bogateer

Ok,

Sorry for the very basic question here but what is it that makes an .051 an .051 and not an .049? Is it bore, stroke, both? What, if any, parts are interchangeable between the engines?

Thanks,

Rob

Tim Wiltse-RCU

It's just the bore. The .051 pistons have a little ring cut into thier piston skirts for i.d. The will fit any other Cox engine. Of course you just have to keep the set together. Note there is no power difference between the two sizes.

LAter,
Tim

lukesp

Tim,
do you know why ? I have read this many times before, something to do with with Cox made them for a certain class or something, but I have never found out why the TD051 has the same power as the TD049. Venturi restriction ?

Luke

Wayne C

Only two thousandths of a cubic inch difference in full swept volume of the cylinder. Every thing else being the same, I wouldn't really expect much if any difference in power. Piston diameter only slightly larger. Oppertunity for friction sees a very slight increase also. Porting, timing, venturi, piston to cylinder fit, number of shims under head, choice of glowhead, all potentially have greater affect on performance than .002 cubic inch. Choice of fuel and prop may have far greater affect than .002 cubic inches.

...just my opinion...

BMatthews

That's right. Technically the extra displacement will result in more power but the increase is so slight that it's easily hidden by other factors.

combatpigg

My Feedback: (3)

There are various versions of the story about why they cut the oil retention groove in the .051 piston. If I remember right, they are technically too big to be classified as 1/2A in the AMA rule book? Makes me wonder why they went to the trouble. I have always thought that some day I would learn how to true up a .051 piston and hone a worn .049 cylinder enough to make a perfectly redone set.

Bipe Flyer

One plane can be flown in a 1/2A event and an Class A event by changing the engine and it will fly the same.

combatpigg

My Feedback: (3)

Maybe so, but that bit of convenience is probably only practical for free flight, if you tried that with combat, your .051 would end up being an hors d'oerve against a .15 !

Jim Thomerson

You have to remember that in the 50's and 60's free flight was a big thing. Several Nats 1/2A FF was the largest event by far. If you check your AMA rule book you will see that definitions of A, B, C, etc engine sizes do vary a bit from event to event.

lukesp

All very reasonable explanations, and of course, an increase that small would not be noticed. Thanks. Another minor Cox mystery (for me) solved.

mylamo

My Feedback: (1)

It is quite a load of airplanes if you have one for
each class, so if you can still fly four classes of
free flight with 2 airplanes that gave room for one
more flier in the old Ford. .049/.051-.29/.32.
Ralph

bogateer

Can a TD .051 be turned into a TD .049 by switching out the cylinder and piston? The reson I ask is spare parts....there seem to be more available for the .049 and if an .051 goes belly up I was wondering if it could continue its life as an .049.

Thanks,

Rob

lukesp

Yes, of course. Same threads for the cylinder.

dennis

My Feedback: (90)

Yes the TD051 was made primarily for free flight. The reason there is not a bit of difference in the power output is that if there was you would have to retrim the plane to handle the additional power. Not something that you want to do when you at a contest.
Oh and a properly trimmed 1/2A or A plane only has to do the time specified/Max so while altitude might be given to the 15 sized plane a lighter 051 plane can conceivably do well .
Dennis

jessiej

"In the day " I flew several FFs in 1/2 A and A with Holland Hornets in .049 and .051.

jess

ffkiwi

This approach goes a long long way back-we've touched on the TD 049/051 (there was also a Medallion 051 produced for a very short time-essentially in response to NFFS pressure for a Nostalgia legal engine) Holland did it with the Hornets and so did Atwood.
In the larger sizes you had the K&B 19/23, Ohlson ditto, Fox 19 and the (very rare) .201, and Forster 29/31 plus as has been mentioned K&B 29/32...
As always the intent has been to allow the same aircraft to compete in two different categories simply by changing the engine. There have been a few odd ball 'mutants' done over the years as well-the Chamberlain .42 which was several different models of OS 40 combined to produce a class D F/F motor. The other side of the coin-overboring an existing motor to compete in the next class up-a few of the Brits experimented with 2.6cc diesels (such as an overbored Eta 15) in class B team race. Of course the opposition was .29 glows, so it was a totoise and hare approach.....
If you want to get creative you can interchange bits on the K&B 20 and 28 Sporters to produce two hybrid capacities as well.....(but why would you want to.........)
'ffkiwi'

combatpigg

My Feedback: (3)

Might as well enter A with an .049 then. Anyone who would / could object to someone doing that is either chemically imbalanced, or works in civil service.

rainedave

My Feedback: (1)

It's definitely true that there have been and probably always will be a select few 1/2A FF designs that can beat the pants off of the stuff designed specifically for .19s. Otherwise there would have never been a market for .051s in the first place.

Tim Wiltse-RCU

There was about 265 Medallion .051's made FYI.

LAter,
Tim

rainedave

My Feedback: (1)

They should have been making more Medallion .049s. It's the only Cox front rotor allowed in 1/2A NosGas. Others that come to mind are the Holland Hornet, Fox FAI, Testors/McCoy. Wen-Mac and OK Cub. With the exception of the Hornet, it's about the hottest ticket going right now.

Tim Wiltse-RCU

ALL true factory Medallion .051's will have a nunber on them. Cox made them special for Bob Bearcroft in CA. As far as I know they were never sold at retail stores.

LAter,
Tim

rainedave

My Feedback: (1)

Beecroft and Bob DeShields, too, for that matter, are world masters with jap tissue. Their work makes me want to quit the hobby in shame.

Check out these Cox engine's on Beecroft's web site:

http://www.theaerosmith.com/photo4.html

Tim Wiltse-RCU

Bob is a great guy. Leo, who's 1/2a engines are pictured on Bob's site is a great guy too and has bought about 10 of my custom engines. Heck the first anodize engines Leo sold had crankcases anodized by me.

Later,
Tim

rainedave

My Feedback: (1)

Tim, that is really cool! So, are you active in FF in NC? I've all but given up on finding a field large enough for even the 1/2A stuff, much less my B and C models. I'm afraid most are collecting dust in the garage until I can find a locale.

Tim Wiltse-RCU

Dave,

No ...no FF for me. Just the thought of letting a model go without control scares the heck out of me. I'm just a run of the mill 1/2a engine freak!

Later,
Tim