Posts: 239
Joined: 9/25/2002 From: East Greenwich, RI,
RI, USA Status: offline
It's not at all that difficult to figure wing loading and engine choices once a model is built. All measurements are in front of you and you can just weigh it.
I'd like to do this "before" I start my build. That is, determine the model's weight.
In all honesty, I've never really given any thought, to the weight of any model I've designed or built. I've taken a "whatever it turns out" attitude.
My next project is special. It's a life long dream and a ten year effort, with what I can honestly say, has so far been with little results.
I've been patiently waiting for someone else to do my work for me. That is, design, build and offer retractible gear for the F3F-1. Please, and I'm begging, DON'T suggest or even mention the Wildcat. Any conversation about the gear used for the Wildcat would be a waist of time and spirit. They are absolutely not in any way the same, but it's obvious they retract in the same configuration.
I'm not waiting any longer. I've decided to design and build the gear myself at 1/5 scale.
To do this correctly, I should have a "close" approximation as to the weight of the model. The last thing I need is to "over" design and overbuild the gear, creating unnecessary weight and work. I also have to maintain the scale size, look and operation.
"Has anyone else ever attempted to determine the approximate weight of a model "before" the build?"
This is what I'm asking and I'm not quite sure how to go about it? Weigh all parts and pieces?
Certainly I'll provide measurements. and a dicsription.
Grumman Gulfhawk G-22 at 1/5 scale. Same aircraft as the F3F-1 with mods.
Top wingspan and cord: 69.5" X 12" with 44 ribs. +/-, Alerions top wing only. Warbird style. Bottom wing and cord: 64" X 10" with 38 ribs +/-, no ailerons.
Fuselage length: 55" Cowling diamiter: 11" +/- Fuselage height at cockpit: 13.5" +/- Fuselage thickness at cockpit: 9.75" +/-
Stab span: 25" at scale but I will increas it slightly. Stab and Elivator cord: 10" tapered to 4.75" oner 11" cord to cord.
Rudder and Vert Stab" 13" tapered to 4.5" over 9.75". This will be slightly increased.
Tire size: 5.5" Track 15" Prop: 22" minimum, max. 24", hopefully 3 blade with hub. Engine: Considering options because I'm researching, but it appears as though the Robart R780 is currently the best choice.
If anyone needs more information I'll provide it.
As you can see, this is a serious and special project which needs special considerations.
I would appreciate any and all help.
Thanks in advance.
Charles
< Message edited by Avaiojet -- 5/13/2008 8:59:26 PM >
Posts: 10035
Joined: 12/12/2001 From: slc, UT, USA Status: offline
You have your work cut out for you The model will be about 1300 square inches total- so a really good flying weight is 15 lbs 18 tops . If you follow the typical "warbird" construction -you will be heavier than that . I have built warbirds for others -using th kits -and all of em were really structurally way overweight - not over strength - just overwight Try this - lookat th latest best of the ARFS from China - the competition aerobatic ones study how they eliminated weight THEN design your structure and IF possible do it for cutouts with laser .
Posts: 113
Joined: 5/13/2003 From: Quinlan,
TX, USA Status: offline
Charles,
Forgive me for saying this, I don't mean to sound insulting, but you may be "over engineering" a little. If you wanted to know the weight to the ounce, then your only way would be to determine the weight of each part. But if you are using wood, there are too many variables in the structural components to determine the weight before you make the piece. The density varies too much.
My suggestion would be to estimate the uncovered airframe weight from weighing the approximate amount of wood you will use. Then add the known weight of the other components. Those are really the heavy items anyway, such as covering, engine, radio, prop, wheels, etc. The final variable is the paint. Paint weighs a lot more than most people think. You can get pretty accurate numbers by weighing an empty container and comparing it to a full one. But even this is not perfect because if you spray, much of the paint is blown by the airplane. If you know about how many containers of paint you will use, you can get close.
Regarding the strength of the gear, remember the loading on the gear during landing can be tremendous, depending on the sink rate at touch down. So knowing the weight of the plane is only a starting point when trying to determine the strength of the gear. I would build a simple prototype gear to experiment with structural issues and then build the final version after determining the strength needed. Of course, you would want to test the gear on a spare plane of the same weight as your model, not the model itself.
I wish you luck. I've always loved that plane and only the landing gear has stopped me from building it.
Posts: 239
Joined: 9/25/2002 From: East Greenwich, RI,
RI, USA Status: offline
"Forgive me for saying this, I don't mean to sound insulting, but you may be "over engineering" a little. If you wanted to know the weight to the ounce, then your only way would be to determine the weight of each part."
