上个月，一家做 eVTOL 的初创公司来问结构件。
他们想减重，把铝合金的梁和肋换成碳纤尼龙，顺口还问了一句："电池仓是不是也用同一种料就行？"
我问他两件是不是一个工况。他愣了一下。
这两件差得很远：结构件要的是轻和刚，电池仓要的是阻燃和尺寸稳——把电池仓也按结构件去减重，是 eVTOL 上最容易出大事的误会。
这篇把 eVTOL 的结构件和电池仓拆开讲：它们分别被什么约束，以及什么条件下这条路该收手。
一、eVTOL 和多旋翼，不是同一个重量级
先把 eVTOL 的特殊性说清楚。
它比多旋翼大得多、重得多，还要载人。载人对材料意味着两件事同时升级：结构件的刚强度要托住人的重量，电池仓的阻燃要兜住热失控。
结构件——梁、肋、舱壁、连接件——要的是比强度，在更轻的重量下扛住同样的载荷。铝合金密度约 2.7，玻纤增强尼龙约 1.4，碳纤增强更低，密度差不多是铝的一半。同样刚度下，尼龙件能比铝件轻三成上下，这是 eVTOL 盯上它的根本原因。
电池仓是另一本账。它贴着电池，电池一旦热失控，温度能在短时间内冲到几百度的量级。电池仓材料要阻燃、低烟低毒、尺寸稳定，不能让箱体在高温下变形把电池挤移位，也不能让燃烧产物堵住逃生通道。
一句话：结构件管"轻"，电池仓管"稳"，两件事用的不是一种思路。
二、两件被什么夹击：六个维度
温度。 结构件在机身，温度相对温和；电池仓紧邻电芯，热失控时是极端温度，日常也是四十度上下。
载荷。 结构件是静载加机动过载，量级大；电池仓是自重加振动，量级小但常年。
介质。 电池仓接触电解液泄漏、冷却液，耐化学是基础项。
寿命。 eVTOL 按飞行小时和起降循环算，验证周期比多旋翼长。
外观。 结构件多在内部，外观要求低；外露件另算。
合规。 载人 eVTOL 涉及适航与阻燃烟毒强制标准，这是硬门槛，不是加分项。
把六维摆在一起：结构件的账在"比强度"，电池仓的账在"阻燃与尺寸稳"，它们连被什么卡住都不一样。
六维里最硬的一维是合规。
载人机型的阻燃烟毒不是"做好了加分"，是"不过就不许飞"。
所以电池仓的选料顺序应该是合规在前、性能在后。
先确认过不过得了认证，再谈能减多少重。
三、两条路线怎么分工
| 路线 | 组成 | 给什么 | 代价 |
|---|
| PA66-GF50 / 碳纤 | 高玻纤或碳纤增强 | 高刚高强、轻 | 成本高、耐温上限、韧性降 |
| PA66-GF30 + 无卤阻燃 | 阻燃体系 + 中玻纤 | 阻燃 V-0、低烟毒、尺寸稳 | 刚性低于结构件路线 |
| 碳纤维复材 | 环氧 + 碳布 | 比强度最高 | 工艺重、贵、维修难 |
第一行是主结构件的主流。 梁、肋这类载荷大的位置，要玻纤或碳纤把刚强度顶上去；但韧性和耐温要一起算，GF50 之后韧性掉得快，不能一味往上加。
第二行是电池仓的主流。 它不追求最高刚性，追求阻燃和低烟毒——含卤阻燃燃烧会放有毒烟雾，载人场景多数认证明确不接受，所以走无卤路线。这一行和第一行几乎不重叠。
这三行还有一个隐藏的排序。
位置越靠近主承力，越往第一行靠；
越靠近电芯和线束，越往第二行靠。
同一个机身里，位置比材料的名字更决定选型。
还要提醒一件和助剂直接相关的事。
无卤阻燃剂加量大，有些体系会把 CTI 拉低一到两级。
选料时要把"阻燃等级"和"漏电起痕"放在同一张表上看。
只比 V-0 不比 CTI，等于只看了半张报告。
一句话：先认准件是"结构"还是"容器"，再谈料，别用一套思路套两件。
四、选型判据表（这一页最该收）
下表的门限是方向性建议，不是验收标准——实际数值必须由具体项目、具体工况和实测确定。
| 指标 | 方向性门限 | 验证方法 / 标准 | 常见失效 | 通行解法 | 对应助剂体系 |
|---|
| 结构件弯曲模量 | 参考 10000–15000 MPa 量级 | ISO 178 | 变形、刚度不足 | 碳纤 / 高玻纤 | 偶联剂（纤维界面） |
| 阻燃等级（电池仓） | 无卤 V-0 量级 | UL 94 / GB/T 2408 | 燃烧滴落、烟毒 | 无卤阻燃体系 | 阻燃剂（磷氮系） |
