JPO assess speed limiter implementaton issues?
 

As others have pointed out, the handwriting is on the wall - limiting jet speeds in a "definitive" fashion is the AMA hot button. I suggest the JPO take up the issue and form a technical committee to define and address all the issues associated with limiting jets speeds. Presumably the topic will be, uhh, speed limiters. Not everyone agrees they work consistently, let alone reliably, in all flight modes. But we have to get beyond that.

You guys (JPO) need to think way out of the box on this one. Don't just do a cavalier hand wave and point to one turbine mfgr's solution or an aftermarket add-on device as a fits-all. There are relevant issues pertaining to each and every installation; on each and every airframe, let alone where the pitot tube needs to go and where the reference needs to be...

Mike

RE: JPO assess speed limiter implementaton issues?
 

This is part of a post from another thread.
*******************************

The speed limit is a myth as well as any attempt to control it, and we know it. Dave Brown told just last Saturday that the 200mph limit was based on nothing, and was simply pulled out of thin air. The obvious solution is eliminate it, or increase it. Speed limiters are in the same catagory. No speed limit or a higher speed limit, and the limiter becomes a non issue. The PW raito could also be increasedd to 1.5 to 1 creating an additional solution. This is all with the pre-text that they really want a solution which is becoming less certain every day. The jet populaton makes up less than 1/2 of 1% of the total AMA membership. This fact alone will not adversely effect the insurance rates for the entire goup/membership.
aware.

RE: JPO assess speed limiter implementaton issues?
 

How's that evaluation of a "Fits All" speed limited solution coming along?

RE: JPO assess speed limiter implementaton issues?
 

Well Mr. Mike this is already in the works. Steven Ellzey has a couple of the currently available addon speedlimiters that he has been running some tests on at his lab at work. He is not necessarily testing them with each different radio system as much as he is testing the actual function and precision of the available units.

RE: JPO assess speed limiter implementaton issues?
 

MrMike,

It's not just "you guys (JPO)", we're all in this together. Solutions come from all sources......

RE: JPO assess speed limiter implementaton issues?
 

Let's all think about this a minute ------- solutions are being "fingered" out for problems that don't exist. Is it any wonder you can't get any two of us to agree as to what a solution should be. Let's keep things as simple as possible... if a problem doesn't exist why try to correct it? The best example I can think of is notice how NO ONE objects to having crash site fire control (water) available... Any regulation should garner 95% or better agreement of need, or it shouldn't be a regulation.... cause it won't be enforceable...
Lee H. DeMary
AMA 36099

RE: JPO assess speed limiter implementaton issues?
 

Lee,

The AMA EC are the ones dictating that they percieve a need for the speedlimiters. The "Turbine rules comittee" (for lack of a better term) are saying no we don't need speedlimiters. The opinion is that a single manufacturers unit that is NOT integrated with the ECU's and has NOT been tested with every radio/engine combination out there should also NOT be mandated for EVERY turbine powered airframe. The other side of the coin is that several of us that have had experience with this particular speedlimiter have had mixed emotions about the accuracy and reliability of this device. Anyone that cares to PM me I will go further into my personal experiences with some of the products by the same company.

RE: JPO assess speed limiter implementaton issues?
 

I brought this up before when speed limiters were all being touted as the cure-all. It's sort of ironic now how those who were in favor of them before now seem to be against them. I don't remember, who got us the current regs requiring speed limters if thrust goes over .9 to 1?

Anyway, a pitot based speed limiter will always have errors unless the pitot and static are located properly on the airframe. This often can only be located by flight test. Even then there can at times be significant error. That is why there is indicated airspeed vs calibrated airspeed. Some of the installations I have seen in models up close and in pics were located very poorly. This may very well be the supposed problem with the mini-hobby unit.

The speed limiter requirement will be at best a poor solution. Before everyone jumps on me, I don't know what the ultimate solution would be, but I am definitely against any additional equipment to be required in the model.

RE: JPO assess speed limiter implementaton issues?
 

Steve Elzey,

How about the "wetted perimeter" you discussed a long time ago? Why couldn't that work instead of a speed limited? No additional hardware required.

Mike J

RE: JPO assess speed limiter implementaton issues?
 

Well the word I have heard, is that if we cannot come up with a "definitive" way to control speed, SOME in the AMA hierarchy say they will move to drop to some ridiculous thrust level like 22 pounds or something.

RE: JPO assess speed limiter implementaton issues?
 

