Increasing wing area and other measurements

[Khan]

My interest in the F-20 has been rekindled by the recent changes to the F-20 homepage, and I'm reminded of a blurb I once read about how the 4th prototype was going to have a 10% increase in wing area. I've read about that done to other aircraft too. How do they do that? Is there some particular algorithm they use to optimize increases in width/span and the chord? Would LERXs be included? I don't have any engineering software or a wind tunnel, so if I were going to put in a strip or two of evergreen, is there some quick and dirty way to figure how to do it aside from just an arbitrary cut here and there?

That's my main question, but I've also thought about transplanting the landing gear and wells from a Hasegawa X-29 onto their F-20 as part of a what-if to free up space on the wing for ordnance. Since I'm going that far I figure I could transplant the vertical stabilizer from the X-29 too. It'd be better aesthetically, but, in theory, would something like that have a significant impact on aerodynamics and/or center of gravity?

[Andrew D. the Jolly Rogers guy]

Only way to answer the tail question is knowing how much more area one has than the other. You don't want to replace it with a tail of less area, AFAIK.

[lockheed2004]

I'm not an AE (yet), but I do know enough to answer your question. There are several factors that have to be accounted for in both questions. I'll start with the issue of the wings. This was only a drawing board type concept that never even resulted in a flying aircraft, so you're free to do as you choose. The easiest thing would be to increase the chord length by extending the trailing edge. Basic math will tell you how much plastic to add. From an engineering perspective, the chord could be increased and the span kept the same, this would affect lift, drag, moments produced, importantly: where the transition point occurs, and a whole other list of items essential to the design. However, if you increased the span of the wing, keeping the chord fixed, you're going to get an increase in spanwise lift, moments produced about the centerline, and again, several other factors involved would change. The LERX might be affected, however when scaled down, this would be negligible. The contribution from the LERX is far less than the lift produced by the wing. Yes the LERX is there, but more for high angles of attack and not level flight. Unless there is hard evidence stating which route Northrop was choosing to go, it is entirely up to you as to increasing span or chordlength.

As for the second portion of the question. Without knowing the material makeup, and total area or volume of the two tails, it's difficult to know how COG will be affected. As long as the tails are comparable in size, my guess is COG will not move fore or aft more than a few inches. The 4th prototype probably would have used the same engines, thus the tail height would have been the same. If they replaced the engines with ones producing larger thrust, then we would have to account for that. Larger thrust translates into more torque, and a larger rudder would be needed to offset this. The tail is there to provide directional control via the rudder. As long as you don't replace it with a T-tail, you would be fine.

I think this answers your question. I'm sure someone will find something wrong with this. In the end, it's a theoretical design, do whatever looks good to you. Only the people at Northrop will have a definitive answer.

Brian

[Khan]

I checked the area of the vertical tails for both the F-20 and X-29 and they work out to be the same. Cutting and pasting confirmed that, yes, the F-20 looks better with an X-29 vertical stab. The rudder is bigger (ie takes up most of the trailing edge), so I could just say that accounts for the stronger version of the F404 they were going to put in the later F-20s.

I also screwed with a little algebra and figured out a way to increase both span and width about equally, so now the wing just looks bigger.

Thanks for the advice.

[Andrew D. the Jolly Rogers guy]

Don't forget to post pics!

[Khan]

Right now this is just a concept. I made a 3-view by scaling and then cutting and pasting from one of an X-29 and an F-20. I increased the area of the wings by 10% as I described, and pasted in the landing gear and vertical stabilizer of an X-29.

Here's an original F-20 for comparison (almost, but not quite to scale--you can't really see the changes in the wing):

I might get the kits and start the surgery over Christmas break. I'm in grad school now, so I won't get to do any consistent building until my program finishes next spring. On top of that, I have another F-20 that's almost finished except for some difficulties with the clear coats and weathering that's going to require a lot of inspecting and delicate stripping along with a host of other unfinished business. That's what I get for being in denial about rushing.

At any rate, I'll have some time to think about how to paint and equip this new project, on top of the lessons I learned from (what's not actually*) the first one: detailing the cockpit, fixing the seat, canopy mechanism, etc. As it came together I also realized just how limited the F-20's underwing capacity was on account of the F-5 landing gear. Its limitations seem not so much a matter of weight, but space. I figure using the X-29 parts would remedy that to a degree (ironic, considering that the X-29's landing gear is from an F-16).

