Conquering Survivability?

This is the thread to aid in development of new ideas and classes. Post working rules and gather feedback!

Moderator: hbartel

Admin
Posts: 309
Joined: Sun Dec 24, 2000 1:00 am
Location: USA
Contact:

Conquering Survivability?

Post by Admin »

I have a few theories I’d like to share. These ideas are based on my experience designing, flying, and analyzing combat ships.

There has been a great deal of discussion lately about the future of RC Combat. If you’re looking for more crystal ball vision in this post, you’ve come to the wrong spot. This post is simply intended as a way to capture some of my experience and ideas about survivability for people to reference in the future.

Recently, members used kinetic energy comparisons to try and quantify the relationship between damage and speed. This showed the fact that velocity^2 is the dominating factor in combat airplanes available impact energy. Kinetic energy is a good method of comparison but in my opinion makes some overly conservative and poor assumptions. I hope to present you with a few of the bigger picture, smaller then just KE, opinions I have about mid-air survivability based on the underlying theories and the hundreds of planes I’ve had mid-airs with.

First, let me give you my definition of survivability:

<b><font face="Verdana">The ability for a combat plane to take an impact, recover, and continue flying for the remainder of the round with minimal repair time required to return the aircraft back to it’s original state. </font id="Verdana"></b>

All mid-airs are not fatal due to how energy is dissipated and how much energy is transferred between aircraft. If you just look at KE, you are assuming that a mid-air always transfers all that aircrafts entire KE to the other plane. Since KE=.5mV^2 (one half mass times the velocity squared), either the mass or the velocity has to go to zero. Since we’re not near the speed of light, I think it’s safe to conclude the velocity must go to zero to fully dissipate KE. Good for worst case comparisons, but how often do you see both airplanes completely stop in the air following a mid-air. Statically, I'd say that number is fairly low, let's theoretically say 1 out of 10 mid-airs for ease in the math, or 10%. I believe, “Bone Crushersâ€
User avatar
Ed Kettler
Posts: 3437
Joined: Sat Dec 15, 2001 6:05 pm
Location: USA
Contact:

Post by Ed Kettler »

AJ,

Thanks for broadening the discussion and applying engineering principles. I'd like to take a slightly different tack on mid-air frequency relative to speed. Your thesis states that the slower the speed, the longer the planes are closer to each other. Here's some observations based on what we've seen in 2548:

1) We've had a lot more pursuit flying and very little furballing. Why?
- Power-to-weight is down, reducing the ability for sustained turns
- Historical aircraft designs have higher stability than many of the open planes, reducing the ability for extremely tight turns

2) Pursuit flying spreads out the planes, reducing midairs.

3) Spread out planes allow the target pilot to see the attacker and avoid the attack, requiring better tactics and flying.

The foregoing may or may not be relevant to Slow B. The efficient SSC designs we fly here in TX have good recovery given enough altitude (~50'). Where I've had problems in SSC is where I get a solid hit in the center section that damages the spar or loosens servos. Wing slaps are not really an issue anymore; they spin around and keep flying after getting the nose down to regain flying speed.

Great discussion!
Ed

Image
Ed Kettler
RCCA 533
AMA 730493
Plano, TX
BigCountry
Posts: 479
Joined: Fri Sep 14, 2001 12:14 am

Post by BigCountry »

I can't speak as to the engineering speak that AJ uses but do understand what he's saying. To relate it to our real world experience here in the Swamp at this point. We are seeing very much what AJ described and that is the planes cannot maintain the constant turning that the Open B ships can. Proof in point Jimbo and I are both flying Open B ships altered to meet Limited B requirements and have both experienced the difference. We've been out almost four weekends in a row flying the concept and it's very noticeable. Our matchs become predominantly pursuit due to this fact and it is definitely a change. Will carnage rates lower? I believe so, Jimbo and I experienced our first Limited B mid-air and while Jimbo's Raptor didn't fair really well I think that the lawn dart portion of incident did as much damage as the actual midair. I was able to fly my WASP out of the midair and bring it down safely with the only damage being to the fuel tank. Certainly the entire case cannot be built upon that one incident but it's a good example. I think as more demos are held and more pilots try the concept they'll see the same thing...

Image
headshot
Posts: 55
Joined: Mon Feb 10, 2003 10:19 pm
Location: USA

Post by headshot »

I have to agree with everything said.

To further reference one of AJ's points:

In a "furball" situation, we have a large number of aircraft in a confined space. They are able to loop an indeterminate number of times, thus keeping them within said space. This likewise increases the amount of time aircraft are in close proximity of each other, hence AJ's 1 in 10 "bone crusher" becomes a distinct possibility.

Swinging now to agree with Ed and Big Country, if the planes are limited as in limited B, there will be markedly less ability to maintain the furball (1 or 2 loops at best before losing airspeed).
Thus the match will fall into a pursuit type of combat (that those of us from near the beginnig all remember). Subsequently the spacing between aircraft will open up, and the "crash" factor will decrease. Also, it seems like with a pursuit style, we seem to get less and less of the head to heads that are so common in Open B right now.