Well, I haven't been flying Jets as long as some of you, but I remember when the --- big thing for some ---at a Jet Rally was diving toward a speed trap straight down from a position almost directly overhead. Boy was that stupid, and pointless ---- do you suppose the powers that be still think we are setting up speed traps and doing speed runs? You also may recall we only had about 11 or 12 lb max of push available ---those speed run events --- with DF powered aircraft, I believe are the reason we live with restrictive regulations to this day!
My conclusion is speed can only be truly controlled by the attitude/willingness/maturity of the person at the controls.
Lee H. DeMary
AMA 36099

RE: JPO assess speed limiter implementaton issues?
 

Lee,

You hit the nail on the head! As far as the DF speed runs we were limited by what we could ultimmately get out of the fan/airframe combinations. Not so with turbines. I have not seen a speed run at a jet event for years so speed runs are really a mute point.

RE: JPO assess speed limiter implementaton issues?
 

Hi David, ---- yes as we all know the speed runs are gone --- and that's a good thing --- my point is the stigma of those days and those events might be the perception guiding the powers that be to this day... There are a few among us, those entering AMA scale events that are changing the general perception..... all these things do is go fast......
Lee

RE: JPO assess speed limiter implementaton issues?
 

Lee,

It's just plain and simple another case of some of the members of the EC not throughly educating themselves about jet modelling. I know at the Hearne, TX event last weekend that the JPO speed traps were set up specifically to measure the speeds. Not for attempted speed runs but to collect some actual data to support our position that the majority of the airframes out there today are not being flown at 200+ mph.

RE: JPO assess speed limiter implementaton issues?
 

In the last few jet events I have been to, there was a speed trap set up. It was used ONLY for the slowest flight of any jet at that meet. I think that the jet community, in general, is very safe and responsible regarding speed limits. I do hope that the AMA can allow themselves to recognise that fact and take it into account when making such rules.

As suggested here, the best speed limiters are our gray cells.....I know I use what's left of my gray cells[8D] when flying jets.

RE: JPO assess speed limiter implementaton issues?
 

I have a question...

The thrust to weight rule has been around for many years...

How many here, have ever seen a planes' thrust measured, then weighed... ?


Anyone.. ??


I know of one case where a cat showed up with a Pegasus on a Kangaroo and
was correctely told to test fly that thing after the event.


Eddie Weeks

RE: JPO assess speed limiter implementaton issues?
 

Why not?

Can't the tailpipe velocities of turbines be tailored by the manufacturer? For example, do turboshaft engines such as are used by turbine powered helos or turboprop engines produce thrust? Couldn't a diffuser tailcone be employed to limit the tailpipe velocities to, let's say, 250mph without affecting static thrust?

Dan

RE: JPO assess speed limiter implementaton issues?
 

I agree with you 100% on this. I think that a pitot-based speed limiter (or really any other limiter, even one based on GPS, or a combination of the two), is just another thing to go wrong, and in this case, it has the possibility to interfere with our control of the model. In this sense, it can actually decrease safety!

We need to be proactive in killing the requirements for speed limiters. Call your AMA District VP (I've already done so several times and will again before the Feb. EC meeting) and explain to them your feelings on speed limiters. Also remind them that ANYTHING that is required to limit speed can be defeated by a modeler who wants to do so, so the best method is to put the onus on the pilot and leave it at that. My reading of the EC from my District VP is that Dave Brown is in the minority on the speed limiter issue and he's the one that threatened the "22 lb. thrust limit" if something wasn't done. However, he can't make the rules without the approval of the EC - let them know what the facts are and what your opinion is!!!!

Bob

RE: JPO assess speed limiter implementaton issues?
 

Correct me if I am wrong, but isn't HE (Dave Brown) the one that got the whole set of rules "put into abeyance, suspended", whatever you want to call it.

Some of you guys treat Dave Brown like he is a loose cannon, but he managed to OVERTURN (or stop or suspend or put into abeyance) the new rules basically on his own force of will....will he do it again? You guys act like he will not be able too....what do you base that on? THe 25 emails the ENTIRE EC has receieved so far, versus the 170K members that DB can appeal to each month? Get real...

To me he is the big dog in this, I just don't understand the "take no prisoners" attitude some of you are taking, to the point of claiming speed limiters have some
fatal flaw in order to FORCE the EC to drop the T/W limits!! Do you REALLY think that the next time around Dave Brown will just cry "uncle" and let us have 45 pound limits with no "definitive" control of the speed....do you think he pulled the word "definitive" out of the air??

Save your breath, a lot of you have written me privately that I am overreacting, and that Dave Brown will be handled by the EC (same EC that put a new set of regulations "in abeyance" about a week after they voted on them).

A VERY dangerous game many of you are playing, IMHO. My friend "Cougar" here is wondering what he will do with his new toy if you guys are wrong.....$5K paperweight I guess.

