viperred

Greetings fellow builders and flyers. Here is my latest concept Experimental Persuit (XP) Aircraft the "ORION". The Orion is a ficticious (Vietnam-era) prototype aircraft. I have just set out on this project. The Orion is literally a fusion of the P-51 (the wing) and a modded OV-10 Bronco. Two classic aircraft that really come together in the ultimate fighter aircraft design. Decided to go with the V-tail mainly for looks, although I think it will make a slightly faster ship. I have just finished my first model of this aircraft in 1/48 scale. I will probably make another 1/32 or 1/25 scale as I size this slowly up and get out the kinks into a flying 1/6 scale aircraft. (Going to steal the wing from the TopFlite P-51 giant scale kit)

here are the pics.. this is a rough fast built scale of the ship.. so there's not much detail..
http://home.bendcable.com/viperred/o...Warbird)01.jpg
http://home.bendcable.com/viperred/o...Warbird)02.jpg
http://home.bendcable.com/viperred/o...Warbird)03.jpg
http://home.bendcable.com/viperred/o...Warbird)04.jpg
http://home.bendcable.com/viperred/o...Warbird)05.jpg
http://home.bendcable.com/viperred/o...Warbird)06.jpg
http://home.bendcable.com/viperred/o...Warbird)07.jpg
http://home.bendcable.com/viperred/o...Warbird)08.jpg
http://home.bendcable.com/viperred/o...Warbird)09.jpg
http://home.bendcable.com/viperred/o...Warbird)10.jpg


A few major hurdles of course.. a full scale brono has a 40' WS and a P-51 has a 35' WS so i'll actually be using the 1/5scale P-51 top flite kit to be making a 1/6'th scale Orion. Wing loading will be much higher due to the twin's. I'm thinking the .40 or .60 range, as the wingspan of the 1/6'th scale orion will be 84.5"

Wingspan is a minor problem as I have to sort out the V-Tail surface area and calibrate it to this aircraft... thank god I have a Ti-92 calculator! Thank you "Ask DJ. Aerotech". The current problem that stresses me is that I wish to use a standard P-51 pnuematic retract Gear, and this may prove a problem with the nacelle placement. More models and scaling will reveal answer to this.

I'm sure it will be quite a handful to fly (a twin taildragger) but in the air i'm hoping for some good fast flying. Special thanks to the twin tips at rcwarbirds.com As I complete more of the models and scale work i'll put them up here for you guys to check out.

Happy Hunting!

-Paul Anthony

William Robison

My Feedback: (3)

Paul:

Looks interesting, but some caveats.

As shown I'm afraid you will find it impossible to balance. The major mass of the fuselage, and the engines, are all forward of your probable center of lift.

Your model can be built with a Vee tail if you wish, but the vertical projection of your model is such that you will have very little rudder authority, and if you make it large enough to have sufficient rudder effect with an engine out you will greatly increase the aerodynamic drag, as the two surfaces have to work in opposition to be effective as a rudder.

Vee tails work well on racers, the bank and yank style doesn't need much rudder, and on a sailplane which doesn't use much control deflection anyway.

But a twin with one dead needs a lot of rudder. And as little added drag as possible.

So. If you build it as shown and get it to balance, it will probably be a good plane with electric power. And it also will probably do well with piston power. Until one engine quits.

I'd rethink the vee tail. Might be a little faster flat out, but you will have controllability problems.

Bill.

viperred

Thanks for the response,

Yah know i'm kinda undecided how I feel on the weight and balance.. i guess right now i can't see ahead far enough to see engine weight, how heavy the nose will be, gear etc. I'm not as worried about the balance as I am the V Tail situation

Your model can be built with a Vee tail if you wish, but the vertical projection of your model is such that you will have very little

hehe yeah that's a screw up.. the V tail is way to low on that model.. they need to be angled up much more, on future models they will be closer to 45dgs or more. Now at that angle do you think I'll have much better yaw/rudder throw. What about larger control surfaces and adding larger throw. Do you think i'll be able to pin that rudder hard enough into that good engine should I have a flame out? There's gotta be a way to do this.. are there any twins out there that have V tails(in any scale)?

As for weight.. the protruding nose, and twin engines are the exact placement as they are on the bronco. However i've greatly reduced some weight in the aft....as the bronco has two booms and massive horizontal stab, and my Orion has a V tail and only one boom back to that tail. I may have to wait the tail or put reciever battery in the tail to help balance it out. Might as a worse case add some weight as well to the tail.

