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Why Hasn’t Somebody Built A 3/4 Scale OV-10? Hmmm?

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berridos

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That's the title in www.airpigz.com.
The truth I saw the plane and fell in love with it.
I am nearly finished with my cnc-cutter and am doubting on my initial project.
Imagine this plane configuration with a single pusher engine.

What I like:
What I like is you could make it easily laminar.
You have plenty of space for a simple retractable landing gear.
You could build it efficiently with 4 not so huge molds.
Could be build fairly silent
Plenty of space
Fuel efficient
The original has stol caracteristics

What I dont like:
Vertical stabilizer surface produces a lot of drag
As an ultralight, due to the prop size the two tail booms would be wider than 6+2/3 feet (2m) and the thing would be hardly transportable


Questions:
Couldn't I reduce the vertical stabilizers?
Couldn't I put the horizontal stabilizer in the prop stream to increase effectiveness and reduce vertical stab height?
How much could I shorten the distance between the two tail booms so that a wheel fits into every boom and the pusher prop still has a decent size?
In a non tapered wing the stall starts at the center back. Having there a vacuum due to the pusher prop, shouldn't that improve the stall caraceteristics forcing the flow to keep attached?

Anybody knows if the thing flies nicely?
 

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orion

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The OV-10 by all accounts is a very good airplane with good flying characteristics and very good performance. It may be a bit on the heavy side but then it is designed for a relatively rough military mission so that's to be expected.

In scaling the airplane though you do change a lot of features and of course, certain things don't scale as well - the bottom line of that is simply that the moment you start making changes and scaling an airframe you pretty much need to approach the project as if doing a whole new airplane. This means redoing all the performance and stability stuff, so that in the end you'd be able to pretty much answer your questions. But I'll post a few thoughts in order to clarify some of the issues.

Couldn't I reduce the vertical stabilizers?

If you keep the same general layout, probably not. In dong the scale version, you may actually have to increase their size or possibly, move them further back. The verticals provide control, yaw stability and of course, they need to counter that sizable cabin area forward of the wing. If you keep the general arrangement the same and wish to do more of a general aviation product, it'd be a good idea to stay a bit on the conservative side.

Couldn't I put the horizontal stabilizer in the prop stream to increase effectiveness and reduce vertical stab height?

Not a good idea - while control power would increase with the power induced stream flow, when the props are off or windmilling they will of course create a bit of a blanketing effect and it's that that you need to design for. Also, it is best if the stabilizers see the free-stream flow since in that they'll provide the aircraft with the best stability characteristics. Placing surfaces in the flow off the prop actually negates some of the stabilizing effect since in that condition they see the flow induced by the props, not so much the flow based on how the airplane is flying.

How much could I shorten the distance between the two tail booms so that a wheel fits into every boom and the pusher prop still has a decent size?

This is a function of performance requirements and engine choice, which is all part of the design process. Also keep in mind that the closer you get the prop tips to the side of the cabin, the noisier it will be inside.

In a non tapered wing the stall starts at the center back. Having there a vacuum due to the pusher prop, shouldn't that improve the stall caraceteristics forcing the flow to keep attached?

Where do you see a pusher prop here?
 

berridos

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Thanks for your comments.

My idea was to keep the configuration, but simplifying the project with a single pusher engine behind the wing, at the end of the central body.
Also putting emphasis on making the thing laminar and as clean as possible.
 
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MalcolmW

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Jan 21, 2007
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Hello, berridos;

I don't know if anyone has built a 3/4 scale OV-10, however, there is an aircraft which bears some similarity to your wish for a single engine pusher with the same configuration of the OV-10 called the 'Patriot.' I'm not sure if they are still selling kits for this aircraft, however, take a look...
American Patriot Aircraft :: Home
It isn't the prettiest aircraft on the block, but then again, neither is the OV-10.

MalcolmW
 

berridos

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Thank you guys.
I will entertain myself doing a cad design to see if I manage to fit everything and the concept remains clean.

I will average out the dimensions/proportions of the Ion, the piranha and the Patriot...very scientific approach!

I think what would make sense is to do a landing gear where the frontwheel is like a motorglider, very close to the ground
Midwing approach as it has the lowest drag.
Horizontal stabilizer like in the Bronco or the Ion.
Side by side cabin

Do you believe two tail boom ruin the drag advantages of the pusher configuration?
 

autoreply

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Do you believe two tail boom ruin the drag advantages of the pusher configuration?
Definitely, when there ever is a drag advantage in the first place.
To avoid the whole pusher-tractor discussion, in general the difference between them is marginal at best. A tractor has a higher efficiency (clean airflow), but given the higher induced velocity (several dozens of mph during cruise, compared to the IAS) it's as efficient as one would think. A pusher is working in "dirty" air, how dirty is highly dependent on fuselage shape, wing placing and dimensions and the slenderness. If well designed, a pusher sucks off the boundary layer, making it possible to maintain a laminar airflow over much of the fuselage. In reality I've never seen ANY aircraft with more then 30-40% laminar fuselage flow. Any other claim would (from my point of view) be highly unlikely.

As for the separate tail, the drag increase is significant. I've considered the A500 layout for my design, but it's drag was quite a bit higher than "clean", from the top of my head almost 20% higher than my current design, though those are all estimates.

Also structural design of the wing/tail junction is quite complicated and have caused Adam some problems. It's even more complicated if you want to tuck away the landing gear over there.
 

Yogi

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Check out the Sadler Vampire. It,s a similar design but with a shoulder wing. Been around a long time but I think the company commercialized it. Was based with a squadron of OV 10 during a little 'police action' 35 years ago.They are very rugged and good looking A/C.
 

