Turboprop PJ experiment update

[racketmotorman]

Hi Guys
The turboprop PJ is getting closer , the freepower turbine wheels made , mounted , transmission to the prop finished , inlet guide vane (IGV) set for the freepower finished , just need to make a ~50 lb/25kg thrust engine to provide "the wind" for the turbine .
I'm looking for plans to build a valved engine with a ~4 inch /100mmdia exhaust pipe , this will suit the dimensions of the freepower turbine .
So if anyone knows of some suitable plans it would be appreciated if they could point me in the right direction , otherwise ...LOL ....I'll have to design one myself , and I don't want to have to "reinvent the wheel"as there are undoubtedly some perfectly suitable designs out there .
I'm interested in extracting shaftpower , not designing PJs , theres plenty of you guys doing a great job in that direction , no need for another :D
Cheers
John

[racketmotorman]

LOL... Thanks for all the replies and help in finding plans for a suitable engine .

Looks like I'll just have to design my own , shouldn't take too long :-))

It appears as though no one's interested in anything other than wimpy pure thrust engines .

Your loss not mine .

I'll post results when they start coming in on the off chance a new member might be interested :-))

Cheers
John

[El-Kablooey]

It isn't that we aren't interested. Have you considered valveless engines? Maybe if this were posted in the valveless forum you would see more response.

[El-Kablooey]

if the inlet to his turbine was designed sort of like an augmentor, and placed a fair distance behind the pj's tailpipe, the exhaust temp would be dramatically reduced. Once the turbine spooled up and the "augmentor" was able to entrain some fresh air anyhow (assuming that it was able to).

[racketmotorman]

Hi Guys
LOL...Thought that might flush a couple of replies out of the woodwork :-))
I've already started construction of the engine , using reed valve sets (4 of) from yamaha motors with some special mods to isolate them from the fire and extend their life span .
The reason I wanted a valved engine is the fact that theres only one "exhaust " to worry about , and those positive valves at the other end can't be so easily upset by my experiments downstream .
Having looked at a fair few pics of engines running , it looks like theres a temperature gradient from the main combustion area out to the extremities of the exhaust , I'm using stainless steel for everything that'll be subjected to hot high speed gases .
The freepower is setup in a sort of augmentor , pics in my folder over on the Yahoo DIY Gas Turbines site , so there will be some ambient airflow mixed with exhaust gases , hopefully this will limit blade temps .
The turbine will only be turning 15,000 rpm max, so the loads won't be too great on the blades .
Anyway back to my workshop , I'm currently constructing a wooden mockup of the valve holder before making it in steel , the whole valve head at the end of the PJ will be held on by a Vband clamp for quick removal , sorta like the housings on a turbo .
Thanks for the input , hopefully I'll have the engine fired up in a coupla weeks and I'll let you know what happens .
Cheers
John

[El-Kablooey]

come to think of it, I don't believe you will have any EGT problems. Running my lockwood one day, I held a piece of aluminum flashing about 8" behind my tailpipe. I only managed to hold on to it for about 10 seconds while it vibrated violently then it pulled free from my fingertips and flew about 30 feet across my yard. My point is that it did not melt, or even show any signs of being heated. I know inside the tailpipe temperatures are extreme, but I think exhaust gases are rapidly mixed with fresh air as they exit. Another time I had my engine about 5 feet from a small but bushy shrub, the shrub layed back from the wind and finally broke, but it's leaves did not even curl up.

[racketmotorman]

Thanks for that encouraging news on the temps , I was hoping that there'd be a "slug" of cold air between each hot pulse going thru the turbine , giving a much reduced mean temp .
Cheers
John

[El-Kablooey]

One more thing, I'm no expert on valved engines (or valveless for that matter) but I think aluminum is a better material for your valve head than steel, because it dissipates heat so much better. This should be good news to you< since aluminum is much easier to work with>

[racketmotorman]

Hi
The main reason for going steel is the fact I can weld the bits together ,If it works I might get a casting made in alloy at a latter date , though I don't want too much heat transfer to the reed valve sets , I'm thinking of useing compressed air (low pressure) to insulate them , at a latter date I can run a low pressure airpump off the shaft drive to do the job .
The reeds will be set into pockets with only a connecting port to the actual combustion area (two stroke technology)
Cheers
John

[El-Kablooey]

I see.. Hey if you do decide to have a casting made let me know, I have a furnace and complete sandcasting outfit, and a fair amount of experience. I haven't messed with any alloying, but I could cast you one out of Al. I would do it just out of interest, all it would cost you is shipping your valve head here, and both of them back to australia.

