Question about Big Boys

[dtrainBNSF1]

Maybe you can see why it's taken me many months of trials (some on Sherman Hill, some on the fast sections of the NEC) to tune the FEF-3's performance

And how.

[dtrainBNSF1]

At the end of the day this is what I've got: Effectivity is now set as low as .98. With dampers and blower on and ideal fuel mass, full throttle and 10% cutoff the loco got up to 79.9mph. To nudge it that last .1mph I had to increase cutoff to 11%. I'm getting closer. I'll start speed trials again tomorrow. After that it'll be on to Sherman main track one.
If everything works out right, I should be able to drag 3250t. over the 1.5% slope from Cheyenne to Buford at a max speed of 24mph, give or take. We'll see what happens...

[mrennie]

At the end of the day this is what I've got: Effectivity is now set as low as .98. With dampers and blower on and ideal fuel mass, full throttle and 10% cutoff the loco got up to 79.9mph. To nudge it that last .1mph I had to increase cutoff to 11%. I'm getting closer. I'll start speed trials again tomorrow. After that it'll be on to Sherman main track one.
If everything works out right, I should be able to drag 3250t. over the 1.5% slope from Cheyenne to Buford at a max speed of 24mph, give or take. We'll see what happens...

Looks like you're getting there

[dtrainBNSF1]

Finished another test on Sherman Hill. I took 2925t. (including auxiliary tender, tool car and caboose) over the hill to Hermosa this time 3985 style with double stacks at an average speed of 32mph. Cutoff fluctuated between 75-52% ascending depending on the grade profile. I reduced cutoff when steam usage exceeded steam production, however on the steep 1.5% grade to Granite due to the load being so heavy speed would drop naturally so to keep speed up I had to increase cutoff to maximum a few times which at such low speeds did not exceed steam production values and didn't slow me down but actually sped me up. When I hit the .8% grade at Buford speed increased and then full cutoff caused my steam usage to exceed steam production so I would reduce cutoff. Same for when I came over the summit down to Dale Junction and through Hermosa tunnel.

[mrennie]

Finished another test on Sherman Hill. I took 2925t. (including auxiliary tender, tool car and caboose) over the hill to Hermosa this time 3985 style with double stacks at an average speed of 32mph. Cutoff fluctuated between 75-52% ascending depending on the grade profile. I reduced cutoff when steam usage exceeded steam production, however on the steep 1.5% grade to Granite due to the load being so heavy speed would drop naturally so to keep speed up I had to increase cutoff to maximum a few times which at such low speeds did not exceed steam production values and didn't slow me down but actually sped me up. When I hit the .8% grade at Buford speed increased and then full cutoff caused my steam usage to exceed steam production so I would reduce cutoff. Same for when I came over the summit down to Dale Junction and through Hermosa tunnel.

It's getting closer, but what speed were you doing when you put the cutoff to maximum and didn't exceed the boiler output? If it was more than about 5mph, then if it were me, I'd yank up the cylinder effectivity a bit so that you'd have to shorten the cutoff to around 55% in those conditions. But then again, I've never been at the controls of a Big Boy, so I'm just saying what I think might feel convincing to me, but it might not be convincing to someone else. In the end, you should settle on something that feels convincing to you ("feels right"), gives a good impression of the power of a Big Boy, and makes for an enjoyable time, which for me means that it should provide a challenge, so that you do have to keep adjusting the controls quite often, but without becoming a boring 5mph slog up the hill (but other people might disagree ... it's impossible to satisfy everyone).

[dtrainBNSF1]

Yeah, it was more than 5mph (I never allowed the train to drop below 20). I'm doing another heavy haul this time out of Laramie to Buford. The grade is a constant .8% all the way to Hermosa and the Big Boy was rated at 5800t. for this section of line, perfect for good hard results.

[mrennie]

Yeah, it was more than 5mph (I never allowed the train to drop below 20). I'm doing another heavy haul this time out of Laramie to Buford. The grade is a constant .8% all the way to Hermosa and the Big Boy was rated at 5800t. for this section of line.

There's probably some more tweaking to be done in that case - I doubt very much that the boiler would be able to keep up if you put the reverser at maximum while going at 20mph.

[dtrainBNSF1]

There's going to be plenty of work to do. Judging by how much has been done already I think I'll post again in a couple of days.

