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Old Oct 03, 2006, 03:14 PM
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tris10g's Avatar
Worthing,West Sussex, England
Joined Aug 2004
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Build Log
Colonial Viper depron pusher jet

Hi,
I'm starting this thread to show the progress of my winter project. I've disscused it in other threads but I think its time to start my own. I'm still in the planning stage. I plan to design this plane as I build. Although I'm capable of using auto cad I don't feel confident enough to try and design it using cad. I will
be using 3 views and photoshop to resize the image to the right dimensions.
I will be build this plane using the the famous Steve Shumate techniques and design principles. Talking to some of the guys in this forum I have started with the wing area. 250 sqin sounds like a good place to start. There isn't a real viper but it has been discussed on other web sites. The overall length is supposed to be 29 ft. My viper will have an overall length of 29 in, making it 1/12th scale.
I am planing to use reasonably price electronics. It will be designed to use a bp21 powered by a 3 cell lipo. I will use 3 servos, rudder and elevons.
When I have cut panel to the correct size I will place it on plane paper and trace the outline. This means when I have finished I can make some plans.
For those of you that don't know what a colonial viper is, Here are some pictures?
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Old Oct 03, 2006, 04:30 PM
Use the Force!
LBMiller5's Avatar
San Marcos, CA
Joined Jan 2005
2,179 Posts
Looking at your photos, you might need to reconsider the size of the model if you intend on having 250 Sq. In. of wing area. It would appear that the root chord of the wing appears to be about 50% of the fuselage length and the tip chord looks to be about 30% of the fuselage length.

In the top view, the wingspan looks to be just a little over 50% of the length.


Here is a site I found from Wikipedia that has info on the Viper craft. Viper info on Wikipedia


They have info on 2 models, the Mark II and the Mark VII. The one you have pictured in your post is the original Mark II. According to the specs provided, the Mark II has an overall length of 8.4 meters (27.6 feet) and a wingspan of 4.7 meters (15.4 feet) with a height of 2.7 meters (8.9 feet).

So using these numbers, I get a wingspan of 56% of the fuselage length. I measured a side view photo of the Mark II if I got a 50% fuse length root chord and 30% tip chord. With these numbers, I can calculate the Wing area to fuselage length ratio, and solve the equations for fuselage length given a 250 Sq. In. wing area.

Without boring you with the math, if you keep the same proportions as the original, the wing area (in Sq. In.) is equal to the fuselage length squared (In inches) divided by 4.545. Conversely, if you know the wing area, and want to find the fuselage length then the length is equal to the square root of the length x 4.545

Fo example, a Viper 10" long would have a wing area equal to (10x10)/4.545 or 22 square inches. One that is 29" long (your proposed size) would have a wing area equal to (29x29)/4.545 or 185 square inches.

Using the other formula, to solve for fuselage length based on a known wing area, the fuselage length would be equal to the square root of (250 x 4.545) or the SqRt of 1136.25 which is 33.7 inches long.

If you plan on cheating the scale outlines a little bit, and increase the wingspan slightly, you could acheive your desired 250 Sq. In. of wing area with a 29" long fuselage. At true scale, a Viper with a 29" fuselage would have a wingspan of 16.24", a root chord of 14.5" and a tip chord of 8.7 inches. If you stretched the wingspan to 21.5", and left the root and tip chords the same, then the wing would have 249.4 square inches of wing area.

How does that sound to you?

Lucien
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Old Oct 03, 2006, 04:47 PM
Don't look at me like that....
62pilot's Avatar
United States, AR, McDougal
Joined Aug 2005
2,801 Posts
I'm wth Lucien on this one, you'll need more wing area and a taller tail. Most models need the bigger fin to help stabilize them. And you'll definetly need rudder, plenty of it. With the BP21 ( about 150 watts ?) keep her around 16-17 oz auw if possible. Should look good in the air but prob. will be real twitchy even with a forward CoG.




Good Luck
Tom
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Old Oct 03, 2006, 05:37 PM
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tris10g's Avatar
Worthing,West Sussex, England
Joined Aug 2004
190 Posts
Yeah, I agree with you its gonna be a handfull. I reckon there's a reason why there hasn't been many built before.

Thank you for your help Lucien. I hadn't decided it has to be 29" long, I was going to go with 36" , but doing some rough maths at work I thought I'd over estimated. The wing area of 250sqin isn't set in stone either. I really wanted to be able to hand launch it so I thought it was a good starting point. I was going to leave the inlet open on the nose and duct the air to the rear. I hoped this would have a slight lifting effect. I was actually going to build the mk1. I have 3 views of the mk1,mk2,mk4 and mk7. The mk7 looks like the best flier but it doesn't look like a viper as much as the mk1. It also looked like the mk1 has the most wing area.

