Ace the Technical interview by G.Bristow
SR71,
The suggestion was that a bi-plane would automatically have twice the lift of a mono-plane with half the wing area- Clearly not true as the airflow interference of the bi-plane configuration reduces it's efficiency.
In any case, doesn't Reynolds affect amongst other things mean that simply doubling the area of a wing DOESN'T automatically double the lift (A of A and Rho being equal)?
John, interesting CL discussion (I'm certainly learning a lot), but obviously completely off topic. Could we carve it off to a seperate thread?
The suggestion was that a bi-plane would automatically have twice the lift of a mono-plane with half the wing area- Clearly not true as the airflow interference of the bi-plane configuration reduces it's efficiency.
In any case, doesn't Reynolds affect amongst other things mean that simply doubling the area of a wing DOESN'T automatically double the lift (A of A and Rho being equal)?
John, interesting CL discussion (I'm certainly learning a lot), but obviously completely off topic. Could we carve it off to a seperate thread?
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Wizo,
Typically the kinematic viscosity of air is ~10^-5, which means that a commercial aircraft tends to fly in a regime where the Reynolds number is ~10^7.
You can see as a result, that you'd need to change the velocity of a flow by a hell of a lot to get a significant change in Re.
As John said, Re is a dimensionless number used to denote similarity of flow regimes. If you are testing a model of aforementioned commercial aircraft in a wind tunnel, you need to match the Re during testing.
Depending on what you're trying to measure you may need to match the Mach Number as well. Mach is just another dimensionless number like Re.
Re denotes the ratio of inertial to viscous forces in a flow.
In the regime we are typically interested in, inertial forces are large compared to viscous ones.
You won't see much dependence of lift coefficient with Re but, conversely, it will be important to match Re if you want a good drag estimate.
I remember when doing my PhD some colleagues trying to obtain laminar flow over wings at high Re with the intention of applying this technology to commercial aircraft.
They laser drilled thousands of minute holes in the upper surface of their wing and attempted to suck away the boundary layer, thereby delaying transition.
Of course, in any technical undertaking like this one has to deal with bugs.
In this case, the bugs kept blocking the laser drilled holes and the exercise was less than satisfactory.
NASA claim to have made progress on this front though:
http://www.nasa.gov/centers/langley/...HSR-Wings.html
with their F-16XL:
Typically the kinematic viscosity of air is ~10^-5, which means that a commercial aircraft tends to fly in a regime where the Reynolds number is ~10^7.
You can see as a result, that you'd need to change the velocity of a flow by a hell of a lot to get a significant change in Re.
As John said, Re is a dimensionless number used to denote similarity of flow regimes. If you are testing a model of aforementioned commercial aircraft in a wind tunnel, you need to match the Re during testing.
Depending on what you're trying to measure you may need to match the Mach Number as well. Mach is just another dimensionless number like Re.
Re denotes the ratio of inertial to viscous forces in a flow.
In the regime we are typically interested in, inertial forces are large compared to viscous ones.
You won't see much dependence of lift coefficient with Re but, conversely, it will be important to match Re if you want a good drag estimate.
I remember when doing my PhD some colleagues trying to obtain laminar flow over wings at high Re with the intention of applying this technology to commercial aircraft.
They laser drilled thousands of minute holes in the upper surface of their wing and attempted to suck away the boundary layer, thereby delaying transition.
Of course, in any technical undertaking like this one has to deal with bugs.
In this case, the bugs kept blocking the laser drilled holes and the exercise was less than satisfactory.
NASA claim to have made progress on this front though:
http://www.nasa.gov/centers/langley/...HSR-Wings.html
with their F-16XL:
SR71
Thanks- but we are now officially in WAY over my head!!
The reasearch on laminar flow is interesting though. At least one glider has reached production with a similar system, a venturi being used to provide suction to a series of small holes on the surface.
Thanks- but we are now officially in WAY over my head!!
The reasearch on laminar flow is interesting though. At least one glider has reached production with a similar system, a venturi being used to provide suction to a series of small holes on the surface.
