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Counting When Starting A Radial Engine?  
User currently offlineTimePilot From Switzerland, joined Sep 2005, 296 posts, RR: 0
Posted (4 years 2 months 3 days 7 hours ago) and read 12456 times:

I've seen a few videos on YouTube of classic planes (DC-3 and some warbirds), in which the pilot(s) count the prop rotations while/before starting the engine(s). I don't really understand engines (like, at all), so can someone explain what they're doing? Why is this necessary?

22 replies: All unread, jump to last
 
User currently offlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Reply 1, posted (4 years 2 months 3 days 5 hours ago) and read 12429 times:

Quoting TimePilot (Thread starter):
I don't really understand engines (like, at all), so can someone explain what they're doing? Why is this necessary?

They are counting prop blades going by. This is a pretty common procedure so that you know when to introduce primer, move mixture controls, etc.

Some big radials are very finicky engines, and will not properly cold start unless you follow these checklists to the "T"  

Basically, a radial engine won't start if: A) the phase of the moon is wrong, B) you look at it funny, or C) you or it is in a bad mood.

There is definitely an art to starting a round engine....

What is going on inside the engine, though, is you are (hopefully) getting the cylinders in the engine full of just the right amount of fuel and air that one of them will fire the next time a piston hits Top Dead Center (TDC). Any piston engine (your car included) usually requires a very rich mixture (lots of fuel) to get going, but not too rich. If you overprime the engine, you can flood it (i.e. the cylinders become full of gasoline, and then will refuse to start). Also, some of the prop counting can be "walking" the prop (ensuring in a radial that the lower cylinders of the engine aren't full of oil, due to sitting on the ramp all night). If a cylinder is full of oil, and you attempt to start a radial, you will destroy the engine through a process known as hydraulic lock (basically, thick liquids like oil won't compress, so they break the connecting rod on the piston of the cylinder that is full of oil when another cylinder fires...)



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineje89_w From United States of America, joined Mar 2002, 2362 posts, RR: 9
Reply 2, posted (4 years 2 months 3 days 3 hours ago) and read 12378 times:
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http://www.youtube.com/watch?v=EkcX0KGIBwk

 


User currently offlineDashTrash From United States of America, joined Aug 2006, 1550 posts, RR: 2
Reply 3, posted (4 years 2 months 3 days 2 hours ago) and read 12339 times:

Quoting KELPkid (Reply 1):
This is a pretty common procedure so that you know when to introduce primer, move mixture controls, etc.

Kinda.

Quoting KELPkid (Reply 1):
Basically, a radial engine
won't start if: A) the phase of the moon is wrong, B) you look at it funny, or C) you or it is in a bad mood.

Very true.

When a radial engine has been sitting a while oil collects in the bottom cylinders. During the walk around you pull the engine through "X" amount of blades to begin pulling the oil out of the bottom cylinders and back into the crankcase. When you start it, you let the starter do the work, but for the same purpose. On a R985, pulling a 3 bladed prop through 9 blades before turning on the mags allows all 9 cylinders to go through all four strokes. This way you minimize the chances of oil remaining in the bottom cylinders and the associated hydraulic lock.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 4, posted (4 years 2 months 3 days 2 hours ago) and read 12334 times:

Quoting KELPkid (Reply 1):
Some big radials are very finicky engines, and will not properly cold start unless you follow these checklists to the "T"

As KELPkid once said in another thread, and I've never forgotten:
"If you've ever seen a radial start up, you know it's a miracle when two or three cylinders fire, and then you have to coax the rest to act in agreement that the engine should be in a state called "started" "

Tom.


User currently offlineDashTrash From United States of America, joined Aug 2006, 1550 posts, RR: 2
Reply 5, posted (4 years 2 months 2 days 16 hours ago) and read 12182 times:

BTW....

You don't start a radial. You wake it up.


User currently offlineAviopic From Netherlands, joined Mar 2004, 2681 posts, RR: 41
Reply 6, posted (4 years 2 months 2 days 10 hours ago) and read 12051 times:

Quoting KELPkid (Reply 1):
This is a pretty common procedure so that you know when to introduce primer, move mixture controls

The mixture is just on full rich during startup.

