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Old Jul 02, 2014, 06:32 PM
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Ne Project inspired by Experimental Airlines

Hello Forum!

I am new and am starting a scratch build with dollar tree foam board. I would like to show everything step by step and take input from you guys as I go along. My goal is to build a stable relatively slow flying, high wing aircraft. I would like to eventually get into fpv, and that is much later, but I want there to be room for it on the aircraft. All of your input is welcome and please give me any advice you'll think I'll need. Ill keep you updated on the build with pictures!
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Old Jul 03, 2014, 12:15 AM
You laugh... But it flies!!!
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Welcome to the forums.

This first aircraft wont be the one that you eventually fly FPV with. Although there may be a resurrection of sorts to put FPV into whatever airframe you go with first. But, my guess is by the time you get to FPV there will have been many different airframes flown.

Good to see that you are starting out with reasonable expectations. If you already fly RC and scratch building with foam board is the new part, then it will be easier. If you are also new to RC flying, choose wisely. The first plane should be a practical decision about learning to fly. Forget the cool look factor or the eventually grow into concept. Make something simple, light, and easy to repair. Choose an airframe that is slow and stable. If you plan to belly land on rough terrain, go with a pusher. If you have a nice landing area, wheels on a tractor will do well. My personal opinion is that for learning to build and fly, the FT Old Fogey would be a good choice. I have not flown or built one. But, I have never heard negative about them and every one I have seen was impressively slow and stable. If you are an experienced flyer, then most of that advice was irrelevant.

Good luck. Be safe and have fun. Keep us updated.

Tommy
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Old Jul 03, 2014, 09:06 AM
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Yeah, it's not clear if you're a new RC pilot as well.
Or maybe you're like me - someone who had a 25 year hiatus from the hobby. In which case, the flying is not the issue. Rather, it's the drastic change in building materials, electronics, powerplants, etc.
Anyway, if you're a beginner in any of these respects, this forum will be useful: http://www.rcgroups.com/beginner-tra...ft-electric-8/
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Old Jul 06, 2014, 04:53 AM
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Progress so far.

Hello and thanks for the welcome to the forum. I am newish to the rc world. I have friends that fly and who have let me fly their planes. I also subscribe to several rc channels on YouTube for how tos and reviews.

Anyways, this is what I have put together so far. The fuselage and tail section are pretty rigid. I'm thinking of making the wings out of two pieces of foam board. The total wing length would be 60". The rudder is 7" tall. The elevator is 15" long.

I did have a question about a motor for this. Should I go with an edf through the fuselage or a normal prop? The fuselage is 3" by 3" on the inside.

Also I was thinking about winglets on the ends of the wings for the improved efficiency.

Let me know of any advice you have. Thanks.
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Old Jul 06, 2014, 05:15 AM
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James,

You need to triple your elevator area (move-able portion) and rudder area (as it is now you will have very little control authority). This is a common error for first time builders that are not working from plans (I'm guessing you're not).
You 60" wing WILL need a good spar (do a search for spar options).
Yes, winglets will give some advantage, in general (despite the added parasitic drag) - again, this is discussed by me and others extensively in other posts.
This is a journey and will involve lots of experimentation and learning - when your plane finally flies well (after several crashes), it is incredibly rewarding.
Start with a normal prop.

Again, you need to do quite a bit of reading in the beginner's section about building.

Good luck!
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Old Jul 06, 2014, 07:01 AM
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Thank you!

When you say triple the elevator area do you mean literally triple the area? It is currently 30" squared (15" x 2"). Or do you mean triple the length, while keeping the same width (45" x 2")? Or do you mean to triple the width while keeping the length the same (6"x15")? Or do you mean something else? Thanks for the input and let me know!
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Old Jul 06, 2014, 08:39 AM
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Quote:
Originally Posted by jamestwojames View Post
When you say triple the elevator area do you mean literally triple the area? It is currently 30" squared (15" x 2"). Or do you mean triple the length, while keeping the same width (45" x 2")? Or do you mean to triple the width while keeping the length the same (6"x15")? Or do you mean something else? Thanks for the input and let me know!
James,