750Bldr

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Sheldon, Iowa
The original specs for the Light Armed Recon. Aircraft (LARA) called for an aircraft with a wingspan short enough to allow for landing on a road so that it could be co-located with ground units. Convair built the Model 48 Charger prototype with the following specs:
2-place Cabin mid-wing monoplane retractable landing gear
2 x 650hp P&W-Canada T74 (PT6) turboprops
span: 27 feet 6 inches wide
length: 34 feet 10 inches long
load: 6003#


However, North American won the contract and the result was a 30-40% larger plane needing airfields to operate from.
The following make for some interesting reading:

Clean Sheet Designs: Swarms of Lightweight Scout/Attack Aircraft

Convair Model 48 Charger - Wikipedia, the free encyclopedia

North American Rockwell OV-10 Bronco - Wikipedia, the free encyclopedia

The OV-10 Story

Hmmm!, perhaps we could obtain some of the Convair drawings.
 

orion

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I actually have those (the Convair Charger drawings) - my first job out of college was for GD Convair at Kearny Mesa in San Diego. In my work there I was able to get access to quite a few historical programs, including the Charger. Somewhere in my files I have the program proposal and summary, including the drawings and inboard layouts. I also got to see the videos (movies actually) of the prototype in operation - a **** impressive airplane.
 
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gahan

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I was In Marine aviation from 65 to 85 the Bronco was an awsum close support aircraft, I got many a ride in pendelton I guess helicoptors took over their spot and besides they didn't cost enough
 

berridos

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I guess the vertical stabilizers are proportionally so large in order to be able to fly with a single engine in an emergency case.
The concept would make a safe ultralight plane with two cheap light 60hp engines.
 

wayne sprigle

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Hello all, it has been a long time since I have posted, and it was on the same subject a couple of years ago. I have done a lot of studying since then.
I am in the process of desiging my own (one off) no scale OV-10. What I have done is to take drawings from A.F. Museum of the Bronco and drawn out what looks good for 1+1 seating, tandem. I have been informed and brow beaten that you cannot scale down an aircraft and have good flying charicteristics. I have based the design arround LSA chriteria using the Corvair engine as my power in a pusher config. I have learned that to stay in the stall range for LSA, the wing loading must be under 12 lbs/sq ft. Sooo, my plans, at the moment has 10.9 lbs/sq ft. The length is 21' height 7' and span of 28'. My intention is basicly a single seat with baggage behind but a person would fit. As you can tell by the dimentions, there is no scale per se.
I know I am going to catch a lot of flack from the engineer types, but that is ok. I origionally designed of wood, but after estimating weights found it was going to be very heavy empty, definately making it a single seat. A friend of mine convinced me of trying all metal. The cockpit area is made of steel tube covered in sheet aluminum ala Titan T-51 and the wing (hershy bar ala Zenith CH650 with the chord of my choice, for the look and wing loading) and the booms made ala CX4 (formers and longerons), the vertical fin/rudder and horizontal stab/elev are equal in size as the CH650 with exception of vert fin/rudder as there are two of them. This config is considerably lighter than the wood version. There are liberties taken in the cockpit area, such as canopy style (opening) and height (for head clearance), it actually looks good, for it's size.
I know this thread is about "Why hasn't anyone designed a 70 % scale OV-10". I believe it's because it would be such a huge project and very complicated, especially if retracts are encorperated. And the cost would be outragous.
The reason why I am doing this is that I am a retired AF Seargemt and want something to keep me busy in my retirement, after I finish my near completed 1/2 size P-51 (modified Taylor Titch), (just to show I did not try to scale down the full size P-51).
I have been following the posts on desiging aircraft and I think I have this one right (I could be wrong), so let the FLACK begin.
Wayne
 

snaildrake

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Orion, that Convair Charger is a perfect of how many great military designs and prototypes there were that didn't get adopted. I'm surprised those stubby wings could generate enough lift.

Wayne, do you have any pictures of the plans you can post? -Dan
 

wayne sprigle

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Well Dan I have photos saved to my computer but I can't attach them. It seems that the photo must have a url to put it into the message. I found that if I drag and drop it shows up full screen. If I could get them posted you might be impressed.
 

wayne sprigle

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Well Dan I was able to upload a photo of my drawing into my profile photo album. I could not figure how to load it into the message. I have more but will wait for request. It is a shame that I do not have a computer program to draw all this stuff out, but my only experience is with the manual drafting, long time to create but so gratifying.
Wayne
 

Dana

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Well Dan I have photos saved to my computer but I can't attach them. It seems that the photo must have a url to put it into the message. I found that if I drag and drop it shows up full screen. If I could get them posted you might be impressed.
Wayne, you need to add it as an attachment to the message, not an included image. To do that you can't use "quick reply", instead click "go advanced" and go down to "manage attachments.

-Dana

A cement mixer collided with a prison van on the highway. Motorists are asked to be on the lookout for sixteen hardened criminals.
 

wayne sprigle

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OK, Hopefully they come thru. These are my wooden version figuring on 1/16" ply stressed skin. But I feel that aluminum with a cockpit with steel tube covered with aluminum would be lighter. Enclosed also is a picture of my current project, hopefully to be completed and flying next year.
 

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wayne sprigle

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Hello all, I want to appologise for my previous posts. It was never my intention to imply any negativity on any of your replies. I was only looking for criticism of my ideas (good or bad). How else am I going to learn if I don't get any responses. Am I blacklisted? Is that what the check mark is for in the title line (do not respond)? Just currious and wand to learn. I have been a lurker for a long time, and I just feel I had to respond to the OV-10 post as it is one of my favorite aircraft.
Wayne
 
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