turbine clutches

[hornblower]

I just found out some turbines have a clutch and some do not. I am confused. my benzins must have a clutch to start the engine whilst holding on to the head, or it would stall. But if I have an electric start two stage turbine, is a clutch essential or just a bonus?

[uberlution]

A clucth is not essential on a turbine I have been operating my turbine for nearly two years without a problem. It could be considered a bonus if you wanted to make any adjustments without shutting it down,but the way i see it is by the time you have made any adjustments the engine will have cooled down, & with autostart you don't need to take it back to the pits to re-start just light it up & carry on.

[chopper jockey]

well we`ve all got used to having a clutch now haven`t we. We are all used to having the engine idle when starting and then carry it to the flight line. Clutches are necessary for IC engines and single stage turbines. With the advent of the second stage however, a clutch merely becomes a usefull, but not a vital accessory. The advantage of having a clutch is you can stand really close to the turbine when it`s idling, even make adjustments to the blade tracking etc, which is fine if you like doing that sort of thing with the turbine running! The advantages of a clutch-less 2 stage system though, less parts to go wrong, therefore more reliable, lighter weight and simpler design, just like the full size. It can be a pain in the butt when setting up for the first time, but when set up the lack of a clutch is not a problem. Most designs however do have a clutch, which is fine and not really much of a penalty anyway. IMHO :)

[Heli_jack]

Well here in the states our governing agency regs state that the blades must come to a stop at an idle. That kinda makes a clutch mandatory here. I am currently waiting for clarification from them on this very topic.

Would a brake on the main injure the second stage?

[chopper jockey]

I don`t know about state side, was that rule brung in before electric start and 2 stage turbines arrived? Also if a brake was used I don`t think it would harm the second stage wheel if the revs were low enough, say idle rpm of 32,000, for a short period of time. I suppose I could try it and monitor my gearbox temp indicator, then we would know. Anyway, why would your governing body insist the blades have to stop turning whilst the engine is idling?, what`s wrong with just stopping the turbine? with auto start it`s a doddle in any case? :?

[DavidH]

Well here in the states our governing agency regs state that the blades must come to a stop at an idle. That kinda makes a clutch mandatory here. I am currently waiting for clarification from them on this very topic.



Really no clarification is needed. These rules were amended by the AMA EC on 10/15/05. So I would think they are the latest requirements.

Here is what page 2 of the Safety Regulations for Turbines in Model Aircraft.

For rotary wing aircraft: The rotor head must be disengaged from the power source and
remain stationary when the engine is at idle.

http://www.modelaircraft.org/PDF-files/510-A.pdf

Just my opinion. But all the regulations in the above document are pretty clear to me. Doesn't seem to be in any grey area to any of them.
Personally I don't see the turbine helis as being any more dangerous than a glow model. But I would guess due to our lawsuit happy society here in the USA. That AMA has to put regulations out there to cover there ass's also.

David

[cbergen]

I think where the problem comes in, David, in is the 2 stage system like the Wren, the rotor system is ALWAYS disengaged. There is no direct drive from the Turbine shaft to the rotor head.

The first stage (gas generator) drives the second stage(or interstage) and gear box with air pressure only.

It could be argued(not that I agree with it) that a low enough air pressure(low enough idle) will not turn the second stage, therefore not turn the rotor head.

I would be concerned that the heat generated from the Gas generator would cause harm to the second stage if it wasn't spinning........

Therefore we installed a clutch system in the Intrepid Turbine, now there is NO question as to meeting the regs, and being able to adjust anything on the bird without having to worry about the blades hitting you in the head (Gary!!) while the turbine is running. It's no more complicated than any other helicopter on the market with a clutch system.

[wolfdad]

Chris/David,
I think the AMA made the wording very specific in the 10/15/05 update/changes and that they carefully chose the words "the blades must be stationary at idle" to include all turbines regardless of configuration with or without clutches.

Chris, I think you and I among a number of others who understand the "no mechanical link" between the gas generator and second stage on the two stage turbines, however, like you, I think that holding the second stage completely still while the gas generator section continues to run is potentially damaging and, after giving it a lot of thought, I don't believe the "no mechanical link" is a valid argument any longer. Quite honestly, I think we are looking at operating with clutches in the future regardless of two stage or thrust type turbine configuration. And, quite honestly, and even though I am sucking mud with one of my aircraft, I think the AMA is on the right track with this from a safety standpoint.

So, we adapt and overcome.
Doc

[Heli_jack]

I had a set of emails with AMA reps regarding this. There is not a demand for a clutch, just that the blades are at standstill at idle. They are firm on that. There only way to effect a change is through the exectutive committee and all sorts of work, so I think I would just make sure the blades are at standstill at idle.

My system you don't have to worry about that anyhow. I would think that it would be bad for the second stage turbine wheel to not turn, but I know nothing.

Regardless I remember the day that turbine was not allowed at all.
Jack

[wolfdad]

Jack,
Your CRS is far better than mine :wink: . Just kidding....I, too remember when turbines were not allowed, period and no questions asked. I think the entire heli community has made a "quantum leap" during this past year, however, along with a more pronounced understanding and, along with that, a lot more press, all involved are getting a lot smarter about turbine heli's.

Like you, my BK is not affected and, quite honestly, looks very scale as it sits at idle, then starts spooling up....in fact, it is really hard to tell the difference between the scale BK at full RPM and the full-size replica :wink: . I love the two-stage Wren's, however I just continue to be more impressed with the Jaka.

The wise folks at the AMA held off on their decision during previous years with regard to blades being still at idle until they developed what I consider to be a solid understanding of the dynamics involved and, even when they came out with the rule, they chose to word it very carefully and, in my opinion, very wisely. They did not dictate clutches to us, but simply said, "the blades shall remain still at idle RPM." How we choose to do that is now up to us.

By the way, somebody has a birthday tomorrow, 4 March. HE shall remain nameless, however his initials are Dr. T. HAPPY BIRTHDAY Dr. Tim...OOOOPs
:wink: Doc

[chopper jockey]

Doc,
would you interperet that as meaning you can hold the blades static with your hands, whilst starting? that`s if you want to idle, because with an idle of 32,000 rpm that`s easier than at 45,000. Then no more idling untill shutdown... :?:
Thinking about it though, I rarely have mine at idle anyway, I just start up, wind her up and go fly, then when finished shut her down. :D

[wolfdad]

Phil,
Not trying to be a smart-a$$ or anything, however I interpret the AMA rule as the blades being still, on their own (no hands allowed) at idle RPM.

Now, let me tell you a little story that you alone will appreciate, along with a caution. I have been starting my TurBen (Hobbyparts Benzine conversion) with external gas for some time now (since last summer). I got behind the power curve in getting the external gas disconnected and attempted to hold the blades long enough to disconnect the external gas....the operative word here being "attempted." For those who have not experienced this situation, in a word "don't!" You cannot hold the turbine by hand....period....don't care what anyone else tells you and, if they tell you they have, I would have some serious doubts as to their credibility....it ain't gonna' happen. I realized this fact rather quickly and backed out of the rotor arc, let the aircraft spool up, then shut it down and re-started and, stayed ahead of the aircraft in removing the external gas.

Like you, Phil, I have always spooled up, let her stabilize at ground idle, taken her on up and went flying.

The AMA, in my opinion, very wisely stayed away from the word "clutch," however, with a two stage, trying to hold the blades is NOT the way to go and, although a bit tricky and involving some prior planning, I can SAFELY start the TurBen on external gas.
Doc