| CTI / GWIT | 漏电起痕 ≥ 250 级量级 | IEC 60112 / GB/T 4207 | 潮湿漏电 | 高 CTI 基材 | 阻燃剂（不拉低 CTI） |
| 干湿态尺寸差 | 尺寸变化 ≤0.1% | 调湿前后实测 | 电池位移 | 低吸水基材 | 材料本征，不靠助剂 |
| 长期热保留率 | 100℃×1000h 后 ≥75% | ISO 527 | 发白脆化 | 耐热稳定化 | 抗氧剂（受阻酚 + 亚磷酸酯） |
| 玻纤取向一致性 | 收缩差 ≤0.4% | 模流 + 实测 | 翘曲、孔位偏 | 调浇口与流动平衡 | 偶联剂（降界面应力） |
| 热失控后的结构完整性 | 按模拟工况定 | 热失控模拟 + 外观与尺寸 | 箱体变形挤电池 | 低蠕变 + 高耐温基材 | — |
| 绝缘电阻（受潮后） | 按安规口径定 | 湿热后绝缘实测 | 漏电、报警 | 低吸水 + 高 CTI 体系 | 阻燃剂（不拉低 CTI） |
怎么用这张表：不要逐行打分。先看第一行和第四行——结构件盯模量，电池仓盯阻燃，认准了再填表。
还有一句：这张表的上下两半不要互相借用。
结构件的模量门限，拿去要求电池仓没有意义；反过来也一样。
一张表两套考核，串着用就会选出两头不靠的料。
五、六类常见失效，和它们的真根因
失效一：只看 V-0，安规过不了。
根因是漏掉了 CTI 和 GWIT。很多电池仓壳体的硬门槛不是 V-0，是漏电起痕和灼热丝。只凭一张 V-0 报告选料，件做出来了，安规卡在 CTI。阻燃剂选错了，还会把 CTI 拉低，等于按下葫芦浮起瓢。
失效二：电池仓用久了箱体变形，电池被挤。
根因是长期蠕变加吸湿膨胀。电池仓常年持荷，尼龙慢慢走，加上吸湿尺寸变，箱体间隙就漂移。解法不是换更贵的料，是选低蠕变、低吸水的基材，并留设计余量。
失效三：阻燃剂析出，表面发黏、绝缘下降。
根因在助剂侧——阻燃剂添加量大，与基材相容不好时会往表面迁移，污染表面、影响绝缘和粘接。这一条只有做料的人讲得出，因为"哪里在析出"是配方的活。看到发黏、析出，先查阻燃剂与基材的相容性，别急着换基材。
失效四：同一批壳体，有的阻燃有的不阻燃。
根因是阻燃剂分散不均或母粒化没做好，导致一批件阻燃等级波动。先查混料工艺，再谈配方。
六、上机要盯的几件事
干燥。 尼龙必烘，含水率超标件发脆、表面缺陷多，对阻燃件尤其重要——水分会干扰阻燃体系。
模温与浮纤。 结构件是大平面薄壁，浮纤第一顺位原因常常不是玻纤多了，是模温太低。提到 110–120℃ 上下，浮纤常常基本消失。
浇口与取向。 大件翘曲由取向决定，浇口要先做模流分析。
阻燃剂分散。 阻燃件的命门是分散均匀，母粒化和混料顺序要定死。
嵌件与金属件界面。 电池仓里的金属嵌件、螺钉柱是薄弱环节。
两种材料收缩不同，冷却时留下应力，装配再一拧就容易裂。
嵌件预热、收缩间隙留够，是这类件的固定动作。
这类裂口，多半在装配那一刻就已经开始了。
包装与转运。 大平面薄壁件在堆压和长途运输中容易变形。
内衬和堆码层数要一起定，这属于交付的一部分。
运到现场已经变形的件，谁也说不清是谁的问题。
验证顺序。 建议这样排：
1. 材料级：模量、阻燃、CTI
2. 件级：尺寸与翘曲，调湿后测
3. 结构件：静载 + 过载台架
4. 电池仓：热失控模拟 + 长期蠕变
5. 环境叠加：高低温循环 + 湿热老化
顺序不能换。 前一项不通过就往下走，后面数据没有解释意义。
打样实录。 有客户拿着一张 V-0 报告来定电池仓，我们第一句问的是 CTI 和 GWIT 要多少级。他答不上来——只盯 V-0 漏掉 CTI，是新能源和储能件最常踩的坑。 后来我们把"阻燃三件套：V-0、CTI、GWIT"写进了打样确认单。
七、什么时候这件事不该谈
以下四种情况，eVTOL 结构件与电池仓走改性尼龙这条路不建议推进：
其一，主承力大梁且要求极高安全系数。 这部分本来就是碳纤维复材或金属的活，尼龙进去是越界。
其二，载人适航的强制阻燃烟毒要求极严苛。 这类验证周期以年计，没有认证资源不要开这个头。
其三，长期温度持续越过所选体系窗口。 热老化顶不住就是定时炸弹。
其四，用量小到摊不平专用模具与长周期验证。 阻燃料和碳纤料都要专门配，年用量小不划算。
