Definition of a profile fuselage

[James H. Dean]

Question for the masses. What constitutes a profile fuselage? At what point would it be considered a full fuselage? I am building a profile based off a vector 40 size airplane. The wing is vector 40 the " profile fuselage is of my own design.  It is electric and all the electric components will be hidden in the cowling/ fuselage.  It will be a radical design so I want to have the fuselage "full" infront of the wing and will be a profile from the leading edge back. I want to flybit in the profile class but don't want to ruffle any feathers.

[Brent Williams]

Depending on where you live, and which contest rules that no longer exist or matter, profile is generally anything up to 3/4" thick.

[John Miller]

It cannot be thicker than 3/4" aft of the wing trailing edge. I don't think they've changed that.

John Miller

[James H. Dean]

From mid wing back it will be 1/2".. I'm just concerned about from the cowling back to mid wing

[BillLee]

AMA Rules define "Profile":

10. Profile Definition
The fuselage of a profile model resembles that of a conventional airplane in the
side (profile) view and appears as a thin flat sheet in the plan (top) view. When a
conventional, single cylinder, internal combustion engine is used, the engine shall
be completely exposed from the centerline of the crankshaft to the top of the
cylinder head when viewed perpendicular to both the crankshaft centerline and
the cylinder centerline. In the case of internal combustion engine with multiple
cylinders, the preceding rule shall apply to all cylinders with allowances made by
the officials for appropriate mounting of the engine. No fairing may be added to
the engine which violates the “completely exposed” requirement of the previous
sentences, and the engine cylinder shall not be contoured to present a streamlined
cross section to the airflow. Additional reinforcements such as plywood nose
doublers and cheek cowls or fairings are permitted within the width limits defined
in the accompanying table. Such additional fuselage reinforcements may extend
from the prop drive washer to a point 25 percent of the wing root chord back of
the wing leading edge at the root and may be faired in. Cheek cowls used in
racing events may be of unlimited width, but may be used only on the side
opposite the engine and only on models with side-mounted engines. In the case of
inverted or upright engine installation, engine mounts may protrude from the
fuselage sides beyond the width limitations of the table. They may extend no
further aft than 25 percent of the wing root chord back of the leading edge at the
root. Any such protruding engine mounts shall be of constant cross sectional
shape and dimensions, without tapering. The rear portion of those mounts shall
terminate in an angle of at least 45 degrees to the longitudinal axis of the fuselage
unless they terminate within the wing structure. Nacelles, as used on multi-engine
models are subject to the requirements of this definition.

[realSteveSmith]

Question for the masses. What constitutes a profile fuselage? At what point would it be considered a full fuselage? I am building a profile based off a vector 40 size airplane. The wing is vector 40 the " profile fuselage is of my own design.  It is electric and all the electric components will be hidden in the cowling/ fuselage.  It will be a radical design so I want to have the fuselage "full" infront of the wing and will be a profile from the leading edge back. I want to flybit in the profile class but don't want to ruffle any feathers.

This will probably be more complicated to build than would a full fuse....what's the reasoning?

[Dan McEntee]

AMA Rules define "Profile":

10. Profile Definition
The fuselage of a profile model resembles that of a conventional airplane in the
side (profile) view and appears as a thin flat sheet in the plan (top) view. When a
conventional, single cylinder, internal combustion engine is used, the engine shall
be completely exposed from the centerline of the crankshaft to the top of the
cylinder head when viewed perpendicular to both the crankshaft centerline and
the cylinder centerline. In the case of internal combustion engine with multiple
cylinders, the preceding rule shall apply to all cylinders with allowances made by
the officials for appropriate mounting of the engine. No fairing may be added to
the engine which violates the “completely exposed” requirement of the previous
sentences, and the engine cylinder shall not be contoured to present a streamlined
cross section to the airflow. Additional reinforcements such as plywood nose
doublers and cheek cowls or fairings are permitted within the width limits defined
in the accompanying table. Such additional fuselage reinforcements may extend
from the prop drive washer to a point 25 percent of the wing root chord back of
the wing leading edge at the root and may be faired in. Cheek cowls used in
racing events may be of unlimited width, but may be used only on the side
opposite the engine and only on models with side-mounted engines. In the case of
inverted or upright engine installation, engine mounts may protrude from the
fuselage sides beyond the width limitations of the table. They may extend no
further aft than 25 percent of the wing root chord back of the leading edge at the
root. Any such protruding engine mounts shall be of constant cross sectional
shape and dimensions, without tapering. The rear portion of those mounts shall
terminate in an angle of at least 45 degrees to the longitudinal axis of the fuselage
unless they terminate within the wing structure. Nacelles, as used on multi-engine
models are subject to the requirements of this definition.

