Snoopy and Snoopy2

[Jim]

I had the privilege of spending several hours with a former pilot and ground crew member of the Met Life Snoopy and Snoopy2 airships.  He was responsible for the maintenance of the two Rotax 912's on each of the airships.  Here are some of the things I learned...

 

Throttles were modified to go to idle rather than full if the throttle cable breaks.   The same chronic problems with sensors, ignition modules and exhaust springs that we've seen.  No problems with low rpm cruising.  The blimps often loiter at less than 3000 rpm and idle was set to 1400 rpm.  Despite Rotax saying that this was bad for the engines, they always made 1500 hours TBO without issues.

 

He said that in spite of the sensor and ignition problems, the engines were a joy to fly and maintain compared to anything else and that they were a great fit for the airship application

[Anticept]

912 UL or ULS? It is the 100 hp engines that rotax talks about with low rpm due to the high compression.

 

Also, tbo/overhaul does not mean replacement of parts. Overhauling engines means disassembly to assess health, and replacement of *worn* parts, along with some precautionary things like bearings. Taking care of the engine means it can last a couple overhauls before something needs serious work.

 

Finally, rotax modifies bing carbs to go full throttle. Originally, they spring load to idle.

[Jim]

100 hp engines.  He said they overhauled the engines at 1500 hours regardless of condition.  He said the throttle system was specifically modified to fail to idle. 

 

I didn't buy an argument.  Just saying what I learned.   If every post has to end up in a debate, I have better things to do with my time.

[Anticept]

Hi Jim!

 

Not trying to argue, just bringing what I have to the table . Every engine has a personality, I wouldn't doubt for a bit that the low RPM argument was because of a few engines that came back from testing or observations in the field, so it's said everyone should avoid it as a precaution. A lot of stuff the factory changes or recommends is due to anecdotal evidence from the field.

 

Since it's hard to say exactly which engines are sensitive to what, it's best to focus on one operating range and engineer towards it.

[FastEddieB]

I'll testify that BING carbs historically have been spring loaded to go to idle in non-aviation applications.

 

Logical, since they were designed to work with a twist grip, and going to full power unexpectedly on a motorcycle could have dire consequences.

 

You can see that here:

 

 

 

Also not arguing - just trying to clarify!

[ctfarmer]

Good post Jim. Your comments are just that and not opinion.

 

Refreshing. Thank you.

[FredG]

Jim, thank you for your original post.  I found it interesting.  

[Anticept]

In this conversation you guys are comparing apples and oranges and have not been specific enough.

There are several factors you you have left out and not identified others. Eddie's heading down the right path.

What do you mean?

[FastEddieB]

What do you mean?

I assumed he meant my vegetarianism!

 

Apples and oranges, yum!

[Anticept]

I assumed he meant my vegetarianism!

Apples and oranges, yum!

I love oranges. i will empty a bag of 8 in an hour just munching on them.

[Anticept]

Lots of stuff

 

Oh, you. For some reason I thought you were wagging your finger at me saying I got a bunch of stuff wrong  .

[Anticept]

Hi Corey,

 

You didn't get anything wrong.  My wife is gone for two weeks and I was just bored. 

Now wait a minute. You have a CT and you are bored? That means that poor little plane is cooped up eager to fly and you aren't paying her any mind!

[Jim Meade]

Thanks for the report, Jim.

[cdarza]

I recently purchsed a Super Drifter with a 912 80hp that is setup to idle if cable snap. I thought this was odd and perhaps set up wrongly. Checked the manual and it was indeed correct to be set to idle. I would prefer it set to full throttle.

[Ed Cesnalis]

When the friction lock on the throttle fails the result is full throttle.  Don't shut your engine off if your throttle lever is advanced, just control the lever until you land and taxi and shut down.

 

Going full throttle on a cable break is what you want.  Better to have power to get you to a runway and then dead-stick as opposed do gliding and landing off-field at idle.

[Ed Cesnalis]

  Better to go to idle, then at least you have the option of landing on a road or an airfield if you are close enough on glide.

 

That's a big if.  

• With a WOT I"m ok if I"m close enough or not.  I will kill the engine when the field is assured and dead-stick the landing.
• With a throttle at idle I"m going to land whether there is a field or not.

IMO a throttle cable issue is not sufficient cause to deploy the chute.  I would not want to total the CT and give up control over a problem that I could easily deal with.

 

Far better to go wide open, that is why aircraft do in fact go wide open ( in most cases, a blimp being an obvious exception )

 

Its easy to practice dead-sticks just by approaching and landing without power as well as slipping.  Slipping is an important skill because your practice will be mostly with idle power, when doing a real dead-stick you need to aim farther down the field in case you hit sink, then you might need to slip if the field is short. 

[Tom Baker]

I tend to agree that with full throttle you get to choose where you will make your emergency landing. with it at idle the choice has already been made for you.

 

Did you know that in the first world war many aircraft didn't have a throttle. They simply turned the ignition on and off to control power.

[Doug G.]

Tom, It is always fascinating to watch some of the old movies and hear the engine cycling on and off as they land.

[FastEddieB]

I don't know if this has happened to anyone, but...

 

...if you were cruising at full throttle, you would not even realize a throttle cable had broken.

 

UNTIL you throttled back for descent and things would get VERY rough all of a sudden as one cylinder bank stayed full throttle while the other dutifully got reduced.

 

Especially in our planes, good first instinct on a rough engine might be to immediately apply full throttle before anything else.

 

Agreed?

[Tom Baker]

As i noted, a WOT default still requires an engine out, dead stick landing.  How far one is from an airfield or road is more up to the pilot than anything.

 

Are you saying a SPAD S.XIII with a Hispano-Suiza 8BEc 235hp engine was flown without a throttle and full out, and did a full engine out dead stick for each landing?

Yes, a failure of the throttle at wide open will require a dead stick landing, but the pilot gets to choose where it happens. Maybe you didn't mean what you said, but here it is, "Better to go to idle, then at least you have the option of landing on a road or an airfield if you are close enough on glide." We have been talking failure of the throttle. My point is failure to full throttle gives you far more choices about where you are going to land compared to throttle failure to idle.

 

As for the WW1 aircraft I didn't mention any specific aircraft. I don't know about the Spad, but any WW1 aircraft that used a rotary engine landed dead stick.

http://en.wikipedia.org/wiki/Rotary_engine