Jay L.

Out of the sun, onto your streamer!
User avatar
Ed Kettler
Posts: 3437
Joined: Sat Dec 15, 2001 6:05 pm
Location: USA
Contact:

Post by Ed Kettler »

Also, the loops and turns in 2548 are about 2x the SSC diameters, somewhat spreading out the planes, too.

Ed

Image
Ed Kettler
RCCA 533
AMA 730493
Plano, TX
Lou Melancon
Posts: 2389
Joined: Wed Apr 04, 2001 5:16 pm
Contact:

Post by Lou Melancon »

There are two aspects of speed that are being overlooked and they are: reaction times, and field of vision. With slower planes the time to react can be slower as the closing rate is less than with faster planes. Also one's field of vision is wider when the objects they are viewing are slower, this is a postulate to AJ's "soft vision, hard vision" theorem.

Given that you can watch a wider field action, are able to see mid airs coming to a much greater extent with slower airplanes than faster airplanes, and that you have more time to react because closing speeds are less, I think speed does play a very significant role in increasing survivability.

To sum up the opposing viewpoint, the issue of planes not having enough thrust to recover from impacts and thereby being rudely introduced to terra firma is no longer an issue. It was an issue a couple of years ago but today's designs (unless driven into terra firma at speed) survive ground impacts very nicely. They also have adequate thrust to recover from most situations.

I do agree that flying more planes in a confined space increases the chances for impacts. But, it is the pilot who overshoots an opponents streamer and turns 180 degrees to go head on back to it that creates more destruction than anything else. Lets ban 180 degree turns or head on passes. Just kidding, but I've often wondered how you can cut someone's streamer by first flying through their engine, prop, and airframe to get to it.

Lou Melancon
Alpharetta, Georgia
Admin
Posts: 309
Joined: Sun Dec 24, 2000 1:00 am
Location: USA
Contact:

Post by Admin »

Good! Got you thinking a little bit didn’t I. It’s easy to go drudging down the same path if you don’t stop to think about the bigger picture. Furballs only happen when available thrust combined with lift is sufficient to overcome the drag induced by high angles of attack. There’s a trade off there too. Too much thrust, you get back to a furball situation with MORE airplanes closer for longer periods of time…

It’s all a big compromise, but tweaking all of these and being conscience of the effect on other areas will eventually lead to planes lasting MUCH longer.

Ed,

I think your biggest challenge with 2548 will be thrust and mid-air recovery. Smaller wing areas make it tougher. Looking back at the NATS demo, I spent a lot of time on the deck battling back and forth with Kirk. We came close but never touched and you definitely had to work to get in behind one another. So, cutting back on the number of mid-airs with better separation may be the answer for improved Scale survivability. You guys are definitely on to something in my opinion. Don’t let these ideas slow the progress, just keep them in mind.

BC,

I think your biggest challenge with Limited B will be wing strength. 72â€
User avatar
Which_way_is_up
Posts: 1637
Joined: Tue Feb 12, 2002 8:54 am
Location: Dallas, Texas

Post by Which_way_is_up »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Admin</i>
<br />. . . . . . . . . . . . How many Cobras did Lee loose in Sherman, TX? What was the cause of those wing/spar failures? Speed, Mid-air Frequency or something else?

Why did none of the reports mention these failures?

It’s hard to improve survivability with out first admitting there may be a problem with it...

A.J. Seaholm
TEAMseaholm
[url="mailto:seaholm@teamseaholm.com"]seaholm@teamseaholm.com[/url]
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Do I smell a conspiracy theory in the making? [:0]
[:o)]


<hr noshade size="1">

Image
"Tail end Charlie"
Matthew 7:6
<b>Cobra and Smack II Kits at</b> http://www.texascombat.com
Jimbo
Posts: 1082
Joined: Sat Apr 07, 2001 11:28 pm
Location: USA

Post by Jimbo »

AJ the 72" max span is temporary. It will be lowered to 64" on 1-1-05. If it had been up to me there would never have been a combat plane with more than a 48" wing.

Limited-B
Try it,you'll like it !
Jimbo
Posts: 1082
Joined: Sat Apr 07, 2001 11:28 pm
Location: USA

Post by Jimbo »

What's with Limited-B ?[:(!] I can't beat Travis anymore[B)] We may have to scrap this whole idea[;)] I can take him in SSC and OpenB but I suck at Limited-B [:0]

Limited-B
Try it,you'll like it !
headshot
Posts: 55
Joined: Mon Feb 10, 2003 10:19 pm
Location: USA

Post by headshot »

Now, all of the thought with the forces involved here has been in the "head-on". Like AJ said previously, head ons are a minimal percentage of the mid-airs, I see alot more of the nose to wing root/nose to underside/nose to wing/wing to wing/wing to tail type.