   And please correct me if I'm wrong, what Bill Lee presents here is from the scale portion of the AMA rule book?? There never has been an official profile stunt class at the NATS or presented in the rule book. Local clubs make there own rules for competition and they can be all over the place.
   
  I like to define a profile for stunt as having an engine mounted in a side winder position on fuselage, more or less as presented in the rule Bill posted. I like to also point out that it can be defined as presented by the hundreds of kits produced over the years with a 1/2" thick fuselage and the countless number  of designs and plans published and printed that show the same thing. Having a double or tripler to stiffen the front end to help the run does not offend me. A further definition was made by SIG when the released the Primary Force and promoted the P-40 event, meaning Profile  model with a limit of a .40 engine, and a side winder mounted engine. No Rabe noses with an upright or inverted engine allowed, no tuned pipes. To encourage participation by the under classes, any plane without flaps received a 10 point bonus!! This helped SIG sell a lot of Primary Force ARF kits!! One of the challenges of the event is to get a good run on a sidewinder engine. When electrics came along, there was no way to denote what was a "sidewinder mount" or what the equivalent to a .40 was, so with electric having a clear and definite advantage but still allow them to fly, we added a 10 point penalty for using an electric power plant. That could be negated by flying a design that had no flaps and you were back on even ground again. I think the SIG P-40 class rules are the best, to keep it as a sort of entry level event to encourage beginners and intermediates to participate. They are simple and easy to understand. To allow electrics, at least state that the motor, battery and electronics must be exposed on the side of the fuselage, either inboard or outboard. That still gives them a distinct advantage.

    The model you describe that you have designed would not be a profile by the scale definition, or by a lot of other definitions.  profiles, as designed by kit manufacturers and published by many designers, were the simple 1/2" sheet balsa fuselage  for simplicity, ease and quickness of construction and strength. I think the precedent set by years and decades of kit design and production plus published plans defines what a profile is. When you build a model for an event, you should build it to the published rules, if any. Not build the model and then try to get rules to accept your variations of the rules.

   Type at you later,
  Dan McEntee

[James H. Dean]

I think what I will do is slim down the cowling. I am running the brodak electric mount, so it has the motor mount and battery box all one unit. I will just make the "cowling" area just big enough to come to the edge of the motor mount/ battery box combo which will be 2 inches wide total. It will still have the radial look just not as round as a yak-11  nose would be..

[BillLee]

   And please correct me if I'm wrong, what Bill Lee presents here is from the scale portion of the AMA rule book?? There never has been an official profile stunt class at the NATS or presented in the rule book. Local clubs make there own rules for competition and they can be all over the place.

O.k., Dan you're are being corrected. These are the AMA rules found in the Control Line General section. Apply to all CL classes flown in competition.
   
 

I like to define a profile for stunt as having an engine mounted in a side winder position on fuselage, more or less as presented in the rule Bill posted. I like to also point out that it can be defined as presented by the hundreds of kits produced over the years with a 1/2" thick fuselage and the countless number  of designs and plans published and printed that show the same thing. Ha.....
   Type at you later,
  Dan McEntee

Yes, local rules can always be made, but if used in an AMA Sanctioned contest are supposed to be pre-approved by the Technical Director. (At least that used to be a part of applying for a sanction. Don't know for sure what they have morphed the process into with the online sanction application. ) That being said, I wonder if any Technical Director in memory has ever ruled on a local rule that differs from the rule book.

Bill
 

[Dave_Trible]

Bill this is interesting and I am glad you found it- exactly where nobody thought to look.   Several years ago the topic was brought up in the PAMPA council and LONG discussion ensued.   There were as many different ideas as people involved.   In the end it was determined to let it go and just be regulated on the local basis since nobody would really agree about it.   If we had known about these written rules we would have just pointed to them and closed the case.  NOW I promise there are a number of profiles out there being flown in profile events that likely won’t pass muster with these rules…..my reasoning about trying to sort it out was I thought to propose have profile stunt as another unofficial Nats event.   It is hugely popular around the country and so felt it might increase participation some.   In some places it has more draw than most other events.