What do you think the pro's or con's are of the wing loading? and Wing area? Do you think i'll have enough lift there? the Orion has 1245 sq (84.5") in in 1/6'th-ish scale. and the bronco normally in 1/5 scale (palmer plans) has 1670.4 sq. in. Granted the Bronco is a slow and low type ship and my Orion is a racer. Just wondering if i'm gonna have any problem there?

Appreciate the help a lot!!

Thanks,

Paul Max Anthony

William Robison

My Feedback: (3)

Paul:

Looking at the fuselage shape and weight/balance first.

Slimming the afterbody will not make any amount of difference in the air drag, once you have the larger cross section forward you have established the "Base" air drag, making the after body decrease sharply in cross section will give less surface area "Wetted" by the air flow, and consequent lessened skin friction. But the amount of air drag decrease is minimal.

If you want the "Pod and Boom" shape for appearance, have at it, just bear in mind that conventional shapes are easier to build and balance.

On to the vee tail.

An item I didn't mention before is roll coupling of the rudder.

A "Conventional" rudder, mounted above the roll center of the aircraft, will, on deflection, not only induce yaw, but being all above the roll center will also induce an amount of roll. This is somewhat countered by having a high wing, and with enough dihedral the effect can be reversed. This is how rudder only RC planes are designed. Note the high dihedral in such planes.

Roll coupling of the rudder can also be minimized by tapering the rudder sharply, with the center of area closer to the roll center. Look at the popular aerobatic planes, the Cap series is the extreme example. Another way to do it without extreme taper of the surface is to lower the surface. By altering the design to include a sub fin under the tail, the rudder can then be moved downward, again lowering its aerodynamic center nearer, or even on the roll center. Going with this aligned center of force all roll coupling is eliminated.

But it's not good with a tail dragger. The tail wheel strut has to be long enough to hold the sub fin off the ground Mounting it to the sub fin makes the sub fin that much larger to get the strength necessary, and so forth.

So what does all this have to do with a vee tail? Simple. You cannot eliminate roll coupling from a vee tail. You can't even minimize it.

Consider the left engine dead, power on the right.

You will have, working against controlled flight:
1) Left yaw due to off center thrust.
2) Left roll due to greater lift on the right wing, caused by greater air flow on the right wing from the running engine.

To counter these forces you must use right aileron for the roll, and right rudder for the yaw.

And that's where the problems will bite you in a hurry.

With a vee tail, and a dead left engine we have a left roll induced. The right rudder needed has to have the left tail surface deflected upward and the right surface deflected downward. While this gives us effective right rudder, it also adds a lot of induced left roll, opposite to what we need. Not a good thing. To counter that we have to add even more aileron deflection, it's a nasty circular thing. Add more of one and have to add the other, all the time increasing air drag due to the deflection of the surfaces.

None of this is to say you can't build a twin with a vee tail, but there are problems that just do not occur with a conventional tail, and you should be aware of them.

You can have an airplane that flies great with two turning, but if the peculiarities of a vee tail are overlooked, the first dead engine can easily lead to a dead airplane some very few seconds later.

So. I recommend saving yourself a lot of bother and possible heartbreak standing over a pile of splinters.

Build two or three with a conventional tail to get your feet wet, then later work your way into vee tails.

Bill.

viperred

But it's not good with a tail dragger. The tail wheel strut has to be long enough to hold the sub fin off the ground Mounting it to the sub fin makes the sub fin that much larger to get the strength necessary, and so forth.

Yeah I think that will prove to be to much a pain.. How much difference does it make in the angle of the V tail that is producing yaw. Does higher V tails help give more control in an engine out scenario.


You can have an airplane that flies great with two turning, but if the peculiarities of a vee tail are overlooked, the first dead engine can easily lead to a dead airplane some very few seconds later.

Can I ask you this one.. Can independent retractible spoilers on the top surface of the wing help yaw into the good engine. What if the spoilers are angled ?

Also will bigger rudder surface area help in the V-tail?

Thanks,

PA

JohnBuckner

My Feedback: (1)

With 'V' tails the V angle is critical to pitch and yaw stability as well as pitch and yaw response to the rudavators. look at a V tail directly from the top, what you see is the effective surface area avaliable for pitch stabiliazation. Now look at it directly from the side what you see is the avaliable area times two that will provide yaw stabilization.

