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For the real engineers here



 
 
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  #1  
Old June 25th 08, 06:56 PM posted to rec.aviation.piloting
[email protected]
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Posts: 181
Default For the real engineers here

I'm thinking of a clean glider, one that might weigh 1500 pounds and
has a glide angle of say 1 in 25. At 50 miles an hour, that would mean
in an hour's time it might descend two miles (of course scale it
reasonable numbers, I chose those for ease of calculation). That means
it's losing about 1500 * 5280 * 2, or about 16 million foot pounds of
energy an hour.

Now if I add an engine swinging an 8 foot diameter prop, maybe as a
pusher, the question is, how big an engine for cruise only? A
horsepower is 550 foot lbs a second, or about 2 million foot pounds
an hour. If all of that is correct, it suggests with a 50% efficient
prop a little 16 horsepower engine could pretty much keep this thing
at constant altitude.

It passes the reasonableness test as far as I can see. Any serious
disagreements?

For those of you who do things in metric units? I went to school a
long long time ago, and here in the US I can buy a little Briggs and
Stanton (spelling?) engine with a horsepower rating, not a kilowatt
one.
  #2  
Old June 25th 08, 07:10 PM posted to rec.aviation.piloting
Bertie the Bunyip[_24_]
external usenet poster
 
Posts: 2,969
Default For the real engineers here

wrote in news:f21210b7-96ff-44c6-9b4b-120e489e7682@
59g2000hsb.googlegroups.com:

I'm thinking of a clean glider, one that might weigh 1500 pounds and
has a glide angle of say 1 in 25. At 50 miles an hour, that would mean
in an hour's time it might descend two miles (of course scale it
reasonable numbers, I chose those for ease of calculation). That means
it's losing about 1500 * 5280 * 2, or about 16 million foot pounds of
energy an hour.

Now if I add an engine swinging an 8 foot diameter prop, maybe as a
pusher, the question is, how big an engine for cruise only? A
horsepower is 550 foot lbs a second, or about 2 million foot pounds
an hour. If all of that is correct, it suggests with a 50% efficient
prop a little 16 horsepower engine could pretty much keep this thing
at constant altitude.

It passes the reasonableness test as far as I can see. Any serious
disagreements?

For those of you who do things in metric units? I went to school a
long long time ago, and here in the US I can buy a little Briggs and
Stanton (spelling?) engine with a horsepower rating, not a kilowatt
one.


Here ya go...

http://www.usenet.com/newsgroups/rec.../msg06267.html
  #3  
Old June 25th 08, 07:16 PM posted to rec.aviation.piloting
[email protected]
external usenet poster
 
Posts: 181
Default For the real engineers here

On Jun 25, 2:10 pm, Bertie the Bunyip wrote:
wrote in news:f21210b7-96ff-44c6-9b4b-120e489e7682@
59g2000hsb.googlegroups.com:



I'm thinking of a clean glider, one that might weigh 1500 pounds and
has a glide angle of say 1 in 25. At 50 miles an hour, that would mean
in an hour's time it might descend two miles (of course scale it
reasonable numbers, I chose those for ease of calculation). That means
it's losing about 1500 * 5280 * 2, or about 16 million foot pounds of
energy an hour.


Now if I add an engine swinging an 8 foot diameter prop, maybe as a
pusher, the question is, how big an engine for cruise only? A
horsepower is 550 foot lbs a second, or about 2 million foot pounds
an hour. If all of that is correct, it suggests with a 50% efficient
prop a little 16 horsepower engine could pretty much keep this thing
at constant altitude.


It passes the reasonableness test as far as I can see. Any serious
disagreements?


For those of you who do things in metric units? I went to school a
long long time ago, and here in the US I can buy a little Briggs and
Stanton (spelling?) engine with a horsepower rating, not a kilowatt
one.


Here ya go...

http://www.usenet.com/newsgroups/rec.../msg06267.html


Yeah, that gives some comfort that the decimal point at least is in
the right place. Thanks
  #4  
Old June 25th 08, 07:17 PM posted to rec.aviation.piloting
Bertie the Bunyip[_24_]
external usenet poster
 
Posts: 2,969
Default For the real engineers here

wrote in news:f21210b7-96ff-44c6-9b4b-120e489e7682@
59g2000hsb.googlegroups.com:

I'm thinking of a clean glider, one that might weigh 1500 pounds and
has a glide angle of say 1 in 25. At 50 miles an hour, that would mean
in an hour's time it might descend two miles (of course scale it
reasonable numbers, I chose those for ease of calculation). That means
it's losing about 1500 * 5280 * 2, or about 16 million foot pounds of
energy an hour.