I'm referring to the move-able portion, which is called the "elevator" (the non-move-able portion is called the "horizontal stabilizer"). So if its chord is 2" now, make it 6". Yes that sounds crazy, but it's not. It's much better to have a large control surface move a little than a tiny control surface move a lot. You can always cut it down, if needed (but there should not be a need to - adjusting control throw will yield the correct result anyway).
Same goes for your rudder (the move-able portion).
You also need to go through definitions/terminology for all the basic parts of the airframe so you know what people are referring to (elevator, aileron, rudder, chord, span, aspect ratio, wing loading, etc., etc.).
You also need to learn about mechanical actuation terminology (control horn, servo arm, control throw). Again, if you don't, you'll be perplexed when people give you advice about these very fundamental control actuation issues.
Also, you might be better off basing the proportions of your plane on a "known good" design instead of just guessing. I'm all for experimentation afterwards, but you want that first scratch build to have a decent chance of flying.
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Old Jul 06, 2014, 09:34 PM
Old age is not for sissies
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You need to read this article. It's a basic no frills formula for a successful plane. The ratio of moveable surfaces to their stabilizers seem fine to me, particularly for a trainer. However, the size of the tail surfaces need to be related to your wing area - you're basically designing it backwards, your wing span/area will determine the size of your tail surfaces.

https://www.rcmplans.com/issues/requ...101989-1-1.pdf

Azarr
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Old Jul 07, 2014, 01:03 AM
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Quote:
Originally Posted by Azarr View Post
You need to read this article. It's a basic no frills formula for a successful plane. The ratio of moveable surfaces to their stabilizers seem fine to me, particularly for a trainer. However, the size of the tail surfaces need to be related to your wing area - you're basically designing it backwards, your wing span/area will determine the size of your tail surfaces.

https://www.rcmplans.com/issues/requ...101989-1-1.pdf

Azarr
He mentioned a 60" wing span. I'm assuming he will have a typical chord for that span (based on his first post). So, on that fuselage (his wing can't be too forward on that "medium length" fuselage), there's no way his current tail surfaces will give him enough authority for ALL phases of flight. We see this mistake again and again on this site. What would suffice "proportionally" for a full scale plane simply will not do for our RC planes for a beginner (because of Reynolds number). Why should he struggle to keep the thing flying when he can have some built in "help". Light wing loading, large control surfaces, angled winglets, sufficient thrust, proper CG. These are the basics for what the OP wants: "stable relatively slow flying, high wing aircraft". I also urge drooping leading edge cuffs for the outboard third of each wing - again, for a beginner, why not have some "built in" tip stall prevention.
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Old Jul 07, 2014, 06:11 AM
Old age is not for sissies
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Quote:
Originally Posted by nuteman View Post
What would suffice "proportionally" for a full scale plane simply will not do for our RC planes for a beginner (because of Reynolds number).
Could you show us some examples of trainers that have an elevator 50% larger than the horizontal stabilizer. From his pictures it appears that the elevator is ~ 30% of the total chord. Based on his saying the elevator chord is 2" it looks like the stab is around 4", the 6" elevator you recommend would be larger than seen on most 3D planes. However, with a 60" wing his stab span should be closer to 20" than the stated 15" which is why I said he's designing it backwards. Most would start from the wing first and then design the stab based on the wing span/area.

The Chuck Cunningham formula in the link I posted has been used for years as a basic starting point.

To the OP: Experimentation is great and the numbers I quote are just basic starting points and definitely not firm rules. Let us know how it works for you.

Azarr
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Old Jul 07, 2014, 07:35 AM
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Quote:
Originally Posted by Azarr View Post
Could you show us some examples of trainers that have an elevator 50% larger than the horizontal stabilizer. From his pictures it appears that the elevator is ~ 30% of the total chord. Based on his saying the elevator chord is 2" it looks like the stab is around 4", the 6" elevator you recommend would be larger than seen on most 3D planes. However, with a 60" wing his stab span should be closer to 20" than the stated 15" which is why I said he's designing it backwards. Most would start from the wing first and then design the stab based on the wing span/area.

