MR engine reviews

Yeah, the "average" thing is kind of lame. If you look at the small print describing the graph, it explains that the average is just a real average of several previously reviewed locos (of the same type as the current one).

And they don't really say if the "same type" is just diesel or steam or do they break it down further into number of axles, etc.

So, if they reviewed few really heavy locos lately, the average would be quite high. I think it is really pointless fluff.

Peteski

Which nicely sums up ALL MR reviews.

-- Cheers

Roger T.

Home of the Great Eastern Railway

An interesting comment.. can you (or anyone) give specific example(s) of a review like that? It sure sounds like they are misleading us.

____ Mark

Model locomotive pull is proportional to weight. Heavier locomotives pull more. The motors always have enough torque to spin the wheels, so tractive effort is limited by the onset of wheel spin. For metal wheels on nickel silver rail, the coefficient of friction is about 0.25. The means the wheels start to slip when the tractive effort is 0.25 * locomotive weight. So a 16 oz locomotive can create 4 oz of draw bar pull. Double the weight and you double the draw bar pull. The only way to improve on this is to improve the coefficient of friction by the use of rubber traction tires. Rubber on nickel silver has a coefficient of friction of 0.5 or better, so you get double the pull for the same locomotive weight. HO diesels pull better than HO steamers, especially plastic HO steamers. All my diesels pull enough cars up my grades. None of my steamers pulls as many cars as I would like. I have packed as much lead as will fit into all of them, and they still don't pull as much as I would like. If you like steamers, consider keeping the grades gentle to give your locomotives a break.

David Starr

David Starr wrote: [...]

Prototype diesels pulled more than prototype steamers, too. Not that it matters much, since other factors determined the locos' actual tonnage rating. For both, grades severely reduced ratings. 1% generally cuts the rating in half - that's why real railroads tried to keep grades well below 1%, and mountain lines bought huge locomotives. Recall that the biggest engines of all, the Big Boys and the Yellowstones, were built to haul 5,000-10,000 ton trains on grades of about 1%!

A locomotive's tonnage rating was what it could pull _safely_ over the route it was assigned to. The same loco could have very different ratings over different divisions, even with the same ruling grades.

Example: the Huron Central operates between Sudbury and Sault Ste Marie. It's a very hilly line. Trains are generally around 50 cars, hauled by four rebuilt GP-40s. That's 10,000hp for a 4,000-5,000 ton train**. (The Big Boy rated about 6,000hp.) 50 cars stretch about half a mile. The line has many short but relatively steep hills, with little or no level stretches between crests and troughs. That makes train handling tricky; it's easy to pull train apart on such a line. Those four GP-40s are needed as much to provide good braking as pure haulage.

IOW, modellers tend to overestimate tonnage ratings, and so often think a perfectly prototypical train is too short. Especially on grades.

HTH

Dave:

Well, this is said a lot, and it probably should be qualified somewhat.

A one-pound model diesel with all axles powered and a one-pound model steamer with all drivers powered (such as an 0-6-0), equal motor powers, and equal drive efficiency and gear ratios, both with nickel silver tires, will pull the same number of cars on straight track. Increase the grade, and both will lose the same amount of pulling capacity.

On curves, the diesel will likely pull slightly better, because it has a shorter rigid wheelbase (the truck wheelbase) than the steam engine.

Add leading & trailing trucks, and the steam engine will not pull as well, as some weight has been lifted off its drivers. The more weight the trucks carry, the less tractive effort the model can develop.

I suspect a lot of the 'model steam engines pull less' belief comes from the usual equivalence of two or three model diesels to one model steamer at the head of a train. Very often these several diesels together carry a much greater weight on drivers than the single steam loco they substitute for. I think we do this because steam models cost more than diesels, and diesels look much better in groups than alone, especially cab units.

Cordially yours: Gerard P.

Dave:

Well, this is said a lot, and it probably should be qualified somewhat.

A one-pound model diesel with all axles powered and a one-pound model steamer with all drivers powered (such as an 0-6-0), equal motor powers, and equal drive efficiency and gear ratios, both with nickel silver tires, will pull the same number of cars on straight track. Increase the grade, and both will lose the same amount of pulling capacity.

On curves, the diesel will likely pull slightly better, because it has a shorter rigid wheelbase (the truck wheelbase) than the steam engine.

Add leading & trailing trucks, and the steam engine will not pull as well, as some weight has been lifted off its drivers. The more weight the trucks carry, the less tractive effort the model can develop.

I suspect a lot of the 'model steam engines pull less' belief comes from the usual equivalence of two or three model diesels to one model steamer at the head of a train. Very often these several diesels together carry a much greater weight on drivers than the single steam loco they substitute for. I think we do this because steam models cost more than diesels, and diesels look much better in groups than alone, especially cab units.

Cordially yours: Gerard P.

Didn't the recent review of the Bachmann 2-10-2 say something about it be ing a real drag engine? The first line in the review reads, "This powerful HO 2-10-2 may be called a "light" 2-10-2, but it's still a big steam locomotive by most model railroad standards." Yet, it is about 1.5oz. less than the "average" in terms of draw bar pull.

dlm

Dave,

Thanks. This is good information!

dlm

Shows how believable the MR advertisements, sorry "reviews" are when on Bachmann's own board people are complaining about how this loco can't pull a decent train and has a tendency to derail. No mention in the MR review of any of that, nor that fact that the loco though advertised with Walchearts gear comes with Southern except one road name that comes with Baker.

-- Cheers

Roger T.

Home of the Great Eastern Railway

All true. Plus, the plastic steamers lack the internal volume to carry enough ballast to make them as heavy as the typical road switcher. Especially the small ones. I have a pair of plastic IHC Moguls, tiny engines, small diameter boilers, which are completely filled with factory weight. I couldn't find anywhere to stuff in more weight. My Bachmann Spectrum Consolidation is bigger, and hence heavier than the Moguls, and it pulls better too. The older all metal Bowser and Mantua steamers are heavier than the new highly detailed plastic ones.

David Starr

Dave:

You might try carving out the factory zinc weights and replacing with home-cast lead weights, as lead is about 1.7 times as dense as ZAMAC alloys. Wasn't there a thread about tungsten weights a while back...?

Cordially yours: Gerard P.

alloys. Wasn't there a thread about tungsten weights a while back...?<

True if we got rid of Zamax as weight and used lead it would be better but then there's EPA. I checked on Tungsten and if you can find it the cost is extremely high. I tried various stores that deal in reloading but all they had was boxes of ammo and the cost was very high but then it was big game ammo. It's probably as easy to get depleted uranium* as tungsten!

• This was used in some N scale engines and it really works .

Jon:

Now we don't want to reactivate THAT old argument, do we now? Anyway, model trains are nominally toys, which probably is why the mfrs don't use lead...but it's still quite usable at home, unless you're in Europe and under heinous EU overregulation.

They say you can get tungsten welding rod rather easily. I don't know if this is so.

Cordially yours: Gerard P.

snipped-for-privacy@gannon.edu spake thus:

Maybe somebody returning from serving in Iraq can bring back some D.U. Plenty of it flying around over there.

I'd expect that a 2-6-0 would only pull a few cars though so that wouldn't bother me as much as a 2-10-2... or my USRA 2-6-6-2 which is pretty weak as well.

An engineering friend told me that a 1% grade usually cuts pulling power in half. I'd guess even more than that as it would have to pull itself as well. So one needs to interpert the "pulls x cars on straight & level track" kind of remark. Few of us have layouts that are "straight & level."

dlm

Wow, this discussion went a tad OT...

Peteski