其五，结构上无法做绝缘隔离。 碳纤件导电，靠近电气件又没有隔离空间，这类要先改结构。
其六，验证资源撑不到认证周期。 载人机型的阻燃烟毒验证以年计，
没有这个资源和周期，先把不涉及认证的件做起来更实际。
把这六条写在前头，不是劝退，是省时间。
八、两件分开算：一张对照表
把两条账摆在一起，分工就很清楚了。
| 件 | 主要需求 | 硬门槛 | 关键指标 | 典型失效 |
|---|
| 结构件（梁、肋、舱壁） | 轻与刚强 | 载荷与安全系数 | 比强度、模量、蠕变 | 变形、刚度不足 |
| 电池仓与盖板 | 阻燃与尺寸稳 | 适航阻燃烟毒 | V-0、CTI、GWIT、尺寸 | 漏电、箱体变形 |
这张表最该带走的不是"两套料"，是那句"硬门槛不一样"。
结构件的门槛在载荷，算错了会变形；
电池仓的门槛在认证，过不了就是不许飞。
同一种尼龙，换个角色就换了一套考核标准。
换料风险清单（从金属 / 原方案换到改性尼龙，要动什么）
| 环节 | 要动什么 | 容易漏的点 |
|---|
| 模具 | 大件按件做收缩补偿 | 玻纤取向导致方向性收缩差 |
| 干燥 | 按实测含水率定窗口 | 阻燃体系对水分更敏感 |
| 料温 / 模温 | 模温提到 110–120℃ 控浮纤 | 只按牌号推荐值给，不看件 |
| 阻燃体系 | 确认 CTI / GWIT 不降级 | 只盯 V-0 漏掉 CTI |
| 调湿 | 强制调湿 + 复测尺寸 | 按平均壁厚估时间，厚壁没吸透 |
| 色差 | 外露件色板提前确认 | 玻纤件批次有色差 |
| 验证顺序 | 模量 / 阻燃 → 台架 → 环境 | 前一项未过就往下走 |
一页纸汇报表（给要向上汇报的人）
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项目：eVTOL 结构件 / 电池仓 · 材料路线评估
结论方向：改性尼龙可作候选，能否落地取决于四项前置条件
一、必须守住的三条
1. 结构件与电池仓分两套料，不混
2. 阻燃看 V-0 + CTI + GWIT 三件套
3. 无热失控模拟与长周期数据不进入验证
二、前置条件（任一不满足则建议暂缓）
· 长期工作温度 ≤ 所选体系持续使用区间
· 有适航 / 安规认证资源与周期
· 年用量足以摊薄专用料与模具
· 主承力位置已确认交给复材 / 金属
三、下一步动作
1. 取真实载荷与电池仓温度，定指标
2. 做阻燃 + CTI + GWIT 全套
3. 电池仓做热失控模拟 + 长期蠕变
风险提示：本路线主要不确定性在阻燃合规与长期热老化。
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读者常问的三句
问：结构件能不能也用阻燃料？
看位置。结构件一般不在电芯旁边，阻燃不是它的第一需求，刚强度才是。硬加阻燃剂会拉低刚性和 CTI，得不偿失。分清楚件贴不贴电池，再决定加不加阻燃。
问：碳纤和玻纤，结构件选哪个？
碳纤比强度更高、尺寸更稳，但导电、贵；玻纤成本低、韧性好。主承力又要求尺寸稳的位置，碳纤理由更充分；但要考虑绝缘隔离和验证重做。
问：电池仓能不能靠金属外壳解决阻燃？
金属能兜住阻燃，但重量、成型复杂度和绝缘隔离都要重新算。
常见做法是金属框架配阻燃尼龙内衬，两件分工。
没有哪种做法能单独把减重和阻燃都收下，只能分工。
结语
eVTOL 结构件和电池仓的选材，说到底是一道分工题，不是材料题。
判断链只有三条：
件是结构还是容器 → 温度定体系 → 认证定成败。
三条都定完，"这料能不能减重"才有答案。
如果你手上正有一个 eVTOL 结构件或电池仓要定料，把三样东西发过来就能给方向：是主承力还是次承力、电池仓挨着什么温度、载人还是载货。
这三件事我们从不猜：耐温、寿命、成本。
没给使用温度，不猜；没给服役时长，不猜；没给用量，也不猜。猜出来的方案，最后都要用返工和索赔还回去。
我们做的事很具体：把 PA6、PA66、PA46、PA11、PA12、PA6T、PA9T 和尼龙合金这些树脂，改成某个件真正能用的样子；顺带做改性 PPO、PPS 和热塑性弹性体。
同时经营各大化工巨头的尼龙树脂、副牌料与大包料，另长期收尼龙原料、水口回料与各类尼龙废料，有正规处置渠道。
