Are venturi + needle assemblies available for the AP 061 ?

I have 2 of these, and they are great , except for very fiddly

needle setting with the carb wired open, wonder would they

be more stable with a conventional venturi / needle setup ?

Vincent

Way to go Larry,,  i am anxious to see if you can fit a spraybar thru that small hole in the crankcase or if you have to put it above in the venturi itself.. Hurry up!! 

"Does that mean that conversion parts could be imported

direct from source ?"

I would think so.  I am going to investigate that too.

First off, after a bit of thinking and measuring and thinking some more I was still stumped on how to make a nice control line venturi/needle valve for the AP061. The two small holes on the crankcase where the two small retaining screws for the throttle go are too small to fit a needle valve and the there is not enough meat to comfortably thread so as to take a couple of grub screws to hold something in place.

So, a bit more thinking, fussing, measuring and some more thinking the answer popped into my head - I found I could mount a Cox 049/051 Tee Dee venturi/needle valve assemble to the AP061 and all I needed to do was make a small adapter and glue it into the AP061 crankcase.

Easier said than done in fact.  This small adapter needed to be threaded 1/4-32 so that the Cox venturi would screw into it like it does on the Tee Dee's and it needed to fit the small diameter of the AP061 crankcase as well. To put it into perspective, the outside diameter of the 1/4-32 thread is 1/4" or .250 (in reality a wee bit less) and the outside diameter of this small adapter needs to be .276". Not a lot of room.

Drilling and tapping a 3/8" piece of 6061-t6 aluminum was easy as was turning - carefully - down to .276" diameter. Parting the piece off was another story. I would just get started parting the piece off and it would shear off on one of the internal threads leaving a piece as long as I needed plus the length of the parting tool. I managed to clean it up however, just required 10 minutes of fussing to get it done. I tried cutting one off using a Zona razor saw but once I got the cut started the blade was dragged off course by the internal thread.

All in all, not a difficult machining job just one that was fussy. The end result is a little adapter that I will glue or rather retain in the AP061 crankcase with Loctite 609 retainer. 620 or 648 would work too but I happen to have 609. These types of retainers are not the same as thread lockers. They are made to cure in the absence of air and are used to fix parts together that have close fitting tolerances such as a gear or pulley on a shaft.

Photo one shows the AP061 with the Cox Tee Dee venturi assembly fitted, photo two shows the parts of the Cox venturi assembly and the adapter is the little aluminum piece in the foreground.

Dimensions for those interested are .276" diameter by .165" long.

An even easier way of making a servicable control line venturi for the AP061 is to use the throttle that it comes with. No, I am not talking about wiring the throttle wide open and leaving it at that but the end result is pretty much the same.

It seems the steel barrel screws onto the brass fuel nipple/orifice and is what retains the barrel in the carb. Basically what you do is

1) remove the needle valve
2) remove the clickers and throttle arm by removing it's retaing nut - use a 5mm nut driver
3) unscrew the steel throttle body
4) degrease and clean the carb body and throttle barrel
5) using Loctite 609 or similar retaining product (not threadlocker) on the inside surface of the throttle body and externally on the throttle barrel - screw the barrel back onto the brass fuel nipple/orifice. Be careful not to get any retaining fluid on the brass orifice or you will never get the brass fuel nipple out again (unless that is of course if you want)
6) reassemble and replace the throttle arm with a washer and you now have a serviceable control line venturi for the cost of a bit of time and some Loctite retaining compound.

Photo three shows the venturi mounted on the engine and photo four shows the parts of the throttle


cheers, Graham in Ottawa Canada

Good show! and great photos.  How does the Tee Dee venturi run?  Are you using it to fly aerobatics?

Thanks.  I am more a sport flyer than anything else.  One of these engines will be going a White Lightning all sheet design, details here: http://www.hippocketaeronautics.com/cl_sp_white_lightening.htm

I measure the Tee Dee venturi at .116" diameter and the AP 061 carb at .120. the air flow through the Tee Dee venturi is cleaner with less sharp bumps than the AP061 carb and a more "venturi" like profile rather than just a straight sided hole.

 I have only run the Tee dee mod a couple of times on the bench and it is runs pretty much the same as with the AP061 carb. With a Cox gray 5x4 prop and AP061 carb I was taching around 19.5K. I didn't tach it with the Tee Dee mod. The Tee Dee needle has a finer thread and has a bit more feel. My preference is for the Tee Dee version.

Of course, if you have one of the KK needle valve assemblies that would work too.  Hank Nystrom of Texas Timers still sells a KK like needle valve assemble, details here:

http://www.texastimers.com/accessories/needle_valves.htm

cheers, Graham

Great work Graham, thanks for the report!!  Did the carb barrel fix last summer, runs fine but i couldn't get the hole lined up in the exact center of the venturi , may try to make a washer to shim it out a little or drill the hole in the barrel out a little but it does run okay. Had thought about the tee dee venturi and even trying to drill out the holes in the crankcase to fit a Driskill spraybar but both seemed too "iffy" . I now run one AP with the throttle wired and one with the barrel fix, both run fine, but both have had the venturi screws in the crankcase come loose at least once!!    Ray

I several cases with the venturi screws coming out on the AP's to the point I finally just took them out, mixed up some JB Weld, and cemented the venturi in place.  No issues to date, plus if you go in inverted, it doesn't crack the casing, the Venturi just releases from the body.  Recement it in place with some more JB and your back to flying in a couple hours.

