The next step is to try a longer motor.

Making 90 seconds on an indoor flight with my first Flat Iron is going to be difficult.  Ultimately I think I will need to reduce the weight from about 13 grams to around 10 grams, or even less.  This of course will require building a new Flat Iron with more careful wood selection.  I may have to take a few of the diagonals out of the stab. I might also switch to sheet balsa tip plates, which would save some weight, since the consensus seems to be that this would be legal under the FAC Embryo Endurance rules.

The plan is still being worked on but it is looking good after a few iterations. Ultimately it will be posted in the Plan Gallery.  I will let you all know when that happens.  Thanks for reading this, and for your continuing interest.  
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dorme
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« Reply #28 on: March 13, 2015, 01:03:48 PM »

I would think that the tip plates are part of the wing thus that area is also included in the overall wing area.
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Hepcat
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« Reply #29 on: March 13, 2015, 02:09:46 PM »

Ref replies #27 and #28.

Cal. When I saw the photo of your delightful Embryo my only mental' criticism was, 'I wonder why he put so many diagonals in the tailplane'.  I seem to recall in an early Sympo that a structural engineer said that a 45 degree angle was the most efficient (and emphatically that full 'geodetic' ('X' ribs) was far better).

Dorme.  I thought that most rules specify projected wing area in which case vertical tip plates would not be included,

John
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dorme
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« Reply #30 on: March 13, 2015, 02:39:20 PM »

Hepcat

The rules for a lot of these aircraft were made before tip plates came into fashion and have not been mentioned in the rules, as far as I know.  But I am sure that Dave Mitchell of FAC can answer the question.  I'll get in touch with him and try to get an answer to this.
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Dave Andreski
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« Reply #31 on: March 13, 2015, 05:52:54 PM »

dorme,
Can you please tell us when tip plates came into 'fashion'?
Do you have a date?
How about twin fins? Do these count as area?
Thanks,
Dave
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calgoddard
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« Reply #32 on: March 14, 2015, 10:21:51 AM »

HEPCAT, thanks again for the complement and the recommendation of 45 degree ribs on the stab. This will lessen the number of ribs, and the weight of the stab.

90 seconds indoors in 23 feet is the goal for the Flat Iron.  I don't expect to compete against any two minute Embryos in the gym where our local flying club has its contests.

From the FAC Embyro Endurance rules:

"Wing Area (WA) is measured off the flat plan."

I included the chord (2 1/2 inches) and width (1/16 inch) of the tip plates in concluding that the WA of the Flat Iron is under the maximum 50 square inches allowed for a monoplane.

Hopefully the person that is drawing up the plan in a CAD program can confirm this.

In regard to origin of tip plates, Wikipedia states "The initial concept dates back to 1897, when English engineer Frederick W. Lanchester patented wing end-plates as a method for controlling wingtip vortices."

Also from the FAC Embryo Endurance rules:

"The wing and tail must be built up and covered on both sides with Japanese tissue or equivalent."

My argument in favor of the legality of sheet balsa wood tip plates on an Embryo is simple.  Since they are not lifting surfaces, they are not part of the wing.  On the Flat Iron, the tip plates are lateral stability control devices.

Dave, you asked whether twin fins would count as area.  If you are referring to twin vertical stabilizers, I do not believe their area counts toward the limit on the horizontal stabilizer area (50% of the WA).  

This latter point raises another issue.  The FAC Embryo Endurance rules also state:

"Stab area not to exceed 50% of WA."  

I have interpreted "stab area" in this context to be the horizontal stab area.  Regardless, I think the combined area of the horizontal stab and vertical stab on the Flat Iron is under 50% of the WA, but again, I hope the person that is drawing up the plan with the CAD program will confirm this.

It's funny how a blog on a quick custom Embryo build can lead to so much constructive discussion.  I guess that is the point of the HPA Builder's Forum.    
 

 
« Last Edit: March 14, 2015, 10:47:46 AM by calgoddard » Logged
calgoddard
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« Reply #33 on: March 23, 2015, 11:01:05 AM »

The very skilled person drawing the Flat Iron plan with a CAD program reports that the wing area is 46 square inches and the stab area is 13 square inches.

The plan will be posted in the HPA Plan Gallery soon, after a final review. 
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Maxout
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« Reply #34 on: March 23, 2015, 01:34:03 PM »

The very skilled person drawing the Flat Iron plan with a CAD program reports that the wing area is 46 square inches and the stab area is 13 square inches.

The plan will be posted in the HPA Plan Gallery soon, after a final review. 

He's a mighty fine draftsman, isn't he?
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calgoddard
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« Reply #35 on: March 23, 2015, 04:26:41 PM »

Yes he is. And his name will be on the plan so that he gets the credit for his efforts.
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calgoddard
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« Reply #36 on: April 20, 2015, 04:25:57 PM »

The plan for the Flatiron Embryo has been posted in the Plan Gallery.  It may be hard to find. Click on the search icon.  Enter "embryo" as the key term. Once you command the search, Embryo plans will come up.

I was not able to download and/or open the plan, but this may just be a problem with my computer.
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calgoddard
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« Reply #37 on: April 27, 2015, 06:19:00 PM »

I was able to download and open the Flat Iron plan via the HPA Plan Gallery today.
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