配方里的助剂体系按件的工况配——常规助剂常备现货，特殊型号按需配套；你报工况和牌号，料和助剂一次配齐。
Last month, a startup making eVTOL came to ask about structural components.
They wanted to lose weight, so they replaced the aluminum alloy beams and ribs with carbon fiber nylon, and casually asked, 'Can the battery compartment use the same material?'
I asked him whether the two things were the same working condition. He was stunned for a moment.
These two parts are vastly different: structural components need to be light and rigid, while the battery compartment needs to be flame-retardant and dimensionally stable—trying to reduce the weight of the battery compartment the same way as structural components is the easiest way to cause major problems on an eVTOL.
This article separates the structural components and battery compartment of the eVTOL: what constrains them respectively, and under what conditions this path should be abandoned.
1. eVTOL and multirotors are not in the same weight class
First, clarify the special characteristics of eVTOL.
It is much larger and heavier than a multirotor, and it is also manned. Being manned means two things must be upgraded in the materials at the same time: the structural components must be strong enough to support a person's weight, and the battery compartment must be flame-retardant to contain thermal runaway.
Structural components—beams, ribs, bulkheads, connectors—require specific strength, carrying the same load with a lighter weight. Aluminum alloy has a density of about 2.7, glass fiber reinforced nylon about 1.4, and carbon fiber reinforced is even lower, roughly half the density of aluminum. With the same stiffness, nylon parts can be about 30% lighter than aluminum parts, which is the fundamental reason eVTOLs are focusing on it.
