Questions about 2 Engine Application

Sandman1
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Questions about 2 Engine Application

Post by Sandman1 » June 12th, 2012, 7:41 pm

In the manual page 12, paragraph 9 " , which is not the same fan used for the single engine version," forms the question: What is the recommended fan for the 2 engine version?
I have a 20hp Briggs and Stratton opposed twin which i tried to replace the 12 hp engine on my Scout with. I never got the performance i had originally. That experiment taught me that I don't understand the critical characteristics of the sev related to performance. When modifying the Scout I added a floation chamber as Mr. Palmer suggested. i choose to put it at the aft wall of the craft, 6 inches front to back, spanning the space between the left and right floatation chambers in the Sevtec design. I eventually moved the skirt spliter bar forward 2 inches with no noticeable performance change. Since i dont understand how the spliter location is optimized; What is the recommended splitter bar location for the 2 engine version with the lift engine moved forward as defined in the manual?
In the same paragraph of the manual it is suggested to move partition skirt back XX inches compared to the single engine version. There is then mention of both arcs being moved. The plan shows two partion skirts the same XX dimension apart. Does the craft as designed have 2 partion skirts? If so do they both move the same dimension? or do the plans show both the single engine partition skirt location and the 2 engine version partition skirt location?
Please forgive the cryptic references. I am trying to respect Sevtecs intellectual property.
The Scout when i originally built it about 10 years ago worked wonderfully, with the exception of my execution of the belt tensioner, until the availible operators mass exceeded the load carrying capability. In that context, with hesitation, i pose this question: assuming the discouraged 2 engine version and the additional availible thrust, what are the arguments for and against increasing the width of the hull 12 inches?
Questions not related to the plan set:
I plan to use an air cooled Harley Davidson engine for thrust. it will be considerably more compact and lower mass that the GEO engine. Would this impact the lift fan location? Is the move for the 2 engine version dictated by mas distribution and or "packing space" for the related drive train components? The the hieght of the center of mass from the ground have a significant impact on function and lift fan location?
i am considering laying up the hull panels on old glass panels from patio doors to reduce finishing time and wieght. Any comments on this process concept?
Thanks for your attention.
i live about an hour from Louisville, Ky. I believe someone there has built a Geoduck. I would like to meet you and see it. If you are watching this forum suggest how we could meet if your willing.

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bphillip2
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Re: Questions about 2 Engine Application

Post by bphillip2 » June 12th, 2012, 10:11 pm

I'm guessing you are building a Surveyor? How much does this 20hp engine weigh? Horizontally opposed sounds old and heavy. If you really want to build with two engines I would scale the hull up to 15x7.5 (1.0714*every dimension) and the add a foot in length if you wish.

I don't know what fan Barry had in mind, maybe 28".

You only get one partition skirt with each plans purchase. The two sets of hard points give you options.

The fan is placed so the lift engine and the thrust engine don't mate.

Your laminating idea is not lightly to work without vacuum bagging. The simple act of joining different panels will nullify the effort anyway. You can minimize the finish work by building a fabric deck like the Vanguard or be careful and use veil on the seams.

My suggestion would be a single engine craft.

Sandman1
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Re: Questions about 2 Engine Application

Post by Sandman1 » June 13th, 2012, 8:42 pm

Thank you for the reply. I apologize for not specifying which sev. I am questioning the geoduck plan set manual. I though this was implied by posting in the folder labeled geoduck. Perhaps my plan set and manual reference will make more sense now. The plans call for a 30 inch fan for the single engine version. My quess is the 2 engine craft has more wieght it might need a bigger fan?
My 2 frustrations with the quality of my Scout build the first time: applying the air craft fabric and the belt life. I would have a belt loosen up and get cut by the prop about every 2 to 4 hours of operation. i accept this as some deficiency of mine not the design but it was severly limiting. Perhaps I couldnt grasp the complexity of operating a 2 engine craft if i cant grasp the belt issue.
A 2 engine craft eliminates the belt from the drive train.
I would rather fill and sand than work with the fabric again. I also am quessing you would not recommend this for the geoduck.
So the Scout is too small; i am 220 pounds and my son, who was 120 pounds 10 years ago is now 275. I dont comprehend the application of belts to the Scout. We would like a sev we could use together.
What model would you recommend we build this time. I just purchased the Geoduck plans on 4/30 but i can buy another. i considered Mariner but it is allot of money and time if i have another fundamental comprehension failure and trailering something that large is not attractive. I live to learn.
Thanks for your time.

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bphillip2
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Re: Questions about 2 Engine Application

Post by bphillip2 » June 13th, 2012, 9:46 pm

Good point on the folder name, but I just click on "unread posts" and never noticed the heading above.

