On June 28, 2017 Flight Rail Corp. received a letter from three students in the Netherlands with questions about building a small scale atmospheric train. They began conversing with Flight Rail Corp.'s Engineering Manager, Eric Schlienger Ph.D. regarding their class project:
Wednesday, June 28, 2017
My name is Remco Gloudemans, I'm 17 years old, I live in the Netherlands and I'm doing a school project with two friends. We saw a video of your train and we thought it was a great project for us. We are now trying to build a train by ourselves because we think it is a great train for the future.
We only have some problems. We made a scale model of 70 centimetres (2 feet 39⁄16 inches). This model was working. (You can see in the video in the appendix.) Now we are trying to make a bigger model of 4 metres (13 feet 131⁄64 inch) but the model isn't working.
Could you tell me how we could make a better or good scale model?
Thank you in advance,
Thursday June 29, 2017
Thank you for your interest, I am certain you will find this to be an interesting project. I assume that you are only talking about a difference in the length of the tube and changing that length from 70cm long to 4m long. It looks like the diameter of the tube is about 5cm, and I assume that has not been changed. The only difference the length of the tube should make is that it might take a longer time for the train to start moving since your vacuum pump might require more time to remove the air from the tube in front of the train.
Some things to check:
Does the train car move as freely on the new tube as it did on the first one?
With the vacuum pump running, if you use your hand to cover the tube behind the train, can you feel a vacuum being pulled? If so, and you wait a minute then remove your hand, does the train move? It might be that your vacuum seal in the tube is not good enough.
Without the train on the tube, have you been able to verify that the vacuum pump is working as well as it should be?
Are all of your plumbing connections tight?
My guess is that your problem is either more friction than you had before, a vacuum leak, or the pump is not operating properly. As mentioned earlier, the only scaling issue with increasing the length of the track should be in the time it takes for the train to start moving.
Please let me know how you progress and please let us know if we can provide you with any further assistance.
Eric Schlienger Ph.D.
Flight Rail Corp
Thursday, June 29, 2017
Dear Mr Schlienger,
Thank you very much for your quick response. The diameter of the small tube (70 cm) was 3,03 cm and the diameter of the big tube (4 metre) is 3,36 cm. Because of the change of the diameter we changed the thrust carriage. We made the thrust carriage out of heating tube isolation and it worked in the small tube and a few times in the big tube.
The answers on your questions: Yes, the train car moves as freely as it did on the first tube. Yes, you can feel the vaccuum when the pump is running. Yes, we were able to verify that the vacuum pump is working as well. We don't have plumbing connections because the tube is made out of one piece of PVC.
With the help of your information ánd questions we were able to make the train ride again! Thank you very much! We think our thrust carriage was too wide for the tube so there was too much friction and it wasn't moving. We made the thrust carriage thinner so air could pass along the tube.
We're looking forward to hearing your reaction,
Friday, June 30, 2017
Good to hear it! I am glad you were successful.
I have included a photo that shows one of our early test systems. This system uses a 30cm diameter tube. As you can see, it is powered by 3 vacuum cleaners. If you have a vacuum cleaner available to use in your experiments, you might be surprised at how well it works.
We found that the system operates most effectively when both sets of magnets are supported so that they do not contact the power tube. If the system design allows the magnets to pinch the power tube, then the friction can make motion very difficult.
Friday, June 30, 2017
Hi Mr. Schlienger,
We use a vacuum pump instead of a vacuum cleaner which works pretty fine as you can see in the video in the appendix. The pictures show our tube, the thrust carriage and the train car. We have lowered the magnets in the thrust carriage so they don't touch the tube. It works even better now!
Thank you for your advice and interest in our project! We'll keep in touch
Friday, June 30, 2017
It looks great! I am impressed with your design and system. I mention the vacuum cleaner because of the typical pumping characteristics of a vacuum pump vs. a vacuum cleaner.
I believe you will find that lower pressure that may be achieved using a vacuum pump cannot be effectively used due to the limited gas flow that your vacuum pump delivers. On the other hand, although only able to provide a smaller ultimate pressure differential, the higher gas flow available with a vacuum cleaner type blower may actually be better suited to the application.
As an example, our large system out in the vineyard only achieves a maximum differential pressure across the thrust carriage of about 130 Torr. Our speed limitation is due to gas flow, not pressure differential. Although scaling (cross sectional area of the power tube vs. volume of gas which must be removed) has an impact, an experiment with a vacuum cleaner might result in a higher velocity than you have at present.
Keep me posted and good luck!
Thursday, July 6, 2017
I have been out of town and I suspect that your project is now complete. I hope it went well.
We would like to mention your experiments, may we use your video on our blog?
There are multiple formulae for the train design and many of the are specific to what you are trying to determine. Train weight, track grade, top speed, acceleration, distance between pumping stations, leakage, wheel friction, seal friction, aerodynamic drag, distance between trains, temperature swing, etc. all factor into a successful design. The most important formula is the one for the cross sectional area of the power tube PI*R^2. This area used in conjunction with the pressure differential provided by the pump determines the static force available to begin moving the train and must exceed the breakaway force of the system in order to allow motion to start. Once motion starts, the ability of the pump to move air must be compared to the maximum achievable pressure differential. This is where pumping curves become important and why a vacuum cleaner might have given you a higher speed, while your vacuum pump would have allowed the train to climb a steeper hill.
Hopefully you were able to arrive at formulae sufficient to complete your project satisfactorily.
Friday, July 7, 2017
We would be honored if you use our video on your blog!
We've used the by you named formulas: they worked out really fine. We're now finishing our report. By the time you'll read this, it will be done.
Thank you very much for all your helpful advice,