Michael,

I am well aware of the limitations placed on Giant scale racing with regard to the distances etc... but nowhere in the documents that you pointed to do they mention anything about speed. It also appears that the majority of those regulations are placed upon the aircraft construction as well. Most of which no experienced modeller would ever attempt anyway, Nyrods on a giant scale racing plane?? There is no verbage to restrict the speed just make sure that your servos are a certain torque. And what happens if that is not sufficient? And who is writing the giant scale rules? The same antique bunch of rubber band twisters that are trying to regulate the jets.

Well, I guess Ill jump in now,

Matt, you have noted many, many, times the success with your JetCat speed limiter. You stated that it has worked for more than a 1000 flights. I was just wondering what the indicated versus calibrated speeds were on the models that you have !QUOT!tested!QUOT! for those 1K flights. To say that it worked is really saying that it hasn't caused a crash ...yet. You don't really know how fast you really were flying. How often should we be required to calibrated these systems? And what about the liability to the Mfg. when it is determined through video that the model that hit the bus load of nuns was actually doing about 207...or so? And we rely on the limiter to keep us in strict compliance with the AMA insurance limits. I realize that we have some sharp guys in this hobby, but ponder this. A few years ago an airplane builder named DeHavaland of Canada who has been in the game for quite a while, designed and built the!QUOT!next generation!QUOT! turboprop called the Dash 8. What does this have to do with jet modeling? Here's the connection. These guys at DH put the pitot tubes and static ports exactly where they should have been according to years and years of experience and testing. But there was only one problem...the system was highly inaccurate. So the guys with the pocket protectors and TI calculators spent months and $250,000 (that's U.S. dollars) redesigning the WINDSHIEL WIPERS so that they didn't interfere with airspeed readings. I'm not an engineer, aerodynamisist, or hell, even Canadian but I don't want to think about installing the system.

Now let's just say we iron out the accuracy issues. If we want to limit the speed to any value, why don't we do what the auto industry does. Give us or require us to carry an airspeed indicator just as tp777fo mentioned. It could be configured to sense the speed and then transmit an aural warning telling us to either look for the cops....Uh, I mean pull the throttle stick back or pull up or both when we approach the limit.

I don't want another failure point in the airplane. No speed limiter of any design will eliminate a crash of any kind...period. It's up to the pilot to maintain 200 or less

Enough for now,


John

!!How do you think the speed limiter that tp777f0 mentions works!!


Same pitot tube and static sensor I am talking about!! Funny

Yeah, Matt....I was gonna jump all over that one but decided to let you handle it since it was directed at you. I guess that GPS is the only real way to get an accurate ground speed if the refresh rates were fast enough...Just more crap to worry about.

Kevin

Gordon/David/All -

My point is simply that jets are not the only ones being regulated in some form or manner. Not to compare whether or not apples and oranges taste alike. I think many feel the pain of their form of R/C being placed with additional limitations in the past few years. That's all I'm trying to say. It's not just being applied to jets.

On the giant scale racing rules, the racing leagues, just like the JPO has done with AMA, have had to argue with each other for some common ground. Many think that the AMA does not want racing at all... Obviously some have the same opinion for jets.

If we were to say speed is the limiting factor in the equation of AMA, then all planes should have speed limiters. How about the diamond dusts and quarter midgets up there?

I was just at the local shop looking at Jet Power International... Pipes designed for afterburners? What a difference the ocean makes. Obviously we live in a litigous society.

If SFA were still around today, I would bet things would be different.

Michael

Hey Matt,

Relax with THE FREAKING BOLD PRINT! Re-read the post..........I qualified the concept of the INDICATOR with the statement, "Now let's just say we iron out the accuracy issues."....got it? You haven't addressed the issue of installed accuracy with your so-called "working system". We are nowhere near ironing out the accuracy issues...that's my point...just stop plugging the JetCat system for awhile and think about the BIG future picture. GPS is probably going to be the answer...if we want to go there. How about "we" stop overpowering these things and try to fly under 200 on purpose using our judgement.............Again...no speed gizmo will eliminate a crash. If you or Kevin have any other questions about aviation or the use of the English language, just PM me.