Again in a pursuit style of combat, you will find that there are more bumps and glancing blows (low angle of impact) type hits, due to less up and down action. I remember back in the good ole balsa scale days, you would pass another plane, tap wings and remove their wings (and usually yours) resulting in a specaular lawn dart. With todays construction techniques, and slower speeds, I think these examples would become more of a bump and go type hit.

Just some thoughts

Jay L.

Out of the sun, onto your streamer!
User avatar
Ed Kettler
Posts: 3437
Joined: Sat Dec 15, 2001 6:05 pm
Location: USA
Contact:

Post by Ed Kettler »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">How many Cobras did Lee loose in Sherman, TX? What was the cause of those wing/spar failures? Speed, Mid-air Frequency or something else?

Why did none of the reports mention these failures?

It’s hard to improve survivability with out first admitting there may be a problem with it...
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

I don't know about Lee, but I had two Cobras damaged. One took a wing-to-wing hit that cracked the spar 6" inboard of the tip and whip-cracked the center section, delaminating the wood in the glue joint. It took 20 minutes to diagnose and fix (disect, glue, clamp, re-tape). The second plane took two hits: a midair followed by nose in ground impact. This broke the plywood tongue and delaminated the glue joints at the root. The ground impact caused most of the damage, as it appears that the midair was a prop sliced EPP leading edge and a spinner dent near the wing root. I had to rebuild the center section of the plane due to having to replace the tongue and reassembling the spars. 1.5 hours expended.

Image
Ed Kettler
RCCA 533
AMA 730493
Plano, TX
Lou Melancon
Posts: 2389
Joined: Wed Apr 04, 2001 5:16 pm
Contact:

Post by Lou Melancon »

AJ,
I can't speak to Lee but I can tell you about my damaged Cobras. I lot three in the last contest, having lost only one in all the other events leading up to it. All the Cobras had the same failure points, none were due to mid-airs. My thumbs are a far more fierce opponent than other fliers, as I drove all three into the ground hard.

In an effort to go lighter I skimped on some areas of the design. Bad idea. Those left out parts contributed greatly to foam splits along the fin area. Also the bass spars will crack if the wing flexes. The good news is LE strikes cause virtually no damage and only spin the plane around. I am now beginning Cobra's #7 & #8. I still have numbers 5&6, so in about 60 rounds I've lost four planes.

The new ones I am building will be light but slightly different. First I want to shorten the nose, which is a heavy combination of HDPE and 1/4" ply sticking out 6 inches. To shorten it I need to lighten the tail and move the CG rearwards, which will be done by adding more LE sweep. I will also use glass rods as spars because they can flex without breaking. The way I assembled the spars caused stress risers at the ply doublers. Bad idea on my part.

The Cobra is pretty much as durable as anything else in a mid air. Maybe better than most because of its EPP LE. It suffers damage when the engine is slammed into the ground transferring all the shock into the spar and the wing. I think I have a work around by making the motor plates shear off in a dirtnap rather than transferring energy into the structure.

I need to send you a DVD of the latest SSC ships in combat, they are not rockets but they are pretty darn agile.

Lou Melancon
Alpharetta, Georgia
slam
Posts: 834
Joined: Wed Sep 05, 2001 8:14 pm
Location: USA

Post by slam »

in reference to the proximity of many airplanes contributing to midairs (furball).

i love the furball but it takes guts to run in it. you have to have faith in your design and be willing to take the big hits.

i really think 2548 will have more survivability built in. it will be because of a combination of factors.

1. high wing loading will encourage more pursuit and less furball.

2. slower speeds and more thrust will help with some dumb thumb situations and lighter impacts.

3. more time investment = more restraint. people will be less inclined to put their works of art in harms way.

ssc when we first started would loop once or maybe twice before falling out of the sky. things have changed drastically. ssc has a better furball then open b [:D].

limited be will be the same thing. when the wing loadings go down with second generation limited b designs we will have unlimited loops and we will have the furball back[8D]

just my .02

one thing not discussed is the soft leading edge argument. it has worked for slope combat.

slam
User avatar
boiler
Posts: 3336
Joined: Wed Jan 01, 2003 8:16 pm
Location: Ohio
Contact:

Post by boiler »

Lou, after reading AJ's post I will agree that the epp leading edge helps reduce the crash force. The chanege in momentum of the plane (mass x change in velocity) is equal the impulse stopping it. (force x time of force acting) The soft leading edge lengthens the time of the impact therby reducing the force. It's like a modern designed car verses the car that Gilkey would like to have. The saying "They don't make them like they used to" refers to extensive damage to modern cars in slow impacts compared to older cars. They are designed that way because a ccrruunncchh takes longer than a boink. The result is a much smaller force on the driver. The car is sacrificed for the driver.[8]

Bob Loescher
Lima Ohio
Post Reply

Return to “Proposed Provisional Classes”