stunthanger.com
Building Tips and technical articles. => 1/2 A building. => Topic started by: Motorman on March 12, 2017, 12:09:40 PM
-
blank
-
What's a good .049 for stunt? I've got Fox FAI, Cox TD, Cox Medallion, CS, Picco PZero with Gifford crank and Cox Black Widow.
Thanks,
MM
Hi MM, of the engines you've listed; the Cox Medallion is the best choice. It produces the right amount
of torque in the right RPM range. The only engine that is better for 1/2A stunt; and when I say 1/2A,
I mean engines up to .504 cu"; is the PAW .049sbr or tbr diesel engine. Sorry folks, a 1.0cc or .061cu"
engine is not a half A engine! Look in your AMA rule book for engine classes. :o
The Cox .049cu" Medallion will fly a Pinto beautifully. Barry Baxter used a .049 Medallion in his
230 sq" 1/2A Stuka design. The Paw .049sbr or tbr diesel can fly a stunt model up to 250 sq"s.
I use PAW .049's because of the perfect torque/RPM ratio and the Paw requires less than half the
fuel amount compared to a glow engine. Good luck with whatever you choose to use. H^^
Tony ;D
-
blank
-
There is a guy in Oregon who was a fanatic over flying 1/2A stunt. He would go to extremes to built a very light ship which at the times, (1980's) the most powerful Tee Dee he could build. High nitro and all in the name of power. He flew them on ,,,,not sure but thing over 50 ft lines in PA. The airplane was named The "Ridiculous" and it flew so very well. My point being that what engine gives you the most power per ounce is the right choice.
K
-
Would a Cox TD with medallion venturi work the same? I think the medallion has the smaller transfers right? Are you using the 1702 or the low compression head?
Thanks,
MM
Yep, it should. That would solve the TD's problem of drawing fuel on suction.
Cox International will sell you it's version of a TD P/C and they work as well as the old #4 that was on the original engines. The Merlin clamp ring heads and drop-in plugs work great too, but they are too high compression unless you use extra copper head gaskets, usually 3-5 of them hits the sweet spot. It's about the same as the Norvel 1/2A head/plug. Cox Int. sells them too. So does Brodak and others.
Rusty
EDIT: I wrote this ignoring the object of the question was for a stunt run. The Medallion is tamer with the porting and crankshaft intake timing. The guys below set that straight.
-
Would a Cox TD with medallion venturi work the same? I think the medallion has the smaller transfers right? Are you using the 1702 or the low compression head?
Thanks,
MM
Hi MM, Nope! The problem with using a TD is what I said in my prior response;
the TD makes max power in the wrong RPM range for Stunt flying. The TD was a great
engine in it's day for Speed, Combat, and Free Flight; or even for fun sport flying.
Changing the venturi will not change the max torque range at all; it also may not
slow the TD down much either. For example I used the stock TD venturi id for
my 1/2A combat models and for a 1/2A speed ship. My 1/2A Combat models
flew between 71-74 mph, depending on particular props used, and my
1/2A speed ship went over 103 mph with a well fit TD engine. all this was with
good old Cox 30% nitro fuel. Again best of luck;
Tony
-
My Sig Sky Ray has Black Widow and is a pain to get a good full tank run....and I know what I am doing with Tanked Reed engines..
All my combat planes use NV, Fora, Pico, TeeDee power--- all on bladder
All my 1/2a balsa stunt planes; Black Hawk PT 19, Baby Clown, Lil Jumpin Bean, and Baby Ring master Bi-Plane are powered by Cox .049 Medallions and balloon tank
The Medallion has several reasons for being a good choice...
1. Easy starting on a standard or balloon tank
2. Run time easy adjusted by tank size
3. More power than any of the typical reed engines
4. Beam OR radial mount ( with a Texas Timers screw in back-plate)
5. Likes anything from 15% to 35% N
6. Wide range of usable propellers
7. Can be made a tad hotter with a .051 P/C set
8. Galbraith and others make a good head that adds power if needed ( I run Galbraith heads and Nelson Plugs)
9. Also uses (as I do) the currently available TeeDee P/C assy from Cox International
NOTE...The Medallion Crank inlet is round hole Vs the TeeDee square inlet and has a slightly different timing...So just putting a Medallion Venturi plastic part does not really Tame the TeeDee
Note2 ...Do use a very good polish of the Medallion crank nose bearing areas...this adds a noticeably fair amount of RPM
Note3...Follow Paul Gibeault's Mouse Race engine hints of P/C fit
-
All excellent advice, I couldn't have said it better! H^^
-
I decided not to use my trust TD 051 in my new Pinto and opted for my G Mark .061 .....Why? Because the G Mark seems to have a very flat torque curve and is not sensitive to needle valve settings. The fuel draw was great running on suction with an ancient 3/4oz Perfect wedge tank. I ran it on homebrew 25% .If you can get your hands on one of these engines you would not be disappointed....PhillySkip
-
Skip, what is a G Mark?
-
When did you get a G-mark? By now that is a pretty rare beastie!
-
I know MM didn't ask for a particular engine but rather a choice of what he offered, Larry has had very good success using the AP Wasp .061. I'm also well aware that the .061 isn't true 1/2A but many allowances have been made for situations like this. It rendered my true .049 bushed engines obsolete in 1/2A combat. For stunt though, it really has benefits knowing you have a little extra grunt if you need it. The AP can still be found but not as readily as it once was. I tried it in 1/2A combat and I had a major problem with the shaft wearing out the bushing in the case. In addition, the engine kept blowing plugs which sidelined the engine due to the fact I spent more on plugs than the entire engine. Seeing MM's posts, he likes a bit of tinkering and machining which I enjoy myself. I had my flying friend machine a aluminum adapter to the AP case with the 1/4-32 threads internally which allows a Cox TD needle valve assembly to be screwed into it. I want to explore this avenue myself again but rather use it for stunt vs combat. I was using a small prop and really running the engine over it's prescribed rpm parameters. I think this engine would be a neat little project as I know Larry talked about this engine for a good bit of time. Remember, the AP was the only engine available for quite a spurt. Jan Holuszko made the venturi assembly for the AP .061. Sadly these are no longer offered. However, if tinkering is in the plan, a simple adapter which uses the TD assembly works equally as well. I used wheel collar screws to hold the venturi in place by just tapping the existing holes in the case. My setup used to be on the sticky bulletin board but I no longer can find it, maybe a search on here can dig it out of the archives. Anyway, I think it could be a very inexpensive alternative which could be real fun. Ken
-
I've run Medallion front ends on TD's with no problem.
I've also downsided TD venturis with good success. Fill the spray holes with greased pins, then epoxy it shut. Withdraw the pins and redrill to a smaller size.
The proper RPM for any event is the RPM the engine wants.
If I had need for another 1/2A stunter I'd make a 4' model with a Ukrainian combat engine.