Now if I add an engine swinging an 8 foot diameter prop, maybe as a
pusher, the question is, how big an engine for cruise only? A
horsepower is 550 foot lbs a second, or about 2 million foot pounds
an hour. If all of that is correct, it suggests with a 50% efficient
prop a little 16 horsepower engine could pretty much keep this thing
at constant altitude.

It passes the reasonableness test as far as I can see. Any serious
disagreements?

For those of you who do things in metric units? I went to school a
long long time ago, and here in the US I can buy a little Briggs and
Stanton (spelling?) engine with a horsepower rating, not a kilowatt
one.


http://www.aircraft-spruce.com/da11.html

Even better


Lots of motorgilders have been built with some truly dinky engines and
flown quite well, not to mention the Columban Cri cri...


Bertie
  #5  
Old June 25th 08, 07:18 PM posted to rec.aviation.piloting
Bertie the Bunyip[_24_]
external usenet poster
 
Posts: 2,969
Default For the real engineers here

wrote in news:b6c58e3d-f0ee-4d52-842a-
:

On Jun 25, 2:10 pm, Bertie the Bunyip wrote:
wrote in news:f21210b7-96ff-44c6-9b4b-120e489e7682@
59g2000hsb.googlegroups.com:



I'm thinking of a clean glider, one that might weigh 1500 pounds

and
has a glide angle of say 1 in 25. At 50 miles an hour, that would

mean
in an hour's time it might descend two miles (of course scale it
reasonable numbers, I chose those for ease of calculation). That

means
it's losing about 1500 * 5280 * 2, or about 16 million foot pounds

of
energy an hour.


Now if I add an engine swinging an 8 foot diameter prop, maybe as a
pusher, the question is, how big an engine for cruise only? A
horsepower is 550 foot lbs a second, or about 2 million foot

pounds
an hour. If all of that is correct, it suggests with a 50%

efficient
prop a little 16 horsepower engine could pretty much keep this

thing
at constant altitude.


It passes the reasonableness test as far as I can see. Any serious
disagreements?


For those of you who do things in metric units? I went to school a
long long time ago, and here in the US I can buy a little Briggs

and
Stanton (spelling?) engine with a horsepower rating, not a kilowatt
one.


Here ya go...

http://www.usenet.com/newsgroups/rec.../msg06267.html

Yeah, that gives some comfort that the decimal point at least is in
the right place. Thanks


BTW, your glider will need to be a good bit lighter to have anythign
more than marginal perfoemance. With that much HP you should be grossing
about 700 lbs max.



Bertie


  #6  
Old June 25th 08, 07:27 PM posted to rec.aviation.piloting,rec.aviation.soaring
Larry Dighera
external usenet poster
 
Posts: 3,953
Default For the real engineers here

On Wed, 25 Jun 2008 10:56:07 -0700 (PDT), wrote in
:

I'm thinking of a clean glider, one that might weigh 1500 pounds and
has a glide angle of say 1 in 25. At 50 miles an hour, that would mean
in an hour's time it might descend two miles (of course scale it
reasonable numbers, I chose those for ease of calculation). That means
it's losing about 1500 * 5280 * 2, or about 16 million foot pounds of
energy an hour.

Now if I add an engine swinging an 8 foot diameter prop, maybe as a
pusher, the question is, how big an engine for cruise only? A
horsepower is 550 foot lbs a second, or about 2 million foot pounds
an hour. If all of that is correct, it suggests with a 50% efficient
prop a little 16 horsepower engine could pretty much keep this thing
at constant altitude.

It passes the reasonableness test as far as I can see. Any serious
disagreements?

It looks reasonable to me, but I'm not qualified to judge.

For those of you who do things in metric units? I went to school a
long long time ago, and here in the US I can buy a little Briggs and
Stanton (spelling?) engine with a horsepower rating, not a kilowatt
one.


Here's a solution for SI conversions:
http://online.unitconverterpro.com/

[rec.aviation.soaring added]
  #7  
Old June 25th 08, 07:55 PM posted to rec.aviation.piloting,rec.aviation.soaring
Darryl Ramm
external usenet poster
 
Posts: 2,403
Default For the real engineers here

On Jun 25, 11:27*am, Larry Dighera wrote:
On Wed, 25 Jun 2008 10:56:07 -0700 (PDT), wrote in
:



I'm thinking of a clean glider, one that might weigh 1500 pounds and
has a glide angle of say 1 in 25. At 50 miles an hour, that would mean
in an hour's time it might descend two miles (of course scale it
reasonable numbers, I chose those for ease of calculation). That means
it's losing about 1500 * 5280 * 2, or about 16 million foot pounds of
energy an hour.


