Deciding on design

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Tamecat

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Oct 23, 2003
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Teaneck New Jersey
Hi everyone,

I am so glad I finally found a site with people who give constructive criticism and guidance. I, like many, want to build an airplane. I am an avid airplane flyer who designed a couple of cool planes that would be really cool if full scale. One is called the SST 440. A high wing trainer with twin tails like the Ercoupe. The second is a low wing sport plane that looks like the Shakir (I think that's how it is spelled.) and lastly one is a pusher designed called the L-39. I think that one has possiblilities because I like the lay-out of the plane.:gig: As for which one, the second seem like my choice because of ease of building. I will have to get photos of each so you know what I'm talking about and to give better advice. I almost have the second one designed out but I want feedback to start the project.
 

StRaNgEdAyS

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Oct 20, 2003
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816
Location
Northern NSW Australia
Good to hear!
I look forward to seeing pictures of your designs.
Yes they are a friendly bunch here, only being new myself, I have found them to be a helpful and encouraging lot.:D
 

Tamecat

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Oct 23, 2003
Messages
33
Location
Teaneck New Jersey
Here are the three projects

The first plane I'm actually working on. (Making the plans that is). Based on a model plane called Sunbird. Since it was a single seater, I kept the basic structure turning it into a two seater. :ban: I am using the KRS 1 plane to lay out the internal structure.:gig:
 

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Tamecat

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Oct 23, 2003
Messages
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Teaneck New Jersey
Bad Pictue

The last picture of the plane is bad:wail: Sorry about that:whistle: Here is a picture of the airplane and what it is supposed to look like as a single seater.:D
 

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Tamecat

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Oct 23, 2003
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Dream plane Maybe

Another plane I am considering is called the L-39 (rear prop) From the model plans, it looks doable from a structure point of view. My greatest concern is how the engine would be seated in the rear. Because the vertical and horizontal stabs are right over it. If you have any suggestions, I'm all ears. I think this plane would be fun to build as well as a blast to fly!:devious: Hey guys, I really really like this one but I don't want to finance a crash!
 

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Tamecat

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Oct 23, 2003
Messages
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Teaneck New Jersey
Last angle of the SST-440.:gig: What makes this a good plane is because of the wing layout. Basic hersey bar that is wide from LE to TE.
Don't know how that would work in the real world! :p: But all three planes have possibilities.
 

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StRaNgEdAyS

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He00y.
Looks like you have some work ahead of you.
I like the looks of the pusher design, then I have this thing about being thrust thru the air rather than being dragged...
:)
 

Tamecat

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Oct 23, 2003
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Teaneck New Jersey
I like the L-39 also. Since it is a pusher design, and everything is on the tail, I'm a little reluctant on trying it even though I like the plane alot. I might make the R/C model first. If I can build that without too much fan fare, I'll try it full scale.
 

HeliDev

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Jul 7, 2003
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JUst a suggestion, if youre going to build a full scale version, make sure you design it full scale, then scale it down for the model. Many a designer has come undone starting small and going big.
Good luck.
 

orion

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The last post had an excellent point, one that many would-be designers tend to miss. Having been an RC flyer and instructor for some time, and now providing design and engineering services to airplane developers, I have also run across many designs that I thought would have made really great full sized airplanes.

The fact is though, that things in the aeronautics world do not scale very well, up or down. I've posted similar notes on other discussions within this site so I won't rehash them here but the major point is that unless you design for full scale, your small airplane designed to be a big airplane won't work very well at all.

Regarding the L-39: This is a scale model of a Czech jet powered airplane, one that is used as a trainer and a light ground attack fighter. Due to the light weight nature of jet engines, it is virtually impossible to take that configuration and make it a full sized recip and prop powered aircraft without some major redesign work.

First, the recip engine is way too heavy to simply place in the back and make the whole thing balance. At least four or five projects have tried this in the past twenty years, all of them failing in a very short amount of time, after spending a whole gob of money.

Second, you need at least a ten to twelve degrees of angle between your main landing gear and the lowest point of your aircraft's tail end. A fourteen or fifteen degree angle is better. This means that if you put a prop back there, your landing gear gets very long.

Given the weight and balance issues, and the overall characteristics of the design, I'd say stop before you start and don't waste your time and money.
 