Paul,
Thanks for the reply. Without trying to be a comic, I'd be happy with weight to the pound!
I'm hoping other guys with biplanes can offer weights and wing loadings. Most of this is about engine choice and gear strength.
"The final variable is the paint. Paint weighs a lot more than most people think."
Paint is something I have a lifetime of experience with. Did painted graphics and airbrush work professionally plus I restore sports cars. I do know tricks to keeping weight down with paint. I've painted planes for years and sometimes for customers.
"Regarding the strength of the gear, remember the loading on the gear during landing can be tremendous, depending on the sink rate at touch down."
Absolutely! I have five aviation ratings and my last airplane was a Lake LA4-200T. I know exactly of what you speak.
"I would build a simple prototype gear to experiment with structural issues and then build the final version after determining the strength needed."
I built the prototype out of balsa, 2/3 the scale. I really didn't want to test anything flying because I haven't flown in years. I'm far from set-up to do that. But it is a good idea. I'll get a guy to work with me on the test. For testing, I was thinking more of attaching the finished gear to a 5 gallon barrel, a stick out the end with a tail wheel, and dropping it at various heights. I can control the weight with sand. BTW. Some people refer to this model as "The Barrel." I don't like that.
They actually test "real" gear that way, by dropping.
"Of course, you would want to test the gear on a spare plane of the same weight as your model, not the model itself."
I'll take that advice. Shouldn't be to difficult a set-up because the gear would only have to be in the down position and not working as retracts. Getting it to retract and deploy is another issue. I'll talk to the manufacturers for assistance with that. I'm not shy.
"I wish you luck. I've always loved that plane and only the landing gear has stopped me from building it."
I can say the same, and I did. Now I'm changing that.
Please keep an eye on me as I progress, I'll need advice.
Posts: 10035
Joined: 12/12/2001 From: slc, UT, USA Status: offline
My Buckers weighed 17 lbs at 1800 sq inches - there is a target weight for you - These were high performance models tho here is a pic of one a customer did. Hope you figure out a good strength to weight setup for yours -
< Message edited by dick Hanson -- 5/13/2008 8:51:43 PM >
Posts: 10035
Joined: 12/12/2001 From: slc, UT, USA Status: offline
quote:
ORIGINAL: Avaiojet
I made an error with the wingspan.
It's actually 69.9" on the top wing.
I corrected it.
Dick,
Great model. You always do great work.
Charles
thanks - the originals were TOC models 2nd place in 1990 flown by friend Steve Rojecki I had to make em as light as practical the airframes were 9 lbs complete. inc a shock strut gear I designed The F3F is a project -for certain - I would do it with sheeted 1 lb foam flying surfaces -cap stripped to look like ribs - best weight strength -I know this -tried em all fuselage two half shells planked like a ship then joined -you end up with a big "eggshell" no real interior structure except as needed to support engine/gear and wing attachments . I do this on super light pattern models they look like glass structures when done.
< Message edited by dick Hanson -- 5/13/2008 9:30:18 PM >
Posts: 239
Joined: 9/25/2002 From: East Greenwich, RI,
RI, USA Status: offline
Dick,
I'm probably putting the "short" on my own thread, but I gotta tell ya, what do we see in these two photos?
Can anyone guess the year? Who are these guys? Someone has a nice maple field kit?
The model on the left is a Dalotel. Designed by Dick Hanson. 68" in span and flies the FAI or AMA pattern.
The model on the right is the Zlin. Possibly a little smaller but a great performer. I don't have the specs and should know more about that model because I purchased one from Dick Hanson Models in 1986! 1986!!
Yipes, has time flown by! No pun intended. God am I getting old or am I getting old?
In all honesty, the closest I ever got to flying any pattern was reading the illistrated articles written by Dick himself. I still have all that stuff. Gee, ebay memorabilia? I'll be stinkin rich!
Dick, was it you who designed the Tipo or modified the Tipo? The Tipo was a great looking model. I have a pattern ship styled after that design.
Dick, thanks for holding my interest in model aviation.
Posts: 10035
Joined: 12/12/2001 From: slc, UT, USA Status: offline
Holy cow - I ain't old enough to remember those models tho I still have the glossy of that Tipo "Avenger The red n white Zlin-I am doing again same scale scheme too The Dalotel - That one is a twin of the one Chip Hyde flew to 1st place in 1984 Nats FAI- and thoroughly pied off the "pattern plane junkies . They thot a semi scale model was incapable of flying as well as the "pattern" designs. guess again It's been fun to watch the "Theory" Fans and their ideas get gently scuttled , a piece at a time ah luv it
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Determining weight "before" the model is built. - 