[Ray(GB)]

Hello John, R.M.M.,
Seems like a great idea to have a pj driven shaft for turbo prop,for aeroplanes.
Well done.
I wish you every success.
Might buy one from you if the price and thrust is right.
Ray.

[Mike Everman]

Best of luck, Racket. Even if you don't go for shaft power, I think that a ducted free turbine itself will make the ultimate augmentor, making thrust even during the intake phase. My efforts of the last year have been toward a free turbine/fan something like the attached, only now I'm supporting the fan, which is smaller than shown now, from the front, with a tricky way to keep the bearings cool. Hopefully we can come at this from different angles and learn something!

[racketmotorman]

Hi Ray (GB)
The prop's there to put load on the freepower , and has a variable pitch capacity ,so I can sorta "dyno tune" the PJ output , I've got the fan blades set at full pitch at the moment, just in case, don't want an overspeed on my homemade turbine wheel :(
I'll check the rpm of the shaft and then adjust the pitch to get turbine rpm up to design speed .
Changing pitch means pulling the fan apart and setting the blades into new locating lugs , a bit time consuming but at least its available .
With the horrendous thirst of PJs , I don't think one would get very far on a tank of fuel in an aircraft situation , I'm thinking more maybe for a ground based vehicle , perhaps another shaft driven kart project where the extra fuel won't be a problem.
It'll be a "one off" project for me before going back to making turbine engines , I wanted to do something different for a little while , been at the turbines for going on 14 years so needed a break .
I'll make all my results available , so if anyone wants to continue on , they might get some help from them .
Cheers
John

[racketmotorman]

Hi Mike
Yep a fan/turbine combo would certaily be the ultimate augmentor for a high speed airbourne application , they did something similar with full sized turbine engines , the only problem was the extra loading on the hot blade/fan root section , but with our reduced rpm from the lower gas speeds into the turbine it shouldn't be a problem with a rotating assembly made from a decent Inconel .
Have you been able to have a look at my freepower pics over on the Yahoo DIY Gas Turbines site ( Rackets folder)

http://photos.groups.yahoo.com/group/DIYGasTurbines/lst

for some idea of where I'm heading with regards the inlet guide vanes for the turbine .
I gather you'll be pumping fuel thru the bearing area for cooling , with so much being consumed , a perfect solution :D

I'm still a little concerned about my IGV blades being able to handle the temps ( they're only sheet steel),.
I'm contemplating running water to the centre spike, which will be a small resevoir, from which the water will squirt from a small hole in front of each IGV , a windscreen washer motor and large water tank I had for water injection experiments on my turbine engine should do the trick of spreading a little cooling over the hot bits , which in conjunction with the "normal" augmentor type ambient air that will also be entering the setup hopefully will keep things from being overstressed .
The PJ's stainless pipe work is being made up this week by the sheet metal guys , I dont have the facility to weld thin stainless :(
Then just the valving and fuel systems .
Its getting closer .
Cheers
John

[Mike Everman]

they did something similar with full sized turbine engines , the only problem was the extra loading on the hot blade/fan root section ,

I have seen your work, John. Very nice.

I hadn't thought of fuel cooling... hmmm.

My shot at it was for my blades to be hollow, airfoil section made from sheet ss. If the blades have exits at the tips, then the whole fan becomes a centrifugal air mover, drawing cool air in and about the bearings at the center, through a tube that extends outside the hot jet.

The other way was a bent motor, with the advantage that the blades are in cool air most of the time. See attached.