Dave

[Brett Buck]

  I think you are much better off running with local rules. As soon as you try to make the rules universal, and in particular, put them in the rulebook or worse, run it at the NATs, you are making it a big enough deal for the experts to move in, and you get in the spiral of ever more restrictive rules trying to keep it "simple", which leads to a search for loopholes, which makes it even more dominated by experts. And you have made it a big enough deal that the experts will bother with it. BTR -> Rat -> Slow Rat is the hallmark example. The fact that you had a long debate about in the EC just shows the tip of that iceberg.

    Absolutely no one asks the AMA technical director whether or not they can run local rules, they just do it, with the usual cryptic announcements on the flyer, and no one complains because the locals want it that way.

   So far, what seems to dominate profile stunt is that almost no one can make their engine run properly. I sat there and watched profile closely a few times at various contests, and it was just one borderline meltdown after another, with no one seeming to recognize there was anything wrong. The chrome on Brodak 40's must be pretty tough, one squeaky lean run after another, courtesy the stock .305 or .308 venturi.


     Otherwise the airplanes fly pretty OK even with whatever fuselage and variable alignment you get from a profile fuselage. Using electric removes the engine run issue, of course. I can guarantee you can make a competitive profile airplane well within the existing "official" definition and the classic 1/2" slab fuselage from 1948, so I don't see a critical need to fix the rules or define it a lot better.

     Brett

[Dan McEntee]

O.k., Dan you're are being corrected. These are the AMA rules found in the Control Line General section. Apply to all CL classes flown in competition.
   
 
Yes, local rules can always be made, but if used in an AMA Sanctioned contest are supposed to be pre-approved by the Technical Director. (At least that used to be a part of applying for a sanction. Don't know for sure what they have morphed the process into with the online sanction application. ) That being said, I wonder if any Technical Director in memory has ever ruled on a local rule that differs from the rule book.

Bill

    Well hush my puppies!! I stand corrected. I have not flown hardly any competition the last 5 years or maybe more so have not paid attention to the rule book much and I know I have missed some changes. I built my Dusty profile stunt/scale model way back in 2014 or 2015 and I remember looking up the rules to make sure I built a legal airplane for scale. I notice that the posted rule here does not have any mention of a 3/4" wide max fuselage limit, so if that is still in effect that may be listed in specific rules for scale in the book? I have not had a chance to go to the website and look. The 3/4" thing gets mentioned a lot, and so  does the " 1/2" behind the wing" part of the definition that second one has never been in print anywhere that I can remember, and really doesn't have anything to do with what a profile is. I have an old Curtiss P-40 model here that I acquired years ago that was probably built in the 1960's. It had a less than 1/2" thick fuselage aft of the high point of the wing, and it blends in very well with a fully enclosed inverted mounted engine and tank at the nose. The airplane looks pretty sharp and some one did a nice job with it. This was obviously pre-Al Rabe, or at least it looks like it to me, but I would not ever consider it a profile model.
   Type at you later,
    Dan McEntee

[BillLee]

It is hoped that this discussion will cause all to have a look at the the AMA rule book, for enjoyment and possible enlightenment. Unfortunately, every time I look once again I find something else "strange".

As an example, in the CL Racing Unified Rules, the order of paragraphs start out at 11, increase for a while, through 19, and then jump to 110. Then 111 through 113, and then back to 21. Not to mention subparagraph numbers that are nowhere appropriate for the paragraph number! Sheesh!

But for the subject at hand, the definition of "Profile" has always included a table specifying the widths.  I had to look, but it is still there. Up in Paragraph 7 of the CL General rules, not associated with paragraph 10 I quoted above.   

Attached here. Note, Dan, that the 3/4"  width is included there in various places, but no mention is made of applicability to Stunt. Looked over the PA rules and found nothing. Has PAMPA ever made a SIG decision? Bottom line IMHO: Local Rules Rule!

FYI: the definition of "Profile" has been in the AMA rule book for something on the order of 50+/- years. (At least.) Changes to it in that time: probably/surely. I was involved in making that definition  after the Oshkosh NATs where a Profile Carrier model was ruled illegal because it had a nose cowl reinforcing the usual weakness at the fuselage/wing joint, and it was discovered that there was no rule that made the definition.

Regards,

Bill

[Dave_Trible]

Bill as mentioned above PAMPA was not successful at the attempt to specify much of anything.    Actually PAMPA hasn't in recent memory ever actually made or changed ANY rules.   That has always been accomplished  by individuals making proposals directly to the AMA contest board.   What rules (unofficial and official) that PAMPA supports were to my knowledge created by others and simply adopted.   In other words PAMPA hasn't really been in the rules making business,  just adopting and following.

