GR Engine Series Q&A

       I receive numerous e-mails every week asking a variety of questions about the GR Engine Series. I figured that a Q&A page would help those that had general questions about my projects. I can add questions as they are sent to me so feel free to ask a question by contacting me.

Thanks, Don Giandomenico

Updated on September 9, 2011

Q: Why did you build the GR-1, GR-5A and GR-7 engines?

A: Being fascinated with my friends turbine powered model aircraft, I searched the internet for information on gas turbines to learn what I could about them. After some time contemplating the theory, I set out to build one as this would further my understanding of gas turbine operation. I had no idea it would become one of my favorite hobbies :0)

Q: Why did you post your project on the internet?

A: I wanted to post my findings for other enthusiasts to see. I found that what others posted had helped me with my project so I figured it would be only fair to repay the favor.

Q: Can I use your articles to build my own engine?

A: My articles are not set up specifically as how-to articles so important details may be left out. I simply do not have the time to post all of the construction details. Although you are welcome to study my work and use the information to help in researching your own project. RCDON.COM or it’s publisher WILL NOT assume any responsibility for damages to persons or property from the use of said information. It is important to realize that this hobby is not for everyone as the dander of operating turbo machinery is real.

Q: Is there any danger in running a home-built gas turbine?

A: YES !!!! I cannot stress how dangerous a gas turbine can be if there is a failure or malfunction. A spinning turbine wheel can generate incredible centrifugal and kinetic force that if released could easily KILL someone. Turbine wheels have shattered and compressor housings have blown apart before. There is no guarantee that a gas turbine won’t experience a catastrophic failure, commercial or home-built. Liquid and gaseous fuels are also lethal if incorrectly handled or used. A fireball could easily engulf an unsuspecting operator causing serious injury or death.
       In the hands of an inexperienced operator, a gas turbine can be just like a hand grenade! Extreme caution must always be used when experimenting with gas turbines or tragedy could be the result!!!
Sorry for being such a downer but it sometimes is necessary :0(

Q: Will you sell me plans for the GR-1 , GR-5A or GR-7 engines?

A: I am currently not offering plans for the construction of these engines as most of the information I am willing to share is already posted on my site.

Q: Will you build me a turbojet/turboshaft engine or parts?

A: I am currently not building any engines or parts for sale to the public.

Q: How much money did you engines cost?

A: The GR-1 had cost me about $650 USD using mostly used and rebuilt parts. The GR-5A had cost about $350 USD additional to the initial investment in the GR-1. New parts would have doubled the final cost. The GR-7, GRV-1 and GRV-2 projects have cost me more than I would like to admit however the learning experience has been worth many times the monetary cost of the builds.

Q: How much time did it take to build the GR engines?

A: The GR-1 had taken about 75 hours to build and the GR-5A about 85 hours.  The GR-7 project took over 400 hours to design, build and test (over a four year period).

Q: Where did you get all of your parts?

A: I purchased about 80% of the parts on eBay. I couldn’t of built my engine without the service that eBay provided me. I was able to find surplus parts at a fraction of the list prices. I use eBay to find all of my “hard to find” parts. McMaster-Carr is another valuable source of parts for my builds as well as Summit Racing and Burns Stainless.

Q: Where did you get your Mini-Lathe and Micro-Mill?

A: I purchased my Central Machinery Mini-Lathe and Micro-Mill at Harbor Freight online.

Q: What kind of welders do you use?

A: I have a Lincoln Weld Pack 100 MIG welder. I use .035 Innershield flux core wire in my welder because I am too lazy to fill an argon/co2 tank :0) This welding setup has served me well for over ten years! For stainless and precise work I use a Hobart Tigmate which does use the argon/co2 mix ;0)

Q: Could you have built the GR-5A without your welder and lathe?

A: Probably not. The steel parts I fabricated would of been extremely difficult to build any other way. If I had hired a fabrication & welding shop to make the parts it would of cost me a small fortune, many times the cost of my equipment.

Q: Why do you use “EMT” or electrical conduit to build parts for your engines?

A: I use EMT because I run into a lot of scrap pieces at work. Stainless tubing can cost a bundle as I have found out with my GR-7 Project!

Q: Why do you choose to use propane as a fuel in your GR-5A engine?

A: The main advantage in using propane is that it is already pressurized and does not require a pump to deliver it to the combustor. Propane also burns very clean compared to diesel, kerosene and jet-A.

Q: Have you considered using a second turbo as a power turbine instead of the axial flow turbine you built for your GR-5A project?

A: Well there are a few reasons I chose to not use a second turbo as a power turbine. One of them would be that a reverse flow radial turbine used in a turbocharger would need to turn very fast to flow the amount of gasses produced by the GR-5 engine. This means that a ultra high speed gearbox would be needed to reduce the turbines RPM to a more useable speed. Not only would this gearbox be hard to find/design it would be expensive. My “slow speed” axial design allows more gas flow with less RPM, even allowing the engine to run while at a stall safely. The 17,500 RPM limit to my turbine is easily geared down with a modified commercial gearbox unlike the 50 to 75,000 RPM produced by a turbo turbine.
       Another reason I chose to avoid using a turbo turbine is that it would need to be a very large one to handle a high gas flow properly without a bypass system. This means the overall physical size of the engine would be bigger and heavier. I would need at least a T-50 sized turbine to do the job and the turbine and volute of a T-50 weighs at least 30 pounds (unless a custom volute is fabricated). This added size and weight was not what I wanted at all for the GR-5A.
       To top off my reasons to not use a commercial turbo turbine is that I wanted to build my own turbine and prove it could work ;0) I agree that the efficiency of turbo turbine is higher than my turbine but not enough to outweigh the hardships of making one work. If I do design another turboshaft engine it will employ a slow speed axial turbine wheel.

Q: Have you run the GR-1 combustor on liquid fuel?

A: The GR-1 combustor formula has been successfully used to build the GR-7 engine although it was modified to accommodate a liquid fuel evaporative system. The formula was key in the design and works quite well.

Q: Will your combustor formula work with any turbocharger?

A: Turbochargers vary from model to model. Some are better suited than others for use as a gas turbine. The GR-1 combustor is a very basic combustor design which may or may not be compatible with certain compressor/turbine combinations. There have been many experimenters that have used my design successfully.

Q: What do you do for a living? Do you hold any degrees?

A: I am an IBEW Union electrician and have been working on industrial & commercial building projects in Southern California for ten years now. I do not have any formal education outside of high school, a couple years of jr. college and my electrical apprenticeship. Most of the fabrication knowledge I have is self taught. I had spent a good part of my childhood taking various gadgets apart and reassembling them for fun.
       I have an uncanny ability to mentally visualize how a machine will work even before I build it. I call it “intuitive fabrication”. 90% of what I have built has never been drawn on paper. This sometimes is bad because I can’t remember what I did later on ;0)

Q: What are your plans for the future:

A: I hope to be able to build new engines and experiment with alternative fuels. I believe that there are new ideas still waiting to be explored. Who knows, maybe one day I will stumble on one of them............

Thanks for looking at my projects.

Don Giandomenico


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