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Search: Posts Made By: JetPlaneFlyer
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02-15-2011, 11:34 AM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

I've seen people check speed using Doppler effect...

I've seen people check speed using Doppler effect based on a video clip.. Quite how it's done and how accurate it is I'm not sure but perhaps worth looking into?
Failing that, a low tech approach...
02-15-2011, 07:09 AM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Does this mean that so far you have not verified...

Does this mean that so far you have not verified top speed? Given the title of the thread I though you must have checked it already.

I know you don't much like Motocalc but FWIW it predicts you...
02-13-2011, 08:56 AM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Z8, I've had time to sleep on this and I think...

Z8,
I've had time to sleep on this and I think I now understand where you are getting confused.

For optimum efficiency a prop should have 'uniform disk loading...
02-12-2011, 11:59 PM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Velocity at the hub is zero (and that's a...

Velocity at the hub is zero (and that's a fact)... how wide would a chord have to be to produce thrust with zero airspeed:confused::rolleyes:

Nowhere in that article does it say that ideal thrust...
02-12-2011, 11:19 PM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Z8 Great find on the article.. It proves once...

Z8
Great find on the article.. It proves once and for all that lift/thrust increases toward the tips, thanks for finding it..

Figure 3.7(b) clearly shows the thrust distribution across a...
02-12-2011, 11:02 PM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Exactly what NJ said.. linear lift distribution...

Exactly what NJ said.. linear lift distribution does not mean constant lift distribution.. In fact if the lift distribution is linear then it disproves your theories about either constant or...
02-12-2011, 02:18 PM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Picking up on this last point by NJSwede.. yes...

Picking up on this last point by NJSwede.. yes 'any' prop would have zero lift right at the precise 'tip of the tip'.. this is undoubtedly true for any prop regardless of shape.

It's really the...
02-12-2011, 01:28 PM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Some observations about your spreadsheet... ...

Some observations about your spreadsheet...

First the photo uses the 'horizontal datum' of the photo frame to measure prop angle from. Unless you had she camera resting flat on the table than that...
02-12-2011, 11:58 AM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Thrust is a type of 'force'.. Force is measured...

Thrust is a type of 'force'.. Force is measured in units on Newtons in the metric system or kips or perhaps 'pounds force' in the imperial system.. Point being that thrust is a force and force...
02-12-2011, 10:09 AM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Actually I'd have to take the opposing view on...

Actually I'd have to take the opposing view on this one. High aspect ratio is to reduce induced drag. Induced drag is drag that occurs due to downwash caused by tip vortexes.

The formula for...
02-12-2011, 09:44 AM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

On this highlighted point we agree 100%.. So if...

On this highlighted point we agree 100%.. So if we agree as you clearly stated that AoA is constant how does the lift reduce toward the tip when the tip it travelling infinity faster than at the prop...
02-11-2011, 08:26 AM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

57sailplane, I like your thinking but...

57sailplane,

I like your thinking but despite the apparent logic of your thinking the conclusion is incorrect. Ignoring effects of any fuselage volume that may be in the way the air actually...
02-10-2011, 08:04 AM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Z8, If the tip is so narrow then how did you...

Z8,

If the tip is so narrow then how did you accurately measure the blade angle? If the chord of the blade was, say 1/8", then a few thousanths of an inch in inclination of the leading edge would...
02-09-2011, 11:04 PM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

This is always a good one to start a debate. The...

This is always a good one to start a debate. The answer is not simple because it depends on the pitch/diameter ratio, among other things. For a truly freewheeling prop then the info I have shows that...
02-09-2011, 10:26 PM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Most (if not all) props will go to zero AoA at...

Most (if not all) props will go to zero AoA at the root first. The tip will generally be the last part of the prop to stop producing thrust and so unless you were in a very steep dive it would not...
02-09-2011, 07:09 PM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Looks like Master Airscrew got it horribly wrong...

Looks like Master Airscrew got it horribly wrong when they made their props then.

I just checked a 13x6 Master Airscrew prop.

I took measurements at two stations:

1/3rd 'span' (55mm from...
02-09-2011, 03:58 PM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Then explain why helicopter rotors (which are...

Then explain why helicopter rotors (which are optimised to hover rather than move through the air) have no twist???

The answer by the way is that twist is there to do exactly what I said.. To...
02-09-2011, 06:58 AM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

That's incorrect. The twist on the blade is to...

That's incorrect. The twist on the blade is to achieve constant pitch (and therefore approx constant blade angle of attack when in flight) not constant lift. The outer part of the blade will always...
02-08-2011, 12:51 PM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Or perhaps not.. Prop pitch is the distance...

Or perhaps not..

Prop pitch is the distance a prop would 'screw' through the air if a prop worked exactly like the thread on a bolt screwing through a nut. That's not really how a prop works of...
02-08-2011, 10:00 AM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Sounds about right.. A motor of about 1200kv...

Sounds about right.. A motor of about 1200kv running on 4 cells would spin at about that speed under load.
02-08-2011, 07:46 AM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

You are not by any chance trying to drive two...

You are not by any chance trying to drive two motors from one ESC are you? If so that would explain your problems.
Easiest solution is to use two ESC's.. It 'should' also work on one ESC if you...
02-08-2011, 06:43 AM
Replies: 160
Views: 27,728
Posted By JetPlaneFlyer

Why go to all that complexity when you could just...

Why go to all that complexity when you could just go for a larger motor capable of generating twice the torque of the Super Tiger 10's with a similar kv:confused:
One large motor should work out...
Showing results 1 to 22 of 22


 
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