Regards,


John

FYI: If the Fiorenze airspeed sensor only has a pitot tube (not a combined pitot-static) and senses the static port from inside the fuselage, there is potential inaccuracies, especially given if the plane is an internal turbine where pressures fluctuate inside the fuselage.

I can agree with many as the speed limiters will not be totally accurate, but place some limit on speed, given the quality of installation.

Michael

Who determines the quality of the installation? Do we have the system re-calibrated after every maintenance action and/or 24 calendar months whichever comes first......YADA, YADA, YADA.....???? I guess we could build a super accurate system that reads airspeed and then up-links to a satellite which is interrogated by The AMA (and associated insurance claims adjusters) to identify any violations...Hmmm what a way to collect AMA revenue! Requiring everyone to have a speed limiter is just as ridiculous...

John

BTW, we have a working GPS speed sensor too, although something tells me you do not care about that either.

Matt
Slow down, take a deep breath...maybe eat a sandwich (like the nuns used to tell me when I was upset). I have "cared" about this hobby a very long time. If you ..ugh..once again re-read my post ...s-l-o-w-l-y this time, I stated that I thought that GPS was probably the way to go. Somehow I think that you don't listen very well....Oh, and Bravo to JetCat for the forward thinking regarding GPS.

The more gadgets that we a required to have, the more failures we will endure and the less attractive this HOBBY will become. We should just promise to stay under 200 and face the consequences of exceeding the limit. If a person wants to rely on a speed limiter, then make it at their own discretion, not a mandate. Remember the number one rule...FLY THE PLANE.....+

oops! I see that you edited your post. So now I'll edit my response to your edited ranting.

Tailwinds,

John

AW shucks....I take it all back!

After seeing this picture, I now realize that I can have a scale jet AND get some reeeealyy awsome pitot/static air data for just about any speed limiter...


John

Hi Matt,
Your comments about static/dynamic is spot on of course. I have done many hours of datalogging on a current RPV project where we use GPS and airspeed extensively. The autopilot we used unbeknown to us actually used different sensors for alt(static) and dynamic. After finding discrepancies and dismantling the autopilot we found the dynamic sensor to pick up static from within the unit..... At different aircraft pitches the airspeed would vary quite a lot from GPS during level flight, probably due to ram/venturi effects on the various retract wells etc. Also GPS would give wild errors on anything more than 30 deg from vertical orientation of the antenna. I base this on a few MB of datafiles we collected.
If the speed limiters are to be of any value a proper dynamic/static pitot tube is absolutely a requirement.
As an example, if a fuselage picked up static pressure from a forward facing hole of some sort the airspeed could seriously under-read. The opposite could also happen when picking up static within the fuselage.
Cheers
Andre Baird

EXACTLY,

If, if if ...ad infinitum.......case closed.


John

Michael,

Exactly and I agree fully that all of us see our particular branch of the hobby as being over regulated. Let us get out an have fun with our models. The fact is that the high perfomance end of the hobby attracts the same people that are attracted to fast cars....etc....oftentimes even when they are not high performance pilots. I believe that the AMA is trying to make a generic set of rules that will apply to everyone and it limits the individuals that have the necessary skill set, and experience level and does little to prevent the checkbook pilot from wrapping up an airplane.


JPO's thoughts EXACTLY!

I also have an extensive amount of time with the Jetcat speedlimiter, and the GPS installed in the same airframe. I have also (at the risk of being chastisied for doing speed runs) flown the same airframe through the JPO speed traps on several occasions. THe GPS gave the most inaccurate results when compared to the other two. THe speedlimiter and speed traps agreed most of the time within a few mph. On this particular airframe the pitot is on a short standoff from the side of the fuselage. Just out of curiousity how much variance do you think we really are seeing with the different installations of the same speedlimiter?

Hi Andre,

Can you rig up a double wall Piot/Static tube, and run the reference port from your current fuse reference to the tube? It seems to work well for me.

I found a picture of the one I had on a BVM F-4. I worked well in the scale fin location. Noce the static port is located on the outside section of the double wall.


And John, I think we can agree that if either of us were AMA Presidents we would not have mandated speed limiters.

