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Old 5th November 2005, 11:29   #16
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A K,

lemme appreciate the efforts first, man, and my 2 cents (based on the assumption that the pics are of a testbed for the engine and not the "production version" of the airframe) here:

- it looks more like a microlight, and not like a drone. I understand the level of usage of composite will push us the costs to stratosphere, butttt, upto what level you are planning to use composites?

- do you share the view that most of the modern propeller-driven drones are "push-types", that is the propeller is placed in the rearside of the aircraft?

- will it be a canard design? Since a canard helps you to boost (means reduce) the stall speed, this will come handy with the low expected outputs from the powerplant. You can also omit the horizondal tail...

- how many design iterations you are planning to have?
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Old 5th November 2005, 15:47   #17
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Quote:
Originally Posted by sandeepmdas
A K,

lemme appreciate the efforts first, man, and my 2 cents (based on the assumption that the pics are of a testbed for the engine and not the "production version" of the airframe) here:

- it looks more like a microlight, and not like a drone. I understand the level of usage of composite will push us the costs to stratosphere, butttt, upto what level you are planning to use composites?

- do you share the view that most of the modern propeller-driven drones are "push-types", that is the propeller is placed in the rearside of the aircraft?

- will it be a canard design? Since a canard helps you to boost (means reduce) the stall speed, this will come handy with the low expected outputs from the powerplant. You can also omit the horizondal tail...

- how many design iterations you are planning to have?

Sandeep thanks for the reply....I am not competent enough to answer your questions..So over to friend and team-member S. Shubha Chethan who is designing the airframe and wing:

"--First of all microlights are driven by pilots & so different from UAVs. And the level of composites used are determined on the levels of refinement achievable for the specific purpose.

--Not necessarily all the modern prop-driven drones are push-types as drones basically are target vehicles. So propulsion type is not the criteria.

--Canards are a good idea but, other than stall speeds there are key issues to be considerded like utilities as it is designed to be unmanned aerial vehicle.

--Design iterations...hmmm....at last count we had built 3 fuselages, 2 wing sections, and 2 chambers for the engine. So its anybody's guess as to how many iterations there were."

I hope this answers your queries.
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Old 5th November 2005, 18:02   #18
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Hey ananth thats a very interesting project you are working on, keep us updated about it. Keep up the great job.
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Old 6th November 2005, 02:07   #19
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keep us updated on how its going.... Good luck
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Old 6th November 2005, 10:36   #20
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Hey Ananth

Cool project, dude! Best of luck with it...I know nothing about what you're doing so no comments except that the engine DOES seem to be rather underpowered. Perhaps you can consider an Enfield Mofa engine for subsequent builds, or even the lightweight Peuguot Sportif aluminium engine...

Keep us posted and all the best !
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Old 7th November 2005, 14:57   #21
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Nasty, isnt it?

This happened yesterday when we finally got the engine running at peak RPM. Although we don't have a tachometer yet, it definitely sounded like it was past 8000 rpm. So on the upside, the porting & chamber do work! Stock engine could never go past 5000 rpm under the same load.

Later we found that the prop had a small fault in it.....the wood had a discontinuity (the black dot you see in the first pics) from where the crack originated & propagated.
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Old 7th November 2005, 14:59   #22
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Quote:
Originally Posted by ananthkamath


Nasty, isnt it?
Yeah...good that you found this out on terra firma
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Old 7th November 2005, 15:30   #23
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@ananthkamath
One very important fact about propeller speeds. At very high rpm the tips of the propellow can go supersonic. this will lead to destruction of propellor. Make sure that the radial velocity is not supersonic.
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Old 7th November 2005, 15:33   #24
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Yeah Tsk we ve taken that into account. With the 20 inch our max tip velocity comes in the region of 900 km/hr which is slightly less than supersonic...so it may hold up.
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Old 7th November 2005, 18:31   #25
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Quote:
Originally Posted by ananthkamath
Yeah Tsk we ve taken that into account. With the 20 inch our max tip velocity comes in the region of 900 km/hr which is slightly less than supersonic...so it may hold up.
ermm...with that 20-inch tip (50.8 cm propeller dia.), doesn't the velocity come to around 766 km/hr @8000 revs...?? and, erm...supersonic's at 1170 or something, isn't it..??

p.s- i may be wrong; so, how did you come up with that velocity..?

and yes, with the sort of jump in revs that you have mentioned, the porting definitely seems to have worked...

keep us posted on the developments, eh...?
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Old 7th November 2005, 22:36   #26
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You're absolutely right, Veyron; that was just a quick and dirty calculation done in the back of my mind...it was done taking into account the max. over-rev rpm (with a factor of safety), which I have tentatively taken as 9500 rpm.

As you know the fomula for tip velocity (km/hr) is pi * D * RPM * 3.6 / 60, where D is in meters. So putting the numbers you get about 900 km/hr.

The jump in revs is just as I had anticipated. But this stage is only a "Stage 1" for the engine....we havent even touched compression yet.

The carb has helped immensely. Note the trick manifold used for mounting the carb.

Last edited by ananthkamath : 7th November 2005 at 22:38.
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Old 7th November 2005, 23:33   #27
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so back to wood carving for now? wont it be dangerous if that prop breaks apart when it was tested at high rpms? and why wood , aint ther a substitute?
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Old 8th November 2005, 12:23   #28
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Quote:
Originally Posted by jkdas
so back to wood carving for now? wont it be dangerous if that prop breaks apart when it was tested at high rpms? and why wood , aint ther a substitute?
wood, mainly because it's easier to fabricate, and keeps the costs and weight low....but i suppose plastic would be better- and finding one shouldn't be that tough; biggies like almonard use twin-blade or triple-blade plastic props for some of their fans...

but then, there's a problem : plastic blades would flex at high revs, and would deviate from the desired angle, and hence not give enough thrust...stiffness is key factor...

hmm..dilemma...perhaps somebody could check out whether the blades from almonards, etc. are stiff enough...

Last edited by veyron1 : 8th November 2005 at 12:25.
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Old 8th November 2005, 13:45   #29
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Wood is still being used for making propellers. Here's a generic page for making wooden props:
http://www.wood-carver.com/articles.html

Would a fixed pitch prop be sufficient enough for self-powered take-off? Or a catapult is required? Or you are going for a variable-pitche prop assembly, AK?

Last edited by sandeepmdas : 8th November 2005 at 13:47.
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Old 8th November 2005, 13:48   #30
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Almonard is a fan if I'm not mistaken, right? I am not too sure, but I think it couldn't function as a prop at all. Fans are meant to swirl airflow with minimum noise, but in props there is no noise consideration; hence they produce more thrust inch-for-inch.

As I said earlier this prop was used only for testing. We have other "proper" props with us. For subsequent testing I am going to use the original blower that came with the engine used for spraying fertilizer.

No Sandeep; there are no plans for variable pitch as of now.

Last edited by ananthkamath : 8th November 2005 at 13:49.
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