Tamecat

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Wow:wail: Talk about torpedoing an idea! :eek: It was a dream plane that was just under consideration!:angry: For a full scale version of a model, I was thinking on the basic concept the Cezh used in his model with interlocking joints with four beams in the center holding the structure together. :mad:

It's an unrealistic attempt, I must admit. :pout: But the possiblilities are there. :whistle: Still, with all that against it, I would really like to show you how it is as a R/C model and see if the construction could be transferred to full scale. :rolleyes: I am not an aerodynamicist by any means. I'm just thinking that this may have merit because of the way it is assembled.

As for the landing gear, it will be long and there is no way around it. All pusher designs that I read about have long gear with a metal skid in the rear to protect the prop from striking the ground. :lex: I do not argue with Orion's statement. From what he said, he is an expert in the field. :D

I am just saying that before we put a final stamp on something that should have a comma, Lets see the whole proposal before writing it off. :ermm: I don't want to argue and I enjoy the opinions and feedback that you all give. :grin: For this forum, I guess what I am looking for is not why it won't work, but rather how it could. ;)

This design is not even American, that's why I was considering if it could work which I believe it can. But since I'm a novice, and I don't want to finance a crash, my ears are open to your input and guidance. :D
 

HeliDev

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Thanx orion, I was feeling a little shot down after being wrong about the induced drag on a previous post, feel a bit more redeemed now.:D
Great to have someone with your knowledge on the site, learn something ever time you post.
 

orion

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Hi Tamecat;

Sorry if my post sounded like I "shot" your idea down - that's not the intent of my input. However, in the same breath, I've been in this business for over twenty years. That experience has given me a pretty good ability to look at various projects and parts of projects and pretty quickly evaluate their viability. There's a lot of misguided information out there so when I started my company so many years ago, the primary goal was to make sure that the projects I was involved in were first of all safe, and secondly, viable.

I've been a designer on everything from general aviation applications to fighters and transatmospheric vehicles, and most things in between. The experience has given me a fairly good overview of the technologies available to the general aviation arena, as well as a good ability to make fairly quick evaluations of what folks are trying to develop.

I've also done at least two market surveys of our industry. While these do not provide all the answers, they do develop a pretty good picture of what would work as a business and what won't.

One of the biggest problems I've seen in the industry is what I've come to term "design by ego". These programs tend to go blindly in one direction, taking input from no-one, generally ending up in a corner gathering dust or making expensive noises all over a runway. If all that's at risk is a single persons time and personal money, that's one thing.

If however the direction leads to possible injuries or loss of life, then, if asked, I try to at least put in my two cents worth as early in the program as possible.

The other aspect of this is the rather sizeable amount of money that's wasted. The industry is in bad need of capital infusion in order to develop and produce better aircraft and kits. What we generally see however, is charismatic people attracting a lot of funding for programs that do not stand a chance of success. This tends to be frustrating for me as my company has several aircraft developments that would be viable if fully developed however, being the quintessential engineer, I am not the type who attracts money at every turn.

So, in short, when I try to discourage people from trying certain things, it is not just to shoot them down but more so, it is an attempt to try to steer them to concetrate on ideas that have a good chance of success.
 

Tamecat

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Oct 23, 2003
Messages
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Location
Teaneck New Jersey
Feelin better

Thanks for the reply Orion.

I know the cold hard facts of life all too well. As I said before, it was just a dream plane that probably would have been built as a large scale model. (For construction practice) Even if it was possible to build, figuring out how to assemble the tail section would have stopped the project cold (full scale that is).

I have a set of plans for a more conventional plane made of wood. Hopefully, the plans will be done by December and assembly will start in January. If you ever have the chance to see plan number 712 from RCM for kicks and giggles :gig: , check out How the plane is assembled. I never seen a setup like that before. I hope I can ask you question in the future. You seem like a shoot from the hip on nonsense guy.:ban:
 

Tamecat

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Oct 23, 2003
Messages
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Location
Teaneck New Jersey
Plan #712

You can go to www.RCM.com click on plans to sport and scroll down to #712. They won't show the plans but give you a picture of the finished airplane. I'll see if I can take pictures of the plans I have of it. ;)
 

orion

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Hi and yes, I did see the pictures of the finished plane. However, I'm more interested in the unique method of construction you mentioned earlier. If you can send or post a picture of the plans themselves or at least the unique features of the assembly, that would be most helpful in showing the points you are talking about.
 
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