The added weigh does not matter on fan size much, it would be more a matter of matching the engine to the fan.

I can't imagine what was wrong with you scout air drive. I never had any trouble with these mule drives. I replace the belts about every 7 years. Pictures would have been nice. The geoduck drive with a single engine is very robust and won't give trouble if built properly. I worked on and completed an 18x8 1.3L single engine geoduck recently and was most impressed. It is smooth, quite, powerful and great to drive at low speed. It would also reach 42mph. The payload was at least 1100 lbs. I would just hate to see such a nice drive downgraded with a 2 cylinder for lift.

If you can't abide by the right angle drive, build a Prospector, perhaps even with the geo engine.

As for aircraft fabric, I did that on my Vanguard, it took about 3.5 hours and held up great for the 5 years I owned it.

bandit1538
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Re: Questions about 2 Engine Application

Post by bandit1538 » June 14th, 2012, 9:12 pm

Sandman1 wrote:Thank you for the reply. I apologize for not specifying which sev. I am questioning the geoduck plan set manual. I though this was implied by posting in the folder labeled geoduck. Perhaps my plan set and manual reference will make more sense now. The plans call for a 30 inch fan for the single engine version. My quess is the 2 engine craft has more wieght it might need a bigger fan?
My 2 frustrations with the quality of my Scout build the first time: applying the air craft fabric and the belt life. I would have a belt loosen up and get cut by the prop about every 2 to 4 hours of operation. i accept this as some deficiency of mine not the design but it was severly limiting. Perhaps I couldnt grasp the complexity of operating a 2 engine craft if i cant grasp the belt issue.
A 2 engine craft eliminates the belt from the drive train.
I would rather fill and sand than work with the fabric again. I also am quessing you would not recommend this for the geoduck.
So the Scout is too small; i am 220 pounds and my son, who was 120 pounds 10 years ago is now 275. I dont comprehend the application of belts to the Scout. We would like a sev we could use together.
What model would you recommend we build this time. I just purchased the Geoduck plans on 4/30 but i can buy another. i considered Mariner but it is allot of money and time if i have another fundamental comprehension failure and trailering something that large is not attractive. I live to learn.
Thanks for your time.
I had a problem with my Scout spitting the belt off when I first got it running and what I found out by watching was that at lower rpm on one side the belt would get a harmonic vibration and spit the belt off and at hi rpm it would do the same thing on the other side and spit the belt off so I had someone run the throttle and marked on both sides of the air drive frame where the belt moved the most then drilled the frame and cut a length of pipe and ran a bolt through, that solved the problem.
Maybe you might want to look and see if your belt is doing the same and bolt on rub plates or bars.
Pat
If it aint broke, don't fix it.

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bphillip2
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Re: Questions about 2 Engine Application

Post by bphillip2 » June 14th, 2012, 9:57 pm

I don't have a Scout at the present. It could have been a lack of belt tension. Belt touch blocks are commonly used on the mule drives.

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jchovernut
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Re: Questions about 2 Engine Application

Post by jchovernut » June 14th, 2012, 11:37 pm

As Bryan said, the belt touch bars with HDPE tames the slack-side belt flapping issue, which I believe may have lead to your belt jumping the idler. I wholeheartedly agree with Bryan that the single engine 1.3 geo on an 18' hull will pick you an your son up, plus several coolers of beer, and scoot you along effortlessly! It would be nice not to have that opposed twin banging away at the lift!

About the H-D engine: were you going to mount it sideways and belt it up to the thrust? What's the displacement, horsepower, and weight? I haven't seen the HP curves on my 883 Sportster, but you ideally want to have your best torque around 3000rpm or so. The Geo engines are really lightweight, smooth, and bulletproof. You'll be breaking new ground mounting the H-D to the Geoduck and if you had issues with the Scout drive, I'd stick to the plans as closely as possible in this build so others can help out on the forum. If you go the H-D route, no one will be able to guide you if you run into any issues.

The Geoduck in Simpsonville, KY (Louisville area) is owned by John Mills. His neighbor Bruce McElya helped build it and is on this forum. You might PM him to arrange a visit. John also has a Vanguard. Bruce's username on this forum is bmcelya. It is a twin-engine design with a 20 or 22hp Briggs Vanguard V-twin for lift and a Geo 1L 3cyl for thrust.
Bruce has posted some of the construction photos over here: http://groups.yahoo.com/group/sevtalk/p ... 5/pic/list

Andy Tirums is in TN and has a single-fan Honda automotive engined Prospector. His handle is hoverdood over on the SEVTALK yahoo group. There's a folder over there with pics.

