Electric Airspeed Record.
Discussion
IforB said:
Errr. This is an aerobatic aircraft. Why on earth would you want the fuel tanks or batteries in the wings? This isn’t an airliner.
Think about the loads on the wing root in a high G manoeuvre. Would you really want the fuel tank on a long moment arm?
Take the extra 300 for example. It has wing tanks as well as body tanks, but specifically states that the wing tanks MUST be empty before aerobatic manoeuvres are performed.
You're getting it completely the wrong way around.Think about the loads on the wing root in a high G manoeuvre. Would you really want the fuel tank on a long moment arm?
Take the extra 300 for example. It has wing tanks as well as body tanks, but specifically states that the wing tanks MUST be empty before aerobatic manoeuvres are performed.
Edited by IforB on Friday 11th January 23:22
Edited by IforB on Friday 11th January 23:55
The wings provide lift so any items placed within them means less stress at the wing root than mounting them in the body.
The way to think about it is imagine the wing as fixed at the tip and then supported along its length (lift) with the mass of half the body hanging off the end as a cantilever.
This why airliners hang their engines off the wing and why the wing structure of a four engined plane is lighter than a two engined plane.
As to why a plane might limit aerobatics with wing tanks filled.
1: Total mass limits
2: Increased polar moment of inertia limits role rate.
3: Sloshing or other free surface effects, this could be mass shift, fuel leakage under pressure or as structure moves.
Max_Torque said:
This is, on face value a really good idea!
When the plane is flying, and power is being drawn from the batteries, the speed of the airflow over the wings will be, generally speaking ignoring AOA changes) proportional to the power being drawn. Using air cooling via conduction with the (massive) wing surface area would negate the need for additional and potentially complex alternative cooling methods.
But, Charging on the ground becomes an issue. A fast turn around means fast charging, which means lots of heat at zero airspeed! Perhaps we could could fit water jets and spray bars to airport terminals to cool the wings during ground charging?
BTW, i wonder if this speed record plane is going to use an air cooled battery. They have said "the lightest battery ever made" and the minimal drawings released show what looks to be a low cell packing density, with enough space to route cooling air around the cells.......
The prop wash also could be used for targeted cooling
Which ever method of battery cooling they opt for will create some drag. A liquid cooled battery will require a radiator of some form (unless some structural changes are made to route the liquid close to the surface of the wings, for instance). Air cooling will require a drag inducing inlet and outlet. When the plane is flying, and power is being drawn from the batteries, the speed of the airflow over the wings will be, generally speaking ignoring AOA changes) proportional to the power being drawn. Using air cooling via conduction with the (massive) wing surface area would negate the need for additional and potentially complex alternative cooling methods.
But, Charging on the ground becomes an issue. A fast turn around means fast charging, which means lots of heat at zero airspeed! Perhaps we could could fit water jets and spray bars to airport terminals to cool the wings during ground charging?
BTW, i wonder if this speed record plane is going to use an air cooled battery. They have said "the lightest battery ever made" and the minimal drawings released show what looks to be a low cell packing density, with enough space to route cooling air around the cells.......
The prop wash also could be used for targeted cooling
For recharging for the record attempt they could use a powerful fan to drive air past the batteries to keep them cool.
The air cooling method also avoids additional weight and complexity.
The airflow through the duct could also be controlled to optimise battery temperature, and probably closed completely for the short period through the timing equipment.
Ok, I've done some back-of-envelope calculations for an electric version of the C172.
It's definitely picking low-hanging fruit, as the C172 basic design dates to the mid 1950's, but it's still in production, so it's a valid target.
The C172 has fixed undercarriage and strut-braced wings, so there's a lot of potential for reduced drag. It's also got a fixed-pitch prop.
It's dry weight grew from it's predecessor's 550 kg to 770, so modern composites should trim that back.
The C172's most economical cruise is at 55% power, which is 66 kW. It's still doing 185 kph at that speed.
