Aggregate A9 (A4b)
03-05-2022, 03:56 PM
#77
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Don
Just an update.
The degree of control possible by the limited area of elevators in the EDF exhaust proved completely inadequate to resist the initial torque roll so simply allowing the roll proved to be the best way to keep it going straight up!
Eventually the over rated 70 mm EDF shed a blade (actually all of them!) within a couple of seconds of reaching full power which resulted in a very realistic launch failure and not surprisingly very considerable damage.
After a year in storage it was rebuilt using a much lighter power plant, an RS2205 'drone' motor turning a 4x4 four blade as a ducted prop running on a 850 mAh 5s rather than the 1800mAh 4s used with the 70 mm EDF.
As the amps required dropped from 41 to 14 there was a significant saving in the weight of the 1100 mm long motor wires from the ESC & battery in the nose to the motor in the rear. The lighter weight also allowed for a simpler control system using three 3.7g servo rather than four 5g. A Little Bee 20A ESC and 3A UBEC saved another 40g over the 60A ESC used with the 70 mm EDF.
Total weight saving was in the order of 30%. With a similar reduction in static thrust the VTO is about the same. However at low power the 4 blade prop is quite a bit more efficient than the 8 blade EDF so coupled with the lighter all up weight the Mk2 V-2 can 'cruise about' for a good 10 minutes even after a vertical take off.
A rather poor quality video of its maiden.
Just an update.
The degree of control possible by the limited area of elevators in the EDF exhaust proved completely inadequate to resist the initial torque roll so simply allowing the roll proved to be the best way to keep it going straight up!
Eventually the over rated 70 mm EDF shed a blade (actually all of them!) within a couple of seconds of reaching full power which resulted in a very realistic launch failure and not surprisingly very considerable damage.
After a year in storage it was rebuilt using a much lighter power plant, an RS2205 'drone' motor turning a 4x4 four blade as a ducted prop running on a 850 mAh 5s rather than the 1800mAh 4s used with the 70 mm EDF.
As the amps required dropped from 41 to 14 there was a significant saving in the weight of the 1100 mm long motor wires from the ESC & battery in the nose to the motor in the rear. The lighter weight also allowed for a simpler control system using three 3.7g servo rather than four 5g. A Little Bee 20A ESC and 3A UBEC saved another 40g over the 60A ESC used with the 70 mm EDF.
Total weight saving was in the order of 30%. With a similar reduction in static thrust the VTO is about the same. However at low power the 4 blade prop is quite a bit more efficient than the 8 blade EDF so coupled with the lighter all up weight the Mk2 V-2 can 'cruise about' for a good 10 minutes even after a vertical take off.
A rather poor quality video of its maiden.
Last edited by quorneng; 03-05-2022 at 04:14 PM.
03-07-2022, 12:11 AM
#79
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Buck Rogers. I am not sure Von Braun would have been amused!
Although intended to increase the V-2 range Von Braun;s next proposal was a two stage version that could reach America which had in got approved he knew full well would be just one step away from getting into orbit which was what he really wanted to do.
One can understand his alacrity to work for the Americans. The first American tactical nuclear surface to surface rocket, the Redstone, was a direct descendent of the V-2 and had a similar range. .
Although intended to increase the V-2 range Von Braun;s next proposal was a two stage version that could reach America which had in got approved he knew full well would be just one step away from getting into orbit which was what he really wanted to do.
One can understand his alacrity to work for the Americans. The first American tactical nuclear surface to surface rocket, the Redstone, was a direct descendent of the V-2 and had a similar range. .
03-16-2022, 02:03 PM
#81
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SkyersJet
If you scaled up my design to accommodate a 400 mm EDF it would be 4 times the size which would make it 5.6m tall with a wing span of 2.36 m.
It currently weighs 464g so scaling up by the cube law it would weigh around 29 kg. At that weight you would need a maximum thrust in the order of 40 kg for a practical VTO.
In general electric propulsion does not scale up well. It gets disproportionately heavier as the power rises.
What is perfectly possible a small scale becomes progressively harder the bigger it gets.
What would be the thrust to weight ratio of your 400 EDF if you include the weight of the speed controller and the batteries to provide say 1.5 minutes (20c discharge rate) at full power?
The 100 mm unit in my A4b achieves over 3:1.
Unless you can achieve that sort of figure a VTO is not really practical.
If you scaled up my design to accommodate a 400 mm EDF it would be 4 times the size which would make it 5.6m tall with a wing span of 2.36 m.
It currently weighs 464g so scaling up by the cube law it would weigh around 29 kg. At that weight you would need a maximum thrust in the order of 40 kg for a practical VTO.
In general electric propulsion does not scale up well. It gets disproportionately heavier as the power rises.
What is perfectly possible a small scale becomes progressively harder the bigger it gets.
What would be the thrust to weight ratio of your 400 EDF if you include the weight of the speed controller and the batteries to provide say 1.5 minutes (20c discharge rate) at full power?