Quoting KELPkid (Reply 1):
Some big radials are very finicky engines, and will not properly cold start unless you follow these checklists to the "T"

Most big radials are pre-oiled before start up otherwise the 130W oil is way to thick.

Quoting KELPkid (Reply 1):
Basically, a radial engine won't start if: A) the phase of the moon is wrong, B) you look at it funny, or C) you or it is in a bad mood

I understand that for the modern day Fadec driver it sounds a bit complicated but it really isn't that hard.
You just need to develop a little feel for each engine.
Some like to be primed, some a bit more and others less or not at all.
On 4 Connie engines you might have 4 slightly different procedures.

Quoting tdscanuck (Reply 4):
"If you've ever seen a radial start up, you know it's a miracle when two or three cylinders fire, and then you have to coax the rest to act in agreement that the engine should be in a state called "started"

and it looks like this:




or if a little bit of thinkering is still needed like this............




and....




The truth lives in one’s mind, it doesn’t really exist
User currently offlinejetstar From United States of America, joined May 2003, 1658 posts, RR: 10
Reply 7, posted (4 years 2 months 2 days 10 hours ago) and read 12026 times:
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I can tell you from experience that walking the props on the 28 cylinder R-4360 radial engine on the KC-97 before the first start on a cold winter morning will give you your exercise for the day, and that was after preheating the engine. Sometimes it would take 2 of us to walk the props through on each engine.

If I remember back when, we would walk the props on each engine about 20 blades, to make sure there was no hydraulic lock on the lower cylinders, and on the 4 row R-4360, there were 4 lower cylinders on each engine.

The flight engineer had the engine controls on their panel, but could not see the engines so basically they started them using their engine instruments. Either the pilots, or the extra FE on board, we normally flew with 2 FE’s would count 12 blades for the FE at the panel.

Sometimes I would stand fire guard as each engine was started, I would stand next to the exhaust pipe and could hear when the first cylinders started to fire. It took an experienced hand of the FE to coax the engine to start smoothly, especially after the first engine was running and he could not hear the other engines starting up,

When the senior engineers started the engines, they had magic fingers and the engine from the first cylinder firing would accelerate up very smooth to idle without a hiccup, but many an inexperienced FE would either flood the engine with to much fuel, or not give it enough fuel, and there was a very fine line between the 2 and when it finally caught it would run rough, sputter, shake, and sometimes even quit running momentarily until it had enough RPM so the FE could release the starter button.

Once the engines reached idle, then the oil that sat in the exhaust pipes would ignite and this, coupled with the engine still running rich from starting would emit enough smoke that it looked like a smoke screen was being laid down behind the airplane, just like the first picture in the previous post

This past July, I went to the Air Force Museum at Wright Patterson Air Force Base and they have a KC-97 on display and I was able to get very close to the airplane and engines. Last month I was at the Air and Space Annex at IAD, and in the engine section, they had a R-4360 on display, this had apparently been used as a training aid because sections had been neatly cut away to show the insides on the engine and cylinders.

Seeing the KC-97 and the R-4360 engine up close up again after 40 years brought back many memories.

JetStar


User currently offlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Reply 8, posted (4 years 2 months 1 day 11 hours ago) and read 11821 times:

Quoting Aviopic (Reply 7):
and....

Whoa...is that last shot a backfire through the intake?  Wow!



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineTimePilot From Switzerland, joined Sep 2005, 296 posts, RR: 0
Reply 9, posted (4 years 2 months 1 day 10 hours ago) and read 11761 times:

Thank you for all the replies  

Quite interesting. I wish I could see one up close. (And as a Connie fan I should have known she had radials.)

Are radials more reliable?

[Edited 2010-09-24 14:00:10]

User currently offlineAviopic From Netherlands, joined Mar 2004, 2681 posts, RR: 41
Reply 10, posted (4 years 2 months 1 day 9 hours ago) and read 11723 times:

Quoting KELPkid (Reply 9):
Whoa...is that last shot a backfire through the intake?

Yes, we got an engine from the ex Mats Connie installed and this was the first run with the timing a "bit" off  

There is a lot of fuel and air in the engine because you are not filling the cylinders but the blower section(indirect fuel injection although there are also versions with a carburetor like used on the Neptune) and if you have the timing wrong it will come out either through the intake in this case an MCU(master control unit which is connected to the throlltle levers and controls the amount of air going into the blower section) or the exhaust like in the other photo.