In my head I had a target weight of 16ozs, but my aim is to build as light as possible.
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Old Oct 03, 2006, 07:39 PM
Registered User
Ann Arbor, Michigan, United States
Joined Sep 2003
4,778 Posts
this is gonna be great! i'm definitely building one... whether or not it flies! i love the viper... brings back some great childhood memories.
thanks for all the math lucien!... hmmm, where are you when i start in on my new projects that i find out after finishing them that they are too small
-beanie
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Old Oct 04, 2006, 12:11 AM
Live to fly, fly to live!
DCobra's Avatar
New Bern, NC
Joined Dec 2003
4,339 Posts
I'd build one just to have something cool to hang up on the ceiling from the real Battlestar Galactica (not the current wanabe series)

Add this to your calculations...how much lifting surface can be achieved by leaving all three engines hollow, and possibly the nose intake?

I'd guess that would bring the 250 sq in goal closer to reality without making the wings stretch a lot.

This is one that should be built in semi-profile first to see what the challenges are and what the fixes can be.

I'm anxious to see this one develop!

Paul
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Old Oct 04, 2006, 12:45 AM
Watts is life...
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Not a challenge I would take on but… I say it’s doable if you consider the following:

Forget a scale approach an exaggerate the main wings, remove the anheadral, and increase the wing span.

Build a budget foamie mockup at full size, as a test glider and see how it works…

Bob.
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Old Oct 04, 2006, 08:31 AM
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Worthing,West Sussex, England
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I'm sure the viper will fly, wether or not it will fly well is another thing. I want to keep it scale as possible so that its easily recongnisable as a viper. I have seen lawn mowers and cars fly in this forum so I'm sure a plane looking spacecraft will fly.

You will all have to be patient with me as I'm not planning to have this built and flying in a week. I find that when I'm building from a plan its all over too quickly. Thats why I took on a more challenging scratch build.

I too was thinking about loosing some of the anheadral. I really couldn't think of the name for wings that slope downwards. Thank you rcjetpilot. If I lengthen the wings and loose at little anheadral it could still look very scale from the side profile.

I'm not sure how to mount the motor, the bp21 can be stick mounted of firewall mounted. If I firewall mount then the thrust angle could be adjusted on the four mounting screws. If I use a stick mount then I allows for a greater range of motors to be fitted. I'm guessing a thrust angle of 0,0,0 would be fine for a pusher?
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Old Nov 15, 2006, 03:47 PM
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Worthing,West Sussex, England
Joined Aug 2004
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Just a little progress report so far. I have step by step photos that I will use to add some detail to the build when complete. Its starting to look like a viper. I'm not too sure of the effect of the anhedral on the flight charateristics. I did a little search a it seams to make the plane unstable, but wing sweep can have a dihedral effect canceling it out.
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Old Nov 15, 2006, 04:07 PM
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Grafton, Ohio
Joined Sep 2003
760 Posts
Great show when i was a LOT younger! Loved the Viper, regardless of whats possible now with CGI! Never did get the disco danceing with rubber bands though????????
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Old Nov 15, 2006, 04:08 PM
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Grafton, Ohio
Joined Sep 2003
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My son wants me to build one of the cool speedsters from Stargate! All that anhedral scares the H$&^ out of me!!!!
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Old Nov 15, 2006, 05:24 PM
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Ann Arbor, Michigan, United States
Joined Sep 2003
4,778 Posts
tris10- hey man, that looks absolutely awesome!!!! i love battlestar galactica. you've captured the lines amazingly. i hope she flies well. even if she doesn't, i'd love to build one for static display. any chance of plans? le phan flew his f-104 with scale anhedral and it flies quite well... though very quickly given those stubby little wings, not unlike the viper.
anxiously awaiting further updates
-beanie
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Last edited by beanie; Nov 15, 2006 at 11:09 PM.
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Old Nov 15, 2006, 10:58 PM
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New Bern, NC
Joined Dec 2003
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Awesome! Who's the pilot of this one? Starbuck, Boomer, or Apollo?

Paul
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Old Nov 16, 2006, 12:18 AM
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Ottawa, Canada
Joined Apr 2005
119 Posts
Great

That's just great, I want to build one of those Vipers when I get a chance if you decide to post the plans, maybe if you lose some anhedral and get the right CG it will fly fine.

I too did something based on the Viper, it's a mix between the Viper and a conventional jet, the result is this: http://www.rcgroups.com/forums/showthread.php?t=582634

She flies great and it's very stable.

regards!
JR
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Old Nov 16, 2006, 02:31 PM
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Worthing,West Sussex, England
Joined Aug 2004
190 Posts
Thanks for all your kind words. I think apollo can madien it and starbuck can take over when I've iron out the gremlins. Jr, I han a look at your thread and your plane looks great, very imaginative.

I think if I raise the wing a little and fit all the electronics under then I'm half way to a high wing anhedral setup which I read is very stable.

I'm at a crossroads at the moment, I've been thinking about how to control it. If it turns out to be a unstable flyer then I may need a lot of control. I started thinking about using a full thrust vectoring system only, keeping it close to the origonal design. I then thought what if when the battery becomes low, I may loose control.
I then decided to use elevons and rudder, but after maidening my tornado I'm considering tv again. This plane, because of its small wings will need air speed to fly and the control surfaces will be of little use straight after hand launch. If I use tv instead of a elevator then I may have control at stall speeds or until it has enough speed for normal control surfaces.

My tx is computorised but I don't think I can configue it to do both. Maybe I should build it with standard controls and modify it in the future if I need more control.
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