The 100 mm unit in my A4b achieves over 3:1.
Unless you can achieve that sort of figure a VTO is not really practical.
03-17-2022, 03:16 PM
#82
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Join Date: Mar 2022
Posts: 7
Hi, thanks for your reply
The wingspan would need to scale but not necessarily the height. I don't see why the airframe would need to be more than 2m tall and weigh more than 10kg.
Version A with a single inrunner is predicted to produce 22kg thrust @ 210A on 12s. Two 6s 6000mah packs in series would be able to provide that for about 1.7 minutes. The EDF weighs 7kg and the packs weigh 1kg each therefore with the airframe the total weight is 19kg and the thrust to weight ratio would be 1.16:1 without a payload, 0.75:1 without a payload.
Version B with dual inrunners is predicted to produce 40kg thrust @ 225A per motor on 14s. Full-power would be 1.6 minutes with four 7s 6000mah packs (two in series per motor). Assuming a 1kg weight for these packs also that would be 4kg total. The EDF would weigh 8kg (due to the extra inrunner) therefore with the 10kg frame the thrust to weight ratio for this setup would be 40/22 or 1.81:1. With a 10kg payload the ratio is 1.25:1 or with a 5kg payload 1.48:1.
So version A is not feasible but Version B might be. Unfortunately I haven't tested that EDF version yet. I know that none of these numbers are anywhere near 3:1 but the Ryan X-13 Vertijet had a thrust to weight ratio of 1.48:1.
Would the wings work? 2.36m wingspan and lets say a 0.4m chord for an aspect ratio of 5.9 would have a projected area of 0.94m^2. Using the lift equation and a lift coefficient of 1.5 I got a speed of about 40mph to sustain level flight.
Let me know what you think.
The wingspan would need to scale but not necessarily the height. I don't see why the airframe would need to be more than 2m tall and weigh more than 10kg.
Version A with a single inrunner is predicted to produce 22kg thrust @ 210A on 12s. Two 6s 6000mah packs in series would be able to provide that for about 1.7 minutes. The EDF weighs 7kg and the packs weigh 1kg each therefore with the airframe the total weight is 19kg and the thrust to weight ratio would be 1.16:1 without a payload, 0.75:1 without a payload.
Version B with dual inrunners is predicted to produce 40kg thrust @ 225A per motor on 14s. Full-power would be 1.6 minutes with four 7s 6000mah packs (two in series per motor). Assuming a 1kg weight for these packs also that would be 4kg total. The EDF would weigh 8kg (due to the extra inrunner) therefore with the 10kg frame the thrust to weight ratio for this setup would be 40/22 or 1.81:1. With a 10kg payload the ratio is 1.25:1 or with a 5kg payload 1.48:1.
So version A is not feasible but Version B might be. Unfortunately I haven't tested that EDF version yet. I know that none of these numbers are anywhere near 3:1 but the Ryan X-13 Vertijet had a thrust to weight ratio of 1.48:1.
Would the wings work? 2.36m wingspan and lets say a 0.4m chord for an aspect ratio of 5.9 would have a projected area of 0.94m^2. Using the lift equation and a lift coefficient of 1.5 I got a speed of about 40mph to sustain level flight.
Let me know what you think.
03-18-2022, 11:25 AM
#83
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Skyersjet
You are talking of a total plane weight in the order of 27 kg or 60 lbs. I note that such a weight means it would classify as a 'large model aircraft', at least in the UK and EU, that requires construction inspection and permission to fly.
You may be correct at 40 mph being required to maintain level flight although the speed to maintain effective control would higher. This raises the question that anything but a fully controlled vertical landing would likely result in significant airframe damage.
Is a big single fan unit the best way to achieve the require thrust for VTO operations? You still have to consider how the required stability can be achieved.
I note that man carrying drones have been made using multiple commercially available motor & prop units with the advantage that these are also used to achieve electronic control & stability.
Is there a use for a single big fan in a conventional model aircraft?
You have proved such a fan is technically possible but I am not sure I can see a viable application.
That's about as far as my thinking goes. . .
You are talking of a total plane weight in the order of 27 kg or 60 lbs. I note that such a weight means it would classify as a 'large model aircraft', at least in the UK and EU, that requires construction inspection and permission to fly.
You may be correct at 40 mph being required to maintain level flight although the speed to maintain effective control would higher. This raises the question that anything but a fully controlled vertical landing would likely result in significant airframe damage.
Is a big single fan unit the best way to achieve the require thrust for VTO operations? You still have to consider how the required stability can be achieved.
I note that man carrying drones have been made using multiple commercially available motor & prop units with the advantage that these are also used to achieve electronic control & stability.
Is there a use for a single big fan in a conventional model aircraft?
You have proved such a fan is technically possible but I am not sure I can see a viable application.
That's about as far as my thinking goes. . .
