Wren Free Turbine Plans

[Kawka777]

Hello,
I was wondering if anyone out there has built the MW54 MK1 turbine from Wren. I got these plans available for free from Wrens website. It he only tool I don't have is a milling machine, which would make the machining of the diffuser a lot easier. This is my first jet engine I have tried to create. I'd appreciate any ideas or experiences with this build that you might have.

http://www.wrenturbinesusa.net/mw54-turbo-jet-and-turbo-prop-second-stage-plans

 

[rythmnbls]

I have never built a Wren, but I have built a Kamps and a GR180.

There's a build thread on this site here for the GR. http://www.homemodelenginemachinist.com/showthread.php?t=17433

I'd be happy to answer any questions regarding turbine building.

Good luck with your build.

Regards.

Steve.

 

[Kawka777]

Steve,
I've been currently trying to figure out a way to build the diffuser with out a milling machine. All I have at my disposal is a metal lathe, drill press, welder, and a large variety of woodworking equipment. I have also been trying to figure out something that you can probably help me with. My plans are very similar to your engine. I can't figure out how the combustion chamber is attached to the rest of the engine.
I looked through your photos... your engine is quite impressive!

Mike

 

[rythmnbls]

Mike,

Thanks for the compliment.

Looking at the wren plans it looks like the CC is located by the NGV at the rear and by the two glow plugs at the front. This is a fairly common retaining method. The Kamps design is similar.

Not sure how you're going to make the diffuser without a mill, perhaps you could get a milling attachment for your lathe.

Regards,

Steve.

 

[Kawka777]

Thanks Steve! Now that I look at the planes I can see where attaches. I could try to look for a milling attachment. I doing some drawing on CAD to figure out a way to make the diffuser in multiple parts and have it all screw together. Im thinking to make the stator veins out of sheet metal welded to a strip of metal recessed into the diffuser. It would be extremely tedious but it would save money. I'm building this just to build it and make it run, not to put it in a airplane so weight won't be an issue for me.

Mike

 

[blighty]

hi Kawka,

i built a mk1 wren a few years ago. if i can help.........

diffuser..

i take it you talking about the fins and wedges? in the back of the planes (written instructions) there a few pages on how to mod a milling attachment for a lathe. basically you take the lead screw out and have a spring that pulls the slide down. you then have a guide on the bed of the lathe so when you move the saddle toward the chuck. he cutter lifts up and cuts the fin. you then index the chuck 10deg and repeat.

if your just going to run it up to show your mates kind of thing, then stick with a built up SS NGV. if your going to run it up a lot then go with the cast NGV. built up one tend to warp after a few runs.

when it comes to the inlet cone make it from aluminum. the nylon (what the plans call for) WILL melt.

there is an o ring at the back of the shaft tunnel that holds the rear bearing in place. don't bother with it, they melt as well.

the gas injectors are made form hypodermic syringes, if you can find bigger diameter one its best to use them. the kind they use for taking blood out of your arm. makes starting a lot easier.

and when its all made


[ame]https://www.youtube.com/watch?v=4Pjt-WCSEwU[/ame]

 

[Kawka777]

Blightly,

I am building this as a learning curve. I bought a 1930s atlas model d metal lathe in really great shape a few years ago and have been learning how to use it. Most parts for the wren turbine are pretty simple lathe work or sheet metal work except that dang diffuser. I'll take a look at those plans, for some reason my printed copy didn't have that milling attachment. I was planning on using the built up nvg and was going to make the front nozzle of plastic... Not anymore haha. I appreciate the advise!

 

[rythmnbls]

You might consider making a "dump" diffuser rather than the MK1 type, some of the guys in the GTBA used this type with good results.

The diffuser in the GR is a dump style. The wedges are extended to the outer diameter and the material between them is removed back to the 77mm diameter dimension shown on the wren drawing. This style is much easier to make, and could be done on a lathe milling attachment without too much trouble.

Regards,

Steve.