Quoting TimePilot (Reply 10):
Are radials more reliable?

Reliability depends on your reference......... and the amount of maintenance you put into it.
The won't do the number of hours on wing like a modern turbo fan but for the time I would say yes.
Of course the engines I am familiar with(Wright R3350 Connie and R1620 DC2) are museum pieces and get all the love and tender they possibly might need and thus never give a wrong beat.
In operational times this would have been quite different and engine changes were quite common.



The truth lives in one’s mind, it doesn’t really exist
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17109 posts, RR: 66
Reply 11, posted (4 years 2 months 1 day 6 hours ago) and read 11682 times:

Quoting TimePilot (Reply 10):
Are radials more reliable?

As Aviopic says, this depends on what you compare them with. More reliable than modern turbofans? Nope, not even close. For the era they were used, sure.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineViscount724 From Switzerland, joined Oct 2006, 25843 posts, RR: 22
Reply 12, posted (4 years 2 months 1 day 6 hours ago) and read 11677 times:

Quoting TimePilot (Thread starter):
I've seen a few videos on YouTube of classic planes (DC-3 and some warbirds), in which the pilot(s) count the prop rotations while/before starting the engine(s).

Go to about the 6:45 mark in the following video showing engine start (and counting) on an AA DC-7 (Wright 3350s). First part of an interesting 3-part AA PR film covering an IDL-JFK nonstop in early days of AA DC-7 service.
http://www.youtube.com/watch?v=F4d-OFDs1hY


User currently offlinejetstar From United States of America, joined May 2003, 1658 posts, RR: 10
Reply 13, posted (4 years 2 months 1 day 4 hours ago) and read 11648 times:
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An interesting comparison between the R-4360 and the R-3350, while they both put about the same horsepower, about 3000 hp at take off, but the R-3350 did it with 10 less cylinders,1000 less cubic inches and about a 1000 pounds less weight than the R-4360

The R–4360-59B used on the KC/C-97 was turbo charged, so the exhaust pipes all fed into a circular exhaust collector at the rear of the engine and powered the turbo through a waste gate and then the exhaust exited the engine out of a single about 10” exhaust pipe, so the sound from these engines had a nice deep throated sound to them, not like the un-turbo short stack version used on the C-124, which was just plane loud.

My first job I had after I graduated from A&P school, I worked for a engine teardown & buildup company located on Rockaway Blvd, just outside JFK. We worked on the early B-707 and DC-8 engines and the R-3350. Our customers were smaller airlines, both passenger and cargo, some domestic and others foreign who did not have in house capabilities for this work. We would tear the engine down to the basic engine by removing all the components, nacelles and reversers, ship off the engine to the overhaul shop, and another division of our company would overhaul the components and when the engine returned from the overhaul shop, we would build the engine back up again and deliver it to the customer.

I still remember clearly 40 years later one of these airline reps very loudly chewing out the Curtis Wright factory rep on the shop floor for the lack of reliability of their engines and telling the factory rep that he should take their engines and shove them up his a$$.

Just reminiscing about the good old piston engine days.

JetStar


User currently offlineMD11Engineer From Germany, joined Oct 2003, 14127 posts, RR: 62
Reply 14, posted (4 years 2 months 22 hours ago) and read 11582 times:

Early jet engines are just as finicky to start. I do some work on a friend´s T-.33A with an old J-33 engine. We don´t trust the automatic start fuel control unit anymore (after more than 50 years since it was built, it tends to produce hot starts so fast that you can´t shut down the fuel fast enough), instead we always do manual starts (this means moving the thrust lever manually from the cutoff detent to the ground idle detent while watching the rpm and EGT like a hawk until the engine runs stable). A little bit too much fuel and you´ll have a nice flame coming out of the tailpipe, a little bit too little and the engine won´t accelerate. Once the thrust lewver is in the ground idle detent, the engine will just behave like any other jet engine.

Jan


User currently offlineCrimsonNL From Netherlands, joined Dec 2007, 1891 posts, RR: 42
Reply 15, posted (4 years 2 months 21 hours ago) and read 11568 times:
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Can someone please explain what the priming does? It never really became clear to me and I'm having a hard time finding an explanation. I know some engines prime a few shots before starting, but also during the starter engage?

