Lol Dave!!!

I was baiting J.B with my question. I was going to put the hammer down on him once he posts his intelligent response.

BTW, I still look forward to J.B’s prompt response. (lol .......I love RCU)


Regards

Ben

Lol Dave!!!

I was baiting J.B with my question. I was going to put the hammer down on him once he posts his intelligent response.

BTW, I still look forward to J.B’s prompt response. (lol .......I love RCU)


Regards

Ben

I'm not jumping in on anyones side, I just want some clarification. What "rule" is broken by boltin a larger engine on a firewal than is recommended by the manufacturer? I'm not a jet guy (yet, but as with R/C it's only a matter of time/money), but isn't there an AMA Rule about thrust to weight ratio for a jet model?

Thanks in advance for the clarification.

P-51B

There is a T/W rule right now for turbines. The new rules, that are in abeyance, have no T/W rule. It was designed to keep the speed below 200 mph. It was that or a speed limiter that are required in the old rules.

With the new rules, as they stand right now, there is a 200 mph limit, but no way to enforce it. No T/W and no speed limiter. Some of the jets will not exceed 200, period. The guys that fly those planes want additional thrust to add to the manuverability of the plane.

This is the issue stopping implementation of the new rules, at the moment.

The T/W rule calls for a .9 to 1 T/W ratio. Unlike other engines, the thrust of a turbine can be adjusted to meet the rule.

The airframes for the jets generally have a VNE (velocity not to exceed) that the jet guys pretty well follow. The prop planes have recommended engine ranges from the manufacturer, but, as you can see, many people exceed them. There is no rule keeping the non-turbine pilot from bolting on whatever he wants or flying as fast as he can.

Boy is this not fun, when all it takes is common sense building and flying. People make all kinds of excuses to stay out of the real world. Every one nose the buck is the bottom line, and we will do any thing to get it. Look at the PF it is flooding the market and only lasts a short time and its gone ,CHEEP<CHEEP. But I you get what you pay for .
NEXT

Thanks (yet again) JR,

So no RULES are broken when bolting a larger engine on a prop plane.

But an AMA RULE could be broken by putting a larger/more powerful turbine on a jet.



Anyway, back to the ARF debate;

I think we should railroad...er..nominate Mustangfan to begin writing a column for the AMA

No specific AMA rule is being broken. Safety should not have to be mandated we should all be building and flying our airplanes with safety foremost in our minds. With that comes the responsibility to follow manufacturers recommendations when it comes to assembling and gearing up our airplanes. Jim stated that he had "exceeded a manufacturers recommended engine size" by doing that and talking about it in an open forum he effectively says that he does not have to follow the manufacturers recommendations for what engine he should have to use. It does not matter that he altered the airframe to increases the strength (who says he did that correctly, maybe he just shifted the failure point to a different part of the structure) he changed and in a potentially detrimental way the airframe.

Well, Jim??? We're waiting for a reply.......(Crickets chirping...........)

Kevin

David

That brings up an interesting point. EXACTLY how is the VNE on a jet determined?

JR

good question, jr.

because if you look for a way to be an idiot you can find it by picking nits without having the foggiest notion of your subject matter,,,
A kit is just that- A starting point for a finished product. If you build EXACTLY according to instructions, then the engine size should be as recommended (note-that is not, repeat, not "as mandated").
If, like most experienced hobbiest builders and pilots, you start with a kit, and add your own refinements to make it uniquely yours. This includes beefing up the airframe to meet power needs, changing engine size to meet flying style and desired performance, which may include the fact that the density altitude where you live can reach 14000 feet on a hot muggy summer day
When you buy an ARF (bow-wow?), you get something without those goodies. You can make amendments to the structure, but you can't check under the covering without removing it. Thus, tis best to stick to the recommended powerplant.
The Edges I saw go in had the recommended power on them. The wings folded in a normal loop, just as power was added at the bottom. Both airplanes. One folded the right wing, the other folded the left wing. Nothing radical, just the kind of loop you'd expect an aerobatic ship to handle with no sweat.

Pulled from bottom.

Seriously I think it is done empirically by BVM. BVM is one of the few vendors I know that actually publishes a Vne. I know one popular sport model and the manufacturer told me he would NEVER give a Vne, but nobody asked himso it did not come up.


For the manufacturers that do not give a Vne, there planes should not even be going 200, but rather 170 mph.

RW Guinn,

What you posted in your first two paragraphs is EXACTLY what jet guys have been saying about our corner of the hobby ever since our hands were tied by thrust to weight ratios and speed limits.