The Chuck Cunningham formula in the link I posted has been used for years as a basic starting point.

To the OP: Experimentation is great and the numbers I quote are just basic starting points and definitely not firm rules. Let us know how it works for you.

Azarr
Some numbers:
20 x 6 = 120
15 x 10 = 150

150 is 25% larger than 120: (150 - 120) / 120 = 0.25.

1. It's precisely because he has only a 15" horizontal stabilizer that he needs a large elevator. It's easier to add a new elevator than re-do the horiz stab as well, and it will accomplish the goal of sufficient pitch authority.
2. The numbers that I gave show a 25% larger total horizontal surface than what you indicated. Yes, I fully admit that I am a firm believer in over-sizing control surfaces and reducing throw (for a beginner). Then when the beginner gains some confidence, increase throw. This way the same plane can be used to engage in very different input-response experience .

Is he designing the plane backwards? Absolutely. That's why I'm trying to advise the simplest route (with as little re-work as possible).
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Old Jul 07, 2014, 08:36 AM
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Since the wing hasn't been built I'd just leave everything as is and reduce the span to around 45". That leaves the horizontal stab in the correct % range. I would think that an excessively large elevator and a LAR stab would be a problem for a low time pilot, regardless of how little movement it had.

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Old Jul 07, 2014, 04:06 PM
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I would have to agree with Azarr on this one. Leave the tail as is and build the wing for a wing and tail combined wing loading of 3 to 4 oz per sq ft. even down to 2 oz per sq ft if you want a real floater.

Keep all the control surfaces small to start. If you find that you need more control surface you can always add more later.

In designing the wing for a nice slow flier and ease of building I would recommend a poly dihedral flat bottom airfoil.

Check out this thread for some Ideas on what can be built with dollar tree foam.

http://www.rcgroups.com/forums/showthread.php?t=1020909

Go with a prop motor and not a ducted fan. You get more thrust for you money. Ducted fans are terribly inefficient and over priced for what you get.

Remember to use the K.I.S.S (Keep It Simple Stupid) method of building. I always have to remind myself of this in our designs. The above is me talking to myself and when referring to others change it to Keep It Stupid Simple ;-) it is easier on the egos!

Have fun building and designing. Foam is cheep so don't be afraid to fail and try something else if it does not work the first time.
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Old Jul 08, 2014, 01:08 AM
You laugh... But it flies!!!
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United States, MO, Rocky Mt
Joined Oct 2013
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[/QUOTE] Foam is cheep [/QUOTE]

My mantra.

Jamestwojames,

Again, I think you are starting out right. I am a Try and Fly kind of guy. I want to see it for myself. We can spout all the formulas we want. I like to run numbers after I have built what looks good to me. I have found that the numbers for the more successful airframes have fallen closer to what the formulas say the dimensions should be. But each plane, no matter how far away or close to the numbers they have been, has been a growing and learning experience.

Don't let critics keep you from trying what fancies you. Its a hobby. Spend the time (its the most valuable of the investments you will make) and learn to build what you enjoy to fly.

Don't shy away either, some of us are interested to know how this works out for you.

Be safe and have fun,
Tommy
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Old Jul 08, 2014, 09:14 PM
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[QUOTE=nuteman;28838548]James,

I'm referring to the move-able portion, which is called the "elevator" (the non-move-able portion is called the "horizontal stabilizer"). So if its chord is 2" now, make it 6". Yes that sounds crazy, but it's not. It's much better to have a large control surface move a little than a tiny control surface move a lot. You can always cut it down, if needed (but there should not be a need to - adjusting control throw will yield the correct result anyway).
Same goes for your rudder (the move-able portion).
You also need to go through definitions/terminology for all the basic parts of the airframe so you know what people are referring to (elevator, aileron, rudder, chord, span, aspect ratio, wing loading, etc., etc.).
You also need to learn about mechanical actuation terminology (control horn, servo arm, control throw).

I actually find this somewhat insulting. I have 10 hours in a cesna 172 and I the dimensions I gave you were all of those surfaces. Not of the whole horizontal/vertical stabilizer.
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