I several cases with the venturi screws coming out on the AP's to the point I finally just took them out, mixed up some JB Weld, and cemented the venturi in place.  No issues to date, plus if you go in inverted, it doesn't crack the casing, the Venturi just releases from the body.  Recement it in place with some more JB and your back to flying in a couple hours.

That is one way to skin the proverbial cat.  I was chatting with another flyer just recently about this very subject and he mentioned that they (the group he flies with) was making venturis out of delrin and gluing them in with JB Weld. I would have thought that delrin would not bond well with JB weld - I have never tried it so I am just guessing. Their venturis are just turned to size with a conventional needle valve crossways through the tube. I had considered that too but I had a Tee dee assembly sitting around and thought it a better way to do it.  I guess in the end, whatever works and is reliable is just as good as any other - unless you are looking for that last 1%.

Got me thinking though. I often see venturis made from delrin or similar rather than aluminum. Any good reason why? Cost, machinability, or something I hadn't considered?

cheers, Graham

I am surprised no one has mentioned that my AP061's don't have the typical AP061 spinner nut. They both have Norvel cranks and Cox red anodized spinners on them.

cheers, Graham

I think the delrin is used to try to insulate the needle valve assy from engine crankcase heat.  As far as machining, I'd rather make something from 2011 alum bar stock than any plastic, the plastic moves around too much!  I have found 2011 to be the easiest machining alum around, I get mine from McMaster-Carr.

I've seen a picture of the c/l version of the AP .09 . Soon as I get to town again I'm sending the carb off the .09 and a enya .09 needle valve to Lee's machine to make me a venture for the .09 . I'll let you all know how it works. 

Here is a picture of the control line version of the AP .09

Grahm Collins sent me a couple of his adapters.  I installed one and flew it today.  WOW!  I think I both gained rpm and got a steadier run. The plane turned 3.8 second laps on 45 foot lines running 15/24/2 fuel.  Rock solid through maneuvers.  I am one happy camper.

This was using a stock Tee Dee needle assembly.  I will try the Texas Timers fine thread assembly next.

In addition, I started the machining of a custom venturi that uses the smallest of Eric Rule's needle/spraybar assemblies.  What with grandkids and Mother's day, it will probably not be finished until next week.

So Larry, where are we in regard to having a venturi/nva available for these little beasties?

Thanks for the update.  I'll want one when you get it ready.

Larry,

"Well, I tried to turn a new venturi per my drawings out of some plastic I THOUGHT was Delrin, but it must be HDPE, as machining it was a nightmare.  Couple of hours wasted.  I'll do one in Aluminum!"

Just call Henry Nelson.  He makes the cox venturi in quite a few sizes for his rear intake team race engines.  Also can't beat the price and elimination of hassle.

       I purchased one of the Ap's a few months ago. I'm currently building the White Lightning and initially had a TD set for power. Lately, I've been having fuel feed issues with the TD's. I don't seem to have the same issues with the Norvel's and Stel's engines I'm running. It seems that the plane is maneuvering so quickly its running away from the fuel. Looking at my Ap tonight I was noticing the difficulties as described above trying to get a venturi needle set up. I also figured in the event I was to use the stock set up, would opening the venturi hole and also the carb barrel give a bit more performance? Would this enhance performance or comprimise fuel draw? It always seems to me that carbs in general never give the same run or rpm's that the standard venturi and needle give. I was able to build this profile with the ability to switch engines. Larry Renger stated some time ago that even though the bolt pattern is typical the case length is not. I was able to meet in the middle before drilling my holes. I now have a plane with little effort I can switch engines. I feel this Ap is going to be the winner here. I'm quite fond of the price and its availability. I can't wait till my plane is finished. I've had it on the back burner for over a year and made some real headway the last few days. Ken

Good day all,

Thanks for the update Larry and Bill. Glad to hear you are pleased with your results.

I have been doing some more bench running with my AP061 and Tee Dee set up - I haven't had the chance to get out flying much so it is the next best thing.

The engine I modified is still performing well on the bench. Turning a Graupner nylon club of a propeller of size 6x3 it runs pretty steady at 18.5 to 19k. I still have a fuel tank problem and will have to solder up a new one. I have been trying the film container tanks a try and for some reason they are leaking around the snap on cap and I haven't figured out why - makes quite a mess

After a half dozen runs I noticed that one of the head hold down bolts seemed to be missing. After I stripped the engine down it turns out I had somehow managed to twist the head off one of the bolts and hadn't noticed - busted clean off and flush with the crankcase. I use a torque driver just so that I don't overtighten these tiny bolts and these where the original bolts so there must have been one that was a bit "below standard" to have broken off so easily.