J_R,

Matt is correct about BVM but others do post a Vne....My Composite ARF Rookie has a manufacturer recommended Vne of 200 MPH. However, my Composite ARF EuroSport does not have a recommended Vne....Because the manufacturer knows that this particular plane will not go fast enough to cause a problem for itself.

Kevin

Hi Matt

I would have guessed it was empirical. I thought maybe someone was actually engineering a model. That would be something new to all of us.

David and Kevin

Turbines excluded, I do not know of one kit, ARF or set of plans that is truly engineered. (There may be some, but, I am unaware of them.) Engineered to determine what the material qualities are, the bending moments, etc. Most are designed by guys empirically, with a little help from some general guidelines as to the proportions of surfaces, nose moment, tail moment, wing loading,etc.
Recommended engines on planes are more of a suggestion so that the buyer has some clue of what he is getting into.

It has been my experience that if you actually talk to someone who designed a plane, particularly about power plants, that they really have no idea what the limits of the design are. Most can tell stories of their kits being equipped with engines twice the recommended size. Is it safe? Who knows? Without a real analysis the only way to determine the limit is empirically.

Empirically is a nice way of saying 'determined through experience', heuristically, if you will.

Case in point. A .40 size plane. Is that a TT 40, an OS 40 LA, or a Jett or Nelson? Basically, giving a displacement is worthless in the determination of power, other than a guide to the wing loading.

How many other non-turbine planes are tested thoroughly enough to put a VNE on them? That might actually have some use. Don't hold your breathe though.

JR

Jim,
I too am concerned with the shoddy building practices of a few manufacturers of ARF's, and would like to appologize for my assumption that you were for a ban on them period. I think most RCer's are concerned with the safety of their aircraft and will give even an ARF a thourough going over to insure that it is structurally sound prior to starting the engine for the first time. I recognize also that not every detail of the structure will be visible without at least some disassembly. My point was simply that most RCer's that have at least some experience (not totally new to the hobby), will make every attempt to insure the integrity of the airframe. There may be a hidden flaw that is not readily detectable, which is the concern of several of those in this discussion includuing myself but, the builder must satisfy himself that the aircraft is sound. After an accident has occured, and the search for who to blame begins, the end user/builder will still be considered along with the manufacturer and seller of everything from stem to stern on the aircraft for liability whether it was scratch/kit built, or an ARF. I have witnessed shoddy workmanship in built up kits as well as ARF's. My point about the experienced members in the club giving final approval for any new, repaired, or rebuilt model prior to takeoff was to reveal the effort by the members of our club to provide support and expertise to those less experienced. If we are going to refuse to help others insure the safety of their aircraft because of fear of responsibility then why even bother to join a club or the AMA? The club that I belong to has a greater exposure to abuse than most as the feild is located within a river spillway next to a public road. We have had this discussion many times since anyone wanting to fly can do so without being a club member or having an AMA membership (except when one of the members is present to ask them to leave). As far as forcing the manufacturers of those soddy ARF's to change their ways, well good luck! Changes don't generally take place until after the fact but, I'm with you guys when it comes to brainstorming for ideas. Why wait until someone gets hurt?

kevin- I would almost believe you were it not for the generalization "jet guys". I have seen some of the kits, and some of the airplanes, and read a fair number of articles about them. No, I don't fly jets-finances and family concerns prevent that--and there is nowhere close to Roswell to see much in the way of jets, but I have managed to see a large number of DF, as well as large scale prop aircraft.
What the builders and designers of some of those models (particularly the "self schooled" designers) know about structural design scares the pants off of me (that is a sight you don't want to see).
When you are up in the 20+ pound category of high-performance models, you need more than a rudimentary knowlege of structural design. Balsa and fiberglass are wonderful materials, if used appropriately. Unfortunately, in a lot of cases, they are not.
Composite (graphite, fiberglass, boron, etc) are best used with epoxy, not CA. You do not get the strength you need just from the material--you need the carrier, too. and CA is a really crummy glue for high-strength applications in shear.
Heck- I know a guy who thinks that painting the fiberglass onto wood with Acrylic latex gives lots of strength. The guys who vacuum bag with epoxy are doing it correctly-but I want to see more structure under that skin!
And balsa is terribly inappropriate for the strength applications in spars and d-tubes at those levels. I use spruce spars in my .40's, for crying out loud!
The control line guys have to do a pull test. This is a guarantee that the control system won't pull out, and that the plane will stay attached to the control system, barring a cut of the wires. and yes, they do 200+ MPH.
Can you think of a similar test for RC? Are you willing to suspend your airplane by the wing and put 10g's on it? (that's 200lb for a 20 lb model). You pull a lot more than that in some of the manuevers you do--especially the abrupt pull-ups
Even such a test STILL wouldn't guarantee that the control system will stay attached to the aircraft... The vagarities of radio waves, ya know.