 

[blighty]

Blightly,

I am building this as a learning curve. I bought a 1930s atlas model d metal lathe in really great shape a few years ago and have been learning how to use it. Most parts for the wren turbine are pretty simple lathe work or sheet metal work except that dang diffuser. I'll take a look at those plans, for some reason my printed copy didn't have that milling attachment. I was planning on using the built up nvg and was going to make the front nozzle of plastic... Not anymore haha. I appreciate the advise!

delrin cone.......

the plans have never been updated since 1999 when they was first made. even the first loade of MK1's had the delrin cone. over time it was found they would distort and change shape. which would mean they would rib on the compressor fan. obviously i found this out after i had made one from delrin. so i used it, after all the planes said make it from delrin.......... it melted!!

i'll have a look at the free plans from wren if i cant find the mod bit, i'll scan the ones i have.

 

[blighty]

You might consider making a "dump" diffuser rather than the MK1 type, some of the guys in the GTBA used this type with good results.

The diffuser in the GR is a dump style. The wedges are extended to the outer diameter and the material between them is removed back to the 77mm diameter dimension shown on the wren drawing. This style is much easier to make, and could be done on a lathe milling attachment without too much trouble.

Regards,

Steve.

i would go with that as well, there are 3 holes drilled in the diffuser. saying they are a pain in the "*&^^%"(^%(%**^$££%&*&ing ass" to drill would be an under statement.

 

[blighty]

page 11

http://www.wrenturbines.co.uk/plans/part_2_mw54_mk1_plans_turbo_jet.pdf

 

[Kawka777]

So a dump diffuser is a diffuser that doesn't have stator veins? The wedges on the front of the diffuser that direct air extend to where the stator veins would end? I have seen three types of diffusers, the ones with stator veins, the one I described above, and ones that have holes where the stator veins would be.

I got access to my schools 3d printer so I am going to print out a redesigned, simpler diffuser (once I figure out what that is) that can be used to determine if I'm getting as much compression as I would with the normal diffuser (just from spinning it up with a motor to a certain rpm).

View attachment ImageUploadedByModel Engines1427332618.742605.jpg

 

[Kawka777]

View attachment 76157View attachment ImageUploadedByModel Engines1427332671.550862.jpg

These are the two different types I've seen besides one with stator veins.

 

[rythmnbls]

So a dump diffuser is a diffuser that doesn't have stator veins? The wedges on the front of the diffuser that direct air extend to where the stator veins would end

Yes, that's exactly what it is. Testing has shown that there is very little difference in performance by replacing the flow straighteners (which are a pain to machine) with the wedges.

Regards,

Steve.

 

[Kawka777]

That's definitely going to be easier... Il design one on CAD and post a picture to see what you think.

 

[Kawka777]

How's this diffuser look? I designed it like you suggested and simply extended the wedges to the outer diameter and took out the stator vanes.View attachment ImageUploadedByModel Engines1427618107.057687.jpg

 

[rythmnbls]

Looks good to me, you will need to round off the outside corners to provide a smooth passage for the gas flow. Here's a work in progress shot of the GR180 diffuser after rounding off the wedges. The edges between the wedges will need to be rounded off with a small radius as well. I would suggest around 6mm for the wedges and 2mm for channel edges.

http://s87.photobucket.com/user/madluther/media/Turbine%202/t2_diffuser1.jpg.html

Regards,

Steve.

 

[Kawka777]

Thanks a lot Steve, I will do that! I'm going to go ahead and 3d print that part and start building the rest of the engine. Il post pictures as I go along.

 

[Kawka777]

Is have been making the shaft tunnel for the Wren MW54... The plans call for a slide fit for the bearings, that is "not too tight but not too loose." I have the front bearing in a perfect slide fit with no play but the rear bearing is 10 hundredths of a millimeter over the OD of the bearing. I am not sure if this is too much because the bearing will be supported on center with a o-ring that is placed around it. The rear bearing is the bearing that is able to move with the shaft expanding. I'd appreciate your thoughts and opinions!

Thanks, Mike

 

[blighty]

rear bearing should be a as you say a sliding fit. don't fit the o ring it will only melt.

the front bearing housing was made 0.1mm bigger than the bearing (think there 16mm bearing could be wrong was a while ago.) so if you fitted the bearing and turned the tunnel upside down the bearing would just fall out. the O ring is all that holds the bearing in position.

what compressor are you going for? 5 blade or the modified 6 blade?