The battery compartment is another matter. It is in close contact with the battery, and once the battery undergoes thermal runaway, the temperature can surge to several hundred degrees in a short time. The materials of the battery compartment must be flame-retardant, low-smoke, and low-toxicity, with stable dimensions. The compartment must not deform under high temperatures and displace the battery, nor should the combustion products block the escape routes.
In a nutshell: the structural parts are 'light,' the battery compartment is 'stable,' and the two are not approached with the same mindset.
2. What the two things are being pinched by: six dimensions
Temperature. The structural components are on the fuselage, where the temperature is relatively mild; the battery compartment is adjacent to the cells, experiencing extreme temperatures during thermal runaway, and normally is around forty degrees.
Load. Structural components are subject to static loads plus dynamic overloads, with large magnitudes; the battery compartment is subject to its own weight plus vibration, with small magnitudes but over many years.
Medium. Contact with battery compartment electrolyte leakage and coolant, chemical resistance is a basic requirement.
Lifespan. For eVTOLs, calculated by flight hours and takeoff and landing cycles, the verification cycle is longer than that of multirotors.
Appearance. Most structural parts are inside, with low requirements for appearance; exposed parts are counted separately.
Compliance. Manned eVTOL involves mandatory standards for airworthiness and flammability/toxicity, which are hard thresholds, not bonus points.
Putting the six dimensions together: the structural parts are evaluated by 'specific strength', the battery compartment is evaluated by 'flammability and size stability', and even the way they are fixed is different.
The toughest dimension among the six is compliance.
The flame-retardant smoke toxicity of manned models is not 'extra points if done well,' it's 'if it's not adequate, you are not allowed to fly.'
Therefore, the selection order for the battery compartment materials should be compliance first, performance second.
First confirm whether it can pass certification, then talk about how much weight can be reduced.
3. How to divide the work between the two routes
| Route | compose | Give what | Cost |
|---|
| PA66-GF50 / Carbon Fiber | High glass fiber or carbon fiber reinforced | High hardness and high strength, light | High cost, temperature limit, reduced toughness |
| PA66-GF30 Halogen-Free Flame Retardant | Flame retardant system medium glass fiber | Flame retardant V-0, low smoke toxicity, dimensionally stable | Rigidity lower than structural component route |
| Carbon fiber composite | Epoxy carbon fabric | Highest specific strength | Heavy craftsmanship, expensive, difficult to maintain |
The first row is the mainstream of the main structural components. In areas with high loads, such as beams and ribs, glass fiber or carbon fiber is needed to increase stiffness and strength; but toughness and temperature resistance must be considered together. After GF50, toughness drops quickly, so you can't just keep increasing it indiscriminately.
The second line is the mainstream of battery compartments. It does not pursue the highest rigidity, but aims for flame retardancy and low smoke toxicity—halogen-containing flame retardants release toxic smoke when burned, and most certifications for manned scenarios clearly do not accept them, so the route taken is halogen-free. This line almost does not overlap with the first line.
There is also a hidden order in these three lines.
The closer the position is to the main load-bearing structure, the closer it is to the first row.
The closer it is to the battery cell and wiring harness, the more it leans toward the second row.
In the same body, the position determines the choice more than the name of the material.
I also need to remind you of something directly related to the additive.
Halogen-free flame retardants are used in large amounts, and in some systems, they can lower the CTI by one to two levels.
When selecting materials, the 'flammability rating' and 'tracking resistance' should be viewed on the same table.
Only comparing with V-0 and not with CTI is like only looking at half of the report.
In short: first determine whether the item is a 'structure' or a 'container,' then talk about the material; don't use the same approach for two different items.