Believe me...building as close to the plans as possible will alleviate all kinds of headaches, and will also afford you the best opportunity to troubleshoot or conceptualize by participating in this forum and by watching the SEVTEC builders videos.

Cheers,
John Carter
John Carter
SEVs: Vanguard, FanTastic, Prospector, Explorer
Others: StarCruiser, UH-18P, RX2000
http://www.hovernut.com

Sandman1
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Re: Questions about 2 Engine Application

Post by Sandman1 » June 17th, 2012, 7:53 am

Follow up to both Bryan's and John's replies:
After considering your feedback, how well the Scout performed ( except the belt tensioner ) when built to the plans, and how poorly it it performed when i rebuilt the drive around the B&S opposed twin: i have decided not to use the B&S opposed twin for the lift motor on the Geoduck!
Before I rebuilt the drive module around the old engine I contacted Barry Palmer about the belt tensioner. He guided me to some photos of a better concept and suggested rub bars. I constructed the pendulum with idlers on either side angled to the belt path and added the rub bars. The reconfigured craft performed so badly I never operated it long enough to get to the previous belt failure time.
If i build the Geoduck drive with one engine and want the flexibility to change I will just move the fan location as the plans recommend. Do i lose anything besides some cabin space?
The plans show 2 partitions skirt locations as mentioned earlier. What is the trade off between the 2 locations? how do you decide?
I will post pictures of the Scout when i get my current home project done.
i have some data on the Harley engine to try and generate more input on the viability of this idea. This engine is not unitized with the transmission like the Sportster or most motorcycles. The drive tran has 3 main parts: motor, primary drive, and tranny. The primary drive transmits power from the motor to the tranny. The OEM and Aftermarket have offered both belt and chain primary drives. The motor wieghts about 120 lbs ( could not find an official quote ), mine produces 60 hp and 75 ft lbs @ 3500 rpm. It is air cooled so no plumbing, no engine controler, simple dependable, durable, and designed to be bolted directly to a rigid frame.
Based on these values could it be a good performance fit for a Geoduck?
I have considered mounting the motor crank shaft axis at the prop axis so that I could eliminate belts if I went to a 2 engine set up. Any thoughts? I will try single engine first because if i am going to 2 I will buy a Vanguard engine.
With no coolant or cooling system and a small motorcycle battery there is significant wieght saving potential.
Can i use the hubs from the Scout IVO prop and fan with different blades for the Geoduck?
Thank you for your interest.

dnantha
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Re: Questions about 2 Engine Application

Post by dnantha » June 17th, 2012, 8:26 am

Hi Brott.....I got to ride, and help work on a little, the 18' Geoduck that Bryan had in his shop last winter.. It had the 4 cyl. Geo motor. Smooth as silk . Especially at Idle and lower speeds. The Geo motors are a very simple design. Ive been testing my Kholer motor on the surveyor motor Im building and at certain rpms there is some harmonic vibration. It really is multiplied through the solid mounting to the hull. Almost all motors used on SEVS , and ultra light aircraft.have some degree of harmonics at certain rpms. The 4 cyl. Geoduck has almost none. The Harley motor you want to use has some serious vibrations as you go through the different rpms as you go through the revs on your way to full throttle. Harley has patented the sort of syncapathic vibration at Idle.. It seems to me that a vibration at Idle would become very annoying after a while. The Geo Idles smoothly.. Im not trying to dampen your enthusiasm for experimentation. I love experimenting and will surely drive certain purists mad with Ideas when I get my Surveyor done.. (Getting very close YEY!!!!!). Im just saying that Ive been in the Geo powered Geoduck and it was a great performer. single engine presented no problems and the boat was easy to move around by hand while floating in the air at low vibration free rpms... I enjoy following your posts . Please keep them coming. What your doing is very interesting to me. I should say that Im not very experienced yet with hovercrafts. This is only my second and the first was a disappointment. (a repowered Scat 1 with a 250lb operator), But I am experienced with Geo motors and they're great dependable simple and light.....Dan out

bandit1538
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Re: Questions about 2 Engine Application

Post by bandit1538 » June 17th, 2012, 9:39 am

I'm with Dan on this one about the Harley motor, I've had one (Sportster) and I think you'll have problems with the glass cracking on your air frame mounts from the vibrations, plus it will transmit that vibration through the hull making it one big boom box, if you do use it I think you'll find that you're going to have to use rubber motor mounts. Also you will have to use a spring loaded pulley on the return side belt because of the motor pulses at lower RPM.
As for the Brigs motor, I run the 25hp Brigs Intec on my Scout, it's a V twin vertical and I haven't had a problem except with the starter cellenoid, I also have the same motor in my mower with no problems.
Pat
If it aint broke, don't fix it.

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