Dave

[Steve Helmick]

I'd suggest checking the NW rules on FlyingLines. What I recall is 3/4" thick aft of the wing TE, and that the motor mounting lugs must be visible. I think the latter has been pretty much ignored for electron powered models, but that is somewhat satisfied by having a cooling duct in the appropriate place. Mounting the battery so it can't fling out is more important...Velcro isn't to be trusted. Best idea is to mount the battery so that the access is on the inboard side. The other most excellent tip is to not have any screws going through the battery.  Steve

[Brett Buck]

Bill as mentioned above PAMPA was not successful at the attempt to specify much of anything.    Actually PAMPA hasn't in recent memory ever actually made or changed ANY rules.   That has always been accomplished  by individuals making proposals directly to the AMA contest board.   What rules (unofficial and official) that PAMPA supports were to my knowledge created by others and simply adopted.   In other words PAMPA hasn't really been in the rules making business,  just adopting and following.

Dave

  I think that PAMPA can't directly submit AMA rule proposals, they have to come from individual members. In practice, that doesn't really make any difference sine more-or-less everyone in PAMPA is an AMA member. And they are the ones who know what problems stunt might have and how to fix them

    If not, you can have a proxy do it for you if you can convince them it makes sense. I have been one of the more prolific submitters in recent years, batting 1.000 so far, and one of these was me acting as a proxy for someone else.   Several people have asked me to proofread or edit, or just consult on a change they wanted

     It's really easy to submit proposals, so no one should fear it if they have something. Writing a clean and simple rule or rule change is not so easy, there is a craft to it, and usually "less is more" is a good watchword. Kamala Harris-style "word salads" are common -  one of them, I suggested edits that took it from maybe 500 words to one sentence!  Ultimately that one was never submitted.

     Brett

[Steve Helmick]

It is hoped that this discussion will cause all to have a look at the the AMA rule book, for enjoyment and possible enlightenment. Unfortunately, every time I look once again I find something else "strange".

As an example, in the CL Racing Unified Rules, the order of paragraphs start out at 11, increase for a while, through 19, and then jump to 110. Then 111 through 113, and then back to 21. Not to mention subparagraph numbers that are nowhere appropriate for the paragraph number! Sheesh!

But for the subject at hand, the definition of "Profile" has always included a table specifying the widths.  I had to look, but it is still there. Up in Paragraph 7 of the CL General rules, not associated with paragraph 10 I quoted above.   

Attached here. Note, Dan, that the 3/4"  width is included there in various places, but no mention is made of applicability to Stunt. Looked over the PA rules and found nothing. Has PAMPA ever made a SIG decision? Bottom line IMHO: Local Rules Rule!

FYI: the definition of "Profile" has been in the AMA rule book for something on the order of 50+/- years. (At least.) Changes to it in that time: probably/surely. I was involved in making that definition  after the Oshkosh NATs where a Profile Carrier model was ruled illegal because it had a nose cowl reinforcing the usual weakness at the fuselage/wing joint, and it was discovered that there was no rule that made the definition.

Regards,

Bill

Bill, what about that chart says or implies that it also applies to Profile PA? Seems to me that if it doesn't say so, it doesn't. Our own Dave Gardner essentially wrote our NW Profile Stunt rules and said he based the 3/4" thickness aft of the wing TE on the Profile Scale rules. I'm pretty sure we voted on that, somehow...probably online via Flying Lines Forum.

The two things that bother me are tolerences, if any. .750" is legal, but is .755"? What is to be used to measure this feature? The second is folks who decide to be cute and extend the flap fairings back halfway to the stabilizer. On the one hand, is it per the rules, and on the second hand, is a trophy in Profile Stunt all that important? I happen to think the rules are more important, if there was any doubt.  Steve

[BillLee]

Bill, what about that chart says or implies that it also applies to Profile PA? Seems to me that if it doesn't say so, it doesn't. Our own Dave Gardner essentially wrote our NW Profile Stunt rules and said he based the 3/4" thickness aft of the wing TE on the Profile Scale rules. I'm pretty sure we voted on that, somehow...probably online via Flying Lines Forum.

The two things that bother me are tolerences, if any. .750" is legal, but is .755"? What is to be used to measure this feature? The second is folks who decide to be cute and extend the flap fairings back halfway to the stabilizer. On the one hand, is it per the rules, and on the second hand, is a trophy in Profile Stunt all that important? I happen to think the rules are more important, if there was any doubt.  Steve

Steve, as I noted, there is no mention of applicability to Stunt.

Bill