I wasn't sure how I was going to get it out. I tried an old trick of using a warmed solution of alum soaking overnight. The alum will encourage the oxidation of steel/iron and does nothing to non-ferrous metals. Funny thing was that when I checked in the morning the whole crankcase had turned an interesting colour of grey not unlike oxidized magnesium. The soaking loosened up the broken off bolt enough I was able to turn it out through the bottom after much fussing and after a good scrubbing under running water the crankcase looks non the worse for wear except for the tarnished colour. In my notes I had previously noted the weight of this crankcase as 14.6 grams and now it is 14.4 grams - clearly it has lost some of it's metal due no doubt to some sort of oxidation but alum is not supposed to cause aluminum to oxidize! The insert in the venturi for the Tee Dee parts was just a shiny as it was when I put it in (it is made from 6061 aluminum). So the question is - what is the crankcase cast from ? Aluminum no doubt but what else is in it's make up? Silicon? ? ? Anyone care to take stab at an explanation?

And further to the broken bolt I discovered the piston/cylinder has a very nice scratch/gouge in it! Possibly from a blown glow plug. Oh, well it was still running well so I will put this one back together and use it as is. I guess it's time to get another new one!

As to availability and cost of Cox parts - yes these parts are getting harder to find and on the pricey side. However, Bernie AKA Xenalook on eBay is now listing Tee Dee needle valve parts but not the venturi part. I have been meaning to contact him and see if he will be reintroducing these parts as well. He has stated that he intends to start manufacturing some other Cox parts but is pretty quiet on exactly which ones.

http://stores.shop.ebay.com/XENALOOK  Maybe if enough people pester Bernie?

Select Hobbies lists some Tee Dee parts  http://www.selecthobbies.com/enginepartsdata.htm but are a bit pricey.

I am sure Larry will come up with something quite suitable but in the mean time, if someone would like to try the Tee Dee mod I can make up some more of the little sleeves/adapter. email or PM please.

cheers, Graham

The engine I modified is still performing well on the bench. Turning a Graupner nylon club of a propeller of size 6x3 it runs pretty steady at 18.5 to 19k. I still have a fuel tank problem and will have to solder up a new one. I have been trying the film container tanks a try and for some reason they are leaking around the snap on cap and I haven't figured out why - makes quite a mess

All film canisters are not created equal--get a sackful and sort through them. You'll find some will have very tight fitting caps; use those for straight tanks.  The loose ones are still good for balloon tanks or pressure bladders.

You can get them by the carload at any camera store, or anywhere that still develops old-fashioned film!

Maybe you could ask them to save 'em for you rather than recycle.  But camera stores aren't the only source--the last batch I got was from a local drug store that does film developing.  They seemed glad to have me take them off their hands.

Goop adhesive is the stuff to use.  It isn't perfect, but takes about a year to break down from fuel exposure.  Silicone Seal is nowhere nearly as good in my experience.

Larry,

Thanks for the report on your modified AP Wasp engine. Good news indeed. 

I'm going to mount my Wasp on the bench, and do some break in runs on the stock engine. When it's run in a bit, I'll do the TD venturi installation, and get a comparison.

Bill

Larry,

Looking forward to your venturi tests!

I've looked at Eric's web site, but only see the larger Super Tiger needle valves. Which one are you using?

Ran one of my new AP Wasps on the bench today.

None of the shops around here stock the all Castor fuel the AP instructions recommend, so I had to compromise. Used a pint of my thirteen year old Dukes fuel, with added Castor to bring it up from the original twenty percent pure Castor, to twentyeight percent Castor. Added enough Norvel 35 percent nitro fuel, to bring the total nitro closer to fifteen percent. I calculate the blend to be twentyfour percent pure Castor, plus a little synthetic from the Norvel fuel.

The first run (3/4 oz tank), using a 5.7 X 3 APC prop, with the carb wired wide open, gave me a steady 15,300 rpm. The second run showed 16,400 rpm! Both runs were just off peak rpm, so the the engine leaned out normally at the end of both tanks.

Had to use my starter for all starts, because the piston to cylinder fit is very tight. Hand flipping never got it past the first compression stroke.

One thing I noticed while adjusting the needle valve, is that it's very sensitive to touch, and pushing down very lightly on the needle seemed to richen the mixture, and dropped the rpm a noticeable amount. I suspect the R/C carb tolerances are a bit loose, but a fixed venturi should cure that.

Bill

Hi Doc,

The AP carb probably has air leak issues as well, but in this case I think it's loose threads on the needle valve/carb rotor. The engine appeared to richen up and not lean out when pressing on the needle valve knob. I'm going to use a short length of fuel tubing to seal the needle for the next runs.

Bill

Installed a short length of medium fuel tubing under the needle valve, and hope to get some more runs on the bench next week. Easy to see why the needle settings are eratic, as the fit of the needle is very sloppy.

Bill