When you flaten a V tail as you have in your model you will have increased the effective horizontal surface, increasing pitch stability. However when you do this at the same time you will have reduced the avaliable vertical surface to provide yaw stability around the vertical axis. Most V tail aircraft will use from about 105 to 120 degrees between the surfaces. This of course is ignoring other factors such as tail moment along with tail volume. The aircraft you have modeled would not have yaw stability to be controlable as a single let alone as a multi.

'V' tails can of course be used with a multi and can be just as effective. Some of the early experimentation done in this country before world war 11 by Beech Aircraft was on an experimental twin that was a spinoff on some of their early twins. This experimentation came to fruition with the postwar Bonanza.

I would ask here Do you have multi RC experiance? If not this complex project will be a wasted effort. Much better to learn to fly first and then consider some of these more complex aerodynamic projects.

Best of luck

John

William Robison

My Feedback: (3)

PA:
An easy way to figure the effective vertical fin and rudder area of a vee tail is just to look at it in a side view. With the higher angle, the surfaces pointing up more, you effectively have more rudder and vertical fin area. And, looking from the top, you will see the effective horizontal stab and elevator area decrease as the vertical fin and rudder increase.

In designing for a vee tail you have to decide how much vertical and horizontal area you want, then cut the parts to give the desired horizontal and vertical projections. But there is no way to eliminate the roll coupling of a vee tail.

One trick you can use, though it will no longer be a conventional vee tail, is to use anhedral instead of dihedral - invert the vee. Then the roll coupling with the rudder into the live engine will be toward the live engine also. But once again, you'll have that long strut for the tail wheel, unless you go to trike gear.
The "Black Widow," the P-61 night fighter, used spoilers for roll control, so it could be done. it also had very small ailerons to give some "Feel" to the pilot. As I understand it, the plane was not capable of sustained inverted flight, so if you want your plane to have inverted capability forget spoilers. They don't work well on the bottom of the wing, which is where your spoilers would be when the plane is inverted.

Now I may be wrong on this, I've never done any design using them. I only have a few hours in sailplanes with them, and their purpose there is really to spoil the lift for a faster descent without picking up too much airspeed.
With an engine out you will want more rudder than you have. That's a given. But remember the roll coupling.

Look at the vertical fin and rudder on my Tiggerkitty. It's about 150% scale, Times I'd like more yet.

Bill.

viperred

Excellent thanks for the help! I'm very appreciaitive. Seems to be a hard concept to master.. a twin V tail and a tail dragger. I have three things going wrong for me to begin width hehe... I like challenges as you can tell. I am thinking I may try to increase the surface area of the V'tails. Now which is more important having larger control surfaces in the V or having more stab area.

If I increase the stab area for each V angle does that help much, or does it really come down to increasing throw and control surface (ruddervator) side in the V. Who would have known Yaw was so important.

I suppose on aircraft like the pond racer it's not as critical, I just personally would rather not move the props closer together on my prototype as doing so would force the cockpit area up over and ontop of the wing. Not a bad place, but just not an area i'd like to go. I also feel doing so might be harder to get a good CG with this concept. If memory serves there is yet to ever be a Twin engine V tailed aircraft, which either means i'm ahead of my time or i'm incredibly stupid lol

I am looking at buying a 1/25 scale model so will build the aircraft again in a larger scale and we'll see from there. Seems like I have some serious arena's to conquer.

anything i've missed or any other area's where I may be able to substitue something to get that yaw in. I am an amatuer roboticist, so i can pretty much create anything. What about something that works as a fail safe in case of engine out. I could probably create a large retractable fin that would serve as a rudder should an engine go out. Yes there will be wait but not much. I have a lot of tail on this aircraft, i could always drop down a deployable Vertical fin from the bottom of the fuse to act as a rudder in flight. But any other ideas would be much appreciated. To bad I can't feather the prop.

Thanks for all the help

William Robison

My Feedback: (3)

Paul:
When the control surfaces are not deflected they act like the nonmoving fin, either horizontal or vertical. Check this thread, go to post 5. There is a diagram to see how to measure effective area. In fact that whole thread would be good for you to read.
http://www.rcuniverse.com/showthread...48#post1304496
Consider the total area of one fin and movable surface. the greater percentage of the area that moves, the less deflection needed for the control input. So with a larger moving area the more sensitive the control will be, and the more servo power needed to operate it to the same deflection angle. Still, because of the yaw I wouldn't consider a vee tail twin unless it was an inverted vee tail.
When you're inside the Pond Racer you know you have a problem a lot sooner than you do just watching it from the ground, this gives you a lot more time to make corrections. Beech tried a vee tail on a twin in the middle thirties, said forget it. THey did build the Bonanza after WW2, but even that one has been discontinued for many years now. Way too many disadvantages with a vee tail on a twin.
If it flies well as a small airplane it will almost always fly well when scaled up. The reverse is seldom true.
If you insist on a vee tail just invert it. Or expect to crash it.
A device to sense loss of thrust from one engine as a trigger to blow the other engine off the plane?
All of this is adding unnecessary complication and weight. Avoid even the thought of such schemes and devices.