RE: JPO assess speed limiter implementaton issues?
 

Matt,

Dave Brown does have the power to call a special session of the EC (as he did) and does have quite a bit of sway over the EC. However, the EC members are elected by their districts, and mine at least has told me that he will do what ever his membership tells him it wants - as it should be. I am not saying that Dave does not have the largest influence, but it also does not mean that we should just roll over and die because he wants us to. His opinion on this issue is wrong, and we should work to overcome this, not just acquiesce to his demands. Lets let our EC members know what the opinion of their members is and let the process work as its supposed to.

In my opinion, it is not going to be possible to make a speed limiter that is accurate and foolproof, and I don't want one on my airplane. I have not spent 500+ hours, with another like amount to go, on my Panther to loose it on takeoff when the speed limiter cuts the power at the wrong time - especially when the d&%! thing won't go 200 MPH downhill in a hurricane! Its just a stupid solution to the problem. Does "Cougar" want his ride to have that same potential for disaster, and if it did happen and hurt someone or start a forest fire, does he think the jet community wouldn't be in the same mess as it would if someone crashed at 201 MPH and did the same thing?

The guys on the safety committee and the EC I've talked to think that we have a good chance to pass the rules again as they were the first time without adding a "speed limiter for all" requirement. Let's give them a chance and our support to see if they can make this happen...

Bob

RE: JPO assess speed limiter implementaton issues?
 

I agree 100%, Tony. I'm hoping the JPO, as the recognized SIG for the R/C jet world here, will do the necesary homework and present compelling arguments to the AMA against the need for speed limiters. We seem to know the answer already but I want JPO to come to that conclusion and have the data to back it up.

You have already touched on one of the biggest problems: appropriate placement of dynamic and static (air) probes - not everyone will get it "right" and if they do it will be through a process of elimination through trial and error. Then there's the control loop compatibility of the speed controller with the turbine's ECU: there's the need for a little anticipation (or delay in some cases) depending on which "flavor" turbine is being controlled ... If you don't do it right you run the risk of an unexpected unstart - OSOD.

Also, the use of the word "definitive" and its interpretation(s) really puts us in a box.

Mike

RE: JPO assess speed limiter implementaton issues?
 

Boy, I sure hope you guys are right......

We have had speed limiters as part of the rules for YEARS now....now all of the sudden, to keep them from being mandatory on ALL planes we are going to burn them down and basically say they do not work....this can of worms might get them ALL banned. We should be very careful of the classic rule of "unintended consequences"!

IMHO, I think the final (rules) solution will look almost EXACTLY like it does now......there will be some rules changes here and there, but for the high thrust to weight installations, you will need a speed limiter, just like the one I have flown on 3 different planes for about 1000 flights without a problem.

I believe they work, and all of the rhetoric that they do not is very overstated. They need to be carefully designed, and carefully installed. IMHO there is not a unit on the market now that works as well as the fully integrated unit. However, I do believe that one could be made that would work acceptably on all of the turbines if the market demanded it.

I also hope that speed limiters are NEVER mandatory, but I genuinely believe they will need to be available as an option in the rules. I cannot see Dave Brown agreeing to a 45 pound thrust with no "definitive" speed limit.

RE: JPO assess speed limiter implementaton issues?
 

Again, no offense intended to anyone.

I fully support the JPO proposal, and I have indicated such in 2 correspondences with my AMA EC District VP. I have also joined the JPO as a result of all of this, as has my girlfiend.

I just do not want to see the speed sensing technology take such a beating and possible have them banned.

RE: JPO assess speed limiter implementaton issues?
 

Matt, I don't either but the fact is ONLY JetCat - as far as I know - has a solution that's as integrated as it gets for at least the stuff they control. Otherwise, I'm not sure how many understand just how important the placement of the pitot (and reference air) is - you can't just slap 'em on the airplane and go fly. I know JPO's technical-minded mavens can't evaluate or check all situations/installations but that's just my point: speed limiters by themselves are not the be-all, end-all solution.

Mike

RE: JPO assess speed limiter implementaton issues?
 

Matt,

I have also put at least 1000 flights on airplanes with the jetcat speedlimiter installed and think it functions very well but it is the ONLY fully integrated unit. Perhaps if the other turbine manufacturers had the integrated system it would not be a big deal. But currently there is only one. Also there is only one aftermarket speedlimiter that is supposed to work with all systems that is currently available. If there were more than just that one speedlimiter out there maybe there would be far less concern that speedlimiter might be another potential flameout waiting to happen. As far as the higher thrust engines and speedlimiter issue goes, who is to say that the higher thrust automatically equates to higher speed?