I will assume that reduced drag, lower cruise speed, and optimised prop saves us 30%, which gets us down to a cruise power of 50 kW. With 90% combined motor & controller efficiency (YASA spec peaks at over 92), we need 55 kW input.
At 250 Wh/kg, that's 220 kg batteries / hr. Add 5% for supporting structure, thats 230 kg/hr
The C172 engine (wet) weighs around 125 kg. Replacing that with a YASA 750 (37 kg) and controller (5 kg) gains us say 75 kg (I've allowed 7 kg misc).
Assume we can take 20% off the dry weight (767 kg), that's 153 kg. Total saving 228 kg.
So we get around an hour of flight with no loss of payload. Every hour after that adds an extra 230 kg.
The C172 has a total payload of 344 kg, so allowing 2 x 100kg bodies you get another 38 minutes, say 1 hr flight + 40 mins reserve.
I've ignored a lot of stuff, including take-off and climb power, but my envelope says it's worth further study - maybe increase the wing / stiffen the structure to increase payload, etc.
It would probably cost much more than the Cessna, but the design goal is not impossible.
It's definitely picking low-hanging fruit, as the C172 basic design dates to the mid 1950's, but it's still in production, so it's a valid target.
The C172 has fixed undercarriage and strut-braced wings, so there's a lot of potential for reduced drag. It's also got a fixed-pitch prop.
It's dry weight grew from it's predecessor's 550 kg to 770, so modern composites should trim that back.
The C172's most economical cruise is at 55% power, which is 66 kW. It's still doing 185 kph at that speed.
I will assume that reduced drag, lower cruise speed, and optimised prop saves us 30%, which gets us down to a cruise power of 50 kW. With 90% combined motor & controller efficiency (YASA spec peaks at over 92), we need 55 kW input.
At 250 Wh/kg, that's 220 kg batteries / hr. Add 5% for supporting structure, thats 230 kg/hr
The C172 engine (wet) weighs around 125 kg. Replacing that with a YASA 750 (37 kg) and controller (5 kg) gains us say 75 kg (I've allowed 7 kg misc).
Assume we can take 20% off the dry weight (767 kg), that's 153 kg. Total saving 228 kg.
So we get around an hour of flight with no loss of payload. Every hour after that adds an extra 230 kg.
The C172 has a total payload of 344 kg, so allowing 2 x 100kg bodies you get another 38 minutes, say 1 hr flight + 40 mins reserve.
I've ignored a lot of stuff, including take-off and climb power, but my envelope says it's worth further study - maybe increase the wing / stiffen the structure to increase payload, etc.
It would probably cost much more than the Cessna, but the design goal is not impossible.
Looking at it from a very basic perspective, having jettison-able pods for your batteries could be a good idea. In the event of an emergency, you could remove a good proportion of the weight (Assuming at this stage it was useless) allowing for easier gliding? I haven't read the whole thread so apologies if this idea has already been ridiculed for technical reasons - or is already a published feature... 
IN51GHT said:
When considering putting cells in wings, bare in mind wings do flex.......busbars etc less so.
Appreciate that it raises its own issues, but the Chapman approach would be to make the busbars do some of the structural work (ie. conversely, make the main spars double as busbars).Update - apologies if its behind a paywall https://www.telegraph.co.uk/business/2021/02/28/ke...
I may have missed the answer but is this a new airframe or modified ? Looks very swoopy
I may have missed the answer but is this a new airframe or modified ? Looks very swoopy
johnnyreggae said:
Update - apologies if its behind a paywall https://www.telegraph.co.uk/business/2021/02/28/ke...
I may have missed the answer but is this a new airframe or modified ? Looks very swoopy
It's based on a Nemesis NXT, very early on in the project I highlighted how much extra work developing & certifying a new airframe was, especially when trying to develop a new propulsion unit, The decision was made too purchase the NXT, designed by John Sharp, as far as we were aware it was the last unbuilt kit available at the time.I may have missed the answer but is this a new airframe or modified ? Looks very swoopy
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