Really, Paul. Give it some thought. If a vee tail really were better don't you really think all airplanes would have them, and Beech would still be building the V-35 Bonanza?

Lose the idea.

Bill..

viperred

Can you help me to understand why an inverted V is better then an upright V on a highwing-twin specificially? Is this because an Inverted V is that much further out of the prop wash?

Seems to me like they would have the same problems wether they were rightside up or upside down?


Outside of convential tails can you think of anything fancy that might help my design and keep a radical edge.. convential tail as a last resort. I've thought about vertical tail + slightly downward horizontal stabs (like on the F-4 Phantom) but this design is really best suited only for aircrafr with supersonic flight. What would happen with an upright V-tail "with" standard convential horizontal stab. Is this a good idea? Thanks for your help Bill, next time you need your car waxed or boots shined.. i'll fly out hehe.. no favori is to great!

Thanks again,

Paul Anthony

William Robison

My Feedback: (3)

Went over this earlier. Must not have made it clear. If you lose the left engine you need right rudder to counter the offset thrust.

With a conventional tail, and the rudder up on top, that right rudder will also twist the plane a little bit, trying to make it roll to the left. This is adverse roll coupling. If the rudder in below the after body, then the roll coupling from right rudder will tend to roll the plane to the right, along with the right rudder, aiding in making a coordinated turn. Or a counteraction to the offset thrust.

Now with a conventional vee tail, the surfaces angling up from the after body, you get right rudder by raising the left surface and lowering the right. Now think about the ailerons. To roll left you raise the left aileron and lower the right. See the picture? Your ruddervator surfaces, to get right rudder are in effect also operating as a left roll input to the ailerons.

Now if we have the vee inverted, to get the needed right rudder the left surface deflects downward and the right surface deflects upward. Now we have a Right roll coupling from the ruddervators to go with the right rudder, and it is aiding us in maintaining control instead of working against us by giving the left roll the upright vee in right rudder.

So.

Upright Vee tail. Right rudder gives left roll, left rudder gives right roll. Not good.

Inverted vee tail. Right rudder gives right roll. Left rudder gives left roll. Is good.

The real problem with an inverted vee tail is breaking the things off by hitting the ground on take-off and landing.

The only current or past production airplane I know of with an inverted vee tail is the Predator UAV. And it has very long landing gear struts.
Don't you think an inverted vee tail is radical enough? And a flat stab with twin vertical fins angled out is getting you right back to the adverse roll effect. But you could angle them in at the top. Then you have two nasties. Take your choice whether all the needed extra structure for strength is worse, or the complications of making the rudders work. And you have lost the only real advantage of the vee tail - less total surface area.

Bill.

viperred

Okay thanks now It's definitely more clear in my head how the rudder/yaw coupling works.

So what is the function of tail surfaces that have a convential vertical fin and rudder, but the horizontal stab is either slight pitched up or pitched down. I.E like the F-4 Phantom etc. Is there any gain or reason for this or any advantage/disadvantage in prop driven aircraft?

Thanks,

PA

William Robison

My Feedback: (3)

Paul:

The F-4 Phantom (twin turbojet engine) had anhedral in the horizontal tail, and the Douglas A-26 Invader (twin piston engine) had dihedral in its horizontal tail.

And while I am sure the designers had their reasons in each case, I'm also sure I have not the foggiest idea what those reasons were.

Sorry.

Bill.

JohnBuckner

My Feedback: (1)

In the case of propellor driven aircraft and in particular large multi engine boats there has been any number of prototypes built with flat horizontal stabilizers that proved to suffer in pitch stability about the lateral axis while being flown at high angles of attack. The proved to be the stabilizer operating in the disturbed and turbulent air in the downwash of the wing. In many of these cases adding dihedral to the stab provided the solution by getting more of the surface up and out of the disturbed air.