Thanks, Martijn



Nothing's worse then flying the same registration twice, except flying it 4 times..
User currently offline113312 From United States of America, joined Apr 2005, 574 posts, RR: 1
Reply 16, posted (4 years 2 months 17 hours ago) and read 11525 times:

Prime shoots extra raw gasoline directly into some cylinders.

User currently offlineDocLightning From United States of America, joined Nov 2005, 20194 posts, RR: 59
Reply 17, posted (4 years 1 month 4 weeks 1 day 22 hours ago) and read 11404 times:

Why were round engines so popular? Why not use a linear set-up or a V set-up?

User currently offlineGLEN From Switzerland, joined Jun 2005, 225 posts, RR: 2
Reply 18, posted (4 years 1 month 4 weeks 1 day 21 hours ago) and read 11388 times:

Quoting DocLightning (Reply 17):
Why were round engines so popular? Why not use a linear set-up or a V set-up?

Probably due to the reduced overall length of a round engine. With a longer engine I can imagine negative side-effects like a CG which is further fwd, forces on the structure supporting the engine and there are probably others. The bigger the engine the more pronounced these effects would have been.



"The horizon of many people is a circle with zero radius which they call their point of view." - Albert Einstein
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17109 posts, RR: 66
Reply 19, posted (4 years 1 month 4 weeks 1 day 20 hours ago) and read 11371 times:

The most important factors in favor of radials were, I think:
- Cooling. Apparently inlines and Vs needed water cooling while radials could be air cooled. Way simpler, and in combat less prone to damage.
- Higher power to weight ratio and mechanical efficiency. In those days you ran into crankshaft issues when they became as long as would be required for, say, a V-16 engine, as the materials weren't stiff enough. With a radial you could get 21 cylinders in 3/8 of the crankshaft length as a V-16, with 5 more cylinders to boot.
- As GLEN mentions, the overall length was much less.

On bigger aircraft, the large frontal area was not a huge issue. On smaller aircraft such as WWII fighters inlines had a much stronger presence.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineGLEN From Switzerland, joined Jun 2005, 225 posts, RR: 2
Reply 20, posted (4 years 1 month 4 weeks 1 day 20 hours ago) and read 11371 times:

Quoting DocLightning (Reply 17):
Why were round engines so popular? Why not use a linear set-up or a V set-up?

Also temperature control comes now into my mind, as the rear cylinders in a linear set-up get warmed-up air from the front cylinders.



"The horizon of many people is a circle with zero radius which they call their point of view." - Albert Einstein
User currently offlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Reply 21, posted (4 years 1 month 4 weeks 1 day 14 hours ago) and read 11328 times:

Quoting GLEN (Reply 20):
Also temperature control comes now into my mind, as the rear cylinders in a linear set-up get warmed-up air from the front cylinders.

Only if air cooled. Most aero V- and inline-types (after the Curtiss OX-5) have been liquid cooled   Two significant exceptions I can think of are the Ranger, which was an inverted, air-cooled straight six, and the DeHavilland Gipsy Major, an inverted inline four.

Quoting Starlionblue (Reply 19):
The most important factors in favor of radials were, I think:
- Cooling. Apparently inlines and Vs needed water cooling while radials could be air cooled. Way simpler, and in combat less prone to damage.

True, but water cooling leads to lower-drag designs. Although it took Rolls-Royce many years to perfect the Merlin, I don't think it was any less reliable after the development it received through World War II. Although many historians still regard the Merlin as a "hot rod" engine. Apparently, in service, it requires significant cylinder head and valvetrain work every 300-400 hours or so.



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineCanadianNorth From Canada, joined Aug 2002, 3395 posts, RR: 9
Reply 22, posted (4 years 1 month 4 weeks 1 day 6 hours ago) and read 11253 times:

Compared to modern turboprops and turbofans the reliability of the old radials is flat out horrible, but for their time they were good. Back in their day, they were just as reliable as anything else available.

I've been told though that the main reason they became popular was for large piston engines the radial layout has the best power to weight, and also is by far the easiest setup to cool with air - both of which are some of your main concerns when choosing an engine for your aircraft.

As for turning over the engine a few rotations prior to starting, it's done to make sure there's no significant amount of oil pooled up in the lower cylinders and get everything moving as it should.




CanadianNorth



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