4. Selection Criteria Table (This page should be collected the most)
The thresholds in the table are directional recommendations, not acceptance criteria — the actual values must be determined by the specific project, specific working conditions, and actual measurements.
| Indicator | Directional Threshold | Verification Method / Standard | Common Failures | Common solution | Corresponding auxiliary system |
|---|
| Bending modulus of structural components | Refer to the magnitude of 10,000–15,000 MPa | ISO 178 | Deformation, insufficient stiffness | Carbon fiber / High glass fiber | Coupling agent (fiber interface) |
| Flame Retardant Rating (Battery Compartment) | Halogen-free V-0 grade | UL 94 / GB/T 2408 | Burning drips, smoke toxins | Halogen-free flame retardant system | Flame retardant (phosphorus-nitrogen type) |
| CTI / GWIT | Leakage tracking ≥ level 250 magnitude | IEC 60112 / GB/T 4207 | Moisture-induced electric leakage | High CTI substrate | Flame retardant (does not lower CTI) |
| Difference in dimensions between dry and wet states | Dimensional change ≤0.1% | Measured before and after humidity adjustment | Battery displacement | Low water absorption substrate | Intrinsic properties of the material, without relying on additives |
| Long-term retention rate | After 1000 hours at 100℃ ≥75% | ISO 527 | Pale and brittle | Heat resistance stabilization | Antioxidant (hindered phenol, phosphite) |
| Glass fiber orientation consistency | Shrinkage difference ≤0.4% | Mold Flow Actual Measurement | Warping, misaligned holes | Gate Adjustment and Flow Balance | Coupling agent (reduces interfacial stress) |
| Structural integrity after thermal runaway | Set according to simulated working conditions | Thermal Runaway Simulation Appearance and Dimensions | The casing deformed and squeezed the battery | Low creep High temperature-resistant substrate | — |
| Insulation resistance (after moisture exposure) | Determine according to safety regulations | Insulation measurement after damp heat | Electric leakage, alarm | Low water absorption High CTI system | Flame retardant (does not lower CTI) |
How to use this table: Do not score row by row. First look at the first row and the fourth row—focus on modulus for structural parts, focus on flame retardancy for the battery compartment, and only fill in the table after confirming.
There is also one more sentence: The upper and lower halves of this table should not borrow from each other.
The modulus threshold of structural components is meaningless for imposing requirements on the battery compartment; and vice versa.
One form with two sets of assessments, using them together will select material that doesn't fit either end.
Common failures of categories five and six, and their true root causes
Failure 1: Only looking at V-0, it fails the safety regulations.
The root cause is missing CTI and GWIT. The hard thresholds for many battery compartment housings are not V-0, but tracking and hot wire. Relying solely on a V-0 report to select materials, once the parts are made, safety certification gets stuck at CTI. Choosing the wrong flame retardant can also lower the CTI, which is like pressing the gourd and the dipper floats up.
Failure 2: After prolonged use, the battery compartment deforms, squeezing the battery.
The root cause is long-term creep combined with moisture absorption and expansion. The battery compartment has been under load for years, the nylon slowly deforms, and with moisture absorption causing dimensional changes, the gaps in the casing drift. The solution is not to use more expensive materials, but to select a substrate with low creep and low water absorption, and to leave design margins.
Failure 3: Flame retardant exudes, surface becomes sticky, insulation decreases.
The root cause lies on the additive side—the high amount of flame retardant, when not well compatible with the substrate, will migrate to the surface, contaminating it and affecting insulation and bonding. Only those who handle the materials can explain this, because 'where it precipitates' is a matter of formulation. When seeing stickiness or precipitation, first check the compatibility between the flame retardant and the substrate, and don't rush to change the substrate.
Failure 4: In the same batch of casings, some are flame-retardant while others are not.
The root cause is that the flame retardant is either unevenly dispersed or the masterbatching was not done properly, resulting in a batch of parts with fluctuating flame retardant levels. First, check the mixing process, then discuss the formulation.
6. A Few Things to Watch for When Using the Computer
Drying. Nylon must be baked; parts with excessive moisture become brittle and have more surface defects. This is especially important for flame-retardant parts, as moisture can interfere with the flame-retardant system.
Mold temperature and floating fibers. The structural parts are large, flat, thin-walled components. The primary cause of floating fibers is often not that there is too much glass fiber, but that the mold temperature is too low. When raised to around 110–120°C, floating fibers often basically disappear.
Gate and orientation. The warpage of large parts is determined by orientation, and the gate should be analyzed with mold flow first.
