MJD

My Feedback: (1)

I'm about to display my ignorance of the impact of SPI on throttling.

Is it exhaust throttling or carburetting that doesn't work with SPI? I tend to think exhaust throttling, but forget.

I want to kinda throttle a tank mounted TD .049. I have a Cox .05 carb, and I have a nice exhaust throttle.

aspeed

I just looked at an exh. throttle that was made for it. I only bought it because I wanted the twin port cyl. Anyway it has sub piston induction. I think only the mufflers don't like the SPI. I think I had a muffler with the silicon wrap over that worked on a standard cyl too. I machined the muffler so it wouldn't throttle at the time, and then never used it again, but remember it throttled well. It was in the 1970's.

MJD

My Feedback: (1)

I just read on the MH site - the TD .05 with carb and muffler has no SPI because of backpressure from the muffler.

http://www.mh-aerotools.de/airfoils/cox_frameset.htm

Under Tee Dee line, .05 RC


A fellow RCU member was kind enough to give me one of these Medallion exhaust throttle assemblies, just the exhaust side, and I had hoped to put it to good use on something. I'll just try it and see. It fits the thinner walled cylinders.

aspeed

These are the two I have. Is yours a muffler, or just a throttle? I can't tell from the pic really.

combatpigg

My Feedback: (3)

Having SPI with a muffler sounds counter-productive..but I do not know how much difference it makes.
Try it..!

MJD

My Feedback: (1)

It's a variable restrictor only, it is part of the Medallion throttle assembly which was linked to some contraption on the intake, which I have not seen in person only in this pic.

I'll just try it out and see what happens. It will either work or it won't.

Cross Check

Hi MJD,

It works great on my reedy product .049s.
Have not tried it on my TDs.
Much better than the rotary throttle sleeves.
'Angry sewing machine' idle, with instant throttle response !

I did not know it was from a Medallion, hooked to a carb... Forgot where I picked them up...

Thanks for the tour of 'Aladin's Cave'...

Very inspiring !

Give me a heads up when you go flying. (one hr. drive)
I'll bring my 'Doppler' worthy planes ! ! !

Cheers !

Take care,
Have fun,
Dave'crosscheck'Fallowfield
Maac 6437
Unabashed Combat Team

MJD

My Feedback: (1)

Will do Dave - and thanks again. Your bravery when descending into the dungeon was impressive, and you lived to tell the tale. Not everyone has been so lucky, a couple of guys never came out again. My workshop is a good example of the old saying, 10 pounds of **** in a 5 pound bag.

I didn't know what that throttle was from either, at first I thought from a car, but it is too nicely made. BTW it freed up very easily, just gummy castor. 2 minutes in the ultrasonic cleaner.

It will only take 15-20 minutes of fiddling - on a nice day outside that is - to try it out on a few engines.

When the weather gets good, come on up!

I thought it might be fun on a BW or a tank-mount TD, on front of the L'il Jumping Bean. With micro RC, I think any reedie is more than enough power. Not sure I just want "enough" though.

GallopingGhostler

That bottom one looks like the exhaust throttle ring/muffler off my Cox .049 R/C Bee engine. It worked fine on a Minnie Mambo. Silicon cover has two burnt spots on the insides but still seems usable. R/C Bee didn't have SPI. I put over a hundred flights on the plane, thoroughly wore out the cylinder and piston. It is now in its second life with a new cylinder and piston, just haven't put it in a model yet.

MJD

My Feedback: (1)

Hi George,

I tried to post a picture earlier to show exactly what it looks like, I think it failed. I'll do it properly this time. Next post.. I'll go find it again.

But it is a variable restrictor, i.e. exhaust valve, with a lovely reverse trumpet shaped sliding valve mechanism. Each end is tapped what I presume is 2-56, maybe 3-48 - I didn't check yet - and has a slotted screw for the linkage on the Medallion .049. I just have the cylinder clamp/exhaust valve mechanism, but Dave assures me it works well as a stand-alone exhaust throttle and he ought to know. This guy knows more about this stuff than he lets on.. I'm going to have to go check out the 1/2A proto action at Centennial this season.

Paging Dave... let us know when there is some 1/2A ukie action planned.. please!

The forward end links to whatever the rotating mechanism is on the Medallion .049 venturi, I only have seen a side view and not what goes on in there.. I think a simple flap valve according to the MH website, I don't have one.

MJD

My Feedback: (1)

http://www.mh-aerotools.de/airfoils/cox_medallions.htm

Nice picture here.. 4th one down, 1968.

Wow, the .15 was done the same way, see the bottom. Cool. Never seen one around here.

Cross Check

Hi All,

Tough time posting here for some reason... (Lost two long posts)

Check, Check, Check...

Cheers,

Take care,
Have fun,
Dave'crosscheck'Fallowfield
Maac 6437
Unabashed Combat Team

Cross Check

MJD,

I've never flown 1/2A Proto,
It was proposed at the last Balsa Beaver Meeting, I got to...

Got two TD.049s, I'd like to 'Blow Up Real Good' though !