So tell me: F-20C or an F-29? :blink:

* Holiday 2003-04: 3-week rushed attempt to fix the shortcomings of the Hase kit with what very, very little reference material I had at the time. Sloppy.

[Dmanton300]

So tell me: F-20C or an F-29?

F-20C.

I've often thought about doing something with the Hasegawa F-20 along these lines (I really like the X-29 tail and gear!) but have often wondered about the guns. I'm sure that long nose would allow an F-18 style M61 installation in place of the archaic M-39's, bring it's gun up to date. What do you think?

[Khan]

The F-20 homepage (http://www.f20a.com) says that development of a higher-caliber gun with caseless ammunition to replace the M39s was subcontracted out to Ford, but their beaurocracy was so difficult that Northrop abandoned the idea and stuck with the M39s. I'm inclined to take that with a few grains of salt, but otherwise I suspect that it wouldn't have been a very reliable piece of equipment.

I like your idea about the M61, but I'm concerned that there would be enough space. They redid the forward fuselage of the F-20 to make room for a larger radar antenna while keeping the guns; the effect on performance from the resulting sharknose profile was actually an unexpected benefit. I can't find a length for the M39, but the M61 is over six feet long and significantly wider. Considering that further improvements to the design included an even bigger radar, I suspect that space would have been even more tight forward of the cockpit.

Though on the other hand, looking at this cutaway it seems like there might be enough room, especially since there'd be only one M61 versus 2 M39s.

Perhaps it could be done?

[Jay Chladek]

I don't think the landing gear configuration change is really needed. Reason is that the main struts of an F-20 have to fit into a relatively tight wing area while the X-29 gears are fuselage mounted. Given that an F-20 isn't going to land on a carrier, I can't really see the need for the more beefed up looking X-29 gears vs. the original F-20 gear (which had a lot design life from the original T-38/F-5 configuration). The Northrop approach tended to be "if it ain't broke, don't fix it." So although I can see benefits from an M61 cannon, larger wings and a revised tail, the gear change doesn't make all that much sense to me unless a new gear had the advantage of allowing for heavier weapon loads. Even then, the normal F-20 gear probably wouldn't be changed all that much anyway (just thicker structures). Plus, the normal gear has a wider footprint then the X-29 gear, making for easier landings and taxiing.

Now if you did want to stick on a couple additional hardpoints on the wing closer to the centerline, then you could probably do a set of stub hardpoints, like what IAI did on the Kfir C7 (big enough for a rocket pod or a single bomb each). These could be potentially be mounted to the LEX roots I'm thinking just in front of the main landing gear. Even with a 10% wing area increase and more thrust from the engine, additional full hardpoints aren't going to be that much more beneficial in a slim design like the F-20/F-5 family. She's designed to be a nimble all arounder, not a big honkin bomb truck like a Hornet (which has more power to spare from her two engines).

Edited October 6, 2006 by Jay Chladek

[Vesper]

Could also use the stubbies for targeting pods...

Ves :lol:

[Gary F]

Been working on an F-20 lately and looking at these same 3 issues ... gun, gear, and wings.

On the wings, I chose to cut off the leading edge flaps and am installing an extension in that area, then simply adding back the le flap pieces.

At first I hadn't thought of changing the gear around but thought Khan's idea with the X-29 gear was interesting. Then I found the cutaway of the F-20 (same one above) and it looks like putting the large gear bay into the fuselage will cut into the internal fuel tankage ... not so good there, so I've decided to stick with the standard gear.

As to the gun ... I seem to recall from that time period that USAF was trying to standardise on the Vulcan on their fighters and did not care for the older M39's on the F-20, so finding a way to get the Vulcan into my F-20 is still ongoing. At the moment I'm leaning towards a belly fairing (similar to what's under the nose of an F-4E) assuming the associated gear would go into the space just behind the cockpit with that electronics bay stuff relocated to the space made available by deleting the M39's.

After that, it's just needing to add the IFF panel in front of the canopy and an aerial refuel recepticle aft of the canopy ...

regards,

Gary F

ps Vesper, want to trade me one of those F-5F's so I can make a 2 seat F-20!

[Vesper]

GF, I'll think about it, although at the mo' me and my stash are 6hrs apart!

just to whet yer appetite:

Since we're talking USAF F-20's, here's my idea for one:

I re-engineerd this Bstrd for a F110, added bigger intakes & a new radome. More about my build can be seen here: Ves' F-20C on Whiff

I havent finished it yet due to the complexity of the work involved. When it does get finished I'm gonna try and resin-cast it so I can work on a 2-seater & a Israeli fatback bird.