Flame retardant dispersion. The key to flame retardant components is uniform dispersion, and the order of masterbatching and mixing must be fixed.
Interface between inserts and metal parts. The metal inserts and screw posts in the battery compartment are weak points.
The two materials shrink differently, leaving stress when cooling, and assembly can easily crack with just one twist.
Preheating the insert and leaving enough shrinkage gap are the fixing actions for this type of part.
This type of crack has mostly already started at the moment of assembly.
Packaging and transportation. Large flat thin-walled parts are prone to deformation under stacking and long-distance transportation.
The lining and the number of stacking layers must be decided together; this is part of the delivery.
For parts that have already been deformed upon arrival at the site, no one can clearly say whose problem it is.
Verification order. It is recommended to arrange it like this:
1. Material grade: modulus, flame retardancy, CTI
2. Piece level: Size and warping, measured after moisture adjustment
3. Structural Components: Static Load Overload Test Bench
4. Battery Compartment: Thermal Runaway Simulation Long-Term Creep
5. Environmental Superposition: High and Low Temperature Cycling, Humid Heat Aging
The order cannot be changed. If the previous item fails, move on to the next one; the following data has no explanatory significance.
Proofing Record. A customer came with a V-0 report to order a battery compartment. The first thing we asked was the required levels of CTI and GWIT. He couldn't answer—only focusing on V-0 and ignoring CTI is the most common pitfall in new energy and energy storage products. Later, we wrote the 'three-piece fireproof set: V-0, CTI, GWIT' into the proofing confirmation form.
7. When This Matter Should Not Be Discussed
In the following four situations, it is not recommended to use modified nylon for eVTOL structural components and battery compartments:
First, the main load-bearing beam requires a very high safety factor. This part is originally made of carbon fiber composites or metal, so using nylon would be overstepping.
Secondly, the mandatory fire-resistant smoke toxicity requirements for manned airworthiness are extremely strict. This type of validation cycle is measured in years, and without certification resources, don't start this.
Third, the long-term temperature continuously exceeds the selected system window. Heat aging that can't hold up is a ticking time bomb.
Fourth, the quantity is too small to spread evenly in specialized molds and for long-cycle validation. Both flame retardant materials and carbon fiber materials need to be specially prepared, and the annual usage is too small to be cost-effective.
Fifth, it is structurally impossible to provide insulation isolation. Carbon fiber components are conductive, and there is no isolation space near electrical components, so this type needs structural modification first.
Sixth, verification resources cannot last through the certification cycle. The fire-retardant smoke toxicity verification for manned models is measured in years.
Without this resource and timeline, it’s more practical to first work on the parts that don’t involve certification.
Writing these six points at the beginning is not to discourage, but to save time.
8. Count the two items separately: a comparison table
Putting the two accounts together makes the division of work very clear.
| piece | Main requirements | High barrier | Key indicators | Typical failure |
|---|
| Structural components (beams, ribs, bulkheads) | Lightness and Strength | Load and Safety Factor | Specific strength, modulus, creep | Deformation, insufficient stiffness |
| Battery compartment and cover | Flame retardant and dimensional stability | Airworthiness flame-retardant smoke toxicity | V-0, CTI, GWIT, Dimensions | Electric leakage, box deformation |
What should be taken away most from this table is not the 'two sets of materials,' but the phrase 'the threshold is different.'
The threshold of the structural member is subject to load; if miscalculated, it will deform.
The battery compartment is being certified; if it doesn't pass, you won't be allowed to fly.
The same type of nylon has a different set of evaluation criteria when the role changes.