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SR71,
.. as I recall ... indeed we discussed TeX (now that takes me back to the late 60s/early 70s if recollection serves me correctly) .. I'll raise the matter with those further up the totem pole ..
John
.. as I recall ... indeed we discussed TeX (now that takes me back to the late 60s/early 70s if recollection serves me correctly) .. I'll raise the matter with those further up the totem pole ..
John
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Just read a question on the use of the ILS and its limits. Page 297. The question: When, on the ILS can you descend on the GP?
1st part: When cleared for the ILS procedure. ..... Correct.
2nd part: When you have captured the localiser within +/- 5 degrees C...... absolutely incorrect.
Now the second part is obviously a huge mistake but, if the author meant +/- 5 degrees of the centreline (omitting the reference to temperature), which I think he did, isnt he still incorrect.
Please correct me if I am wrong here but I was taught that the approach should be thrown away when you are descending on GP and you go outside either half scale fly up or down or 1/2 scale fly left or right. And ......
On page 145, he says one dot on the ILS indicator = 1/2 degree (which I think is correct) so therefore on a normal HSI when flying the ILS, his answer should be +/- 1.25 degrees (or within half scale). This is a big contradiction to his answer (forgetting the reference to temperature).
I know what I used to know, but the numbers now have me confused big time!
To clarify this..........
Should the answers for the limitis of lateral navigation, when asked when one can descend with the procedure be:
+/- 2.5 degrees for a VOR approach. (full scale deflection = 5 degrees)
+/- 1.25 degrees for an ILS approach (full scale deflection = 2.5 degrees)
This book just gets more and more confusing!
barit1: It has been discussed in depth on Prune as well and the problems still crop up!!!
1st part: When cleared for the ILS procedure. ..... Correct.
2nd part: When you have captured the localiser within +/- 5 degrees C...... absolutely incorrect.
Now the second part is obviously a huge mistake but, if the author meant +/- 5 degrees of the centreline (omitting the reference to temperature), which I think he did, isnt he still incorrect.
Please correct me if I am wrong here but I was taught that the approach should be thrown away when you are descending on GP and you go outside either half scale fly up or down or 1/2 scale fly left or right. And ......
On page 145, he says one dot on the ILS indicator = 1/2 degree (which I think is correct) so therefore on a normal HSI when flying the ILS, his answer should be +/- 1.25 degrees (or within half scale). This is a big contradiction to his answer (forgetting the reference to temperature).
I know what I used to know, but the numbers now have me confused big time!
To clarify this..........
Should the answers for the limitis of lateral navigation, when asked when one can descend with the procedure be:
+/- 2.5 degrees for a VOR approach. (full scale deflection = 5 degrees)
+/- 1.25 degrees for an ILS approach (full scale deflection = 2.5 degrees)
This book just gets more and more confusing!
barit1: It has been discussed in depth on Prune as well and the problems still crop up!!!
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Should the answers for the limitis of lateral navigation, when asked when one can descend with the procedure be:
+/- 2.5 degrees for a VOR approach. (full scale deflection = 5 degrees)
+/- 1.25 degrees for an ILS approach (full scale deflection = 2.5 degrees)
+/- 2.5 degrees for a VOR approach. (full scale deflection = 5 degrees)
+/- 1.25 degrees for an ILS approach (full scale deflection = 2.5 degrees)
Warning Toxic!
Disgusted of Tunbridge
Disgusted of Tunbridge
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I think that book is up to one major mistake per page. It was so outrageous I couldn't read it all. One volubly expletes trying to read it- the dog was hiding in the corner. I don't know how he got away with it. It's the Benny Hill Show of the aviation world. We should sue- a class action for fraud!
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Originally Posted by Rainboe
We should sue- a class action for fraud!
I wonder if the man reads this site and the numerous threads on his book and is feeling a teeny bit embarassed. Or maybe he is laughing all the way to the bank!
We are all obviously smart enough to spot the mistakes.
