BETA Range

[uwochris]

Hey guys,

I have a few questions regarding BETA range. First of all, during BETA, are the props at a negative AOA, or, are they close to 0 degrees (but not quite 0)? I figure that the props can't be at a negative AOA, as this would make taxiing impossible. (i.e. correct me if I'm wrong, but the only time the blades are in a negative AOA are during reverse thrust).

Second of all, according to The Turbine Pilot's Manual (pg. 33), the author claims that "Beta range allows prop pitch be reduced to zero-thrust settings..." If the props are set to zero-thrust, then how is it possible that the a/c can taxi? (i.e. isn't thrust (or any other force for that matter) required to make the a/c move forward?).

Thirs of all, do all turbo-prop a/c have a beta valve? Is it ever possible for the governor to bring the props to a very low pitch setting, or is a beta valve required to do this?

Finally, I always notice that while Dash 8s are taxiing, one engine appears to be idling, while the other is not. Is this done to save fuel? Do other turbo-prop a/c require this same taxi technique?

Thanks in advance,

Chris.

 

[avbug]

Beta is everything beyond the low pitch stops. The degree of the low pitch stop varies with the propeller, but when the low pitch stops are removed, beta controls the governing from that point on, right into full reverse.

Sometimes beta and reverse are referred to as two different functions, when in fact they are not. Beta is the entire range of operation beyond the low pitch stops, while reverse is only that range in which reverse thrust is effected.

The ranges or values vary with the engine and propeller.

Typically some forward thrust is still available in the early stages of beta; often it's used to reduce forward thrust or even provide some braking action (in lieu of using the wheel brakes).

 

[Bongo]

I wrote this before AvBug posted....grrr

Hey Chris,

Beta range occurs any time where the blade angle is controlled by the power levers, and not the prop levers.

As far as zero thrust goes, once you begin to taxi forward, the props can be brought further back into the beta range, to the zero thrust setting and the airplane will continue to move in a forward.

For dash 8's feathering an engine, (usually the left engine) this started at Nor Ontair, for the long taxi in YYZ. I believe the prop must remain in a feathered position for 30 seconds before the engine is shut down. I haven't noticed any other aircraft doing this, so I'm not really sure. We used to do it on the twin otter down in Haiti to make fun of the dash 8 guys. The one engine taxi on startup is fairly common if you are moving to pick up passengers only a short distance away.

I think when the Dash 7 first came out, people would only start two of the four engines, then start the other two when holding short. I'm not 100 % sure about that, somebody with far more time will undoubtably point out if I am wrong.

Cheers,

--Bongo

 

[Donsa320]

, but when the low pitch stops are removed, beta controls the governing from that point on, right into full reverse.

Av, I liked what you said except the part above. I'd say.... BETA controls blade angle directly while the rpm is contolled by the fuel control in response to throttle position and movement while in the BETA range. For any throttle lever position selected, a corresponding prop blade angle will be set and a given fuel flow to support that will occur.

So unlike our old reciprocating engine reverse where selecting reverse sent the prop all the way to full reverse pitch almost instantly and you better follow up with a LOT of throttle or the engine(s) would stall and quit, eh?

Don't ask me how I know. <grin>

 

[uwochris]

Thanks for the responses.

Bongo: you wouldn't happen to fly with Borek would you? I'm a Canadian pilot too (living in CYXU) doing aerial photography. If you're flying in Africa and are not with Borek, are you working for Mr. Deluce?

Thanks,

Chris.

 

[Bongo]

Hey Chris,

I was going to post a pro Canada comment in my reply, but decided not to. I read AvCanada a fair bit, but don't post as much as I should. I was flying the twin otter down in Haiti, not with Borek though. The company I worked for had both twin otter's and dash 8's.

I haven't worked for Mr. Deluce, but have worked with someone who worked for him while on lay off.

Best of luck with your career, too bad the dash 8 thing didn't work out the way that you wanted it to.

Cheers,

--Bongo

 

[pilotyip]

Remember Beta is flight is a big No No, like they rarely recovery the bodies.

 

[EagleRJ]

The Dash-8s taxiing with one engine feathered may be doing something similar to the Saab 340. When the Saab is on the ground in warm weather, it's normal to use high-pressure bleed air from just one of the engines to run both packs, instead of the usual low-pressure bleed air from both engines. The ITT is very sensitive and unstable when you're doing this, so the engine is normally feathered so it can't be used for taxi thrust.

The Saab's AOM has a statement saying something like, "selection of reverse pitch in flight will cause uncontrolled engine acceleration, engine power loss, structural damage, and uncontrolled flight". In other words, Bad Things!

 

[tranceport]

I miss flying the dash 7. I don't miss the days of trying to learn and explain what beta range meant.

Beta = props backwards. there. that's easy to remember.

 

[enigma]

"Beta" is a prop thing, and props are for boats. So what's this question doing on an aviation board?


Just kiddin, good question as usual.

BTW, have you ever asked about jet pumps or the theory behind an ACM?

enigma

 

[pilotyip]

Anyone can fly a jet, it takes a real pilot to fly a prop airplane

 

[enigma]

Anyone can fly a jet, it takes a real pilot to fly a prop airplane

Now, I'm wondering why Gulfstream and their 1900's haven't killed anyone, yet UAL/AAA/AA/DAL/NWA/CAL/etc have had fatal accidents? Pardon the poor grammar.

just yankin your chain. If I get the DTW airbii bid, I'll look ya up.

enigma

 

[I.P. Freley]

BTW, have you ever asked about jet pumps or the theory behind an ACM?