Material Change Risk List (From metal / original plan to modified nylon, what needs to be changed)
| link; segment; part | What do you want to move? | Points that are easy to overlook |
|---|
| Mold | For large items, perform shrinkage compensation by item | Fiber orientation leads to directional shrinkage differences |
| Dry | Set the window based on the measured moisture content | Flame-retardant systems are more sensitive to moisture |
| Material Temperature / Mold Temperature | The mold temperature is mentioned to be 110–120℃ to control floating fibers | Only give according to the recommended value by grade, without looking at the pieces |
| Flame retardant system | Confirm CTI/GWIT is not downgraded | Only focus on V-0, missing CTI |
| Humidity control | Forced humidity adjustment Re-measure dimensions | Estimate the time based on average wall thickness; the thick walls haven't absorbed fully. |
| Color difference | Advance confirmation of exposed parts color board | There is color variation in the batch of fiberglass parts |
| Verification order | Modulus / Flame Retardant → Test Bench → Environment | If the previous item fails, just move on. |
One-page report sheet (for people who need to report upwards)
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Project: eVTOL Structural Components / Battery Compartment · Material Route Assessment
Conclusion direction: Modified nylon can be considered as a candidate, but whether it can be implemented depends on four prerequisite conditions
1. Three Rules That Must Be Followed
1. The structural parts and the battery compartment are two separate materials and should not be mixed.
2. Flame retardant V-0 CTI GWIT three-piece set
3. No thermal runaway simulation and long-cycle data do not enter verification
2. Precondition (It is recommended to postpone if any are not met)
· Long-term operating temperature ≤ continuous use range of the selected system
· Resources and timelines for airworthiness / safety certification
· Annual usage is sufficient to dilute dedicated materials and molds
· The main load-bearing position has been confirmed and handed over to composites/metal
3. Next Steps
1. Take the actual load and the battery compartment temperature to set indicators
2. Make the full set of flame retardant CTI GWIT
3. Battery compartment thermal runaway simulation Long-term creep
Risk Warning: The main uncertainties of this route are flame retardant compliance and long-term thermal aging.
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Three questions readers often ask
Question: Can structural components also use flame retardant materials?
Check the position. Structural components are generally not next to the battery cell; flame retardancy is not their primary requirement—mechanical strength is. Adding flame retardants forcibly will lower rigidity and CTI, which is not worth it. Determine clearly whether the part is attached to the battery before deciding whether to add flame retardants.
Question: Between carbon fiber and fiberglass, which one should be chosen for structural components?
Carbon fiber has higher specific strength and more stable dimensions, but it conducts electricity and is expensive; glass fiber is low-cost and tough. For main load-bearing positions that also require dimensional stability, the reasons for using carbon fiber are stronger; however, insulation, isolation, and re-verification need to be considered.
Question: Can the battery compartment rely on a metal casing to achieve flame retardancy?
Metal can contain the flame retardant, but the weight, molding complexity, and insulation isolation all need to be recalculated.
A common approach is a metal frame paired with a flame-retardant nylon lining, with the two parts dividing the work.
There is no approach that can achieve both weight loss and flame retardancy on its own; the tasks must be divided.
Conclusion
The selection of materials for eVTOL structural components and battery compartments, after all, is a matter of division of labor, not a materials issue.
There are only three judgment chains:
Is it a structure or a container → Temperature determines the system → Certification determines success or failure.
Once all three are set, only then will there be an answer to whether this material can be made lighter.
If you have an eVTOL structural component or battery compartment to determine materials for, you can send these three things over to get guidance: whether it is a primary or secondary load-bearing part, what temperature the battery compartment is adjacent to, and whether it is for carrying people or cargo.
There are three things we never guess: temperature resistance, lifespan, and cost.
If the operating temperature is not given, don’t guess; if the service life is not given, don’t guess; if the dosage is not given, don’t guess either. Any plan guessed will eventually have to be redone and returned for compensation.
What we do is very specific: we take resins like PA6, PA66, PA46, PA11, PA12, PA6T, PA9T, and nylon alloys, and turn them into a form that can actually be used for a certain part; we also do modified PPO, PPS, and thermoplastic elastomers along the way.
At the same time, we operate nylon resins, secondary brand materials, and bulk materials for major chemical giants, and have long been collecting nylon raw materials, sprue materials, and various nylon waste, with formal disposal channels.
The auxiliary system in the formula is matched according to the working conditions per item — conventional auxiliaries are kept in stock, and special models are matched as needed; you report the working conditions and grade, and the materials and auxiliaries are prepared together at once.