Edited October 6, 2006 by Vesper

[Gary F]

Ves,

Neat stuff there. How did you accomplish your 2 seater? The other monster is interesting ... didn't comprehend just how much bigger it is than the standard F-20 til I saw the shot with it and an f-20 together :blink:

Funny, but I searched back on Whif for F-20 stuff and didn't see your article ... glad you mentioned it here. Just curious, but is that an F-16 nose you have faired in to the F110 engined version?

regards,

Gary F

[Khan]

Given that an F-20 isn't going to land on a carrier, I can't really see the need for the more beefed up looking X-29 gears vs. the original F-20 gear (which had a lot design life from the original T-38/F-5 configuration). The Northrop approach tended to be "if it ain't broke, don't fix it."

That's a damned good point, especially about the design philosophy. Still, I don't think the landing gear is necessarily beefed up or strictly unique; it looks like the X-29 struts are from an F-16:

X-29

Similar view of an F-16

I don't think Northrop would have been too happy to do that! :lol:

The stubs are a great idea. Rocket pods would be pretty sweet, but they'd also be a great place for targeting pods, like Vesper said.

Even with a 10% wing area increase and more thrust from the engine, additional full hardpoints aren't going to be that much more beneficial in a slim design like the F-20/F-5 family. She's designed to be a nimble all arounder, not a big honkin bomb truck like a Hornet (which has more power to spare from her two engines).

During my most recent attempt, I was frustrated by my limited ability to include both mavericks and sparrows without resorting to an asymmetrical load just so I could put extra tanks on the inboard wing stations and keep the sidewinders. Switching out the landing gear would give me enough space just to include a BVR or extra maverick. It's not about heavier shots so much as it is about more moderately-sized ones. And yet, in real world physics, I doubt that the benefits of that would justify such a drastic change to the systems and structure.

On top of that, I didn't take into account any further changes to the wing that an extra hard point would require. That is, would a 10% increase be enough to get that lift increase they were after AND compensate for the extra drag? I also just assumed that the extra output of an improved F404 would be able to handle a third wing station.

For now, I'll fall back on aesthetics, since that's a big factor in what I want to do. You definitely know your ****, so I put your more informed assessment ahead of my novice reasoning in terms of how plausible my ideas would be. After all, what works isn't necessarily the prettiest, and I appreciate your insight. ;)

it looks like putting the large gear bay into the fuselage will cut into the internal fuel tankage ... not so good there, so I've decided to stick with the standard gear.

As to the gun ... I seem to recall from that time period that USAF was trying to standardise on the Vulcan on their fighters and did not care for the older M39's on the F-20, so finding a way to get the Vulcan into my F-20 is still ongoing.

I thought about the fuel issue too, but I figure the extra space opened up/added in the wings might compensate for it. My biggest concern has been the effect of the new landing gear wells on the intake trunks. For the time being, I figure that's something I can just say got taken care of since it's all "under the hood."

As for the gun, I found something last night that might be worth considering: http://www.globalsecurity.org/military/sys...ystems/m195.htm

It's a short-barreled version of the M61. It could fit, but the shorter barrels would bring in range and accuracy issues that don't come up with helicopters.

And, Ves, awesome work on the F110. Is that a recent pic? Nice two seater, too. How'd you do it?

[Vesper]

Evergreen is my homie! That bird has been on-going for at least 3 yrs, if not longer and I only have one side done. Since I'm going to eventualy do a 2-seater version & a fatback, I decided to put that baby on ice untill I could perfect my casting skillz. And yes that is a F-16 radome, I tacked it on over the standard radome. I plan to do a starboard-intake mounted M61 at some point.

The 2-seater was accomplished by using a Pioneer F-5B fwd fuseloge grafted onto a F-20 aft body & some other mods thrown in for fun. see here: click You'll need to scroll down a bit, also on page 2 IIRC is my summary of a RCAF CF-120.

Ves :lol:

Edited October 6, 2006 by Vesper

[Gary F]

Ves,

Thanks for the info and links. Good luck with the rest of that project.

regards,

Gary Ff

[Jay Chladek]

Could also use the stubbies for targeting pods...

Ves

Ya know, I hadn't thought about that initially. But that idea makes a lot of sense! It would indeed be the perfect spot to stick a LANTIRN on one pod and a laser designator (ala Pave Penny) on the other.