I didn't, but I was involved in an interview once where another fella on the board asked the interviewee:

"What electrical bus powers the jet pumps?" on the Metroliner (the interviewee's logbook claimed many hundreds of hours and possibly a type, but I don't remember for sure, in the Metro).

Answer?

"Uhhhh, I don't remember for sure, but I think it was the main bus."

Let's just say he didn't get the job.

 

[Buschpilot]

The Dash-8s taxiing with one engine feathered may be doing something similar to the Saab 340. When the Saab is on the ground in warm weather, it's normal to use high-pressure bleed air from just one of the engines to run both packs, instead of the usual low-pressure bleed air from both engines. The ITT is very sensitive and unstable when you're doing this, so the engine is normally feathered so it can't be used for taxi thrust.

Do the Saab's have the same engine as a Dash? We only feather the props for the 30 sec cool down. That's it. On the other hand, I have seen other operators taxiing out with one feathered. I assumed it was to reduce fuel flow, but I really don't know.

 

[I.P. Freley]

Do the Saab's have the same engine as a Dash? We only feather the props for the 30 sec cool down. That's it. On the other hand, I have seen other operators taxiing out with one feathered. I assumed it was to reduce fuel flow, but I really don't know.

Nope. Without researching it, I believe the Dash has Pratts. The Saab has GE's. Basically a helicopter engine on its' side, at least in the A-model.

 

[SuperFLUF]

Inflight BETA = BAD

Here's a little story about what happens when you ingore the POH, just because it worked in the last airplane you flew.

http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001206X00741&key=1

http://www.ntsb.gov/ntsb/GenPDF.asp?id=DCA94MA033&rpt=fi

If anyone remembers the full story on this one, I think the CA flew the Shorts before the SAAB and BETA ops were approved or the norm for that airplane.

 

[English]

Isn't this the accident that led Saab to install the flight idle stop?

 

[I.P. Freley]

Yes, I believe it is.

 

[English]

I can't believe I remember anything about my first love

 

[I.P. Freley]

Heh heh heh... Occasionally, I still call out my first love's name during, uhhh, approach...

"Flaps 17!!"

 

[English]

classic...

 

[avbug]

While I wouldn't do it, I know folks descending after dropping jumpers in King air's that use beta on the way down. I've been known to use beta just above the flare at the runway threshold on short fields in a King Air 200. There are those who decry running over the gate with the nosewheel in the air too, to which I disagree. On ice perhaps...but not on dry cement.

Coming past the gate to plant the airplane can be done gently, and is a similiar short field technique to bringing up the flaps in the flare to accomplish the same purpose. At high speeds and/or reversing, no...but low speeds down low, yes; operational technique.

 

[91100 100 set]

Occasionally, when you see a Dash taxing around with an engine feathered, it could be because the engine ECU is inop. With the ECU working normally, it keeps the prop out of the prohibited range (500-780 prpm if I recall correctly), without the ECU, the unfeathered prop will run rightin the middle of that range unless you push the power lever up a fair bit (too much thrust to taxi around with). So you must run it in feather until you're ready to push it up for takeoff, and then feather it again clearing the runway. At ALG, we could dispatch like this (with one engine ECU inop), but not if the runways had ANY contamination, or any surface had any FROZEN contamination (again, if I remember correctly) because you'd essentially be taxiing around single engine. In five years, I think I only saw 2 or 3 inop ECU's, and it was kind of a hassle, but more so inflight, especially on approach, because the power levers would end up being split quite a bit, and each engine would respond to power lever movements differently, so the approach was very often a little crooked (but not enough to notice unless you were actually flying).

Other times, it's just common practice to save a little fuel. The fuel flow difference is negligable in my opinion.

 

[LearLove]

Occasionally, when you see a Dash taxing around with an engine feathered, it could be because the engine ECU is inop. With the ECU working normally, it keeps the prop out of the prohibited range (500-780 prpm if I recall correctly), without the ECU, the unfeathered prop will run rightin the middle of that range unless you push the power lever up a fair bit (too much thrust to taxi around with). So you must run it in feather until you're ready to push it up for takeoff, and then feather it again clearing the runway. At ALG, we could dispatch like this (with one engine ECU inop), but not if the runways had ANY contamination, or any surface had any FROZEN contamination (again, if I remember correctly) because you'd essentially be taxiing around single engine. In five years, I think I only saw 2 or 3 inop ECU's, and it was kind of a hassle, but more so inflight, especially on approach, because the power levers would end up being split quite a bit, and each engine would respond to power lever movements differently, so the approach was very often a little crooked (but not enough to notice unless you were actually flying).

Other times, it's just common practice to save a little fuel. The fuel flow difference is negligable in my opinion.

Gotta love that Allegheny Dash 8 space shuttle training program. I couldn't really tell you the first thing about the E-170. I still don't completely understand even the E-170 "power up" checklist, but I could take a checkride/type ride in the Dash 8 right now and pass because that crap is burned into my head.

 

[Donsa320]

Seems I recall a CASA accident at DTW wherein the left prop got into BETA on final to runway 21R and the airplane ended up in the terminal gates with fatalities.

As I recall the captain had a history of doing that.

 

[pilotyip]

Yea at DTW he arrived at the gate upside down, lots of people killed.

 

[atrdriver]

Other times, it's just common practice to save a little fuel. The fuel flow difference is negligable in my opinion.

On the ATR the fuel flow at ground idle is about 600 lbs/hour, while it is about 400 lbs/hour in feather. We normally taxi with #1 shut down though to save the gas. If we end up having to wait out a storm or other very long delay you will sometimes see us feather #2 to save the extra 200 lbs/hour, especially if we are tight on min fuel.