Now if I add an engine swinging an 8 foot diameter prop, maybe as a
pusher, the question is, how big an engine for cruise only? A
horsepower is *550 foot lbs a second, or about 2 million foot pounds
an hour. If all of that is correct, it suggests with a 50% efficient
prop a little 16 horsepower engine could pretty much keep this thing
at constant altitude.


It passes the reasonableness test as far as I can see. Any serious
disagreements?


It looks reasonable to me, but I'm not qualified to judge.

For those of you who do things in metric units? I went to school a
long long time ago, and here in the US I can buy a little Briggs and
Stanton (spelling?) engine with a horsepower rating, not a kilowatt
one.


Here's a solution for SI conversions:
* *http://online.unitconverterpro.com/

[rec.aviation.soaring added]


What is the question? Sustainer gliders exist and are available from
most (all?) glider manufacturers. You need to factor increased drag of
the engine mast and maybe other things if a retractable mast, but 25:1
is far from state of the art today. You need to factor engine
efficiency at high density altitudes (most sustainer engines are very
simple and do not have altitude/mixture compensation so this can be a
significant issue) and some ability to climb a little would be nice.
Take a current state of the art sustainer like the ASG-29E for
example, uses a SOLO 2350 engine, 18 hp/13.5 kW. Nominal best L/D
(with engine retracted) is 52:1 with 18m wings.

Practical consideration with modern sailplane design will usual
preclude propellers as large as 8' diameter.

Darryl
(ASH-26E driver)
  #8  
Old June 25th 08, 08:01 PM posted to rec.aviation.piloting,rec.aviation.soaring
[email protected]
external usenet poster
 
Posts: 181
Default For the real engineers here

Thanks. As it happens this is a unique high endurance low level and
slow application, and I want to be sure I haven't missed anything
fundamental. It appears I have not (so far), but we all know when a
project is 95% done the most difficult half is still to come.

..



On Jun 25, 2:55 pm, Darryl Ramm wrote:
On Jun 25, 11:27 am, Larry Dighera wrote:



On Wed, 25 Jun 2008 10:56:07 -0700 (PDT), wrote in
:


I'm thinking of a clean glider, one that might weigh 1500 pounds and
has a glide angle of say 1 in 25. At 50 miles an hour, that would mean
in an hour's time it might descend two miles (of course scale it
reasonable numbers, I chose those for ease of calculation). That means
it's losing about 1500 * 5280 * 2, or about 16 million foot pounds of
energy an hour.


Now if I add an engine swinging an 8 foot diameter prop, maybe as a
pusher, the question is, how big an engine for cruise only? A
horsepower is 550 foot lbs a second, or about 2 million foot pounds
an hour. If all of that is correct, it suggests with a 50% efficient
prop a little 16 horsepower engine could pretty much keep this thing
at constant altitude.


It passes the reasonableness test as far as I can see. Any serious
disagreements?


It looks reasonable to me, but I'm not qualified to judge.


For those of you who do things in metric units? I went to school a
long long time ago, and here in the US I can buy a little Briggs and
Stanton (spelling?) engine with a horsepower rating, not a kilowatt
one.


Here's a solution for SI conversions:
http://online.unitconverterpro.com/


[rec.aviation.soaring added]


What is the question? Sustainer gliders exist and are available from
most (all?) glider manufacturers. You need to factor increased drag of
the engine mast and maybe other things if a retractable mast, but 25:1
is far from state of the art today. You need to factor engine
efficiency at high density altitudes (most sustainer engines are very
simple and do not have altitude/mixture compensation so this can be a
significant issue) and some ability to climb a little would be nice.
Take a current state of the art sustainer like the ASG-29E for
example, uses a SOLO 2350 engine, 18 hp/13.5 kW. Nominal best L/D
(with engine retracted) is 52:1 with 18m wings.

Practical consideration with modern sailplane design will usual
preclude propellers as large as 8' diameter.

Darryl
(ASH-26E driver)


  #9  
Old June 25th 08, 08:44 PM posted to rec.aviation.piloting
Maxwell[_2_]
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Posts: 2,043
Default For the real engineers here


wrote in message
...

Yeah, that gives some comfort that the decimal point at least is in
the right place. Thanks


You are feeding a troll.


  #10  
Old June 25th 08, 09:13 PM posted to rec.aviation.piloting
[email protected]
external usenet poster
 
Posts: 181
Default For the real engineers here

On Jun 25, 3:44 pm, "Maxwell" luv2^fly99@cox.^net wrote:
wrote in message

...



Yeah, that gives some comfort that the decimal point at least is in
the right place. Thanks


You are feeding a troll.


I asked for information and got it. A "thank you" was a suitable
response, and I do not consider it feeding a troll, but a polite reply
to a civil answer. Maybe one person's troll is something else
elsewhere.
 




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