Found the 'white prop' for the TD.020... Thimble Drome 4.5-2...

Getting a 'CombatPig' MegaSonic engine cleaner together with an old orbital sander...

And seeing if I can get over 40%nitro Omega Pink, at the LHS...

See if this post goes through...

Take care,
Have fun,
Dave'crosscheck'Fallowfield
Maac 6437
Unabashed Combat Team

Edit for spelling, Thimble Drome, I was thinking Thunder Dome !

GallopingGhostler

MJD, that sliding medallion exhaust throttle setup with ganged carburetor plate, saw that on at least one of Ken Willard's designs used also by Top Flite for their all balsa school series trainers. From what I understand, it was a very nice and effective set up. Perhaps the additional cost is why that there weren't many sold. I guess the rotating exhaust restriction throttle won out. It was cheaper to make. Also, weren't they a maintenance intense item, since congealed Castor oil would cause them to stick, requiring periodic cleaning?

I found that with the KRD quick blip sequential throttle on the Cox rotating exhaust restrictor (forward, middle, back again to forward or Hi-Med-Lo back to Hi), I could despite its non-linear response, get an effective high, medium and idle out of it. Pulled back to almost shut I got idle. Pushed forward with it cracked slightly more open I got medium. Then somewhere in the middle I got high.

I've got a .049 Sure Start engine that I put my Ace throttle sleeve on. Might try that on my future DeBolt Livewire Kitten build (got the kit).
http://www.outerzone.co.uk/plan_details.asp?ID=275

MJD

My Feedback: (1)

Dave - They both came through.

I thought you were talking about building a proto model at one point, but I could be confused.

MJD

My Feedback: (1)

I'm not sure there's enough incidence in the wing..?

I had to clean this one up, but it freed up with little trouble after sitting for ages. Don't know about them in service, is there a Medallion forum somewhere?

I don't expect to get linear sewing machine response. Low, high, something in the middle.. ok.

AndyW

My Feedback: (1)

Cox engines do suffer with poor throttling because of SPI at the exhaust and at the intake. But only Cox.

VAs, Norvels, Brodaks are not bothered by SPI.

GallopingGhostler

Regarding wing incidence, Hal DeBolt's Livewire Kitten goes back to 1953. Then, they were using heavier tube (valve) type receivers with heavier B supply batteries (up to three 22.5 Volt flashbulb unit batteries for 67.5 Volts, two 1.5 Volt AA's for tube filament supplies, and at least two pencells for the escapement relay supply). AFAIK, on a milder .049 like an OK Cub, one would need that greater incidence in the wing to haul that heavier load with a weaker engine plus balance out the lifting tail for stunting.

Nowadays I guess one could use an oversized battery for an electric outrunner motor, have an extended flight session for considerable loitering time.

GallopingGhostler

Cox AFAIK overcame that by increasing the bypass porting and eliminating SPI for exhaust throttling. My late 1970's Cox .049 R/C Bee reed valve didn't have SPI.

aspeed

http://www.balsabeavers.com MJD, I think they were going to have the 1/2A proto at the Balsa Beavers club last year. Don't think anything came of it. At least nothing was posted. I think the paved circle is a bit big for landing a 1/2A, but a strong landing gear should be ok because it will tumble a bit. I would like to know about the goings on for the 1/2A or A speed there too if anyone knows. It is a 4 hour drive now for me.

MJD

My Feedback: (1)

Maybe it was you I was thinking of that said they might tackle 1/2A proto.

aspeed

I have a couple old ones. Nowhere to fly them, and the one real proto class isn't around any more.

Cross Check

Hi Aspeed,

The BalsaBeaver meetings got changed to Wednesday evenings, right in the middle of my downtown Toronto beer deliveries...
(Avoiding 'rush hours' is my 'bugaboo'...)

I'll make it to the 'Beauty Contest' meeting to rejoin. I'll ask about any 1/2A Proto plans.

I have a CL re-trainer to enter, that will use up/wear out my old .25 R/C Scale Combat engines.

Fantastic Wealth of Knowledge, and really fun people. Long term goal is to be able to qualify for the '100 mile' Sport Race !
(I have counted laps a few times, It looks like a fun challenge !)

As kids, we flew C/L 1/2A reedy 'Mouse Racers'.

Don't get me started on stories...

Take care,
Have fun,
Dave'crosscheck'Fallowfield
Maac 6437
Unabashed Combat Team

Cross Check

Hi MJD,

When the weather breaks, try the 'Medallion' exhaust throttle...

It easily beats any of the 'rotary sleeve' throttles. (I don't know, or measured any SPI...)

Video proof would be nice...

I'll launch the R/C Li'll Jumping Bean test flight for you...

I suggest any prop you choose, on backwards ! ! !

Cheers !

Take care,
Have fun,
Dave'crosscheck'Fallowfield
Maac 6437
Unabashed Combat Team

MJD

My Feedback: (1)

Hey Dave,

If you want to have some fun one day, I can throw some engines and parts and test stand in a box and we can get together to play Cox "a la carte" engines sometime.