David,

I have absolutely no experience with the JetCat setup. My experience is with "speed limiters" of a somewhat larger scale! I would imagine that the JetCat equipment is of the highest quality and accuracy available based on the company's reputation. My point is that I don't have any idea and most of us won't know what the variance is yet, we may be held RESPONSIBLE (in principle) for the accuracy. I am against the requirement for a speed limiter of any sort, in principle. How many years have we been putting fuel tanks in model airplanes? Uh...a lot! Anyway, I still see or hear about flameouts due to "a fuel tank problem". Now EVERYONE is going to be expected to engineer, install and maintain a pitot/static system in order to stay within an insurance limitation...Ya right! Go out and do an outside whooferdill and pinch your static port line and see what happens then.

And now for a "what if" scenario: How long do you think it will take for one of these individuals that I read about here on RCU with "marginal" abilities to RELY on the speed limiter for aircraft control? They will just say when questioned about excessive speed, "Uh, I got the thing set at 195, what's YOUR problem?" Then, when they become accustomed to bending that left stick (mode 2) all the way forward and the pitot line kinks, lookout! By the way, this type of pitot/static anomalies have brought down FAA certified and maintained aircraft in the past.

And yes Matt, we do agree on the mandate issue.

Let's keep this thing FUN,

John

That's 2 things we agree on!

Oh..I'm OK now. I just found a "configuration" for my Viggen that may work with a speed limiter. check out THAT pitot probe!

Matt' If you think THIS is bad, just try flying all the way across the country with me while discussing politics and religion in a seemingly smaller and smaller cockpit!


John

Religion---Politics??? I would be looking for the ejection seat handle---And not for myself... Since it doesn't have one I guess I would just go to the back and talk to the female flight attendants!!![8D]

John...At least we agree that this hobby needs to be fun!!! I have to respectfully disagree with you that the JetCat speed limiter does work as advertised. The JetCat unit reduces the thrust of the turbine in a controlled manner (unlike the other unit) when the pre-set limit is reached. It wasn't designed to keep the airframe to an absolute top speed or to prevent a pilot from deliberately exceeding VNE in a dive. Since it is pitot based it wasn't intended to limit the speed as read from the ground, nor able to compensate for a headwind/tailwind. If you wanted to limit the airframe to a true 200 MPH airspeed as measured from the ground then you would have to ask to speed limiter to do more work---Deploy speedbrakes for an example....Not to mention having it possibly tied to a GPS system.

The JetCat unit works well and follows the KISS principle. Asking it to do more as in maintaining a true airspeed as measured from the ground or to deploy speedbrakes defies the KISS principle, not to mention the high price you would pay for an elaborate unit like this. The pilot is ultimately responsible for the speed the model achieves....When flying a turbine powered model and it "knocks" on the speed limiter, I have the responsibility and maturity to back off on the throttle....Not to just let the model continue to exceed the VNE. Again, this all points to us regulating ourselves which most of us seem to be adequately doing. Just my .02....

Kevin

Kevin,

I'd go back and talk to the female flight attendants too....if I cauld find one! Oh ya, I forgot, I can't even do that anymore....................s-u-c-k-u-r-i-t-y..you know. So I just sit in my place and torment the Fisrt Officer (only if he is'nt a modeller)

HAPPY HOLIDAYS,

John

Hi Matt,
The way you have it on the F4 is as good as any. The step may be a bit of a error on the double wall side maybe. On full size aircraft a static port directly on the fuselage works well if the surface ahead of the port is clean and a good boundary layer is present. In other words the pressure within the boundary layer is measured. Not an expert but it would seem that this may require calibration of some sort. The secret to good static pickup is to have smooth airflow around where the pickup is. If it is to work in all airframes without calibration the only way is with a bullet nosed pitot and four small crossholes about 2 - 2.5 of pitot diameter back. This is how our pitot is made and pretty much the same I think on the JC. Static within a fuselage is NO GOOD. On our RPV we plan on adding another static port for the differential pressure sensor. Our Hotspot testbed is easily capable of 250mph+ so speed limiting is in my opineon a good idea for the less than carefull....

Cheers
Andre Baird