BTW- that is what I do for a living. Making sure things won't break.

Roger

J_R,

Have you seen the internals of any of the Composite ARF line of aerobatic planes? This line of planes, to me, seems to have a had little more thought gone into them than just empiracally designed.

Also, do you know David Ribbe??? David started his career in this hobby working for BVM during his college years. After graduation David went to work for Great Planes. David went on to redesign the old Top Flite series of warbirds into their Gold Editions that we have today. David also designed the BVM MiG 15,applying the same building and engineering techniques to the Gold Edition series of warbirds as to the MiG.....

LOL.....J_R---You need to get out more often!!!

Roger,

You are very right concerning utilizing the right materials for the job!!! As far as testing my wings to 10 g's...How can you do that accurately in a static mode??? When the plane is in flight, loads are distributed along the entire wing, as well as to other structures of the aircraft.

I know of one guy we have in our jet fraternity that applies numbers to everything---Eddie Weeks!!! On one of his jet designs he stood on the wing with his 200 lbs+ weight and the wing didn't break. Not until he ran over it with his truck did it finally fail.....

Kevin

Kevin, not an engineer here, have to leave all that stuff to elder son: BS Aeronautical Engineering, Purdue Uni. W.Lafayette, IN., and Master of Science, Educational Leadership, Troy State, Troy AL.

However I can say that the load factor on a wing results in the center of the wing. Fun to watch the Lead's wing begin to curve up when you're flying the slot in a 6G pull. You know your's are doing same.[X(]
That old Boeing B-47 had a 27 ft radius of curve before destruction. Sometimes in rough air it flapped like a bird -- almost!
Lost a bunch doing the toss-bomb (LABS) maneuvers.
Wanna' check your wing center load capability, then do as your bud did. Weight the center and lift at the tips.

Hey did you know that those big ol' airliners are limited to 2.5 positive G loads? Of course when lighter with fuel, you have a better margin. Think on that when you fly through some rough stuff next time.

Kevin

Did you see the disclaimer "turbines excluded"?

What percentage of non-turbines do you think are engineered, as opposed to designed empirically?

JR

This thread seems based on the assumption that most modeler-built models are stronger and safer than most ARFs. I think that assumption is questionable.

First, most hazards are the same for ARFs and non-ARfs. Poor assembly, poor setup, ill-advised choices of servos, batteries, engines, etc., careless and unskilled operation are all the same for all models. Lots of models are flown in damaged condition until something fails and they crash.

Next, is there that much difference between ARFs and non-ARFs? The assumption is that most ARFs are faulty and most non-ARFs are well-built. We've bought shiploads of ARFs and how many have proven faulty? I've seen some owner-built planes that were downright scary, it was a relief to see them rekitted. Consider the number of kits that are the builder's first kit. How many of those are truly well-built?

My point is that I don't see a significant difference between ARFs and non-ARFs from a safety viewpoint.

J_R,

Did you see me qualify my reply by stating Composite ARF's AEROBATIC planes??? Since when is a Top Flight Gold Edition P-51 and the other Gold edition warbirds considered to turbine powered??? You said that you didn't know of any planes, excluding turbines, that were engineered as opposed to being designed empirically...I was just letting you know of a few. I know that David applied his engineering skills towards the redesigned TopFlite kits as he and I have discussed this.

I think that the percentage of non-turbines planes that are truly engineered are few indeed as opposed to being designed empirically. I wasn't trying to pick a fight---Just pointing out a few since you knew of none.

Kevin

Kevin

Bad knee jerk on my part. Sorry

JR

Overpowered and what possibly lurks under the covering. Mr. Safety has left the building. Maybe it is the glass house deal. Mike K.

You almost have it right the first time! Your comments about the potential hazards of kit built stuff and damaged birds are right on target. I have seen a new built at home bird show up at the flying field that allowed me to see daylight through the fuselage, but that was one of the worst cases. However, there have been too many ARF/RTF's with serious deficiencies the average modeler would not have been able to see, much less fix. Those are the problems I was intending to address as those are the things that impact the new guy who bought his bird more than if he had built it.

I have only two things to say about that.

1. I didn't know the limit was that low.

2. That's scary.