[dtrainBNSF1]

Well over the weekend I mostly toyed around with the volume value since I hadn't done anything with it so far (initial value was set at 990). Unfortunately on my max tonnage test the loco stalled on the hill so that still needs some work. I've also noticed on my tests that with the loco now using lower cutoff the loco does not have access to as much power as before. Just needs more tinkering I guess.
Mrennie when I first contacted you on youtube a few months ago when I was asking for pointers on editing the simulation file didn't you mention that even if the correct value for max force is typed in that the performance would still be off so multiply the theoretical (published) value by 2.6?

[mrennie]

Well over the weekend I mostly toyed around with the volume value since I hadn't done anything with it so far (initial value was set at 990). Unfortunately on my max tonnage test the loco stalled on the hill so that still needs some work. I've also noticed on my tests that with the loco now using lower cutoff the loco does not have access to as much power as before. Just needs more tinkering I guess.
Mrennie when I first contacted you on youtube a few months ago when I was asking for pointers on editing the simulation file didn't you mention that even if the correct value for max force is typed in that the performance would still be off so multiply the theoretical (published) value by 2.6?

Yes, until recently, I'd been multiplying the theoretical (published) starting t.e. by 2.6 to get the correct performance at max speed. However, it resulted in unrealistically high acceleration at low speed. Ed Fisk (Meshtools) suggested a better way: keep the correct max force, so that low speed acceleration is more realistic, but to allow more of that (lower) t.e. to be available for high speed, put something like 0.45 of t.e. at 10% cutoff
It's still not ideal, but I think it's a better solution.

[dtrainBNSF1]

Okay that makes sense now Just looking for clarification.

[dtrainBNSF1]

I'm getting some pretty confusing results in my recent tests. I think it may have to do with my t.e. vs speed worksheet that I customized to be able to reach 80mph, but seeing that I was off on the t.e. vs cutoff worksheet, could someone double check my t.e. vs speed values?
speed/t.e.
0 1
4.2 .927780
8.4 .878541
12.6 .835374
16.8 .795732
21 .758519
25.2 .723134
29.4 .689201
33.6 .656463
37.8 .624735
42 .593878
46.2 .563785
50.4 .534369
54.6 .505560
58.8 .477300
63 .449541
67.2 .422242
72 .395365
75.6 .368882
80 .342764

I can see that when speed is 0 t.e. shouldn't be 1 off the bat, so I'll go ahead and change that. I went ahead and made a graph of it and to me it seems pretty smooth, but I just want to check.

[mrennie]

I'm getting some pretty confusing results in my recent tests. I think it may have to do with my t.e. vs speed worksheet that I customized to be able to reach 80mph, but seeing that I was off on the t.e. vs cutoff worksheet, could someone double check my t.e. vs speed values?
speed/t.e.
0 1
4.2 .927780
8.4 .878541
12.6 .835374
16.8 .795732
21 .758519
25.2 .723134
29.4 .689201
33.6 .656463
37.8 .624735
42 .593878
46.2 .563785
50.4 .534369
54.6 .505560
58.8 .477300
63 .449541
67.2 .422242
72 .395365
75.6 .368882
80 .342764

I can see that when speed is 0 t.e. shouldn't be 1 off the bat, so I'll go ahead and change that. I went ahead and made a graph of it and to me it seems pretty smooth, but I just want to check.

The way t.e. versus speed works in the sim is, I believe, completely messed up. For the FEF-3, I ended up with a flat "curve", with the t.e. fraction at 1 all the way up to 100mph and then tails off at higher speeds. The actual drop in t.e. from 0 to 100mph is already taken care of by the fact that, in order to reduce the braking effect of back pressure and thus be able to continue accelerating, you have to shorten the cut off.

[dtrainBNSF1]

Interesting

[dtrainBNSF1]

Well after a few long days of speed trials and changing values by 1-tenth at a time, I think I've gotten somewhere tonight: took my test consist of 3181t. (as close as I could get without getting over 3250t.) from Cheyenne to Hermosa at an average speed of 41mph. Cutoff ranged anywhere from 10%-22%. Speed coming out of Cheyenne was 55mph, speed never dropped below 35mph on the way to Buford sometimes getting in the lower 40s in between filling the boiler. I tried to keep my steam production up without the safety valve going off. If I got close to the safety valves lifting I'd increase the cutoff a bit more. When the injectors were on I'd lower cutoff to try and preserve steam which didn't impact my speed too much. I'm calling it a night - tomorrow I'll take a 5800t. consist from Laramie to Buford and see how that goes.