Traders - What are your hobbies?

taclander · Apr 29, 2011

Damn you Lucrum! I think I'm going to sign up for one of the factory classes at Sonex to get a feel for building one of their kits. I think I'm going to block you so I don't see your updates and I can't get this craziness out of my head.

I have a buddy who is interested in doing it also. I think we are going to sit down and see if it is feasible to work together and own together.

Lucrum · Apr 29, 2011

Quote from Epic:
Lucrum,
BTW, maybe I missed it, but what was the driver for using black walnut vs a lighter wood. I know that Balsa is used frequently in aircraft. I was under the impression that you were gaining most of your strength from the glass coating. Are you also relying on the strength of the wood core so much that you need to use such a dense wood?

I chose the black walnut for it's strength to weight ratio and for it's hardness. Balsa isn't used for propellers so far as I know. But yes the majority of the blade strength does come from the glass skins.

Quote from taclander:
Damn you Lucrum! I think I'm going to sign up for one of the factory classes at Sonex to get a feel for building one of their kits. I think I'm going to block you so I don't see your updates and I can't get this craziness out of my head. I have a buddy who is interested in doing it also. I think we are going to sit down and see if it is feasible to work together and own together.

We only live once
We're not getting any younger
And we all gotta die sometime

Sonex has a good reputation I believe. And if you get started soon, you'll probably be flying before I am.

Epic · May 3, 2011

Lucrum,

I noticed that you've had a target weight:hp ratio in mind for this project. Have you gone to the trouble yet of estimating weight vs thrust at various velocity, given the specs of your fan design?

{edit}I would think that even an approximation of static thrust at takeoff would be invaluable.

Lucrum · May 3, 2011

Quote from Epic:

Lucrum,

I noticed that you've had a target weight:hp ratio in mind for this project. Have you gone to the trouble yet of estimating weight vs thrust at various velocity, given the specs of your fan design?

{edit}I would think that even an approximation of static thrust at takeoff would be invaluable.

I have although overall drag will be dependent on a drag coefficient that I had to estimate so obviously the accuracy of my estimate will effect the overall accuracy of the numbers. Also there are limited available propulsive efficiencies for a ducted fan this size available making thrust estimates less than precise as well. I'm also going to incorporate a variable duct exit area which, theoretically, will improve my fans performance but again there is only one published study on this, applicable to me, that I know of so that aspect is a bit of an experiment.

Estimated static thrust is at least 840 LBS not counting any benefit from the variable exit area. Which according to Raspet could be another 20% +. But even with out that gain I'd have a static weight/trust ratio comparable to a lightly loaded corporate jet.

AT 250 KTS my estimate is 405 LBS of thrust available. While a study some engineers did some years ago puts it at around 525 LBS. Given my less than perfect construction I'm going with my estimate.

One performance estimate has the plane only producing 349 LBS of total drag at 250 KTS, but I think that's optimistic.

Epic · May 3, 2011

Quote from Lucrum:

I have although overall drag will be dependent on a drag coefficient that I had to estimate so obviously the accuracy of my estimate will effect the overall accuracy of the numbers. Also there are limited available propulsive efficiencies for a ducted fan this size available making thrust estimates less than precise as well. I'm also going to incorporate a variable duct exit area which, theoretically, will improve my fans performance but again there is only one published study on this, applicable to me, that I know of so that aspect is a bit of an experiment.

Estimated static thrust is at least 840 LBS not counting any benefit from the variable exit area. Which according to Raspet could be another 20% +. But even with out that gain I'd have a static weight/trust ratio comparable to a lightly loaded corporate jet.

AT 250 KTS my estimate is 405 LBS of thrust available. While a study some engineers did some years ago puts it at around 525 LBS. Given my less than perfect construction I'm going with my estimate.

One performance estimate has the plane only producing 349 LBS of total drag at 250 KTS, but I think that's optimistic.

Interesting. I performed a quick estimation just from looking at the pics and the specs you've posted and then comparing with certain hovercraft fans with tested specs available. My quick calcs suggested just under 1000lbs gross thrust. But then the fans that I was comparing to were precision built and only operated at about 3500rpm.

I noticed that the actual F16 is close to 1.00 thrust:weight. Obviously you aren't expecting performance in that realm, but I was wondering if you are expecting a gross weight of less than 2,000lbs....

Epic · May 3, 2011

Besides a stress test on the fan, are you going to do a stand test for efficiency as well?

Lucrum · May 3, 2011

Quote from Epic:

I... I was wondering if you are expecting a gross weight of less than 2,000lbs....

With me no baggage and full fuel 1850 LBS is the current gross weight estimate.

Quote from Epic:
Besides a stress test on the fan, are you going to do a stand test for efficiency as well?

I'm not currently planning on it.

Epic · May 3, 2011

Quote from Lucrum:

With me no baggage and full fuel 1850 LBS is the current gross weight estimate.

Nice. That's a bit less than I expected.

I'm not currently planning on it.

No prob, just curious. Figured if you were already doing a stand test on the fan setup that it would be a relatively simple thing to throw an anemometer behind it.

Then thrust calcs are much easier.

Lucrum · May 3, 2011

Quote from Epic:

No prob, just curious. Figured if you were already doing a stand test on the fan setup that it would be a relatively simple thing to throw an anemometer behind it. Then thrust calcs are much easier.

To be accurate it would have to include a duct of the same length and shape/curves as the one I intend to use. At low forward speeds the duct actually improves thrust quiet a bit over just a fan by itself. Assuming I can overcome any torsional resonance and or vibrations issues I'm reasonably confident I can expect decent performance even if I don't reach the design point/goal of 250 KTS at sea level and W.O.T. There are only a handful of smaller home built's that approach 250 KTS anyway.

Epic · May 3, 2011

Quote from Lucrum:

To be accurate it would have to include a duct of the same length and shape/curves as the one I intend to use. At low forward speeds the duct actually improves thrust quiet a bit over just a fan by itself. Assuming I can overcome any torsional resonance and or vibrations issues I'm reasonably confident I can expect decent performance even if I don't reach the design point/goal of 250 KTS at sea level and W.O.T. There are only a handful of smaller home built's that approach 250 KTS anyway.

I was thinking about it more in terms of safety factors. Your design seems like it would have a significantly lower aspect ratio than typical lightweight prop planes. The F16 overcomes this with a thrust:weight ratio close to 1.00 allowing it to takeoff in less than 1/2 mile. If you only ended up with 700lbs thrust, then I'm assuming you'll need a pretty long runway. Although, you did increase the aspect ratio pretty significantly to compensate.

I'm not by any means an aeronautical engineer, so I'm just curiously asking questions and making dumb observations. Let me know if I'm annoying you.