John

William Robison

My Feedback: (3)

John:

I had vague memories of Glenn Martin angling the PBM-3 Mariner's (and his later flying boats) horizontal stab up for that reason, but I wasn't sure.

But that still doesn't tell us about the Phantom.

Further elucidation, please.

Bill.

viperred

I have also posted this question in the Aerodynamics forum should be interesting to know the answer to this.. cause i'm curious if I put a convential vertical fin + rudder, and then add either a slight degree of anhedral or dihedral to my horizontal stab on my twin.

Paul

jrf

My Feedback: (551)

The reason is the same as above. The original prototype had a flat stab, but it proved unstable in pitch at high angles of attack. Because of the broad root chord of the wing, adding dihedral wouldn't get the stab out of the wing wake, but anhedral did.

The prototype didn't have the dihedral wing tips either. Can you imagine the first flight of that turkey? That's why test pilots make the big bucks.

Jim

viperred

Fascinating thanks for clearing that all up. I dont think on most single or twin prop planes though there is to much of a need. I've seen some twins (military) that had it. but I think really you have to have an excessive wing to initiate anhedral or diehedral in the horizontal stab.

PA

flying2bill

My Feedback: (2)

This is all fascinating, and me without any design experiance can not comment on any of the above mentioned problems, however you must do something about the name, first when I seen the name Orion, I think of a jumbo jet with a big radar dish mounted on top, second because it has parts taken from 2 horses it should have a horsie name, mustang and bronco are out, maverick is used by a missle but could be recycled (how many versions of corsair are there?) and some what desribes the nature of your beast. Pinto brings about an image of a cheap car. Just something else to think about when the technical stuff starts to make your head hurt.

AmishWarlord

My Feedback: (5)

William is right on all counts.


However I think your plane looks cool and should should build a flying model of it. Try to balance it out and gyro the hell out of it.

If you do mods to fix the problems with the desighn then your goign to end up with a Bronco. Plenty of RC Broncos crash anyway so why not go with your desighn as is?


Sugestion for a name, Palomino

Link to Palomino

viperred

I chose the "Orion" name after it's mission. That being FAC and seeker/hunter for SAM sites. Slow enough to draw fire over targets, but fast enough to have good diving/climbing capabilities. As "Orion" in mythology is the hunter, so is my ship. This is the prototype version. The military version will probably have some 20mm or 30mm gatling guns that will rotate down from the fuselage.

I did however decide to take Bill's advice I have since replaced the V-tail and put back a convential tail. Doesn't seem to effect the look to much. I think it will also fly a heck of a lot better. I'll put another pic of it up soon when the paint is finished on the tail and you can tell me what you guys think

btw if it was just a matter of looks yes, then i would stay with the V-Tail.. but this plain has to fly well at any scale so function actually does rein supreme

-Paul

viperred

just playing around with some new very rough variations this week in photoshop. What do you guys think?








KEWL?~?



Paul

William Robison

My Feedback: (3)

Ed:

Shouldn"t this latest revision have the "XP-1b" designation?

In full scale forward wing sweep gives almost instant destruction unless instant correction for flexure of the structure is applied.

The experimental prototype flown not too long ago had strain gauges located strategically to sense the flex, feeding a dedicated computer to apply corrective aileron input, preventing flutter and subsequent wing failure.

Just as a swept LE gives he same effect as dihedral, the forward sweep gives effective anhedral. And does it both upright and inverted. This causes the airplane to be much more responsive in roll, but it does this by making the basic airplane much more unstable in normal flight. Just one more reason it requires the dedicated computer.

Another advantage is moving the MAC forward, allowing the CG to be further forward also.

In a model, wing flex is not an issue, and the anhedral effect will help maneuverability. Should do a snap before you can blink.

But I'll bet tip stall will keep you from building the second one.

Bill.

viperred

Do you think it would be an okay flying model? Since it's a highwing should I add any diehedral or anhedral into the wing? I'm sure as you said tip stalls.. are going to mean hot landings and keeping speed up at all times...

Paul

William Robison

My Feedback: (3)

Ed:

With a flat wing upright and inverted will have slightly different characteristics. The high wing by itself gives a little dihedral effect.

Haven't seen the side elevation of the revision, but probably 7 to 10 degrees anhedral will neutralize it.

Then add an equal dihedral angle to the horizontal stab, and it would really look "Tough."

And you can always cheat by putting some washout in the wings, but that would aggravate the tip stall when inverted.

Bill.